Datasheet ADT7468 Datasheet (Analog Devices)

Page 1

Cool™ Remote Thermal

FEATURES

Monitors up to 5 voltages Controls and monitors up to 4 fans High and low frequency fan drive signal 1 on-chip and 2 remote temperature sensors Series resistance cancellation on the remote channel Extended temperature measurement range, up to 191°C Dynamic T

intelligently

Automatic fan speed control mode controls system

cooling based on measured temperature

Enhanced acoustic mode dramatically reduces user

perception of changing fan speeds Thermal protection feature via

Monitors performance impact of Intel® Pentium™ 4

processor Thermal control circuit via

2-wire, 3-wire, and 4-wire fan speed measurement Limit comparison of all monitored values Meets SMBus 2.0 electrical specifications

(fully SMBus 1.1 compliant)

control mode optimizes system acoustics

MIN

output

THERM

input

THERM

Controller and Voltage Monitor

ADT7468

GENERAL DESCRIPTION

The ADT7468 dBCOOLTM controller is a thermal monitor and multiple PWM fan controller for noise-sensitive or powersensitive applications requiring active system cooling. The ADT7468 can drive a fan using either a low or high frequency drive signal, monitor the temperature of up to two remote sensor diodes plus its own internal temperature, and measure and control the speed of up to four fans, so that they operate at the lowest possible speed for minimum acoustic noise.

The automatic fan speed control loop optimizes fan speed for a given temperature. A unique dynamic T enables the system thermals/acoustics to be intelligently managed. The effectiveness of the system’s thermal solution can be monitored using the

THERM

input. The ADT7468 also provides critical thermal protection to the system using the bidirectional

THERM

pin as an output to prevent system or

component overheating.

control mode

MIN

FUNCTIONAL BLOCK DIAGRAM

VID5 VID4 VID3 VID2 VID1 VID0

PWM1 PWM2 PWM3

TACH1 TACH2 TACH3 TACH4

THERM

+12V

+2.5V

Rev. 0

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.

+5V

V D1+ D1– D2+ D2–

CCP

IN IN IN

PWM REGISTERS

AND

CONTROLLERS

HF & LF

VCCTO ADT7468

SRC

BAND GAP

TEMP SENSOR

ACOUSTIC

ENHANCEMENT

CONTROL

ACOUSTIC

ENHANCEMENT

CONTROL

FAN SPEED

COUNTER

PERFORMANCE

MONITORING

THERMAL

PROTECTION

INPUT

SIGNAL

CONDITIONING

AND

ANALOG

MULTIPLEXER

GND

Figure 1.

SCL

SDA

SMBALERT

SERIAL BUS

INTERFACE

AUTOMATIC FAN SPEED

CONTROL

DYNAMIC

MIN

CONTROL

ADT7468

10-BIT

ADC

BAND GAP

REFERENCE

ADDRESS

POINTER

PWM

CONFIGURATION

REGISTERS

INTERRUPT

MASKING

INTERRUPT

STATUS

REGISTERS

LIMIT

COMPARATORS

VALUE AND

LIMIT

REGISTERS

04499-0-001

Page 2

ADT7468

TABLE OF CONTENTS

Specifications..................................................................................... 3

Absolute Maximum Ratings............................................................ 5

Thermal Characteristics .............................................................. 5

ESD Caution.................................................................................. 5

Pin Configuration and Function Descriptions............................. 6

Typical Performance Characteristics ............................................. 8

Product Description....................................................................... 10

Status Registers........................................................................... 23

THERM

Timer ........................................................................... 25

Fan Drive Using PWM Control ............................................... 28

Laying Out 2-Wire and 3-Wire Fans....................................... 30

Operating from 3.3 V Standby.................................................. 34

XNOR Tree Test Mode .............................................................. 35

Comparison between ADT7463 and ADT7468..................... 10

How to Set the Functionality of Pin 14 ...................................11

Recommended Implementation............................................... 11

Serial Bus Interface..................................................................... 12

Write Operations ........................................................................ 13

Read Operations ......................................................................... 14

SMBus Timeout.......................................................................... 14

Voltage Measurement Input...................................................... 14

Analog-to-Digital Converter ....................................................14

Input Circuitry ............................................................................ 15

Voltage Measurement Registers................................................ 15

Voltage Limit Registers.............................................................. 15

VID Code Monitoring............................................................... 15

VID Code Input Threshold Voltage......................................... 15

VID Code Change Detect Function ........................................ 16

Power-On Default ...................................................................... 35

Programming the Automatic Fan Speed Control Loop ............ 36

Automatic Fan Control Overview............................................ 36

Step 1: Hardware Configuration.............................................. 37

Recommended Implementation 1 ........................................... 38

Recommended Implementation 2 ........................................... 39

Step 2: Configuring the MUX................................................... 40

Step 3: T

Step 4: PWM

Step 5: PWM

Step 7: T

Step 8: T

Dynamic T

Settings for Thermal Calibration Channels....... 42

MIN

for Each PWM (Fan) Output....................... 43

MIN

for PWM (Fan) Outputs.............................. 43

MAX

for Temperature Channels ............................... 47

THERM

for Temperature Channels .................................. 48

HYST

Control Mode ................................................... 49

MIN

Step 9: Operating Points for Temperature Channels............. 51

Step 10: High and Low Limits for Temperature Channels ... 52

Additional ADC Functions for Voltage Measurements ........16

Temperature Measurement Method ........................................ 18

Series Resistance Cancellation.................................................. 19

Factors Affecting Diode Accuracy ........................................... 19

Additional ADC Functions for Temperature Measurement. 21

Limits, Status Registers, and Interrupts ....................................... 22

Limit Values................................................................................. 22

REVISION HISTORY

Revision 0: Initial Version

Rev. 0 | Page 2 of 80

Step 11: Monitoring

THERM

................................................... 55

Enhancing System Acoustics .................................................... 56

Step 12: Ramp Rate for Acoustic Enhancement..................... 58

ADT7468 Programming Block Diagram.................................... 79

Outline Dimensions....................................................................... 80

Ordering Guide .......................................................................... 80

Page 3

ADT7468

SPECIFICATIONS

TA = T All voltages are measured with respect to GND, unless otherwise specified. Typicals are at T norm. Logic inputs accept input high voltages up to V logic levels of V not production tested.

Table 1.

Parameter Min Typ Max Unit Test Conditions/Comments

POWER SUPPLY

20 µA Standby mode TEMP-TO-DIGITAL CONVERTER

36 µΑ Second current 96 µΑ Third current ANALOG-TO-DIGITAL CONVERTER (INCLUDING MUX AND ATTENUATORS)

FAN RPM-TO-DIGITAL CONVERTER

MIN

to T

, VCC = V

MAX

= 0.8 V for a falling edge and VIH = 2.0 V for a rising edge. SMBus timing specifications are guaranteed by design and are

MIN

to V

, unless otherwise noted.

MAX

= 25°C and represent most likely parametric

even when device is operating down to V

. Timing specifications are tested at

MIN

Supply Voltage 3.0 3.3 5.5 V Supply Current, ICC 3 mA Interface inactive, ADC active

Local Sensor Accuracy ±1.5 °C 0°C ≤ TA ≤ 70°C

−3.5 +2 °C −40°C ≤ TA ≤ +100°C

−4 +2 °C −40°C ≤ TA ≤ +120°C Resolution 0.25 °C Remote Diode Sensor Accuracy ±1.5 °C 0°C ≤ TA ≤ 70°C; 0°C ≤ TD ≤ 120°C

−3.5 +2 °C −40°C ≤ TA ≤ +100°C; 0°C ≤ TD ≤ +120°C

−4.5 +2 °C −40°C ≤ TA ≤ +120°C; 0°C ≤ TD ≤ +120°C Resolution 0.25 °C Remote Sensor Source Current 6 µA First current

Total Unadjusted Error (TUE) ±2 % For 12 V and 5 V channels ±1.5 % For all other channels Differential Nonlinearity (DNL) ±1 LSB 8 bits Power Supply Sensitivity ±0.1 %/V Conversion Time (Voltage Input) 11 ms Averaging enabled Conversion Time (Local Temperature) 12 ms Averaging enabled Conversion Time (Remote Temperature) 38 ms Averaging enabled Total Monitoring Cycle Time 145 ms Averaging enabled Total Monitoring Cycle Time 19 ms Averaging disabled Input Resistance 40 70 100 kΩ For V

channel

80 140 200 kΩ For all other channels

Accuracy ±5 % 0°C ≤ TA ≤ 70°C , 3.3 V ±7 % −40°C ≤ TA ≤ +120°C , 3.3 V ±10 % −40°C ≤ TA ≤ +120°C , 5.5 V Full-Scale Count 65,535 Nominal Input RPM 109 RPM Fan count = 0xBFFF 329 RPM Fan count = 0x3FFF 5000 RPM Fan count = 0x0438 10000 RPM Fan count = 0x021C

Internal Clock Frequency 85.5 90 94.5 kHz 0°C ≤ TA ≤ 70°C, V

83.7 90 96.3 kHz −40°C ≤ TA ≤ +120°C, V 81 90 99 kHz −40°C ≤ TA ≤ +120°C, V

= 3.3 V

= 3.3 V = 5.5 V

Rev. 0 | Page 3 of 80

Page 4

ADT7468

Parameter Min Typ Max Unit Test Conditions/Comments

OPEN-DRAIN DIGITAL OUTPUTS, PWM1 TO PWM3, XTO

Current Sink, IOL 8.0 mA Output Low Voltage, VOL 0.4 V I High Level Output Current, IOH 0.1 1.0 µA V

OPEN-DRAIN SERIAL DATA BUS OUTPUT (SDA)

Output Low Voltage, VOL 0.4 V I High Level Output Current, IOH 0.1 1.0 µA V

SMBUS DIGITAL INPUTS (SCL, SDA)

Input High Voltage, VIH 2.0 V Input Low Voltage, V

0.4 V

Hysteresis 500 mV

DIGITAL INPUT LOGIC LEVELS (TACH INPUTS)

Input High Voltage, VIH 2.0 V

5.5 V Maximum input voltage Input Low Voltage, VIL 0.8 V

−0.3 V Minimum input voltage Hysteresis 0.5 V p-p

DIGITAL INPUT LOGIC LEVELS (THERM) ADTL+

Input High Voltage, V Input Low Voltage, V

0.75 × V

0.4 V

CCP

DIGITAL INPUT CURRENT

Input High Current, IIH −1 µA VIN = VCC Input Low Current, IIL 1 µA VIN = 0 Input Capacitance, CIN 5 pF

SERIAL BUS TIMING See Figure 2

Clock Frequency, f

10 400 kHz

SCLK

Glitch Immunity, tSW 50 ns Bus Free Time, t Start Setup Time, t Start Hold Time, t SCL Low Time, t SCL High Time, t

4.7 µs

BUF

4.7 µs

SU;STA

4.0 µs

HD;STA

4.7 µs

LOW

4.0 50 µs

HIGH

SCL, SDA Rise Time, tR 1000 ns SCL, SDA Fall Time, t Data Setup Time, t Data Hold Time, t Detect Clock Low Timeout, t

300 µs

250 ns

SU;DAT

300 ns

HD;DAT

15 35 ms Can be optionally disabled

TIMEOUT

= −8.0 mA, VCC = +3.3 V

OUT

= VCC

OUT

= −4.0 mA, VCC = +3.3 V

OUT

= VCC

OUT

HIGH

SU; DAT

Figure 2. Serial Bus Timing Diagram

SU; STA

HD; STA

SU; STO

04499-0-002

SCL

BUF

HD; STA

LOW

HD; DAT

Rev. 0 | Page 4 of 80

Page 5

ADT7468

ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter Rating

Positive Supply Voltage (VCC) 5.5 V Maximum Voltage on 12 VIN Pin 20 V Voltage on Any Input or Output Pin −0.3 V to +6.5 V Input Current at Any Pin ±5 mA Package Input Current ±20 mA Maximum Junction Temperature (T Storage Temperature Range −65°C to +150°C Lead Temperature, Soldering

IR Reflow Peak Temperature 220°C Lead Temperature (Soldering 10 s) 300°C

ESD Rating 1000 V

) 150°C

JMAX

ESD CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.

Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

THERMAL CHARACTERISTICS

24-lead QSOP package:

= 150°C/W

= 39°C/W

Rev. 0 | Page 5 of 80

Page 6

ADT7468

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

SDA

SCL

GND

V VID0 VID1 VID2

VID3

TACH3

PWM2/SMBALERT

TACH1 TACH2

ADT7468

TOP VIEW

(NOT TO SCALE)

PWM1/XTO

CCP

+2.5V

+12VIN/VID5

/THERM

+5V

VID4

D1+

D1–

D2+

D2–

TACH4/GPIO/THERM/SMBALERT

PWM3

04499-0-003

Figure 3. Pin Configuration

Table 3. Pin Function Descriptions

Pin No.

Mnemonic Description

1 SDA Digital I/O (Open Drain). SMBus bidirectional serial data. Requires pull-up resistor. 2 SCL Digital Input (Open Drain). SMBus serial clock input. Requires pull-up resistor. 3 GND Ground Pin. 4 VCC

Power Supply. Can be powered by 3.3 V standby, if monitoring in low power states is required. V

is also monitored

through this pin. The ADT7468 can also be powered from a 5 V supply. Setting Bit 7 of Configuration Register 1 (Reg. 0x40) rescales the V

input attenuators to correctly measure a 5 V supply.

5 VID0 Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). 6 VID1 Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). 7 VID2 Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). 8 VID3 Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). 9 TACH3

Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 3. Can be reconfigured as an analog input (AIN3) to measure the speed of 2-wire fans.

10 PWM2

Digital Output (Open Drain). Requires 10 kΩ typical pull-up. Pulse width modulated output to control Fan 2 speed. Can be configured as a high or low frequency drive.

SMBALERT

Digital Output (Open Drain). This pin can be reconfigured as an SMBALERT interrupt output to signal out-of-limit

conditions.

11 TACH1

Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 1. Can be reconfigured as an analog input (AIN1) to measure the speed of 2-wire fans.

12 TACH2

Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 2. Can be reconfigured as an analog input (AIN2) to measure the speed of 2-wire fans.

13 PWM3

Digital I/O (Open Drain). Pulse width modulated output to control speed of Fan 3 and Fan 4. Requires 10 kΩ typical pull-up. Can be configured as a high or low frequency drive.

14 TACH4

Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 4. Can be reconfigured as an analog input (AIN4) to measure the speed of 2-wire fans.

GPIO General Purpose Open Drain Digital I/O.

Alternatively, the pin can be reconfigured as a bidirectional THERM pin. Can be used to time and monitor assertions

THERM

on the THERM

input. For example, this pin can be connected to the PROCHOT output of an Intel Pentium 4 processor or to the output of a trip point temperature sensor. This pin can also be used as an output to signal overtemperature conditions.

SMBALERT

Digital Output (Open Drain). This pin can be reconfigured as an SMBALERT interrupt output to signal out-of-limit

conditions.

15 D2– Cathode Connection to Second Thermal Diode. 16 D2+ Anode Connection to Second Thermal Diode. 17 D1– Cathode Connection to First Thermal Diode.

Rev. 0 | Page 6 of 80

Page 7

ADT7468

Pin No. Mnemonic Description

18 D1+ Anode Connection to First Thermal Diode. 19 VID4 Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). 20 +5VIN Analog Input. Monitors +5 V power supply.

21 +12VIN Analog Input. Monitors +12 V power supply. VID5

22 +2.5VIN Analog Input. Monitors +2.5 V supply, typically a chipset voltage. 23 V 24 PWM1 Digital Output (Open Drain). Pulse width modulated output to control Fan 1 speed. Requires 10 kΩ typical pull-up. XTO Also functions as the output from the XOR tree in XOR test mode.

Alternatively, this pin can be reconfigured as a bidirectional THERM pin. Can be used to time and monitor assertions

THERM

on the THERM the output of a trip point temperature sensor. This pin can also be used as an output to signal overtemperature conditions.

Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). Supports VRM10 solutions.

Analog Input. Monitors processor core voltage (0 V to 3 V).

CCP

input. For example, it can be connected to the PROCHOT output of an Intel Pentium 4 processor or to

Rev. 0 | Page 7 of 80

Page 8

ADT7468

TYPICAL PERFORMANCE CHARACTERISTICS

100mV

–10

–20

–30

–40

TEMPERATURE ERROR (°C)

–50

–60

1 4.73.3 100 2.2

CAPACITANCE (nF)

Figure 4. Temperature Error vs. Capacitance between D+ and D−

–10

–20

–30

–40

–50

–60

–70

TEMPERATURE ERROR (°C)

–80

–90

–100

CAPACITANCE (nF)

Figure 5. External Temperature Error vs. D+/D− Capacitance

D+ TO GND

04499-0-045

TEMPERATURE ERROR (°C)

–5

–10

60mV

40mV

FREQUENCY (kHz)

1G10 100 1M 10M 100M

04499-0-048

Figure 7. Remote Temperature Error vs. Common Mode Noise Frequency

–1

TEMPERATURE ERROR (°C)

–2

–3

2501020515

04499-0-046

–4

10mV

FREQUENCY (kHz)

20mV

1G10 100 1M 10M 100M

04499-0-049

Figure 8. Remote Temperature Error vs. Differential Mode Noise Frequency

1.40

1.35

D+ TO V

–20

–40

TEMPERATURE ERROR (°C)

–60

–80

RESISTANCE (MΩ)

Figure 6. Remote Temperature Error vs. PCB Resistance

1.30

1.25

(mA)

1.20

1.15

1.10

1000 3.3 20110

04499-0-047

1.05

3.0 3.8 5.23.4 4.43.6 4.83.2 4.0 5.44.6 5.04.2 POWER SUPPLY VOLTAGE (V)

Figure 9. Normal I

vs. Power Supply

04499-0-050

Rev. 0 | Page 8 of 80

Page 9

ADT7468

(

3.0 3.8 5.23.4 4.43.6 4.83.2 4.0 5.44.6 5.04.2 POWER SUPPLY VOLTAGE (V)

Figure 10. Shutdown I

vs. Power Supply

–5

–10

TEMPERATURE ERROR (°C)

–15

–20

INT ERROR, 100mV

POWER SUPPLY NOISE FREQUENCY (kHz)

INT ERROR, 250mV

Figure 11. Internal Temperature Error vs. Power Supply

EXT ERROR, 250mV

04499-0-051

1G10 100 1M 10M 100M

04499-0-052

1.0

0.5

–0.5

–1.0

–1.5

–2.0

ERROR (°C)

–2.5

–3.0

–3.5

–4.0

TEMPERATURE (°C)

Figure 13. Internal Temperature Error vs. ADT7468 Temperature

1.0

0.5

–0.5

–1.0

–1.5

–2.0

ERROR (°C)

–2.5

–3.0

–3.5

–4.0

TEMPERATURE (°C)

Figure 14. Remote Temperature Error vs. ADT7468 Temperature

120–40 –20 0 20 40 60 80 100

04499-0-091

120–40 –20 0 20 40 60 80 100

04499-0-092

EXT ERROR, 100mV

–5

–10

TEMPERATURE ERROR (°C)

–15

–20

POWER SUPPLY NOISE FREQUENCY (kHz)

1G10 100 1M 10M 100M

Figure 12. Remote Temperature Error vs. Power Supply Noise Frequency

04499-0-053

Rev. 0 | Page 9 of 80

Page 10

ADT7468

PRODUCT DESCRIPTION

The ADT7468 is a complete thermal monitor and multiple fan controller for any system requiring thermal monitoring and cooling. The device communicates with the system via a serial system management bus. The serial bus controller has a serial data line for reading and writing addresses and data (Pin 1), and an input line for the serial clock (Pin 2). All control and programming functions for the ADT7468 are performed over the serial bus. In addition, a pin can be reconfigured as an SMBALERT

COMPARISON BETWEEN ADT7463 AND ADT7468

The ADT7468 is an upgrade to the ADT7463. The ADT7468 and ADT7463 are almost pin and register map compatible. The ADT7468 and ADT7463 have the following differences:

1. On the ADT7468, the PWM drive signals can be config-

2. Once the V

3. The fans are switched off by default on power-up on the

4. Series resistance cancellation (SRC) is provided on the

output to signal out-of-limit conditions.

ured as either high frequency or low frequency drives. The low frequency option is programmable between 10 Hz and 100 Hz. The high frequency option is 22.5 kHz. On the ADT7463, only the low frequency option is available.

is powered up, monitoring of temperature

and fan speeds is enabled on the ADT7468 when V powered up, or if V

is never powered up, when the first

CCP

SMBus transaction with the ADT7468 is completed. On the ADT7463, the STRT bit in Configuration Register 1 must be set to enable monitoring.

ADT7468. On the ADT7463, the fans run at full speed on power-up.

Fail-safe cooling is provided on the ADT7468 in that, if the measured temperature exceeds the

THERM

limit (100°C),

the fans run at full speed.

Fail-safe cooling is also provided 4.6 s after V

is powered

CCP

up. See Figure 48. The fans go to full speed, if the ADT7468 has not been addressed via the SMBus within 4.6 s of when the V

is powered up. This protects the system in the

CCP

event that the SMBus fails. The ADT7468 can be programmed at any time, either before or after the 4.6 s has elapsed, and it behaves as programmed. If V powered up, fail-safe cooling is effectively disabled. If V

is never

CCP

is disabled, writing to the ADT7468 at any time causes the ADT7468 to operate normally.

remote temperature channels on the ADT7468, but not on the ADT7463. SRC automatically cancels linear offset introduced by a series resistance between the thermal diode and the sensor.

5. The ADT7468 has an extended temperature measurement

range. The measurement range goes from–64°C to +191°C. On the ADT7463, the measurement range is from −127°C to +127°C. This means that the ADT7468 can measure higher temperatures. The ADT7468 also includes the ADT7463 temperature range; the temperature measurement range can be switched by setting Bit 0 of Configuration Register 5.

6. The ADT7468 maximum fan speed (% duty cycle) in the

automatic fan speed control loop can be programmed. The maximum fan speed is 100% duty cycle on the ADT7463 and is not programmable.

7. The offset register in the ADT7468 is programmable up to

±64°C with 0.50°C resolution. The offset register of the ADT7463 is programmable up to ±32°C with 0.25°C resolution.

8. V

is monitored on Pin 23 of the ADT7468 and can be

CCP

used to set the threshold for

). The threshold for

CCP

= 1.7 V and VIL = 0.8 V on the ADT7463.

THERM

THERM (PROCHOT

PROCHOT

(

) (2/3 of

) is set at

9. On the ADT7463, Pin 22 can be reconfigured as SMBus

ALERT. This is not available on the ADT7468; instead, SMBALERT

can be enabled on Pin 14.

10. A GPIO can also be made available on Pin 14 on the

ADT7468. This is not available on the ADT7463. Set the GPIO polarity and direction in Configuration Register 5. The GPIO status bit is Bit 5 of Status Register 2 (shared with TACH4 and

THERM

, because only one can be

enabled at a time).

11. The ADT7463 has three possible SMBus addresses, which

are selectable using the address select and address enable pins. The ADT7468 has one SMBus address available at Address 0x2E.

Due to the inclusion of extra functionality, the register map has changed, including an additional configuration register: Configuration Register 5 at Address 0x7C.

Configuration Register 5

Bit 0: If Bit 0 is set to 1, the ADT7468 is backward compatible temperature-wise with the ADT7463. Measurements, T

MIN

calibration circuit, fan control, etc., work in the range −127°C to +127°C. Also, care should be taken in reprogramming the temperature limits (T

, operating point,

MIN

THERM

limits) to their desired twos complement value, because the power-on default for them is at Offset 64. The extended temperature range is −64°C to 191°C. The default is 1, which is in the −64°C to +191°C temperature range.

Rev. 0 | Page 10 of 80

Page 11

ADT7468

Bit 1= 0 is the high frequency (22.5 kHz) fan drive signal.

Bit 1 = 1 switches the fan drive to low frequency PWM,

programmable between 10 Hz and 100 Hz, the same as the ADT7463. The default = 0 = HF PWM.

Bit 2 sets the direction for the GPIO: 0 = input, 1 = output.

RECOMMENDED IMPLEMENTATION

Configuring the ADT7468 as in Figure 15 allows the system designer to use the following features:

• Two PWM outputs for fan control of up to three fans (the

front and rear chassis fans are connected in parallel).

Bit 3 sets the GPIO polarity: 0 = active low, 1 = active high.

HOW TO SET THE FUNCTIONALITY OF PIN 14

Pin 14 on the ADT7468 has four possible functions: SMBALERT required functionality by setting Bit 0 and Bit 1 of Configuration Register 4 at Address 0x7D.

Table 4. Pin 14 Settings

Bit 0 Bit 1 Function

00 TACH4 01

10 11 GPIO

THERM

, GPIO, and TACH4. The user chooses the

THERM SMBALERT

FRONT CHASSIS FAN

REAR CHASSIS FAN

AMBIENT TEMPERATURE

TACH2

PWM3 TACH3

D1+ D1–

• Three TACH fan speed measurement inputs.

• V

• CPU temperature measured using Remote 1 temperature

• Ambient temperature measured through Remote 2

• Bidirectional

ADT7468

VID[0:4]/VID[0:5]

THERM

measured internally through Pin 3.

channel.

temperature channel.

Pentium 4 overtemperature programmed as an

PWM1

TACH1

5(VRM9)/6(VRM10)

D2+ D2–

PROCHOT

THERM

PROCHOT

THERM

SMBALERT

CPU FAN

CPU

pin. This feature allows Intel

monitoring and can function as an

output. It can alternatively be

system interrupt output.

3.3VSB

ADP316x

VRM

CONTROLLER

COMP

5V 12V/VID5

CURRENT V

CORE

GND

SDA SCL

SMBALERT

ICH

04499-0-004

Figure 15. ADT7468 Configuration

Rev. 0 | Page 11 of 80

Page 12

ADT7468

SERIAL BUS INTERFACE

On PCs and servers, control of the ADT7468 is carried out using the serial system management bus (SMBus). The ADT7468 is connected to this bus as a slave device, under the control of a master controller, which is usually (but not necessarily) the ICH.

The ADT7468 has a fixed 7-bit serial bus address of 0101110 or 0x2E. The read/write bit must be added to get the 8-bit address (01011100 or 0x5C). Data is sent over the serial bus in sequences of nine clock pulses: eight bits of data followed by an acknowledge bit from the slave device. Transitions on the data line must occur during the low period of the clock signal and remain stable during the high period, because a low-to-high transition when the clock is high might be interpreted as a stop signal. The number of data bytes that can be transmitted over the serial bus in a single read or write operation is limited only by what the master and slave devices can handle.

When all data bytes have been read or written, stop conditions are established. In write mode, the master pulls the data line high during the tenth clock pulse to assert a stop condition. In read mode, the master device overrides the acknowledge bit by pulling the data line high during the low period before the ninth clock pulse. This is known as No Acknowledge. The master then takes the data line low during the low period before the tenth clock pulse, and then high during the tenth clock pulse to assert a stop condition.

Any number of bytes of data can be transferred over the serial bus in one operation, but it is not possible to mix read and write in one operation, because the type of operation is determined at the beginning and cannot subsequently be changed without starting a new operation.

In the ADT7468, write operations contain either one or two bytes, and read operations contain one byte and perform the following functions. To write data to one of the device data registers or read data from it, the address pointer register must be set so that the correct data register is addressed, then data can be written into that register or read from it. The first byte of a write operation always contains an address that is stored in the address pointer register. If data is to be written to the device, then the write operation contains a second data byte that is written to the register selected by the address pointer register.

This write operation is illustrated in Figure 16. The device

address is sent over the bus, and then R/

is set to 0. This is followed by two data bytes. The first data byte is the address of the internal data register to be written to, which is stored in the address pointer register. The second data byte is the data to be written to the internal data register.

When reading data from a register, there are two possibilities:

• If the ADT7468’s address pointer register value is unknown

or not the desired value, it must first be set to the correct value before data can be read from the desired data register. This is done by performing a write to the ADT7468 as before, but only the data byte containing the register address is sent, because no data is written to the register. This is shown in Figure 17.

A read operation is then performed consisting of the serial

bus address, R/

bit set to 1, followed by the data byte read

from the data register. This is shown in Figure 18.

• If the address pointer register is known to be already at the

desired address, data can be read from the corresponding data register without first writing to the address pointer register, as shown in Figure 18.

SCL

SDA

START BY

MASTER

1011

FRAME 1

SERIAL BUS ADDRESS BYTE

SCL (CONTINUED)

SDA (CONTINUED)

Figure 16. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

R/W

ACK. BY ADT7468

Rev. 0 | Page 12 of 80

ADDRESS POINTER REGISTER BYTE

FRAME 3

DATA BYTE

FRAME 2

ACK. BY

ADT7468

ACK. BY

ADT7468

STOP BY MASTER

04499-0-005

Page 13

ADT7468

SDA

SCL

SDA

START BY

MASTER

1011

SERIAL BUS ADDRESS BYTE

FRAME 1

R/W

ACK. BY ADT7468

Figure 17. Writing to the Address Pointer Register Only

SCL

START BY

MASTER

SERIAL BUS ADDRESS BYTE

FRAME 1

R/W

ACK. BY

ADT7468

Figure 18. Reading Data from a Previously Selected Register

It is possible to read a data byte from a data register without first writing to the address pointer register, if the address pointer register is already at the correct value. However, it is not possible to write data to a register without writing to the address pointer register, because the first data byte of a write is always written to the address pointer register.

In addition to supporting the send byte and receive byte protocols, the ADT7468 also supports the read byte protocol. (see System Management Bus Specifications Rev. 2 for more information. This document is available from Intel.)

If several read or write operations must be performed in succession, the master can send a repeat start condition instead of a stop condition to begin a new operation.

WRITE OPERATIONS

The SMBus specification defines several protocols for different types of read and write operations. The ones used in the ADT7468 are discussed below. The following abbreviations are used in the diagrams:

S – START P – STOP R – READ W – WRITE A – ACKNOWLEDGE A

– NO ACKNOWLEDGE

ACK. BY ADT7468

STOP BY MASTER

ADDRESS POINTER REGISTER BYTE

FRAME 2

DATA BYTE FROM ADT7468

FRAME 2

NO ACK. BY

MASTER

STOP BY MASTER

2. The master sends the 7-bit slave address followed by the

write bit (low).

3. The addressed slave device asserts ACK on SDA.

4. The master sends a command code.

5. The slave asserts ACK on SDA.

6. The master asserts a stop condition on SDA and the

transaction ends.

For the ADT7468, the send byte protocol is used to write a register address to RAM for a subsequent single byte read from the same address. This operation is illustrated in Figure 19.

231564

SLAVE

ADDRESS

WASAP

ADDRESS

04499-0-008

Figure 19. Setting a Register Address for Subsequent Read

If the master is required to read data from the register immediately after setting up the address, it can assert a repeat start condition immediately after the final ACK and carry out a single byte read without asserting an intermediate stop condition.

Write Byte

In this operation, the master device sends a command byte and one data byte to the slave device, as follows:

04499-0-006

04499-0-007

The ADT7468 uses the following SMBus write protocols.

Send Byte

In this operation, the master device sends a single command byte to a slave device as follows:

1. The master device asserts a start condition on SDA.

2. The master sends the 7-bit slave address followed by the

write bit (low).

3. The addressed slave device asserts ACK on SDA.

4. The master sends a command code.

Rev. 0 | Page 13 of 80

Page 14

ADT7468

5. The slave asserts ACK on SDA.

SMBALERT

is pulled low.

6. The master sends a data byte.

7. The slave asserts ACK on SDA.

8. The master asserts a stop condition on SDA to end the

transaction.

This operation is illustrated in Figure 20.

24653178

SLAVE

ADDRESS

Figure 20. Single Byte Write to a Register

SLAVE

ADDRESS

DATAAAWSAP

04499-0-009

READ OPERATIONS

The ADT7468 uses the following SMBus read protocols.

Receive Byte

This operation is useful when repeatedly reading a single register. The register address must have been set up previously. In this operation, the master device receives a single byte from a slave device as follows:

1. The master device asserts a start condition on SDA.

2. The master sends the 7-bit slave address followed by the

read bit (high).

3. The addressed slave device asserts ACK on SDA.

4. The master receives a data byte.

5. The master asserts NO ACK on SDA.

6. The master asserts a stop condition on SDA and the

transaction ends.

In the ADT7468, the receive byte protocol is used to read a single byte of data from a register whose address has previously been set by a send byte or write byte operation. This operation is illustrated in Figure 21.

213564

SLAVE

SRAAPDATA

ADDRESS

Figure 21. Single Byte Read from a Register

Alert Response Address

Alert response address (ARA) is a feature of SMBus devices that allows an interrupting device to identify itself to the host when multiple devices exist on the same bus.

SMBALERT

The output or an connected to a common master. If a device’s

output can be used as either an interrupt

SMBALERT

. One or more outputs can be

SMBALERT

line connected to the

line goes low, the following

procedure occurs:

04499-0-010

2. The master initiates a read operation and sends the alert

response address (ARA = 0001 100). This is a general call address that must not be used as a specific device address.

3. The device whose

SMBALERT

output is low responds to the alert response address, and the master reads its device address. The address of the device is now known and can be interrogated in the usual way.

4. If more than one device’s

SMBALERT

output is low, the one with the lowest device address has priority in accordance with normal SMBus arbitration.

5. Once the ADT7468 has responded to the alert response

address, the master must read the status registers and the SMBALERT

is cleared only if the error condition has gone

away.

SMBUS TIMEOUT

The ADT7468 includes an SMBus timeout feature. If there is no SMBus activity for 35 ms, the ADT7468 assumes that the bus is locked and releases the bus. This prevents the device from locking or holding the SMBus expecting data. Some SMBus controllers cannot handle the SMBus timeout feature, so it can be disabled.

Configuration Register 1(Reg. 0x40)

<6> TODIS = 0, SMBus timeout enabled (default).

<6> TODIS = 1, SMBus timeout disabled.

VOLTAGE MEASUREMENT INPUT

The ADT7468 has four external voltage measurement channels. It can also measure its own supply voltage, V

. Pins 20 to 23

can measure 5 V, 12 V, and 2.5 V supplies, and the processor core voltage V measurement is carried out through the V

(0 V to 3 V input). The VCC supply voltage

CCP

pin (Pin 4). Setting

Bit 7 of Configuration Register 1 (Reg. 0x40) allows a 5 V supply to power the ADT7468 and be measured without overranging the V

measurement channel. The 2.5 V input can

be used to monitor a chipset supply voltage in computer systems.

ANALOG-TO-DIGITAL CONVERTER

All analog inputs are multiplexed into the on-chip, successiveapproximation, analog-to-digital converter. This has a resolution of 10 bits. The basic input range is 0 V to 2.25 V, but the inputs have built-in attenuators to allow measurement of 2.5 V,

3.3 V, 5 V, 12 V, and the processor core voltage V external components. To allow for the tolerance of these supply voltages, the ADC produces an output of 3/4 full scale (decimal 768 or 300 hex) for the nominal input voltage and so has adequate headroom to cope with overvoltages.

without any

CCP

Rev. 0 | Page 14 of 80

Page 15

ADT7468

INPUT CIRCUITRY

The internal structure for the analog inputs is shown in Figure 22. The input circuit consists of an input protection diode, an attenuator, plus a capacitor to form a first-order lowpass filter that gives input immunity to high frequency noise.

12V

3.3V

2.5V

CCP

120kΩ

Figure 22. Structure of Analog Inputs

20kΩ 30pF

93kΩ

47kΩ 30pF

68kΩ

71kΩ 30pF

45kΩ

94kΩ 30pF

17.5kΩ

52.5kΩ 35pF

MUX

04499-0-011

Reg. 0x4C, 12 V Low Limit = 0x00 default

Reg. 0x4D, 12 V High Limit = 0xFF default

Table 5 shows the input ranges of the analog inputs and output codes of the 10-bit ADC.

When the ADC is running, it samples and converts a voltage input in 0.7 ms and averages 16 conversions to reduce noise; a measurement takes nominally 11 ms.

VID CODE MONITORING

The ADT7468 has five dedicated voltage ID (VID code) inputs. These are digital inputs that can be read back through the VID register (Reg. 0x43) to determine the processor voltage required or being used in the system. Five VID code inputs support VRM9.x solutions. In addition, Pin 21 (12 V input) can be reconfigured as a sixth VID input to satisfy future VRM requirements.

VID Code Register (Reg. 0x43)

<0> = VID0, reflects logic state of Pin 5.

<1> = VID1, reflects logic state of Pin 6.

<2> = VID2, reflects logic state of Pin 7.

VOLTAGE MEASUREMENT REGISTERS

Reg. 0x20, 2.5 V Reading = 0x00 default

Reg. 0x21, V

Reg. 0x22, V

Reading = 0x00 default

CCP

Reading = 0x00 default

Reg. 0x23, 5 V Reading = 0x00 default

Reg. 0x24, 12 V Reading = 0x00 default

VOLTAGE LIMIT REGISTERS

Associated with each voltage measurement channel is a high and low limit register. Exceeding the programmed high or low limit causes the appropriate status bit to be set. Exceeding either limit can also generate

SMBALERT

Reg. 0x44, 2.5 V Low Limit = 0x00 default

Reg. 0x45, 2.5 V High Limit = 0xFF default

Reg. 0x46, V

Reg. 0x47, V

Reg. 0x48, V

Reg. 0x49, V

Low Limit = 0x00 default

CCP

High Limit = 0xFF default

CCP

Low Limit = 0x00 default

High Limit = 0xFF default

Reg. 0x4A, 5 V Low Limit = 0x00 default

Reg. 0x4B, 5 V High Limit = 0xFF default

interrupts.

<3> = VID3, reflects logic state of Pin 8.

<4> = VID4, reflects logic state of Pin 19.

<5> = VID5, reconfigurable 12 V input. This bit reads 0 when

Pin 21 is configured as the 12 V input. This bit reflects the logic state of Pin 21 when the pin is configured as VID5.

VID CODE INPUT THRESHOLD VOLTAGE

The switching threshold for the VID code inputs is approximately 1 V. To enable future compatibility, it is possible to reduce the VID code input threshold to 0.6 V. Bit 6 (THLD) of the VID register (Reg. 0x43) controls the VID input threshold voltage.

VID CODE REGISTER (Reg. 0x43)

<6> THLD = 0, VID switching threshold = 1 V,

< 0.8 V, VIH > 1.7 V, V

THLD = 1, VID switching threshold = 0.6 V,

< 0.4 V, VIH > 0.8 V, V

Reconfiguring Pin 21 as VID5 Input

Pin 21 can be reconfigured as a sixth VID code input (VID5) for VRM10 compatible systems. Because the pin is configured as VID5, it is not possible to monitor a 12 V supply.

Bit 7 of the VID register (Reg. 0x43) determines the function of Pin 21. System or BIOS software can read the state of Bit 7 to determine whether the system is designed to monitor 12 V or is monitoring a sixth VID input.

MAX

= 3.3 V

Rev. 0 | Page 15 of 80

Page 16

ADT7468

VID Code Register (Reg. 0x43)

<7> VIDSEL = 0, Pin 21 functions as a 12 V measurement input. Software can read this bit to determine that there are five VID inputs being monitored. Bit 5 of Register 0x43 (VID5) always reads back 0. Bit 0 of Status Register 2 (Reg. 0x42) reflects 12 V out-of-limit measurements.

VIDSEL = 1, Pin 21 functions as the sixth VID code input (VID5). Software can read this bit to determine that there are six VID inputs being monitored. Bit 5 of Register 0x43 reflects the logic state of Pin 21. Bit 0 of Status Register 2 (Reg. 0x42) reflects VID code changes.

VID CODE CHANGE DETECT FUNCTION

The ADT7468 has a VID code change detect function. When Pin 21 is configured as the VID5 input, VID code changes can be detected and reported back by the ADT7468. Bit 0 of Status Register 2 (Reg. 0x42) is the 12 V/VC bit and denotes a VID change when set. The VID code change bit is set when the logic states on the VID inputs are different than they were 11 µs previously. The change of VID code can be used to generate an SMBALERT

interrupt. If an required, Bit 0 of Interrupt Mask Register 2 (Reg. 0x75), when set, prevents

SMBALERT

changes.

Status Register 2 (Reg. 0x42)

<0> 12V/VC = 0, if Pin 21 is configured as VID5, then Logic 0 denotes no change in VID code within the last 11 µs.

<0> 12V/VC = 1, if Pin 21 is configured as VID5, then Logic 1 means that a change has occurred on the VID code inputs within the last 11 µs. An function is enabled.

ADDITIONAL ADC FUNCTIONS FOR VOLTAGE MEASUREMENTS

A number of other functions are available on the ADT7468 to offer the system designer increased flexibility.

Turn-Off Averaging

For each voltage measurement read from a value register, 16 readings have actually been made internally and the results averaged before being placed into the value register. For

SMBALERT

interrupt is not

s from occurring on VID code

SMBALERT

is generated, if this

instances where faster conversions are needed, setting Bit 4 of Configuration Register 2 (Reg. 0x73) turns averaging off. This effectively gives a reading 16 times faster (0.7 ms), but the reading may be noisier.

Bypass Voltage Input Attenuator

Setting Bit 5 of Configuration Register 2 (Reg. 0x73) removes the attenuation circuitry from the 2.5 V, V

, VCC, 5 V, and 12 V

CCP

inputs. This allows the user to directly connect external sensors or rescale the analog voltage measurement inputs for other applications. The input range of the ADC without the attenuators is 0 V to 2.25 V.

Single-Channel ADC Conversion

Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the ADT7468 into single-channel ADC conversion mode. In this mode, the ADT7468 can be made to read a single voltage channel only. If the internal ADT7468 clock is used, the selected input is read every 0.7 ms. The appropriate ADC channel is selected by writing to Bits <7:5> of the TACH1 minimum high byte register (0x55).

Bits <7:5> Reg. 0x55 Channel Selected

000 2.5 V 001 V 010 VCC 011 5 V 100 12 V 101 Remote 1 Temperature 110 Local Temperature 111 Remote 2 Temperature

CCP

Configuration Register 2 (Reg. 0x73)

<4> = 1, averaging off.

<5> = 1, bypass input attenuators.

<6> = 1, single-channel convert mode.

TACH1 Minimum High Byte (Reg. 0x55)

<7:5> Selects ADC channel for single-channel convert mode.

Rev. 0 | Page 16 of 80

Page 17

ADT7468

Table 5. 10-Bit A/D Output Code vs. VIN

Input Voltage A/D Output

12 VIN 5 VIN V

(3.3 VIN)

<0.0156 <0.0065 <0.0042 <0.0032 <0.00293 0 00000000 00

0.0156–0.0312 0.0065–0.0130 0.0042–0.0085 0.0032–0.0065 0.0293–0.0058 1 00000000 01

0.0312–0.0469 0.0130–0.0195 0.0085–0.0128 0.0065–0.0097 0.0058–0.0087 2 00000000 10

0.0469–0.0625 0.0195–0.0260 0.0128–0.0171 0.0097–0.0130 0.0087–0.0117 3 00000000 11

0.0625–0.0781 0.0260–0.0325 0.0171–0.0214 0.0130–0.0162 0.0117–0.0146 4 00000001 00

0.0781–0.0937 0.0325–0.0390 0.0214–0.0257 0.0162–0.0195 0.0146–0.0175 5 00000001 01

0.0937–0.1093 0.0390–0.0455 0.0257–0.0300 0.0195–0.0227 0.0175–0.0205 6 00000001 10

0.1093–0.1250 0.0455–0.0521 0.0300–0.0343 0.0227–0.0260 0.0205–0.0234 7 00000001 11

0.1250–0.1406 0.0521–0.0586 0.0343–0.0386 0.0260–0.0292 0.0234–0.0263 8 00000010 00

•

4.0000–4.0156 1.6675–1.6740 1.1000–1.1042 0.8325–0.8357 0.7500–0.7529 256 (1/4 scale) 01000000 00

•

8.0000–8.0156 3.3300–3.3415 2.2000–2.2042 1.6650–1.6682 1.5000–1.5029 512 (1/2 scale) 10000000 00

•

12.0000–12.0156 5.0025–5.0090 3.3000–3.3042 2.4975–2.5007 2.2500–2.2529 768 (3/4 scale) 11000000 00

•

15.8281–15.8437 6.5983–6.6048 4.3527–4.3570 3.2942–3.2974 2.9677–2.9707 1013 11111101 01

15.8437–15.8593 6.6048–6.6113 4.3570–4.3613 3.2974–3.3007 2.9707–2.9736 1014 11111101 10

15.8593–15.8750 6.6113–6.6178 4.3613–4.3656 3.3007–3.3039 2.9736–2.9765 1015 11111101 11

15.8750–15.8906 6.6178–6.6244 4.3656–4.3699 3.3039–3.3072 2.9765–2.9794 1016 11111110 00

15.8906–15.9062 6.6244–6.6309 4.3699–4.3742 3.3072–3.3104 2.9794–2.9824 1017 11111110 01

15.9062–15.9218 6.6309–6.6374 4.3742–4.3785 3.3104–3.3137 2.9824–2.9853 1018 11111110 10

15.9218–15.9375 6.6374–6.4390 4.3785–4.3828 3.3137–3.3169 2.9853–2.9882 1019 11111110 11

15.9375–15.9531 6.6439–6.6504 4.3828–4.3871 3.3169–3.3202 2.9882–2.9912 1020 11111111 00

15.9531–15.9687 6.6504–6.6569 4.3871–4.3914 3.3202–3.3234 2.9912–2.9941 1021 11111111 01

15.9687–15.9843 6.6569–6.6634 4.3914–4.3957 3.3234–3.3267 2.9941–2.9970 1022 11111111 10 >15.9843 >6.6634 >4.3957 >3.3267 >2.9970 1023 11111111 11

The VCC output codes listed assume that VCC is 3.3 V. If VCC input is reconfigured for 5 V operation (by setting Bit 7 of Configuration Register 1), then the VCC output codes

are the same as for the 5 V

column.

2.5 V

Decimal Binary (10 Bits)

CCP

Rev. 0 | Page 17 of 80

Page 18

ADT7468

(

×=∆

TEMPERATURE MEASUREMENT METHOD

A simple method of measuring temperature is to exploit the negative temperature coefficient of a diode, measuring the baseemitter voltage (V current. Unfortunately, this technique requires calibration to null out the effect of the absolute value of V from device to device.

The technique used in the ADT7468 is to measure the change in

when the device is operated at three different currents.

Previous devices have used only two operating currents, but the use of a third current allows automatic cancellation of resistances in series with the external temperature sensor.

Figure 24 shows the input signal conditioning used to measure the output of an external temperature sensor. This figure shows the external sensor as a substrate transistor, but it could equally be a discrete transistor. If a discrete transistor is used, the collector is not grounded and should be linked to the base. To prevent ground noise from interfering with the measurement, the more negative terminal of the sensor is not referenced to ground, but is biased above ground by an internal diode at the D− input. C1 can optionally be added as a noise filter (recommended maximum value 1000 pF). However, a better option in noisy environments is to add a filter, as described in the Noise Filtering section.

Local Temperature Measurement

The ADT7468 contains an on-chip band gap temperature sensor whose output is digitized by the on-chip 10-bit ADC. The 8-bit MSB temperature data is stored in the local temperature register (Address 26h). Because both positive and negative temperatures can be measured, the temperature data is stored in Offset 64 format or twos complement format, as shown in Table 6 and Table 7. Theoretically, the temperature sensor and ADC can measure temperatures from −128°C to +127°C (or

−61°C to +191°C in the extended temperature range) with a resolution of 0.25°C. However, this exceeds the operating temperature range of the device, so local temperature measurements outside the ADT7468 operating temperature range are not possible.

Remote Temperature Measurement

The ADT7468 can measure the temperature of two remote diode sensors or diode-connected transistors connected to Pins 17 and 18, or 15 and 16.

) of a transistor, operated at constant

, which varies

This is given by

)

NnqKTV

where:

K is Boltzmann’s constant. q is the charge on the carrier. T is the absolute temperature in Kelvin. N is the ratio of the two currents.

Figure 23 shows the input signal conditioning used to measure the output of a remote temperature sensor. This figure shows the external sensor as a substrate transistor, provided for temperature monitoring on some microprocessors. It could also be a discrete transistor such as a 2N3904/2N3906.

N2 × IIN1× II

REMOTE

SENSING

TRANSISTOR

D+

D–

Figure 23. Signal Conditioning for Remote Diode Temperature Sensors

BIAS

fC = 65kHz

LPF

OUT+

TO ADC

OUT–

If a discrete transistor is used, the collector is not grounded and should be linked to the base. If a PNP transistor is used, the base is connected to the D– input and the emitter to the D+ input. If an NPN transistor is used, the emitter is connected to the D– input and the base to the D+ input. Figure 25 and Figure 26 show how to connect the ADT7468 to an NPN or PNP transistor for temperature measurement. To prevent ground noise from interfering with the measurement, the more negative terminal of the sensor is not referenced to ground, but is biased above ground by an internal diode at the D– input.

To m e as u re ∆ V

, the operating current through the sensor is

switched among three related currents. Shown in Figure 23, N1 × I and N2 × I are different multiples of the current I. The currents through the temperature diode are switched between I and N1 × I, giving ∆V giving ∆V the two ∆V

. The temperature can then be calculated using

BE2

measurements. This method can also cancel the

, and then between I and N2 × I,

BE1

effect of any series resistance on the temperature measurement.

04499-0-012

The forward voltage of a diode or diode-connected transistor operated at a constant current exhibits a negative temperature coefficient of about –2 mV/°C. Unfortunately, the absolute value

varies from device to device and individual calibration is

of V

required to null this out, so the technique is unsuitable for mass production. The technique used in the ADT7468 is to measure the change in V

when the device is operated at three different

The resulting ∆V low-pass filter to remove noise and then to a chopper-stabilized amplifier. This amplifies and rectifies the waveform to produce a dc voltage proportional to ∆V voltage, and a temperature measurement is produced. To reduce the effects of noise, digital filtering is performed by averaging the results of 16 measurement cycles.

waveforms are passed through a 65 kHz

. The ADC digitizes this

currents.

Rev. 0 | Page 18 of 80

Page 19

ADT7468

The results of remote temperature measurements are stored in 10-bit, twos complement format, as illustrated in Table 6. The extra resolution for the temperature measurements is held in the Extended Resolution Register 2 (Reg. 0x77). This gives temperature readings with a resolution of 0.25°C.

Noise Filtering

For temperature sensors operating in noisy environments, previous practice was to place a capacitor across the D+ and D− pins to help combat the effects of noise. However, large capacitances affect the accuracy of the temperature measurement, leading to a recommended maximum capacitor value of 1000 pF. This capacitor reduces the noise, but does not eliminate it, making use the sensor difficult in a very noisy environment.

The ADT7468 has a major advantage over other devices for eliminating the effects of noise on the external sensor. Using the series resistance cancellation feature, a filter can be constructed between the external temperature sensor and the part. The effect of any filter resistance seen in series with the remote sensor is automatically canceled from the temperature result.

The construction of a filter allows the ADT7468 and the remote temperature sensor to operate in noisy environments. Figure 24 shows a low-pass R-C-R filter, with the following values :

R = 100 Ω, C = 1 nF.

This filtering reduces both common-mode noise and differential noise.

100Ω

REMOTE

EMPERATURE

SENSOR

Figure 24. Filter Between Remote Sensor and ADT7468

100Ω

1nF

D+

D–

04499-0-093

SERIES RESISTANCE CANCELLATION

Parasitic resistance to the ADT7468 D+ and D− inputs (seen in series with the remote diode) is caused by a variety of factors, including PCB track resistance and track length. This series resistance appears as a temperature offset in the remote sensor’s temperature measurement. This error typically causes a 0.5°C offset per Ω of parasitic resistance in series with the remote diode.

The ADT7468 automatically cancels out the effect of this series resistance on the temperature reading, giving a more accurate result, without the need for user characterization of this resistance. The ADT7468 is designed to automatically cancel, typically, up to 3 kΩ of resistance. By using an advanced temperature measurement method, this is transparent to the user. This feature allows resistances to be added to the sensor path to produce a filter, allowing the part to be used in noisy environments. See the Noise Filtering section for details.

FACTORS AFFECTING DIODE ACCURACY

Remote Sensing Diode

The ADT7468 is designed to work with either substrate transistors built into processors or with discrete transistors. Substrate transistors are generally PNP types with the collector connected to the substrate. Discrete types can be either PNP or NPN transistors connected as a diode (base-shorted to the collector). If an NPN transistor is used, the collector and base are connected to D+ and the emitter to D−. If a PNP transistor is used, the collector and base are connected to D− and the emitter is connected to D+.

To reduce the error due to variations in both substrate and discrete transistors, a number of factors should be taken into consideration:

•

The ideality factor, n

deviation of the thermal diode from ideal behavior. The ADT7468 is trimmed for an n following equation to calculate the error introduced at a temperature T (°C), when using a transistor whose n not equal 1.008. See the processor data sheet for the n values.

∆T = (n

− 1.008) × (273.15 K + T)

To factor this in, the user can write the ∆T value to the offset register. The ADT7468 then automatically adds it to or subtracts it from the temperature measurement.

Some CPU manufacturers specify the high and low current

•

levels of the substrate transistors. The high current level of the ADT7468, I is 6 µA. If the ADT7468 current levels do not match the current levels specified by the CPU manufacturer, it might be necessary to remove an offset. The CPUs data sheet advises whether this offset needs to be removed and how to calculate it. This offset can be programmed to the offset register. It is important to note that, if more than one offset must be considered, the algebraic sum of these offsets must be programmed to the offset register.

If a discrete transistor is used with the ADT7468, the best accuracy is obtained by choosing devices according to the following criteria:

•

Base-emitter voltage greater than 0.25 V at 6 µA, at the

highest operating temperature.

•

Base-emitter voltage less than 0.95 V at 100 µA, at the

lowest operating temperature.

•

Base resistance less than 100 Ω.

•

Small variation in h

control of V

, of the transistor is a measure of the

value of 1.008. Use the

, is 96 µA and the low level current, I

HIGH

(say 50 to 150) that indicates tight

characteristics.

does

LOW

Rev. 0 | Page 19 of 80

Page 20

ADT7468

Transistors, such as 2N3904, 2N3906, or equivalents in SOT-23 packages, are suitable devices to use.

Table 6. Temperature Data Format

Temperature Digital Output (10-Bit)1

–128°C –125°C –100°C –75°C –50°C –25°C –10°C 0°C

10.25°C

25.5°C

50.75°C 75°C 100°C 125°C 127°C

Bold numbers denote 2 LSB of measurement in Extended Resolution

Table 7. Extended Range, Temperature Data Format

Temperature Digital Output (10-Bit)1

–64°C –1°C 0°C 1°C 10°C 25°C 50°C 75°C 100°C 125°C 191°C

Bold numbers denote 2 LSB of measurement in Extended Resolution

1000 0000 00 1000 0011 00 1001 1100 00 1011 0101 00 1100 1110 00 1110 0111 00 1111 0110 00 0000 0000 00 0000 1010 01 0001 1001 10 0011 0010 11 0100 1011 00 0110 0100 00 0111 1101 00 0111 1111 00

0000 0000 00 0011 1111 00 0100 0000 00 0100 0001 00 0100 1010 00 0101 1001 00 0111 0010 00 1000 1001 00 1010 0100 00 1011 1101 00 1111 1111 00

ADT7468

Nulling Out Temperature Errors

As CPUs run faster, it is getting more difficult to avoid high frequency clocks when routing the D+/D– traces around a system board. Even when recommended layout guidelines are followed, some temperature errors may still be attributable to noise coupled onto the D+/D– lines. Constant high frequency noise usually attenuates or increases temperature measurements by a linear, constant value.

The ADT7468 has temperature offset registers at Addresses 0x70, 0x72 for the Remote 1 and Remote 2 temperature channels. By doing a one-time calibration of the system, the user can determine the offset caused by system board noise and null it out using the offset registers. The offset registers automatically add an Offset 64/twos complement 8-bit reading to every temperature measurement. The LSBs add 0.5°C offset to the temperature reading so the 8-bit register effectively allows temperature offsets of up to ±64°C with a resolution of 0.5°C. This ensures that the readings in the temperature measurement registers are as accurate as possible.

Temperature Offset Registers

Reg. 0x70, Remote 1 Temperature Offset = 0x00 (0°C default)

Reg. 0x71,

Reg. 0x72,

Local Temperature Offset = 0x00 (0°C default)

Remote 2 Temperature Offset = 0x00 (0°C default)

ADT7463/ADT7468 Backwards Compatible Mode

By setting Bit 1 of Configuration Register 5 (0x7C), all temperature measurements are stored in the Zone Temp value registers (0x25, 0x26, and 0x27) in twos complement in the range −64°C to +127°C (the ADT7468 still makes calculations based on the Offset 64 extended range and clamps the results, if necessary.) The temperature limits must be reprogrammed in twos complement. If a twos complement temperature below −63°C is entered, the temperature is clamped to −63°C. In this mode, the diode fault condition remains −128°C = 1000 0000, while in the extended temperature range (−64°C to +191°C), the fault condition is represented by −64°C = 0000 0000.

Temperature Measurement Registers

Reg. 0x25, Remote 1 Temperature

N3904

NPN

Figure 25. Measuring Temperature Using an NPN Transistor

D+

D–

ADT7468

04499-0-013

Reg. 0x26,

Reg. 0x27,

Reg. 0x77,

<7:6> TDM2, Remote 2 temperature LSBs.

Local Temperature

Remote 2 Temperature

Extended Resolution 2 = 0x00 default

<5:4> LTMP, local temperature LSBs.

N3906

PNP

Figure 26. Measuring Temperature Using a PNP Transistor

D+

D–

04499-0-014

Rev. 0 | Page 20 of 80

<3:2> TDM1, Remote 1 temperature LSBs.

Page 21

ADT7468

Temperature Measurement Limit Registers

Associated with each temperature measurement channel are high and low limit registers. Exceeding the programmed high or low limit causes the appropriate status bit to be set. Exceeding either limit can also generate

Reg. 0x4E,

Reg. 0x4F,

Reg. 0x50,

Remote 1 Temperature Low Limit = 0x01 default

Remote 1 Temperature High Limit = 0x7F default

Local Temperature Low Limit = 0x01 default

SMBALERT

interrupts.

Reg. 0x51, Local Temperature High Limit = 0x7F default

Reg. 0x52,

Reg. 0x53,

Remote 2 Temperature Low Limit = 0x01 default

Remote 2 Temperature High Limit = 0x7F default

Reading Temperature from the ADT7468

It is important to note that temperature can be read from the ADT7468 as an 8-bit value (with 1°C resolution) or as a 10-bit value (with 0.25°C resolution). If only 1°C resolution is required, the temperature readings can be read back at any time and in no particular order.

Table 9. Conversion Time with Averaging Enabled

Channel Measurement Time

Voltage Channels 11 ms Remote Temperature 39 ms Local Temperature 12 ms

Single-Channel ADC Conversions

Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the ADT7468 into single-channel ADC conversion mode. In this mode, the ADT7468 can be made to read a single temperature channel only. The appropriate ADC channel is selected by writing to Bits <7:5> of the TACH1 minimum high byte register (0x55).

Table 10. Channel Selection

Bits <7:5> Reg. 0x55 Channel Selected

101 Remote 1 temperature 110 Local temperature 111 Remote 2 temperature

Configuration Register 2 (Reg. 0x73)

<4> = 1,

averaging off.

If the 10-bit measurement is required, this involves a 2-register read for each measurement. The extended resolution register (Reg. 0x77) should be read first. This causes all temperature reading registers to be frozen until all temperature reading registers have been read from. This prevents an MSB reading from being updated while its two LSBs are being read and vice versa.

ADDITIONAL ADC FUNCTIONS FOR TEMPERATURE MEASUREMENT

A number of other functions are available on the ADT7468 to offer the system designer increased flexibility.

Turn-Off Averaging

For each temperature measurement read from a value register, 16 readings have actually been made internally and the results averaged before being placed into the value register. Sometimes it is necessary to take a very fast measurement. Setting Bit 4 of Configuration Register 2 (Reg. 0x73) turns averaging off.

<6> = 1, single-channel convert mode.

TACH1 Minimum High Byte (Reg. 0x55)

<7:5>

selects ADC channel for single-channel convert mode.

Overtemperature Events

Overtemperature events on any of the temperature channels can be detected and dealt with automatically in automatic fan speed control mode. Register 0x6A to Register 0x6C are the temperature limits. When a temperature exceeds its temperature limit, all PWM outputs run at the maximum PWM duty cycle (Reg. 0x38, Reg. 0x39, and Reg. 0x3A). This effectively runs the fans at the fastest allowed speed. The fans stay running at this speed until the temperature drops below THERM boost bit in Configuration Register 3, Bit 2, Reg. 0x78.) The hysteresis value for that programmed into Reg. 0x6D and Reg. 0x6E (hysteresis registers). The default hysteresis value is 4°C.

Table 8. Conversion Time with Averaging Disabled

Channel Measurement Time

Voltage Channels 0.7 ms Remote Temperature 1 7 ms Remote Temperature 2 7 ms Local Temperature 1.3 ms

THERM LIMIT

TEMPERATURE

FANS

THERM

minus hysteresis. (This can be disabled by setting the

Figure 27.

THERM

temperature limit is the value

HYSTERESIS (°C)

100%

Temperature Limit Operation

04499-0-015

Rev. 0 | Page 21 of 80

Page 22

ADT7468

LIMITS, STATUS REGISTERS, AND INTERRUPTS

LIMIT VALUES

Associated with each measurement channel on the ADT7468 are high and low limits. These can form the basis of system status monitoring; a status bit can be set for any out-of-limit condition and detected by polling the device. Alternatively, SMBALERT microcontroller of out-of-limit conditions.

8-Bit Limits

The following is a list of 8-bit limits on the ADT7468.

Volt ag e Li mi t Re g is ter s

Reg. 0x44, 2.5 V Low Limit = 0x00 default

Reg. 0x45,

Reg. 0x46,

Reg. 0x47,

Reg. 0x48,

Reg. 0x49,

Reg. 0x4A,

Reg. 0x4B,

Reg. 0x4C,

Reg. 0x4D,

Reg. 0x46, V

Reg. 0x47,

Reg. 0x48,

interrupts can be generated to flag a processor or

2.5 V High Limit = 0xFF default

Low Limit = 0x00 default

CCP

High Limit = 0xFF default

CCP

VCC Low Limit = 0x00 default

VCC High Limit = 0xFF default

5 V Low Limit = 0x00 default

5 V High Limit = 0xFF default

12 V Low Limit = 0x00 default

12 V High Limit = 0xFF default

Low Limit = 0x00 default

CCP

High Limit = 0xFF default

CCP

VCC Low Limit = 0x00 default

THERM

Reg. 0x7A,

Limit Register

THERM

Limit = 0x00 default

16-Bit Limits

The fan TACH measurements are 16-bit results. The fan TACH limits are also 16 bits, consisting of a high byte and low byte. Because fans running under speed or stalled are normally the only conditions of interest, only high limits exist for fan TACHs. Because the fan TACH period is actually being measured, exceeding the limit indicates a slow or stalled fan.

Fan Limit Registers

Reg. 0x54, TA C H1 M i ni m u m L ow B y te = 0x00 default

Reg. 0x55,

Reg. 0x56,

Reg. 0x57,

Reg. 0x58,

Reg. 0x59,

Reg. 0x5A,

Reg. 0x5B,

TAC H1 M ini m u m Hi g h B y te = 0x00 default

TAC H2 M ini m u m L ow B y te = 0x00 default

TAC H2 M ini m u m Hi g h B y te = 0x00 default

TAC H3 M ini m u m L ow B y te = 0x00 default

TAC H3 M ini m u m Hi g h B y te = 0x00 default

TAC H4 M ini m u m L ow B y te = 0x00 default

TAC H4 M ini m u m Hi g h B y te = 0x00 default

Out-of-Limit Comparisons

Once all limits have been programmed, the ADT7468 can be enabled for monitoring. The ADT7468 measures all voltage and temperature measurements in round-robin format and sets the appropriate status bit for out-of-limit conditions. TACH measurements are not part of this round-robin cycle. Comparisons are done differently depending on whether the measured value is being compared to a high or low limit.

Reg. 0x49,

VCC High Limit = 0xFF default

Temperature Limit Registers

Reg. 0x4E, Remote 1 Temperature Low Limit = 0x01 default

Reg. 0x4F,

Reg. 0x6A,

Reg. 0x50,

Reg. 0x51,

Reg. 0x6B, Local

Reg. 0x52,

Reg. 0x53,

Reg. 0x6C,

Remote 1 Temperature High Limit = 0x7F default

Remote 1

THERM

Limit = 0x64 default

Local Temperature Low Limit = 0x01 default

Local Temperature High Limit = 0x7F default

THERM

Limit = 0x64 default

Remote 2 Temperature Low Limit = 0x01 default

Remote 2 Temperature High Limit = 0x7F default

Remote 2

THERM

Limit = 0x64 default

High Limit: > Comparison Performed

Low Limit: ≤ Comparison Performed

Voltage and temperature channels use a window comparator for error detecting and, therefore, have high and low limits. Fan speed measurements use only a low limit. This fan limit is needed only in manual fan control mode.

Analog Monitoring Cycle Time

The analog monitoring cycle begins when a 1 is written to the start bit (Bit 0) of Configuration Register 1 (Reg. 0x40). By default, the ADT7463 powers up with this bit set. The ADC measures each analog input in turn and, as each measurement is completed, the result is automatically stored in the appropriate value register. This round-robin monitoring cycle continues unless disabled by writing a 0 to Bit 0 of Configuration Register 1.

Rev. 0 | Page 22 of 80

Page 23

ADT7468

As the ADC is normally left to free-run in this manner, the time taken to monitor all the analog inputs is normally not of interest, because the most recently measured value of any input can be read out at any time.

For applications where the monitoring cycle time is important, it can easily be calculated.

The total number of channels measured is

•

Four dedicated supply voltage inputs Supply voltage (V

•

Local temperature Two remote temperatures

•

pin)

As mentioned previously, the ADC performs round-robin conversions and takes 11 ms for each voltage measurement, 12 ms for a local temperature reading, and 39 ms for each remote temperature reading. The total monitoring cycle time for averaged voltage and temperature monitoring is, therefore, nominally

Status Register 1 (Reg. 0x41)

Bit 7 (OOL) = 1

, denotes a bit in Status Register 2 is set and

Status Register 2 should be read.

Bit 6 (R2T) = 1, Remote 2 temperature high or low limit has

been exceeded.

Bit 5 (LT) = 1, local temperature high or low limit has been

exceeded.

Bit 4 (R1T) = 1, Remote 1 temperature high or low limit has

been exceeded.

Bit 3 (5 V) = 1, 5 V high or low limit has been exceeded.

Bit 2 (V

Bit 1 (V

) = 1, V

CCP

high or low limit has been exceeded.

CCP

Bit 0 (2.5 V) = 1, 2.5 V high or low limit has been exceeded.

Status Register 2 (Reg. 0x42)

Bit 7 (D2) = 1

, indicates an open or short on D2+/D2– inputs.

Bit 6 (D1) = 1, indicates an open or short on D1+/D1– inputs.

(5 × 11) + 12 + (2 × 39) = 145 ms

Fan TACH measurements are made in parallel and are not synchronized with the analog measurements in any way.

STATUS REGISTERS

The results of limit comparisons are stored in Status Registers 1 and 2. The status register bit for each channel reflects the status of the last measurement and limit comparison on that channel. If a measurement is within limits, the corresponding status register bit is cleared to 0. If the measurement is out-of-limits, the corresponding status register bit is set to 1.

The state of the various measurement channels can be polled by reading the status registers over the serial bus. In Bit 7 (OOL) of Status Register 1 (Reg. 0x41), 1 means that an out-of-limit event has been flagged in Status Register 2. This means that the user also needs to read Status Register 2. Alternatively, Pin 10 or Pin 14 can be configured as an interrupt automatically notifies the system supervisor of an outof-limit condition. Reading the status registers clears the appropriate status bit as long as the error condition that caused the interrupt has cleared. Status register bits are “sticky.” Whenever a status bit is set, indicating an out-of-limit condition, it remains set even if the event that caused it has gone away (until read). The only way to clear the status bit is to read the status register after the event has gone away. Interrupt status mask registers (Reg. 0x74, and Reg. 0x75) allow individual interrupt sources to be masked from causing an However, if one of these masked interrupt sources goes out-oflimit, its associated status bit is set in the interrupt status registers.

SMBALERT

output. This hard

SMBALERT

Bit 5 (F4P) = 1, indicates Fan 4 has dropped below minimum

speed. Alternatively, indicates that the exceeded, if the

THERM

function is used.

THERM

limit has been

Bit 4 (FAN3) = 1, indicates Fan 3 has dropped below minimum

speed.

Bit 3 (FAN2) = 1, indicates Fan 2 has dropped below minimum

speed.

Bit 2 (FAN1) = 1, indicates Fan 1 has dropped below minimum

speed.

Bit 1 (OVT) = 1, indicates a

THERM

overtemperature limit has

been exceeded.

Bit 0 (12V/VC) = 1, indicates a 12 V high or low limit has been

exceeded. If the VID code change function is used, this bit indicates a change in VID code on the VID0 to VID5 inputs.

SMBALERT

The ADT7468 can be polled for status, or an

Interrupt Behavior

SMBALERT interrupt can be generated for out-of-limit conditions. It is important to note how the

SMBALERT

output and status bits

behave when writing interrupt handler software.

Rev. 0 | Page 23 of 80

Page 24

ADT7468

HIGH LIMIT

TEMPERATURE

CLEARED ON READ

“STICKY”

STATUS BI

TEMP BACK IN LIMIT

SMBALERT

Figure 28.

(STATUS BIT STAYS SET)

SMBALERT

Figure 28 shows how the

and Status Bit Behavior

SMBALERT

(TEMP BELOW LIMIT)

output and “sticky” status bits behave. Once a limit is exceeded, the corresponding status bit is set to 1. The status bit remains set until the error condition subsides and the status register is read. The status bits are referred to as “sticky,” because they remain set until read by software. This ensures that an out-of-limit event cannot be missed, if software is polling the device periodically. Note that

SMBALERT

the

output remains low for the entire duration that a reading is out-of-limit and until the status register has been read. This has implications on how software handles the interrupt.

Handling

SMBALERT

Interrupts

To prevent the system from being tied up servicing interrupts, it is recommend to handle the

SMBALERT

interrupt as follows:

04499-0-022

HIGH LIMIT

TEMPERATURE

“STICKY”

STATUS BIT

SMBALERT

Figure 29. How Masking the Interrupt Source Affects

TEMP BACK IN LIMIT (STATUS BIT STAYS SET)

INTERRUPT MASK BIT SET

Interrupt Mask Register 1 (Reg. 0x74)

Bit 7 (OOL) = 1

, masks

SMBALERT

for any alert condition

flagged in Status Register 2.

Bit 6 (R2T) = 1, masks

Bit 5 (LT) = 1, masks

Bit 4 (R1T) = 1, masks

Bit 3 (5 V) = 1, masks

Bit 2 (VCC) = 1, masks

SMBALERT

for Remote 2 temperature.

for local temperature.

for Remote 1 temperature.

for 5 V channel.

for VCC channel.

CLEARED ON READ

(TEMP BELOW LIMIT)

INTERRUPT MASK BIT

CLEARED

(SMBALERT REARMED)

SMBALERT

Output

04499-0-023

Detect the

Enter the interrupt handler.

Read the status registers to identify the interrupt source.

Mask the interrupt source by setting the appropriate mask

SMBALERT

assertion.

bit in the interrupt mask registers (Reg. 0x74 and Reg. 0x75).

Take the appropriate action for a given interrupt source.

Exit the interrupt handler.

Periodically poll the status registers. If the interrupt status

bit has cleared, reset the corresponding interrupt mask bit to 0. This causes the

SMBALERT

output and status bits to

behave as shown in Figure 29.

Masking Interrupt Sources

Interrupt Mask Registers 1 and 2 are located at Addresses 0x74 and 0x75. These allow individual interrupt sources to be masked out to prevent masking an interrupt source prevents only the

SMBALERT

interrupts. Note that

SMBALERT

output from being asserted; the appropriate status bit is set normally.

Bit 0 (V

) = 1, masks

CCP

SMBALERT

for V

channel.

CCP

Interrupt Mask Register 2 (Reg. 0x75)

Bit 7 (D2) = 1

Bit 6 (D1) = 1, masks

Bit 5 (FAN4) = 1, masks

If the TACH4 pin is being used as the

SMBALERT

masks

Bit 4 (FAN3) = 1, masks

Bit 3 (FAN2) = 1, masks

Bit 2 (FAN1) = 1, masks

Bit 1 (OVT) = 1, masks

(exceeding

THERM

Bit 0 (12V/VC) = 1, masks

SMBALERT

, masks

SMBALERT

THERM

for a

SMBALERT

temperature limits).

SMBALERT

for Diode 2 errors.

for Diode 1 errors.

for Fan 4 failure.

THERM

input, this bit

event.

for Fan 3.

for Fan 2.

for Fan 1.

for overtemperature

for 12 V channel or for

a VID code change, depending on the function used.

Rev. 0 | Page 24 of 80

Page 25

ADT7468

Enabling the

SMBALERT

The Pin 10 or Pin 14 can be reconfigured as an

SMBALERT

Interrupt Output

interrupt function is disabled by default.

SMBALERT

output

to signal out-of-limit conditions.

Table 11. Configuring Pin 10 as

Configuration Register 3 (Reg. 0x78)

SMBALERT

<0> Pin 10 = ALERT <1> Pin 10 = PWM2

Output

THERM

Assigning

Functionality to a Pin

Pin 14 on the ADT7468 has four possible functions: SMBALERT

THERM

, GPIO, and TACH4. The user chooses the required functionality by setting Bit 0 and Bit 1 of Configuration Register 4 at Address 0x7D.

THERM

is enabled (Bit 1, Configuration Register 3 at

Address 0x78):

•

Pin 20 becomes

•

If Pin 14 is configured as

Configuration Register 4 at Address 0x7D), then

THERM

(Bit 0 and Bit 1 of

THERM

is enabled on this pin.

THERM

•

Pin 20 becomes a 5 V measurement input.

•

If Pin 14 is configured as

is not enabled:

THERM

, then

THERM

disabled on this Pin.

Table 12. Configuring Pin 14

Bit 0 Bit 1 Function

0 0 TACH4 0 1

1 0 1 1 GPIO

THERM SMBALERT

THERM

as an Input

THERM

When assertions on the ing to the

is configured as an input, the user can time

THERM

PROCHOT

pin. This can be useful for connect-

output of a CPU to gauge system

performance.

below T then pulling the Figure 30 for more information.

MIN

THERM

THERM ASSERTED TO LOW AS AN INPUT: FANS DO NOT GO TO 100%, BECAUSE TEMPERATURE IS BELOW T

THERM TIMER

The ADT7468 has an internal timer to measure assertion time. For example, the connected to the measure system performance. The connected to the output of a trip point temperature sensor.

The timer is started on the assertion of the ADT7468’s input and stopped when counts counting on the next continues to accumulate timer is read (it is cleared on read) or until it reaches full scale. If the counter reaches full scale, it stops at that reading until

cleared.

The 8-bit that Bit 0 is set to 1 on the first cumulative of the the timer with a resolution of 22.76 ms (see Figure 31).

or if the duty cycle in manual mode is set to 0x00,

MIN

THERM

Figure 30. Asserting

in Automatic Fan Speed Control Mode

low externally has no effect. See

MIN

THERM ASSERTED TO LOW AS AN INPUT: FANS DO NOT GO TO 100%, BECAUSE TEMPERATURE IS ABOVE T ARE ALREADY RUNNING

THERM

Low as an Input

MIN

THERM

PROCHOT

output of a Pentium 4 CPU to

THERM

times cumulatively, that is, the timer resumes

THERM

assertion. The

THERM

timer register (Reg. 0x79) is designed such

THERM

assertion time has exceeded 45.52 ms, Bit 1

timer is set and Bit 0 now becomes the LSB of

input can be

THERM

input can also be

is unasserted. The timer

THERM

assertion times until the

assertion. Once the

AND FANS

THERM

timer

04499-0-024

The user can also set up the ADT7468 so that, when the THERM

fans run at 100% for the duration of the time that the

pin is driven low externally, the fans run at 100%. The

THERM

pin is pulled low. This is done by setting the BOOST bit (Bit 2) in Configuration Register 3 (Address = 0x78) to 1. This works only if the fan is already running, for example, in manual mode when the current duty cycle is above 0x00, or in automatic mode when the temperature is above T

. If the temperature is

MIN

Rev. 0 | Page 25 of 80

When using the

THERM

After a

The contents of the timer are cleared on read.

The F4P bit (Bit 5) of Status Register 2 needs to be cleared

(assuming that the

THERM

timer, be aware of the following.

timer read (Reg. 0x79):

THERM

timer limit has been

exceeded).

Page 26

ADT7468

THERM

If the

timer is read during a

the following happens:

The contents of the timer are cleared. Bit 0 of the

THERM

timer is set to 1 (because a

assertion is occurring).

THERM

The

If the

timer increments from zero.

THERM

timer limit (Reg. 0x7A) = 0x00, then the

F4P bit is set.

Generating

The ADT7468 can generate

THERM

ble

SMBALERT

Interrupts from

SMBALERT

timer limit has been exceeded. This allows the system designer to ignore brief, infrequent while capturing longer the

THERM

timer limit register. This 8-bit register allows a limit from 0 s (first before an

SMBALERT

THERM

assertion) to 5.825 s to be set

is generated. The compared with the contents of the If the

THERM

timer value exceeds the value, then the F4P bit (Bit 5) of Status Register 2 is set and an SMBALERT

is generated. Note that the F4P bit (Bit 5) of Mask Register 2 (Reg. 0x75) masks out to 1; although the F4P bit of Interrupt Status Register 2 still is set, if the

THERM

timer limit is exceeded.

THERM

assertion, then

THERM

Timer Events

s when a programma-

THERM

assertions,

timer events. Register 0x7A is

THERM

SMBALERT

timer value is

timer limit register.

timer limit

s, if this bit is set

THERM

TIMER

(REG. 0x79)

THERM

TIMER

(REG. 0x79)

THERM

TIMER

(REG. 0x79)

000 00010 765 32104

ACCUMULATE THERM LOW

ASSERTION TIMES

000 00100 765 32104

ACCUMULATE THERM LOW

ASSERTION TIMES

000 01010 765 32104

Figure 31.Understanding the

THERM ASSERTED

≤ 22.76ms

THERM ASSERTED

≥ 45.52ms

THERM ASSERTED ≥ 113.8ms

(91.04ms + 22.76ms)

THERM

Timer

04499-0-025

Figure 32 is a functional block diagram of the

THERM

timer, limit, and associated circuitry. Writing a value of 0x00 to the THERM

be generated on the first

timer limit register (Reg. 0x7A) causes

THERM

limit value of 0x01 generates an THERM

assertions exceed 45.52 ms.

assertion. A

SMBALERT

THERM

timer

, once cumulative

2.914s

1.457s

728.32ms

THERM LIMIT

(REG. 0x7A)

364.16ms

182.08ms

91.04ms

45.52ms

22.76ms

7654321

COMPARATOR

7654321

CLEARED ON READ

Figure 32. Functional Block Diagram of

OUT

LATCH RESET

1 = MASK

MASK REGISTER 2

THERM

2.914s

1.457s

728.32ms

364.16ms

182.08ms

91.04ms

45.52ms

22.76ms

THERM TIMER CLEARED ON READ

F4P BIT (BIT 5)

STATUS REGISTER 2

F4P BIT (BIT 5)

(REG. 0x75)

THERM TIMER

Monitoring Circuitry

(REG. 0x79)

THERM

SMBALERT

04499-0-026

Rev. 0 | Page 26 of 80

Page 27

ADT7468

Configuring the Relevant

1. Configure the desired pin as the

Setting Bit 1 (

THERM

Behavior

THERM

timer input.

timer enable) of Configuration

THERM

timer monitoring functionality. This is disabled on Pins 14 and 20 by default.

Setting Bits 0 and 1 (PIN14FUNC) of Configuration Register 4 (Reg. 0x7D) enables

THERM

timer output functionality on Pin 20 (Bit 1 of Configuration Register 3, THERM

, must also be set). Pin 14 can also be used as

TACH4.

Select the desired fan behavior for

THERM

timer events.

Assuming that the fans are running, setting Bit 2 (BOOST bit) of Configuration Register 3 (Reg. 0x78) causes all fans to run at 100% duty cycle whenever

THERM

is asserted. This allows fail-safe system cooling. If this bit is 0, the fans run at their current settings and are not affected by THERM THERM

Select whether

3. SMBALERT

events. If the fans are not already running when is asserted, the fans do not run to full speed.

THERM

timer events should generate

interrupts.

Bit 5 (F4P) of Mask Register 2 (Reg. 0x75), when set, masks

SMBALERT

out

s when the

exceeded. This bit should be cleared, if

THERM

Select a suitable

events are required.

THERM

This value determines whether an on the first THERM

causes an

THERM

assertion time limit is exceeded. A value of 0x00

SMBALERT

THERM

timer limit value is

SMBALERT

limit value.

SMBALERT

is generated

assertion, or only if a cumulative

to be generated on the first

assertion.

s based

THERM

can be calculated for a fixed example, if it takes one week for a

2.914 s to be exceeded and the next time it takes only 1 hour, then this is an indication of a serious degradation in system performance.

Configuring the

THERM

Pin as an Output

In addition to monitoring can optionally drive PROCHOT

is bidirectional,

processor by asserting

THERM

PROCHOT system-critical thermal limits. If the temperature exceeds a thermal limit by 0.25°C,

THERM

is still above the thermal limit on the next monitoring cycle, THERM

stays low.

THERM

temperature is equal to or below the thermal limit. Because the temperature for that channel is measured only once for every monitoring cycle, after

THERM

remain low for at least one monitoring cycle.

The

THERM

pin can be configured to assert low, if the Remote 1, local, or Remote 2 exceeded by 0.25°C. The

THERM are at Registers 0x6A, 0x6B, and 0x6C, respectively. Setting Bit 3 of Registers 0x5F, 0x60, and 0x61 enables the feature for the Remote 1, local, and Remote 2 temperature channels, respectively. Figure 33 shows how the asserts low as an output in the event of a critical

overtemperature.

THERM LIMIT

+0.25°C

THERM LIMIT

TEMP

THERM

timer limit time. For

THERM

timer limit of

as an input, the ADT7468

low as an output. In cases where

THERM

can be used to throttle the

. The user can preprogram

asserts low. If the temperature

remains asserted low until the

asserts it is guaranteed to

THERM

temperature limits are

temperature limit registers

THERM

output

THERM

Select a

THERM

monitoring time.

This value specifies how often OS or BIOS level software checks the

THERM

the

THERM

tive THERM

assertion time is <22.76 ms in Hour 1, >182.08 ms

THERM

timer. For example, BIOS could read

timer once an hour to determine the cumula-

assertion time. If, for example, the total

in Hour 2, and >5.825 s in Hour 3, this can indicate that system performance is degrading significantly, because THERM

is asserting more frequently on an hourly basis.

Alternatively, OS or BIOS level software can timestamp when the system is powered on. If an SMBALERT is generated due to the

THERM

timer limit being exceeded,

another timestamp can be taken. The difference in time

Figure 33. Asserting

An alternative method of disabling THERM or −128°C or less in twos complement mode; that is, for THERM

respectively,

Rev. 0 | Page 27 of 80

ADT7468

MONITORING

CYCLE

THERM

as an Output, Based on Tripping

THERM

Limits

is to program the

temperature limit to –64°C or less in Offset 64 mode,

temperature limit values less than –63°C or –128°C,

THERM

is disabled.

04499-0-027

Page 28

ADT7468

FAN DRIVE USING PWM CONTROL

The ADT7468 uses pulse-width modulation (PWM) to control fan speed. This relies on varying the duty cycle (or on/off ratio) of a square wave applied to the fan to vary the fan speed. The external circuitry required to drive a fan using PWM control is extremely simple. For 4-wire fans, the PWM drive might need only a pull-up resistor. In many cases, the 4-wire fan PWM input has a built-in pull-up resistor.

The ADT7468 PWM frequency can be set to a selection of low frequencies or a single high PWM frequency. The low frequency options are usually used for 2-wire and 3-wire fans, while the high frequency option is usually used with 4-wire fans.

For 2-wire or 3-wire fans, a single N-channel MOSFET is the only drive device required. The specifications of the MOSFET depend on the maximum current required by the fan being driven and the input capacitance of the FET. Because a 10 kΩ (or greater) resistor must be used as a PWM pull-up, an FET with large input capacitance can cause the PWM output to become distorted and adversely affect the fan control range. This is a requirement only when using high frequency PWM mode.

Figure 34 uses a 10 kΩ pull-up resistor for the TACH signal. This assumes that the TACH signal is an open-collector from the fan. In all cases, the TACH signal from the fan must be kept below 5 V maximum to prevent damaging the ADT7468. If in doubt as to whether the fan used has an open-collector or totem-pole TACH output, use one of the input signal conditioning circuits shown in the Fan Speed Measurement section.

Figure 35 shows a fan drive circuit using an NPN transistor such as a general-purpose MMBT2222. While these devices are inexpensive, they tend to have much lower current handling capabilities and higher on resistance than MOSFETs. When choosing a transistor, care should be taken to ensure that it meets the fan’s current requirements. Ensure that the base resistor is chosen such that the transistor is saturated when the fan is powered on.

Because 4-wire fans are powered continuously, the fan speed is not switched on or off as with previous PWM driven/powered fans. This enables it to perform better than 3-wire fans, especially for high frequency applications.

12V 12V

Typical notebook fans draw a nominal 170 mA, and so SOT devices can be used where board space is a concern. In desktops, fans can typically draw 250 mA to 300 mA each. If you drive several fans in parallel from a single PWM output or drive larger server fans, the MOSFET must handle the higher current requirements. The only other stipulation is that the MOSFET should have a gate voltage drive, V interfacing to the PWM_OUT pin. V

< 3.3 V, for direct

can be greater than

3.3 V as long as the pull-up on the gate is tied to 5 V. The MOSFET should also have a low on resistance to ensure that there is not significant voltage drop across the FET, which would reduce the voltage applied across the fan and, therefore, the maximum operating speed of the fan.

Figure 34 shows how to drive a 3-wire fan using PWM control.

12V 12V

10kΩ

TACH/AIN

10kΩ

4.7kΩ

3.3V

ADT7468

10kΩ

PWM

Figure 34. Driving a 3-Wire Fan Using an N-Channel MOSFET

12V FAN

Q1 NDT3055L

1N4148

04499-0-028

10kΩ

TACH

10kΩ

4.7kΩ

TACH

3.3V

12V FAN

1N4148

ADT7468

665Ω

PWM

Q1 MMBT2222

Figure 35. Driving a 3-Wire Fan Using an NPN Transistor

Figure 36 shows a typical drive circuit for 4-wire fans.

12V

TACH/AIN

ADT7468

PWM

10kΩ

4.7kΩ

3.3V

2kΩ

Figure 36. Driving a 4-Wire Fan

TACH

12V, 4-WIRE FAN

TACH PWM

04499-0-029

04499-0-041

Rev. 0 | Page 28 of 80

Page 29

ADT7468

Driving Two Fans from PWM3

The ADT7468 has four TACH inputs available for fan speed measurement, but only three PWM drive outputs. If a fourth fan is being used in the system, it should be driven from the PWM3 output in parallel with the third fan. Figure 37 shows how to drive two fans in parallel using low cost NPN transistors. Figure 38 shows the equivalent circuit using a MOSFET.

Because the MOSFET can handle up to 3.5 A, it is simply a matter of connecting another fan directly in parallel with the first. Care should be taken in designing drive circuits with transistors and FETs to ensure that the PWM pins are not required to source current and that they sink less than the 5 mA maximum current specified on the data sheet.

Driving up to Three Fans from PWM3

TACH measurements for fans are synchronized to particular PWM channels; for example, TACH1 is synchronized to PWM1. TACH3 and TACH4 are both synchronized to PWM3, so PWM3 can drive two fans. Alternatively, PWM3 can be programmed t o s y nchronize TACH2 , TAC H3, and TACH 4 t o the PWM3 output. This allows PWM3 to drive two or three fans. In this case, the drive circuitry looks the same, as shown in Figure 37 and Figure 38. The SYNC bit in Register 0x62 enables this function.

Synchronization is not required in high frequency mode when used with 4-wire fans.

<4> (SYNC) Enhance Acoustics Register 1 (Reg. 0x62)

SYNC = 1

, sy n c h r o n i zes TACH2, TAC H 3 , and TACH4 t o

PWM3.

12V

PWM3

3.3V 3.3V

1kΩ

2.2kΩ

TACH3 TACH4

Q2 MMBT2222

MMBT2222

1N4148

Q1 MMBT3904

10Ω

04499-0-030

ADT7468

Figure 37. Interfacing Two Fans in Parallel to the PWM3 Output Using Low Cost NPN Transistors

3.3V

10kΩ TYPICAL

TACH4

ADT7468

TACH3

PWM3

3.3V

10kΩ TYPICAL

3.3V

10kΩ TYPICAL

+V +V

5V OR

TACH TACH

12V FAN

Q1 NDT3055L

1N4148

5V OR 12V FAN

04499-0-031

Figure 38. Interfacing Two Fans in Parallel to the PWM3 Output Using a Single N-Channel MOSFET

Rev. 0 | Page 29 of 80

Page 30

ADT7468

Driving 2-Wire Fans

The ADT7468 can support 2-wire fans only when low frequency PWM mode is selected in Configuration Register 5, Bit 2. If this bit is not set to 1, the ADT7468 cannot measure the speed of 2-wire fans.

Figure 39 shows how a 2-wire fan can be connected to the ADT7468. This circuit allows the speed of a 2-wire fan to be measured, even though the fan has no dedicated TACH signal. A series resistor, R commutation pulses into a voltage, which is ac-coupled into the ADT7468 through the 0.01 µF capacitor. On-chip signal conditioning allows accurate monitoring of fan speed. The value of R

chosen depends upon the programmed input

SENSE

threshold and the current drawn by the fan. For fans drawing approximately 200 mA, a 2 Ω R threshold is programmed as 40 mV.

ADT7468

TACH

Figure 40 shows a typical plot of the sensing waveform at the TACH/AIN pin.

, in the fan circuit converts the fan

SENSE

value is suitable when the

SENSE

3.3V

PWM

10kΩ TYPICAL

0.01µF

5V OR

12V FAN

Figure 39. Driving a 2-Wire Fan

Q1 NDT3055L

SENSE

2Ω TYPICAL

1N4148

04499-0-032

For fans that draw more current, such as larger desktop or server fans, R

can be reduced for the same programmed

SENSE

threshold. The smaller the threshold programmed the better, because more voltage is developed across the fan and the fan spins faster. Note that when the voltage spikes (either negative going or positive going) are more than 40 mV in amplitude, the fan speed can be reliably determined.

LAYING OUT 2-WIRE AND 3-WIRE FANS

Figure 41 shows how to lay out a common circuit arrangement for 2-wire and 3-wire fans. Some components are not populated, depending on whether a 2-wire or 3-wire fan is used.

12V OR 5V

TACH

R3 R4

Figure 41. Planning for 2-Wire or 3-Wire Fans on a PCB

TACH Inputs

Pins 9, 11, 12, and 14 (when configured as TACH inputs) are open-drain TACH inputs intended for fan speed measurement.

Signal conditioning in the ADT7468 accommodates the slow rise and fall times typical of fan tachometer outputs. The maximum input signal range is 0 V to 5 V, even when V than 5 V. In the event that these inputs are supplied from fan outputs that exceed 0 V to 5 V, either resistive attenuation of the fan signal or diode clamping must be included to keep inputs within an acceptable range.

1N4148

3.3V OR 5V

Q1 MMBT2222

PWM

FOR 3-WIRE FANS: POPULATE R1, R2, R3 R4 = 0W C1 = UNPOPULATED

FOR 2-WIRE FANS: POPULATE R4, C1 R1, R2, R3 UNPOPULATED

04499-0-042

is less

Figure 40. Fan Speed Sensing Waveform at TACH/AIN Pin

Figure 42 to Figure 45 show circuits for most common fan TAC H ou t p u t s .

If the fan TACH output has a resistive pull-up to V connected directly to the fan input, as shown in Figure 42.

04499-0-033

Rev. 0 | Page 30 of 80

12V

PULL-UP

4.7kΩ

TYPICAL

TACH OUTPUT

TACH

Figure 42. Fan with TACH Pull-Up to V

FAN SPEED

COUNTER

ADT7468

, it can be

04499-0-034

Page 31

ADT7468

If the fan output has a resistive pull-up to 12 V (or other voltage greater than 5 V) then the fan output can be clamped with a Zener diode, as shown in Figure 43. The Zener diode voltage should be chosen so that it is greater than V

of the TACH

input but less than 5 V, allowing for the voltage tolerance of the Zener. A value of between 3 V and 5 V is suitable.

12V

PULL-UP

4.7kΩ

TYPICAL

*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8× V

TACH OUTPUT

TACH

ZD1*

Figure 43. Fan with TACH Pull-Up to Voltage > 5 V, for example, 12 V)

Clamped with Zener Diode

FAN SPEED

COUNTER

ADT7468

If the fan has a strong pull-up (less than 1 kΩ) to 12 V or a totem-pole output, then a series resistor can be added to limit the Zener current, as shown in Figure 44.

5V OR 12V

FAN

04499-0-035

Fan Speed Measurement

The fan counter does not count the fan TACH output pulses directly, because the fan speed could be less than 1,000 RPM and it would take several seconds to accumulate a reasonably large and accurate count. Instead, the period of the fan revolution is measured by gating an on-chip 90 kHz oscillator into the input of a 16-bit counter for N periods of the fan TACH output (Figure 46), so the accumulated count is actually proportional to the fan tachometer period and inversely proportional to the fan speed.

N, the number of pulses counted, is determined by the settings of Register 0x7B (TACH pulses per revolution register). This register contains two bits for each fan, allowing one, two (default), three, or four TACH pulses to be counted.

LOC

PWM

TACH

PULL-UP TYP

<1kΩ OR

TOTEM POLE

*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8× V

Figure 44. Fan with Strong TACH Pull-Up to > V

10kΩ

TACH OUTPUT

TACH

ZD1 ZENER*

FAN SPEED

COUNTER

ADT7468

or Totem-Pole Output,

Clamped with Zener and Resistor

Alternatively, a resistive attenuator can be used, as shown in Figure 45. R1 and R2 should be chosen such that

2 V < V

PULL-UP

× R2/(R

+ R1 + R2) < 5 V

PULL-UP

The fan inputs have an input resistance of nominally 160 kΩ to ground, which should be taken into account when calculating resistor values.

With a pull-up voltage of 12 V and pull-up resistor less than 1 kΩ, suitable values for R1 and R2 would be 100 kΩ and 47 kΩ, respectively. This gives a high input voltage of 3.83 V.

12V

<1kΩ

R1*

TACH OUTPUT

TACH

R2*

*SEE TEXT

Figure 45. Fan with Strong TACH Pull-Up to > V

Attenuated with R1/R2

FAN SPEED

COUNTER

ADT7468

or Totem-Pole Output,

04499-0-036

04499-0-037

Figure 46. Fan Speed Measurement

Fan Speed Measurement Registers

The fan tachometer readings are 16-bit values consisting of a 2-byte read from the ADT7468.

Reg. 0x28,

Reg. 0x29,

Reg. 0x2A,

Reg. 0x2B,

Reg. 0x2C,

Reg. 0x2D,

Reg. 0x2E,

Reg. 0x2F,

TAC H1 L ow B yte = 0x00 default

TAC H1 H i gh B yte = 0x00 default

TAC H2 L ow B yte = 0x00 default

TAC H2 H i gh B yte = 0x00 default

TAC H3 L ow B yte = 0x00 default

TAC H3 H i gh B yte = 0x00 default

TAC H4 L ow B yte = 0x00 default

TAC H4 H i gh B y te = 0x00 default

Reading Fan Speed from the ADT7468

The measurement of fan speeds involves a 2-register read for each measurement. The low byte should be read first. This causes the high byte to be frozen until both high and low byte registers have been read, preventing erroneous TACH readings. The fan tachometer reading registers report back the number of

04499-0-038

Rev. 0 | Page 31 of 80

Page 32

ADT7468

11.11 µs period clocks (90 kHz oscillator) gated to the fan speed counter, from the rising edge of the first fan TACH pulse to the rising edge of the third fan TACH pulse (assuming two pulses per revolution are being counted). Because the device is essentially measuring the fan TACH period, the higher the count value, the slower the fan is actually running. A 16-bit fan tachometer reading of 0xFFFF indicates either that the fan has stalled or is running very slowly (<100 RPM).

High Limit: > Comparison Performed

Because the actual fan TACH period is being measured, falling below a fan TACH limit by 1 sets the appropriate status bit and can be used to generate an

Fan TACH Limit Registers

The fan TACH limit registers are 16-bit values consisting of two bytes.

Reg. 0x54,

Reg. 0x55,

Reg. 0x56,

Reg. 0x57,

Reg. 0x58,

Reg. 0x59,

Reg. 0x5A,

Reg. 0x5B,

Fan Speed Measurement Rate

The fan TACH readings are normally updated once every second.

TAC H1 M ini m u m L ow B y te = 0xFF default

TAC H1 M ini m u m Hi g h B y te = 0xFF default

TAC H2 M ini m u m L ow B y te = 0xFF default

TAC H2 M ini m u m Hi g h B y te = 0xFF default

TAC H3 M ini m u m L ow B y te = 0xFF default

TAC H3 M ini m u m Hi g h B y te = 0xFF default

TAC H4 M ini m u m L ow B y te = 0xFF default

TAC H4 M ini m u m Hi g h B y te = 0xFF default

SMBALERT

Calculating Fan Speed

Assuming a fan with a two pulses per revolution (and two pulses per revolution being measured), fan speed is calculated by

Fan Speed (RPM) = (90,000 × 60)/Fan TACH Reading

where Fan TACH Reading is the 16-bit fan tachometer reading.

Example:

TACH1 High Byte (Reg. 0x29) = 0x17

TACH1 Low Byte (Reg. 0x28) = 0xFF

What is Fan 1 speed in RPM?

Fan 1 TACH Reading = 0x17FF = 6143 (decimal)

RPM = (f × 60)/Fan 1 TACH Reading

RPM = (90000 × 60)/6143

Fan Speed = 879 RPM

Fan Pulses per Revolution

Different fan models can output either 1, 2, 3, or 4 TACH pulses per revolution. Once the number of fan TACH pulses has been determined, it can be programmed into the fan pulses per revolution register (Reg. 0x7B) for each fan. Alternatively, this register can be used to determine the number or pulses per revolution output by a given fan. By plotting fan speed measurements at 100% speed with different pulses per revolution setting, the smoothest graph with the lowest ripple determines the correct pulses per revolution value.

Fan Pulses per Revolution Register

<1:0>

Fan 1 default = 2 pulses per revolution.

The FAST bit (Bit 3) of Configuration Register 3 (Reg. 0x78), when set, updates the fan TACH readings every 250 ms.

If any of the fans are not being driven by a PWM channel but are powered directly from 5 V or 12 V, their associated dc bit in Configuration Register 3 should be set. This allows TACH readings to be taken on a continuous basis for fans connected directly to a dc source. For optimal results, the associated dc bit should always be set when using 4-wire fans.

Rev. 0 | Page 32 of 80

<3:2> Fan 2 default = 2 pulses per revolution.

<5:4> Fan 3 default = 2 pulses per revolution.

<7:6> Fan 4 default = 2 pulses per revolution.

00 = 1 pulse per revolution.

01 = 2 pulses per revolution.

10 = 3 pulses per revolution.

11 = 4 pulses per revolution.

Page 33

ADT7468

2-Wire Fan Speed Measurements (Low Frequency Mode Only)

The ADT7468 is capable of measuring the speed of 2-wire fans, that is, fans without TACH outputs. To do this, the fan must be interfaced as shown in the Driving 2-Wire Fans section. In this case, the TACH inputs should be reprogrammed as analog inputs, AIN.

Configuration Register 2 (Reg. 0x73)

Bit 3 (AIN4) = 1,

of a 2-wire fan using an external sensing resistor and coupling capacitor.

Bit 2 (AIN3) = 1, Pin 9 is reconfigured to measure the speed of

a 2-wire fan using an external sensing resistor and coupling capacitor.

Bit 1 (AIN2) = 1, Pin 12 is reconfigured to measure the speed

of a 2-wire fan using an external sensing resistor and coupling capacitor.

Bit 0 (AIN1) = 1, Pin 11 is reconfigured to measure the speed

of a 2-wire fan using an external sensing resistor and coupling capacitor.

AIN Switching Threshold

Having configured the TACH inputs as AIN inputs for 2-wire measurements, a user can select the sensing threshold for the AIN signal.

Configuration Register 4 (Reg. 0x7D)

<3:2> AINL,

measurements.

00 = ±20 mV

01 = ±40 mV

10 = ±80 mV

11 = ±130 mV

Fan Spin-Up

The ADT7468 has a unique fan spin-up function. It spins the fan at 100% PWM duty cycle until two TACH pulses are detected on the TACH input. Once two TACH pulses have been detected, the PWM duty cycle goes to the expected running value, for example, 33%. The advantage is that fans have different spin-up characteristics and take different times to overcome inertia. The ADT7468 runs the fans just fast enough to overcome inertia and is quieter on spin-up than fans programmed to spin up for a given spin-up time.

Fan Startup Timeout

To prevent the generation of false interrupts as a fan spins up (because it is below running speed), the ADT7468 includes a fan startup timeout function. During this time, the ADT7468 looks for two TACH pulses. If two TACH pulses are not detected, then an interrupt is generated.

Pin 14 is reconfigured to measure the speed

input threshold for 2-wire fan speed

Using Configuration Register 4 (0x40) Bit 5 (FSPDIS), this functionality can be changed (see the Disabling Fan Startup Timeout section).

PWM1 Configuration (Reg. 0x5C)

<2:0> SPIN

PWM2 Configuration (Reg. 0x5D)

<2:0> SPIN

PWM3 Configuration (Reg. 0x5E)

<2:0> SPIN

Disabling Fan Startup Timeout

Although fan startup makes fan spin-ups much quieter than fixed-time spin-ups, the option exists to use fixed spin-up times. Setting Bit 5 (FSPDIS) to 1 in Configuration Register 1 (Reg. 0x40) disables the spin-up for two TACH pulses. Instead, the fan spins up for the fixed time as selected in Reg. 0x5C to Reg. 0x5E.

, startup timeout for PWM1.

000 = No startup timeout

001 = 100 ms

010 = 250 ms default

011 = 400 ms

100 = 667 ms

101 = 1 s

110 = 2 s

111 = 4 s

, startup timeout for PWM2.

000 = No startup timeout

001 = 100 ms

010 = 250 ms default

011 = 400 ms

100 = 667 ms

101 = 1 s

110 = 2 s

111 = 4 s

, start-up timeout for PWM3.

000 = No startup timeout

001 = 100 ms

010 = 250 ms default

011 = 400 ms

100 = 667 ms

101 = 1 s

110 = 2 s

111 = 4 s

Rev. 0 | Page 33 of 80

Page 34

ADT7468

PWM Logic State

The PWM outputs can be programmed high for 100% duty cycle (noninverted) or low for 100% duty cycle (inverted).

PWM1 Configuration (Reg. 0x5C)

<4> INV.

0 = Logic high for 100% PWM duty cycle. 1 = Logic low for 100% PWM duty cycle.

PWM2 Configuration (Reg. 0x5D)

<4> INV

0 = Logic high for 100% PWM duty cycle. 1 = Logic low for 100% PWM duty cycle.

PWM3 Configuration (Reg. 0x5E)

<4> INV

0 = Logic high for 100% PWM duty cycle. 1 = Logic low for 100% PWM duty cycle.

Low Frequency Mode PWM Drive Frequency

The PWM drive frequency can be adjusted for the application. Register 0x5F to Register 0x61 configure the PWM frequency for PWM1 to PWM3, respectively. In high frequency mode, the PWM drive frequency is always 22.5 kHz and cannot be changed.

PWM1 Frequency Registers (Reg. 0x5F to Reg. 0x61)

<2:0> FREQ.

Fan Speed Control

The ADT7468 controls fan speed using two modes: automatic and manual.

In automatic fan speed control mode, fan speed is automatically varied with temperature and without CPU intervention, once initial parameters are set up. The advantage is that, if the system hangs, the user is guaranteed that the system is protected from overheating. The automatic fan speed control incorporates a feature called dynamic T design effort required to program the automatic fan speed control loop. See the Programming the Automatic Fan Speed Control Loop section.

000 = 11.0 Hz

001 = 14.7 Hz

010 = 22.1 Hz

011 = 29.4 Hz

100 = 35.3 Hz default

101 = 44.1 Hz

110 = 58.8 Hz

111 = 88.2 Hz

MIN

calibration. This feature reduces the

In manual fan speed control mode, the ADT7468 allows the duty cycle of any PWM output to be manually adjusted. This can be useful, if the user wants to change fan speed in software or adjust PWM duty cycle output for test purposes. Bits <7:5> of Reg. 0x5C to Reg. 0x5E (PWM Configuration) control the behavior of each PWM output.

PWM Configuration Register (Reg. 0x5C to Reg. 0x5E)

<7:5> BHVR.

111 = manual mode

Once under manual control, each PWM output can be manually updated by writing to Reg. 0x30 to Reg. 0x32 (PWMx current duty cycle registers).

Programming the PWM Current Duty Cycle Registers

The PWM current duty cycle registers are 8-bit registers that allow the PWM duty cycle for each output to be set anywhere from 0% to 100% in steps of 0.39%. The value to be programmed into the PWM

Va lu e (decimal) = PWM

MIN

/0.39

MIN

Example 1: For a PWM duty cycle of 50%,

Va lu e (decimal) = 50/0.39 = 128 (decimal) Va lu e = 128 (decimal) or 0x80 (hex)

Example 2: For a PWM duty cycle of 33%,

Va lu e (decimal) = 33/0.39 = 85 (decimal) Va lu e = 85 (decimal) or 0x54 (hex)

PWM Duty Cycle Registers

Reg. 0x30 PWM1 Duty Cycle = 0x00 (0% default)

Reg. 0x31

Reg. 0x32

PWM2 Duty Cycle = 0x00 (0% default)

PWM3 Duty Cycle = 0x00 (0% default)

By reading the PWMx current duty cycle registers, the user can keep track of the current duty cycle on each PWM output, even when the fans are running in automatic fan speed control mode or acoustic enhancement mode. See the Programming the Automatic Fan Speed Control Loop section for details.

OPERATING FROM 3.3 V STANDBY

The ADT7468 has been specifically designed to operate from a

3.3 V STBY supply. In computers that support S3 and S5 states, the core voltage of the processor is lowered in these states. If using the dynamic T processor changes the CPU temperature and changes the dynamics of the system under dynamic T when monitoring disabled during these states.

mode, lowering the core voltage of the

MIN

control. Likewise,

MIN

THERM

, the

THERM

timer should be

Rev. 0 | Page 34 of 80

Page 35

ADT7468

Dynamic T <1> VCCPLO = 1

When the power is supplied from 3.3 V STBY and the V voltage drops below the V

Status Bit 1 (V

SMBALERT

THERM

3. hold its value prior to the S3 or S5 state.

Dynamic T

being adjusted due to an S3 or S5 state.

The ADT7468 is prevented from entering the shutdown

state.

Once the core voltage, V everything is re-enabled and the system resumes normal operation.

XNOR TREE TEST MODE

The ADT7468 includes an XNOR tree test mode. This mode is useful for in-circuit test equipment at board-level testing. By applying stimulus to the pins included in the XNOR tree, it is possible to detect opens or shorts on the system board.

The XNOR tree test is invoked by setting Bit 0 (XEN) of the XNOR tree test enable register (Reg. 0x6F).

Control Register 1 (Reg. 0x36)

MIN

low limit, the following occurs:

CCP

) in Status Register 1 is set.

CCP

is generated, if enabled.

monitoring is disabled. The

control is disabled. This prevents T

MIN

, goes above the V

CCP

THERM

low limit,

CCP

timer should

from

MIN

POWER-ON DEFAULT

When the ADT7468 is powered up, it polls the V

If V

stays below 0.75 V (the system CPU power rail is not

CCP

powered up), then the ADT7468 assumes the functionality of the default registers after the ADT7468 is addressed via any valid SMBus transaction.

If V

goes high (the system processor power rail is powered

CCP

up), then a fail-safe timer begins to count down. If the ADT7468 is not addressed by any valid SMBus transaction before the failsafe timeout (4.6 s) lapses, then the ADT7468 drives the fans to full speed. If the ADT7468 is addressed by a valid SMBus transaction after this point, the fans stop, and the ADT7468 assumes its default settings and begins normal operation.

If V

goes high (the system processor power rail is powered

CCP

up), then a fail-safe timer begins to count down. If the ADT7468 has been addressed by a valid SMBus transaction before the failsafe timeout (4.6 s) lapsed, then the ADT7468 operates normally, assuming the functionality of all the default registers. See the flow chart in Figure 48.

ADT7468 IS POWERED UP

HAS THE ADT7468 BEEN

ACCESSED BY A VALID

SMBUS TRANSACTION?

CCP

input.

Figure 47 shows the signals that are exercised in the XNOR tree test mode.

VID0 VID1

VID2

VID3

VID4

TACH1

TACH2

TACH3

TACH

PWM2

PWM3

Figure 47. XNOR Tree Test

PWM1/XTO

04499-0-040

IS V

ABOVE 0.75V? CHECK V

CCP

START FAIL-SAFE TIMER

HAS THE ADT7468 BEEN

ACCESSED BY A VALID

SMBUS TRANSACTION?

FAIL-SAFE TIMER ELAPSES

AFTER THE FAIL-SAFE TIMEOUT

HAS THE ADT7468 BEEN

ACCESSED BY A VALID

SMBUS TRANSACTION?

ADT7468 NORMALLY

START UP THE

Figure 48. Power-On Flow Chart

RUN THE FANS TO FULL SPEED

HAS THE ADT7468 BEEN

ACCESSED BY A VALID

SMBUS TRANSACTION?

SWITCH OFF FANS

CCP

04499-0-043

Rev. 0 | Page 35 of 80

Page 36

ADT7468

PROGRAMMING THE AUTOMATIC FAN SPEED CONTROL LOOP

Note: To more efficiently understand the automatic fan speed control loop, it is strongly recommended to use the ADT7468 evaluation board and software while reading this section.

This section provides the system designer with an understanding of the automatic fan control loop, and provides step-by-step guidance on effectively evaluating and selecting critical system parameters. To optimize the system characteristics, the designer needs to give some thought to system configuration, including the number of fans, where they are located, and what temperatures are being measured in the particular system.

The mechanical or thermal engineer who is tasked with the system thermal characterization should also be involved at the beginning of the process.

AUTOMATIC FAN CONTROL OVERVIEW

The ADT7468 can automatically control the speed of fans based upon the measured temperature. This is done independently of CPU intervention once initial parameters are set up.

The ADT7468 has a local temperature sensor and two remote temperature channels that can be connected to a CPU on-chip thermal diode (available on Intel Pentium class and other CPUs). These three temperature channels can be used as the basis for automatic fan speed control to drive fans using pulsewidth modulation (PWM).

Automatic fan speed control reduces acoustic noise by optimizing fan speed according to accurately measured temperature. Reducing fan speed can also decrease system

current consumption. The automatic fan speed control mode is very flexible owing to the number of programmable parameters, including T

MIN

and T temperature channel and, therefore, for a given fan are critical, because they define the thermal characteristics of the system. The thermal validation of the system is one of the most important steps in the design process, so these values should be selected carefully.

Figure 49 gives a top-level overview of the automatic fan control circuitry on the ADT7468. From a systems-level perspective, up to three system temperatures can be monitored and used to control three PWM outputs. The three PWM outputs can be used to control up to four fans. The ADT7468 allows the speed of four fans to be monitored. Each temperature channel has a thermal calibration block, allowing the designer to individually configure the thermal characteristics of each temperature channel. For example, one can decide to run the CPU fan when CPU temperature increases above 60°C and a chassis fan when the local temperature increases above 45°C. At this stage, the designer has not assigned these thermal calibration settings to a particular fan drive (PWM) channel. The right side of Figure 49 shows controls that are fan-specific. The designer has individual control over parameters such as minimum PWM duty cycle, fan speed failure thresholds, and even ramp control of the PWM outputs. Automatic fan control, then, ultimately allows graceful fan speed changes that are less perceptible to the system user.

RANGE

. The T

MIN

and T

values for a

RANGE

REMOTE 1

TEMP

THERMAL CALIBRATION

MIN

THERMAL CALIBRATION

RANGE

100%

MUX

LOCAL

TEMP

REMOTE 2

TEMP

MIN

THERMAL CALIBRATION

MIN

RANGE

100%

Figure 49. Automatic Fan Control Block Diagram

Rev. 0 | Page 36 of 80

PWM

MIN

PWM

MIN

PWM

MIN

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 1 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 2 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 3

AND 4

MEASUREMENT

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM1

TACH1

PWM2

TACH2

PWM3

TACH3

04499-0-054

Page 37

ADT7468

STEP 1: HARDWARE CONFIGURATION

During system design, the motherboard sensing and control capabilities should be addressed early in the design stages. Decisions about how these capabilities are used should involve the system thermal/mechanical engineer. Ask the following questions:

What ADT7468 functionality will be used?

•

PWM2 or

•

TACH4 fan speed measurement or overtemperature

THERM

•

5 V voltage monitoring or overtemperature

function?

12 V voltage monitoring or VID5 input?

•

The ADT7468 offers multifunctional pins that can be reconfigured to suit different system requirements and physical layouts. These multifunction pins are software programmable.

SMBALERT

function?

THERM

How many fans will be supported in system, three or four?

2. This influences the choice of whether to use the TACH4 pin or to reconfigure it for the

Is the CPU fan to be controlled using the ADT7468 or will

THERM

function.

it run at full speed 100% of the time?

If run at 100%, this frees up a PWM output, but the system is louder.

Where will the ADT7468 be physically located in the

system?

This influences the assignment of the temperature measurement channels to particular system thermal zones. For example, locating the ADT7468 close to the VRM controller circuitry allows the VRM temperature to be monitored using the local temperature channel.

REMOTE 1 =

AMBIENT TEMP

LOCAL =

VRM TEMP

REMOTE 2 =

CPU TEMP

THERMAL CALIBRATION

MIN

THERMAL CALIBRATION

MIN

THERMAL CALIBRATION

MIN

RANGE

100%

MUX

100%

PWM

MIN

PWM

MIN

PWM

MIN

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 1 MEASUREMENT

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 2 MEASUREMENT

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 3 MEASUREMENT

Figure 50. Hardware Configuration Example

RAMP

AND 4

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM1

TACH1

PWM2

TACH2

FRONT CHASSIS

PWM3

TACH3

REAR CHASSIS

CPU FAN SINK

04499-0-055

Rev. 0 | Page 37 of 80

Page 38

ADT7468

RECOMMENDED IMPLEMENTATION 1

Configuring the ADT7468 as in Figure 51 provides the system designer with the following features:

Six VID inputs (VID0 to VID5) for VRM10 support.

Two PWM outputs for fan control of up to three fans. (The

front and rear chassis fans are connected in parallel.)

Three TACH fan speed measurement inputs.

measured internally through Pin 4.

CPU core voltage measurement (V

2.5 V measurement input used to monitor CPU current

(connected to V

output of ADP316x VRM controller).

COMP

This is used to determine CPU power consumption.

FRONT

CHASSIS

FAN

CORE

TACH2

5 V measurement input.

VRM temperature using local temperature sensor.

CPU temperature measured using the Remote 1

temperature channel.

10.

Ambient temperature measured through the Remote 2

temperature channel.

11.

If not using VID5, this pin can be reconfigured as the 12 V

monitoring input.

Bidirectional

12.

13.

PWM1

TACH1

PROCHOT

or can be used as an overtemperature

SMBALERT

THERM

pin allows the monitoring of

output from an Intel P4 processor, for example,

THERM

system interrupt output.

output.

CPU FAN

REAR

CHASSIS

FAN

AMBIENT

TEMPERATURE

PWM3

VID[0:4]/VID[0.5]

TACH3

D1+

D1–

D2+

D2–

THERM

5(VRM9)/6(VRM10)

PROCHOT

CPU

ADT7468

3.3VSB 5V 12V/VID5

SDA SCL

SMBALERT

ICH

04499-0-056

ADP316x

VRM

CONTROLLER

COMP

CURRENT V

CORE

GND

Figure 51. Recommended Implementation 1

Rev. 0 | Page 38 of 80

Page 39

ADT7468

5 V measurement input.

RECOMMENDED IMPLEMENTATION 2

Configuring the ADT7468 as in Figure 52 provides the system designer with the following features:

Six VID inputs (VID0 to VID5) for VRM10 support.

Three PWM outputs for fan control of up to three fans.

(All three fans can be individually controlled.)

Three TACH fan speed measurement inputs.

measured internally through Pin 4.

CPU core voltage measurement (V

2.5 V measurement input used to monitor CPU current

(connected to V

output of ADP316x VRM controller).

COMP

This is used to determine CPU power consumption.

FRONT

CHASSIS

FAN

CORE

TACH2

VRM temperature using local temperature sensor.

CPU temperature measured using the Remote 1

temperature channel.

10.

Ambient temperature measured through the Remote 2

temperature channel.

11.

If not using VID5, this pin can be reconfigured as the 12 V

monitoring input.

Bidirectional

12. PROCHOT

or can be used as an overtemperature

PWM1

TACH1

THERM

pin allows the monitoring of

output from an Intel P4 processor, for example,

THERM

output.

CPU FAN

REAR

CHASSIS

FAN

AMBIENT

TEMPERATURE

PWM3

VID[0:4]/VID[0.5]

TACH3

D1+

D1–

D2+

D2–

THERM

5(VRM9)/6(VRM10)

PROCHOT

CPU

ADT7468

3.3VSB 5V 12V/VID5

SDA

SCL

ICH

04499-0-057

ADP316x

VRM

CONTROLLER

COMP

CURRENT V

CORE

GND

Figure 52. Recommended Implementation 2

Rev. 0 | Page 39 of 80

Page 40

ADT7468

STEP 2: CONFIGURING THE MUX

After the system hardware configuration is determined, the fans can be assigned to particular temperature channels. Not only can fans be assigned to individual channels, but the behavior of the fans is also configurable. For example, fans can be run under automatic fan control, can be run manually (under software control), or can be run at the fastest speed calculated by multiple temperature channels. The MUX is the bridge between temperature measurement channels and the three PWM outputs.

Bits <7:5> (BHVR) of Registers 0x5C, 0x5D, and 0x5E (PWM

configuration registers) control the behavior of the fans connected to the PWM1, PWM2, and PWM3 outputs. The values selected for these bits determine how the MUX connects a temperature measurement channel to a PWM output.

Automatic Fan Control MUX Options

<7:5> (BHVR),

000 = Remote 1 temperature controls PWMx

001 = local temperature controls PWMx

Registers 0x5C, 0x5D, 0x5E.

101 = Fastest speed calculated by local and Remote 2 temperature controls PWMx

110 = Fastest speed calculated by all three temperature channels controls PWMx

The Fastest Speed Calculated options pertain to controlling one PWM output based on multiple temperature channels. The thermal characteristics of the three temperature zones can be set to drive a single fan. An example would be the fan turning on when Remote 1 temperature exceeds 60°C or if the local temperature exceeds 45°C.

Other MUX Options

<7:5> (BHVR),

Registers 0x5C, 0x5D, 0x5E.

011 = PWMx runs full speed

100 = PWMx disabled (default)

111 = manual mode. PWMx is runner under software control. In this mode, PWM duty cycle registers (Registers 0x30 to 0x32) are writable and control the PWM outputs.

010 = Remote 2 temperature controls PWMx

REMOTE 1 =

AMBIENT TEMP

LOCAL =

VRM TEMP

REMOTE 2 =

CPU TEMP

THERMAL CALIBRATION

MIN

THERMAL CALIBRATION

MIN

THERMAL CALIBRATION

MIN

100%

RANGE

100%

RANGE

100%

RANGE

Figure 53. Assigning Temperature Channels to Fan Channels

MUX

PWM

MIN

PWM

MIN

PWM

MIN

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 1 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 2 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 3

AND 4

MEASUREMENT

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM1

TACH1

PWM2

TACH2

FRONT CHASSIS

PWM3

TACH3

REAR CHASSIS

CPU FAN SINK

04499-0-058

Rev. 0 | Page 40 of 80

Page 41

ADT7468

MUX Configuration Example

This is an example of how to configure the MUX in a system using the ADT7468 to control three fans. The CPU fan sink is controlled by PWM1, the front chassis fan is controlled by PWM2, and the rear chassis fan is controlled by PWM3. The MUX is configured for the following fan control behavior:

•

PWM1 (CPU fan sink) is controlled by the fastest speed

calculated by the local (VRM temperature) and Remote 2 (processor) temperature. In this case, the CPU fan sink is also being used to cool the VRM.

PWM2 (front chassis fan) is controlled by the Remote 1

•

temperature (ambient).

•

PWM3 (rear chassis fan) is controlled by the Remote 1

temperature (ambient).

Example MUX Settings

<7:5> (BHVR),

PWM1 Configuration Register 0x5C.

101 = Fastest speed calculated by local and Remote 2 temperature controls PWM1

<7:5> (BHVR), PWM2 Configuration Register 0x5D.

000 = Remote 1 temperature controls PWM2

<7:5> (BHVR), PWM3 Configuration Register 0x5E.

000 = Remote 1 temperature controls PWM3

These settings configure the MUX, as shown in Figure 54.

REMOTE 2 =

CPU TEMP

LOCAL =

VRM TEMP

REMOTE 1 =

AMBIENT TEMP

THERMAL CALIBRATION

MIN

THERMAL CALIBRATION

MIN

THERMAL CALIBRATION

MIN

RANGE

100%

MUX

PWM

MIN

PWM

MIN

PWM

MIN

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 1 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 2 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 3

AND 4

MEASUREMENT

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM1

TACH1

CPU FAN SINK

PWM2

TACH2

FRONT CHASSIS

PWM3

TACH3

REAR CHASSIS

04499-0-059

Figure 54. MUX Configuration Example

Rev. 0 | Page 41 of 80

Page 42

ADT7468

STEP 3: T CALIBRATION CHANNELS

is the temperature at which the fans start to turn on under

MIN

automatic fan control. The speed at which the fan runs at T programmed later. The T channel specific, for example, 25°C for ambient channel, 30°C for VRM temperature, and 40°C for processor temperature.

is an 8-bit value, either twos complement or Offset 64, that

MIN

can be programmed in 1°C increments. There is a T associated with each temperature measurement channel: Remote 1 Local, and Remote 2 Temp. Once the T exceeded, the fan turns on and runs at the minimum PWM duty cycle. The fan turns off once the temperature has dropped below T

To overcome fan inertia, the fan is spun up until two valid TACH rising edges are counted. See the Fan Startup Timeout section for more details. In some cases, primarily for psychoacoustic reasons, it is desirable that the fan never switch off below T 0x62), when set, keep the fans running at the PWM minimum duty cycle, if the temperature should fall below T

SETTINGS FOR THERMAL

MIN

values chosen are temperature

MIN

value is

MIN

– T

MIN

HYST

. Bits <7:5> of Enhanced Acoustics Register 1 (Reg.

MIN

Registers

MIN

Reg. 0x67, Remote 1 Temperature T

Reg. 0x68,

Reg. 0x69,

Local Temperature T

Remote 2 Temperature T

= 0x9A (90°C)

MIN

= 0x9A (90°C)

MIN

= 0x9A (90°C)

MIN

Enhance Acoustics Register 1 (Reg. 0x62)

Bit 7 (MIN3) = 0,

temperature is below T

PWM3 is off (0% PWM duty cycle) when

– T

HYST

MIN

Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty cycle

below T

MIN

– T

HYST

Bit 6 (MIN2) = 0, PWM2 is off (0% PWM duty cycle) when

– T

temperature is below T

MIN

HYST

Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty cycle

below T

MIN

– T

HYST

Bit 5 (MIN1) = 0, PWM1 is off (0% PWM duty cycle) when

temperature is below T

MIN

– T

HYST

Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty cycle

– T

below T

MIN

HYST

100%

E L C Y C Y T U

D M W

REMOTE 2 =

CPU TEMP

LOCAL =

VRM TEMP

REMOTE 1 =

AMBIENT TEMP

MIN

THERMAL CALIBRATION

MIN

THERMAL CALIBRATION

MIN

THERMAL CALIBRATION

MIN

RANGE

100%

MUX

100%

PWM

MIN

PWM

MIN

PWM

MIN

Figure 55. Understanding the T

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 1 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 2 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 3

AND 4

MEASUREMENT

Parameter

MIN

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM1

TACH1

CPU FAN SINK

PWM2

TACH2

FRONT CHASSIS

PWM3

TACH3

REAR CHASSIS

04499-0-060

Rev. 0 | Page 42 of 80

Page 43

ADT7468

STEP 4: PWM

PWM

is the minimum PWM duty cycle at which each fan in

MIN

FOR EACH PWM (FAN) OUTPUT

MIN

the system runs. It is also the start speed for each fan under automatic fan control once the temperature rises above T For maximum system acoustic benefit, PWM

should be as

MIN

low as possible. Depending on the fan used, the PWM

setting

MIN

is usually in the 20% to 33% duty cycle range. This value can be found through fan validation.

100%

Programming the PWM

The PWM

registers are 8-bit registers that allow the

MIN

minimum PWM duty cycle for each output to be configured anywhere from 0% to 100%. This allows the minimum PWM duty cycle to be set in steps of 0.39%.

The value to be programmed into the PWM by

Va lu e (decimal) = PWM

Example 1: For a minimum PWM duty cycle of 50%,

Va lu e (decimal) = 50/0.39 = 128 (decimal) Va lu e = 128 (decimal) or 80 (hex)

Registers

MIN

/0.39

MIN

PWM DUTY CYCLE

PWM

MIN

TEMPERATURE

04499-0-061

Figure 56. PWM

MIN

Determines Minimum PWM Duty Cycle

MIN

More than one PWM output can be controlled from a single temperature measurement channel. For example, Remote 1 temperature can control PWM1 and PWM2 outputs. If two different fans are used on PWM1 and PWM2, then the fan characteristics can be set up differently. As a result, Fan 1 driven by PWM1 can have a different PWM connected to PWM2. Figure 57 illustrates this as PWM1

value than that of Fan 2

MIN

(front fan) is turned on at a minimum duty cycle of 20%, while PWM2

(rear fan) turns on at a minimum of 40% duty cycle.

MIN

Note, however, that both fans turn on at exactly the same temperature, defined by T

100%

PWM2

MIN

PWM DUTY CYCLE

PWM1

MIN

Figure 57. Operating Two Different Fans from a Single Temperature Channel

MIN

TEMPERATURE

04499-0-062

Example 2: For a minimum PWM duty cycle of 33%,

Va lu e (decimal) = 33/0.39 = 85 (decimal) Va lu e = 85 (decimal)l or 54 (hex)

PWM

Registers

MIN

Reg. 0x64, PWM1 Minimum Duty Cycle = 0x80 (50% default) Reg. 0x65 Reg. 0x66,

PWM2 Minimum Duty Cycle = 0x80 (50% default)

PWM3 Minimum Duty Cycle = 0x80 (50% default)

Note on Fan Speed and PWM Duty Cycle

The PWM duty cycle does not directly correlate to fan speed in RPM. Running a fan at 33% PWM duty cycle does not equate to running the fan at 33% speed. Driving a fan at 33% PWM duty cycle actually runs the fan at closer to 50% of its full speed. This is because fan speed in %RPM generally relates to the square root of PWM duty cycle. Given a PWM square wave as the drive signal, fan speed in RPM approximates to

10% ×= cycledutyPWMfanspeed

STEP 5: PWM

PWM

is the maximum duty cycle that each fan in the system

MAX

FOR PWM (FAN) OUTPUTS

MAX

runs at under the automatic fan speed control loop. For maximum system acoustic benefit, PWM

should be as low as

MAX

possible, but should be capable of maintaining the processor temperature limit at an acceptable level. If the

THERM

temperature limit is exceeded, the fans are still boosted to 100% for fail-safe cooling.

There is a PWM

limit for each fan channel. The default value

MAX

of this register is 0xFF and so has no effect unless it is programmed.

Rev. 0 | Page 43 of 80

Page 44

ADT7468

100%

PWM

MAX

PWM DUTY CYCLE

PWM

MIN

MAX

TEMPERATURE

/0.39

MAX

04499-0-063

THERM

MIN

Figure 58. PWM

Determines Maximum PWM Duty Cycle below the

MAX

Temperature Limit

Programming the PWM

The PWM

registers are 8-bit registers that allow the

MAX

Registers

MAX

maximum PWM duty cycle for each output to be configured anywhere from 0% to 100%. This allows the maximum PWM duty cycle to be set in steps of 0.39%.

The value to be programmed into the PWM by

Va lu e (decimal) = PWM

Example 1: For a maximum PWM duty cycle of 50%,

Va lu e (decimal) – 50/0.39 = 128 (decimal) Va lu e = 128 (decimal) or 80 (hex)

Example 2: For a minimum PWM duty cycle of 75%,

Va lu e (decimal) = 75/0.39 = 85 (decimal)

Va lu e = 192 (decimal) or C0 (hex)

PWM

Registers

MAX

Reg. 0x38, PWM1 Maximum Duty Cycle = 0xFF (100% default)

Reg. 0x39,

PWM2 Maximum Duty Cycle = 0xFF

(100% default)

STEP 6: T

is the range of temperature over which automatic fan

RANGE

control occurs once the programmed T been exceeded. T value, that is, a T 33%. If PWM

FOR TEMPERATURE CHANNELS

RANGE

temperature has

MIN

is a temperature slope, not an arbitrary

RANGE

of 40°C holds true only for PWM

RANGE

is increased or decreased, the effective T

MIN

RANGE

changes.

RANGE

100%

PWM DUTY CYCLE

PWM

MIN

The T

MIN

Figure 59. T

or fan control slope is determined by the following

RANGE

Parameter Affects Cooling Slope

RANGE

TEMPERATURE

04499-0-064

procedure:

Determine the maximum operating temperature for that

channel (for example, 70°C).

Determine experimentally the fan speed (PWM duty cycle

value) that does not exceed the temperature at the worstcase operating points. (For example, 70°C is reached when the fans are running at 50% PWM duty cycle.)

Determine the slope of the required control loop to meet

3. these requirements.

Using the ADT7468 evaluation software, you can

graphically program and visualize this functionality. Ask your local Analog Devices representative for details.

100%

Reg. 0x3A,

PWM3 Maximum Duty Cycle = 0xFF

(100% default)

See the Note on Fan Speed and PWM Duty Cycle on Page 43.

Rev. 0 | Page 44 of 80

50%

PWM DUTY CYCLE

33%

Figure 60. Adjusting PWM

30°C

MIN

40°C

Affects T

MIN

RANGE

04499-0-065

Page 45

ADT7468

is implemented as a slope, which means that as PWM

RANGE

is changed, T same. The higher the PWM T

, that is, the fan reaches full speed (100%) at a lower

RANGE

changes, but the actual slope remains the

RANGE

value, the smaller the effective

MIN

temperature.

100%

MIN

Example: Calculate T

and PWM

T T T T

= 33% duty cycle = 85 (decimal).

MIN

= T

MAX

+ (Max DC − Min DC) × T

MIN

= 30°C + (100% − 33%) × 40°C/170 = 30°C + (255 − 85) × 40°C/170 = 70°C (effective T

Example: Calculate T

and PWM

= 50% duty cycle = 128 (decimal).

MIN

, given that T

MAX

RANGE

, given that T

MAX

MIN

= 40°C)

MIN

= 30°C, T

/170

RANGE

= 30°C, T

RANGE

= 40°C,

50% 33%

25%

PWM DUTY CYCLE

10%

30°C

40°C

45°C

54°C

MIN

Figure 61. Increasing PWM

For a given T

value, the temperature at which the fan runs

RANGE

at full speed for different PWM

Changes Effective T

MIN

values can be easily

MIN

RANGE

04499-0-066

calculated:

= T

MAX

+ (Max DC − Min DC) × T

MIN

RANGE

/170

where:

is the temperature at which the fan runs full speed.

MAX

is the temperature at which the fan turns on.

MIN

Max DC is the maximum duty cycle (100%) = 255 decimal. Min D C is equal to PWM T

is the duty PWM duty cycle vs. temperature slope.

RANGE

Example: Calculate T, given that T

and PWM

T T T T

= 10% duty cycle = 26 (decimal).

MIN

= T

MAX

+ (Max DC − Min DC) × T

MIN

= 30°C + (100% − 10%) × 40°C/170 = 30°C + (255 − 26) × 40°C/170 = 84°C (effective T

Example: Calculate T

and PWM

T T T T

= 25% duty cycle = 64 (decimal).

MIN

= T

MAX

+ (Max DC − Min DC) × T

MIN

= 30°C + (100% − 25%) × 40°C/170 = 30°C + (255 − 64) × 40°C/170 = 75°C (effective T

MIN

RANGE

, given that T

MAX

RANGE

= 30°C, T

MIN

= 54°C)

MIN

= 45°C)

RANGE

/170

RANGE

= 30°C, T

/170

RANGE

= 40°C,

RANGE

= T

MAX

Selecting a T

The T

RANGE

+ (Max DC − Min DC) × T

MIN

= 30°C + (100% − 50%) × 40°C/170 = 30°C + (255 − 128) × 40°C/170 = 60°C (effective T

Slope

RANGE

= 30°C)

value can be selected for each temperature channel: Remote 1, local, and Remote 2 temperature. Bits <7:4> (T of Registers 0x5F to 0x61 define the T

RANGE

/170

RANGE

value for each

RANGE

)

temperature channel.

Table 13. Selecting a T

Bits <7:4>1 T

RANGE

Val ue

(°C)

0000 2 0001 2.5 0010 3.33 0011 4 0100 5 0101 6.67 0110 8 0111 10 1000 13.33 1001 16 1010 20 1011 26.67 1100 32 (default) 1101 40 1110 53.33 1111 80

RANGE

Summary of T

RANGE

Function

When using the automatic fan control function, the temperature at which the fan reaches full speed can be calculated by

= T

MAX

MIN

+ T

(1)

RANGE

Equation 1 holds true only when PWM PWM duty cycle.

Rev. 0 | Page 45 of 80

is equal to 33%

MIN

Page 46

ADT7468

Increasing or decreasing PWM

changes the effective T

MIN

RANGE

although the fan control still follows the same PWM duty cycle to temperature slope. The effective T

for different PWM

RANGE

MIN

values can be calculated using Equation 2:

= T

MAX

+ (Max DC − Min DC) × T

MIN

/170 (2)

RANGE

where:

(Max DC − Min DC) × T

/170 is the effective T

RANGE

value.

See the Note on Fan Speed and PWM Duty Cycle.

Figure 62 shows PWM duty cycle versus temperature for each T

setting. The lower graph shows how each T

RANGE

setting affects fan speed versus temperature. As can be seen from the graph, the effect on fan speed is nonlinear.

100

PWM DUTY CYCLE (%)

0 20406080100120

100

FAN SPEED (% OF MAX)

0 20 40 60 80 100 120

TEMPERATURE ABOVE T

Figure 62. T

RANGE

MIN

vs. Actual Fan Speed Profile

2°C

2.5°C

3.33°C 4°C 5°C

6.67°C 8°C 10°C

13.3°C 16°C 20°C

26.6°C 32°C 40°C

53.3°C 80°C

2°C

2.5°C

3.33°C 4°C 5°C

6.67°C 8°C 10°C

13.3°C 16°C 20°C

26.6°C 32°C 40°C

53.3°C 80°C

The graphs in Figure 62 assume that the fan starts from 0% PWM duty cycle. Clearly, the minimum PWM duty cycle, PWM performs in the system. Figure 63 shows how T when the PWM

, needs to be factored in to see how the loop actually

MIN

is affected

RANGE

value is set to 20%. It can be seen that the fan

MIN

actually runs at about 45% fan speed when the temperature exceeds T

MIN

04499-0-067

100

PWM DUTY CYCLE (%)

0 20 40 60 80 100 120

100

FAN SPEED (% OF MAX)

0 20 40 60 80 100 120

Figure 63. T

TEMPERATURE ABOVE T

and % Fan Speed Slopes with PWM

RANGE

MIN

2°C

2.5°C

3.33°C 4°C 5°C

6.67°C 8°C 10°C

13.3°C 16°C 20°C

26.6°C 32°C 40°C

53.3°C 80°C

2°C

2.5°C

3.33°C 4°C 5°C

6.67°C 8°C 10°C

13.3°C 16°C 20°C

26.6°C 32°C 40°C

53.3°C 80°C

= 20%

Example: Determining T

The following example shows how the different T

for Each Temperature Channel

RANGE

and T

MIN

RANGE

settings can be applied to three different thermal zones. In this example, the following T

= 80°C for ambient temperature

RANGE

= 53.3°C for CPU temperature

RANGE

= 40°C for VRM temperature

RANGE

values apply:

RANGE

This example uses the MUX configuration described in Step 2, with the ADT7468 connected as shown in Figure 54. Both CPU temperature and VRM temperature drive the CPU fan connected to PWM1. Ambient temperature drives the front chassis fan and rear chassis fan connected to PWM2 and PWM3. The front chassis fan is configured to run at PWM 20%. The rear chassis fan is configured to run at PWM 30%. The CPU fan is configured to run at PWM

= 10%.

MIN

Note on 4-Wire Fans

The control range for 4-wire fans is much wider than that of 2-wire or 3-wire fans. In many cases, 4-wire fans can start with a PWM drive of as little as 20%.

04499-0-068

Rev. 0 | Page 46 of 80

Page 47

ADT7468

100

PWM DUTY CYCLE (%)

0 10203040 10050 60 70 80 90

100

FAN SPEED (% MAX RPM)

0 10203040 10050 60 70 80 90

Figure 64. T

STEP 7: T

THERM

is the absolute maximum temperature allowed on a

TEMPERATURE ABOVE T

and % Fan Speed Slopes for VRM, Ambient, and

RANGE

CPU Temperature Channels

MIN

FOR TEMPERATURE CHANNELS

temperature channel. Above this temperature, a component such as the CPU or VRM might be operating beyond its safe operating limit. When the temperature measured exceeds

, all fans are driven at 100% PWM duty cycle (full speed)

THERM

to provide critical system cooling.

04499-0-069

The fans remain running at 100% until the temperature drops below T

minus hysteresis, where hysteresis is the number

THERM

programmed into the Hysteresis Registers 0x6D and 0x6E. The default hysteresis value is 4°C.

The T

limit should be considered the maximum worst-case

THERM

operating temperature of the system. Because exceeding any

limit runs all fans at 100%, it has very negative acoustic

THERM

effects. Ultimately, this limit should be set up as a fail-safe, and one should ensure that it is not exceeded under normal system operating conditions.

Note that the T

limits are nonmaskable and affect the fan

THERM

speed no matter how automatic fan control settings are configured. This allows some flexibility, because a T

RANGE

value can be selected based on its slope, while a hard limit (such as 70°C), can be programmed as T the fan reaches full speed) by setting T

(the temperature at which

MAX

to that limit (for

THERM

example, 70°C).

THERM

Registers

Reg. 0x6A, Remote 1

Reg. 0x6B,

Reg. 0x6C,

Local

Remote 2

THERM

limit = 0xA4 (100°C default)

Hysteresis Registers

Reg. 0x6D, Remote 1, Local Hysteresis Register

Remote 1 temperature hysteresis (4°C default).

<7:4>,

<3:0>, Local temperature hysteresis (4°C default).

Reg. 0x6E

<7:4>,

, Remote 2 Temperature Hysteresis Register

Remote 2 temperature hysteresis (4°C default).

Because each hysteresis setting is four bits, hysteresis values are programmable from 1°C to 15°C. It is not recommended that hysteresis values ever be programmed to 0°C, because this disables hysteresis. In effect, this would cause the fans to cycle between normal speed and 100% speed, creating unsettling acoustic noise.

Rev. 0 | Page 47 of 80

Page 48

ADT7468

100%

E L C Y C Y T U D

M W

THERMAL CALIBRATION

REMOTE 2 =

CPU TEMP

THERMAL CALIBRATION

RANGE

100%

THERM

MIN

MUX

LOCAL =

VRM TEMP

REMOTE 1 =

AMBIENT TEMP

STEP 8: T

is the amount of extra cooling a fan provides after the

HYST

FOR TEMPERATURE CHANNELS

HYST

MIN

THERMAL CALIBRATION

MIN

temperature measured has dropped back below T fan turns off. The premise for temperature hysteresis (T

RANGE

100%

RANGE

Figure 65. How T

before the

MIN

HYST

THERM

) is that, without it, the fan would merely chatter or cycle on and off regularly whenever temperature is hovering at about the T

MIN

setting.

The T

value chosen determines the amount of time needed

HYST

for the system to cool down or heat up as the fan is turning on and off. Values of hysteresis are programmable in the range 1°C to 15°C. Larger values of T on and off. The T

The T

setting applies not only to the temperature hysteresis

HYST

default value is set at 4°C.

HYST

for fan on/off, but the same setting is used for the T

prevent the fans from chattering

HYST

THERM

hysteresis value, described in Step 6. Therefore, programming Registers 0x6D and 0x6E sets the hysteresis for both fan on/off and the

THERM

function.

PWM

MIN

RAMP

CONTROL

PWM

MIN

PWM

MIN

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 1 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 2 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 3

AND 4

MEASUREMENT

GENERATOR

Relates to Automatic Fan Control

Hysteresis Registers

Reg. 0x6D, Remote 1, Local Hysteresis Register

Remote 1 temperature hysteresis (4°C default).

<7:4>,

<3:0>, local temperature hysteresis (4°C default).

Reg. 0x6E

<7:4>,

, Remote 2 Temp Hysteresis Register

Remote 2 temperature hysteresis (4°C default).

In some applications, it is required that fans not turn off below

, but remain running at PWM

MIN

Acoustics Register 1 (Reg. 0x62) allow the fans to be turned off or to be kept spinning below T T

value has no effect on the fan when the temperature drops

HYST

below T

MIN

PWM

CONFIG

PWM

CONFIG

PWM

CONFIG

PWM

PWM1

TACH1

CPU FAN SINK

PWM2

TACH2

FRONT CHASSIS

PWM3

TACH3

REAR CHASSIS

MIN

. If the fans are always on, the

MIN

04499-0-070

. Bits <7:5> of Enhanced

Rev. 0 | Page 48 of 80

Page 49

ADT7468

100%

E L C Y C Y T U D

M W

THERMAL CALIBRATION

LOCAL =

THERMAL CALIBRATION

REMOTE 2 =

CPU TEMP

VRM TEMP

REMOTE 1 =

AMBIENT TEMP

Figure 66. The T

RANGE

MIN

THERM

100%

RANGE

100%

MUX

RANGE

100%

RANGE

Value Applies to Fan On/Off Hysteresis and

HYST

PWM

MIN

PWM

MIN

PWM

MIN

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 1 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 2 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 3

AND 4

MEASUREMENT

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

THERM

Hysteresis

PWM1

TACH1

PWM2

TACH2

FRONT CHASSIS

PWM3

TACH3

CPU FAN SINK

REAR CHASSIS

04499-0-071

Enhance Acoustics Register 1 (Reg. 0x62)

Bit 7 (MIN3) = 0,

temperature is below T

PWM3 is off (0% PWM duty cycle) when

− T

HYST

MIN

Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty cycle

below T

MIN

− T

HYST

Bit 6 (MIN2) = 0, PWM2 is off (0% PWM duty cycle) when

temperature is below T

MIN

− T

HYST

Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty cycle

below T

MIN

− T

HYST

Bit 5 (MIN1) = 0, PWM1 is off (0% PWM duty cycle) when

temperature is below T

MIN

− T

HYST

Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty cycle

below T

MIN

− T

HYST

DYNAMIC T

CONTROL MODE

MIN

In addition to the automatic fan speed control mode described in the Automatic Fan Control Overview section, the ADT7468 has a mode that extends the basic automatic fan speed control loop. Dynamic T

control allows the ADT7468 to intelligently

MIN

adapt the system’s cooling solution for best system performance or lowest possible system acoustics, depending on user or design requirements. Use of dynamic T

control alleviates the

MIN

need to design for worst-case conditions and significantly reduces system design and validation time.

Designing for Worst-Case Conditions

System design must always allow for worst-case conditions. In PC design, the worst-case conditions include, but are not limited to the following:

Rev. 0 | Page 49 of 80

Page 50

ADT7468

• Wo rs t- Ca se Al ti tu de

A computer can be operated at different altitudes. The altitude affects the relative air density, which alters the effectiveness of the fan cooling solution. For example, comparing 40°C air temperature at 10,000 ft. to 20°C air temperature at sea level, relative air density is increased by 40%. This means that the fan can spin 40% slower and make less noise at sea level than at 10,000 ft. while keeping the system at the same temperature at both locations.

Wo r st - Ca s e F a n

•

Due to manufacturing tolerances, fan speeds in RPM are normally quoted with a tolerance of ±20%. The designer needs to assume that the fan RPM can be 20% below tolerance. This translates to reduced system airflow and elevated system temperature. Note that fans 20% out of tolerance can negatively impact system acoustics, because they run faster and generate more noise.

•

Worst-Case Chassis Airflow

The same motherboard can be used in a number of different chassis configurations. The design of the chassis and the physical location of fans and components determine the system thermal characteristics. Moreover, for a given chassis, the addition of add-in cards, cables, or other system configuration options can alter the system airflow and reduce the effectiveness of the system cooling solution. The cooling solution can also be inadvertently altered by the end user. (For example, placing a computer against a wall can block the air ducts and reduce system airflow.)

VENTS

I/O CARDS

GOOD CPU AIRFLOW

FAN

POWER SUPPLY

CPU

VENTS

I/O CARDS

POOR CPU

AIRFLOW

POWER SUPPLY

FAN

CPU

Worst-Case Assembly

•

Every system manufactured is unique because of manufacturing variations. Heat sinks may be loose fitting or slightly misaligned. Too much or too little thermal grease might be used, or variations in application pressure for thermal interface material could affect the efficiency of the thermal solution. Accounting for manufacturing variations in every system is difficult; therefore, the system must be designed for the worst case.

TIMS

CTIM

TIMC

JTIM

TIM

04499-0-073

HEAT

SINK

THERMAL

INTERFACE

MATERIAL

INTEGRATED

HEAT

SPREADER

SUBSTRATE

PROCESSOR

EPOXY

THERMAL INTERFACE MATERIAL

Figure 68. Thermal Model

Although a design usually accounts for worst-case conditions in all these cases, the actual system is almost never operated at worst-case conditions. The alternative to designing for the worst case is to use the dynamic T

Dynamic T

Control Overview

MIN

control mode builds upon the basic automatic

MIN

fan control loop by adjusting the T

control function.

MIN

value based on system

MIN

performance and measured temperature. This is important, because, instead of designing for the worst case, the system thermals can be defined as operating zones. ADT7468 can selfadjust its fan control loop to maintain either an operating zone temperature or a system target temperature. For example, one can specify that the ambient temperature in a system should be maintained at 50°C. If the temperature is below 50°C, the fans might not need to run or might run very slowly. If the temperature is higher than 50°C, the fans need to throttle up.

FAN

VENTS

GOOD VENTING =

GOOD AIR EXCHANGE

DRIVE

BAYS

POOR VENTING =

POOR AIR EXCHANGE

Figure 67. Chassis Airflow Issues

• Worst-Case Processor Power Consumption

This data sheet maximum does not necessarily reflect the true processor power consumption. Designing for worstcase CPU power consumption can result in a processor becoming overcooled (generating excess system noise).

•

Worst-Case Peripheral Power Consumption

The tendency is to design to data sheet maximums for peripheral components (again overcooling the system).

DRIVE

BAYS

Rev. 0 | Page 50 of 80

04499-0-072

The challenge presented by any thermal design is finding the right settings to suit the system’s fan control solution. This can involve designing for the worst case, followed by weeks of system thermal characterization, and finally fan acoustic optimization (for psycho-acoustic reasons). Getting the most benefit from the automatic fan control mode involves characterizing the system to find the best T control loop, and the best PWM speed setting. Using the ADT7468’s dynamic T

and T

MIN

value for the quietest fan

MIN

settings for the

RANGE

control mode,

MIN

however, shortens the characterization time and alleviates tweaking the control loop settings, because the device can selfadjust during system operation.

Dynamic T

control mode is operated by specifying the

MIN

operating zone temperatures required for the system. Associated with this control mode are three operating point registers, one

Page 51

ADT7468

for each temperature channel. This allows the system thermal solution to be broken down into distinct thermal zones. For example, CPU operating temperature is 70°C, VRM operating temperature is 80°C, and ambient operating temperature is 50°C. The ADT7468 dynamically alters the control solution to maintain each zone temperature as closely as possible to its target operating point.

Operating Point Registers

Reg. 0x33, Remote 1 Operating Point = 0xA4 (100°C default)

Reg. 0x34,

Reg. 0x35,

Local Operating Point = 0xA4 (100°C default)

Remote 2 Operating Point = 0xA4 (100°C default)

Figure 69 shows an overview of the parameters that affect the operation of the dynamic T

PWM DUTY CYCLE

LOWTMIN

OPERATING

POINT

Figure 69. Dynamic T

control loop.

MIN

HIGH

THERM

Control Loop

MIN

RANGE

TEMPERATURE

Table 14 provides a brief description of each parameter.

Table 14. T

Control Loop Parameters

MIN

Parameter Description

LOW

If the temperature drops below the T

limit, an

LOW

error flag is set in a status register and an SMBALERT

HIGH

If the temperature exceeds the T

interrupt can be generated.

limit, an

HIGH

error flag is set in a status register and an SMBALERT

MIN

The temperature at which the fan turns on

interrupt can be generated.

under automatic fan speed control.

Operating point

The target temperature for a particular temperature zone. The ADT7468 attempts to maintain system temperature at about the operating point by adjusting the T

parameter

MIN

of the control loop.

THERM

If the temperature exceeds this critical limit, the fans can be run at 100% for maximum cooling.

RANGE

Programs the PWM duty cycle vs. temperature control slope.

04499-0-074

Dynamic T

Because the dynamic T the automatic fan control mode, program the automatic fan control mode parameters first, as described in Step 1 to Step 8, then proceed with dynamic T

STEP 9: OPERATING POINTS FOR TEMPERATURE CHANNELS

The operating point for each temperature channel is the optimal temperature for that thermal zone. The hotter each zone is allowed to be, the quieter the system, because the fans are not required to run as fast. The ADT7468 increases or decreases fan speeds as necessary to maintain the operating point temperature, allowing for system-to-system variation and removing the need for worst-case design. If a sensible operating point value is chosen, any T system characterization. If the T sooner than required, and the temperature is below the operating point. In response, the ADT7468 increases T fans off longer and to allow the temperature zone to get closer to the operating point. Likewise, too high a T the operating point to be exceeded, and in turn, the ADT7468 reduces T

Programming Operating Point Registers

There are three operating point registers, one for each temperature channel. These 8-bit registers allow the operating point temperatures to be programmed with 1°C resolution.

Operating Point Registers

Reg. 0x33, Remote 1 Operating Point = 0xA4 (100°C default)

Reg. 0x34,

Reg. 0x35,

Control Programming

MIN

control mode is a basic extension of

MIN

control mode programming.

MIN

value can be selected in the

MIN

value is too low, the fans run

MIN

to keep the

MIN

value causes

MIN

to turn the fans on sooner to cool the system.

MIN

Local Operating Point = 0xA4 (100°C default)

Remote 2 Operating Point = 0xA4 (100°C default)

Rev. 0 | Page 51 of 80

Page 52

ADT7468

REMOTE 2 =

CPU TEMP

THERMAL CALIBRATION

MIN

THERMAL CALIBRATION

RANGE

100%

OPERATING

100%

MUX

RANGE

100%

LOCAL =

VRM TEMP

REMOTE 1 =

AMBIENT TEMP

MIN

THERMAL CALIBRATION

MIN

Figure 70. Operating Point Value Dynamically Adjusts Automatic Fan Control Settings

STEP 10: HIGH AND LOW LIMITS FOR TEMPERATURE CHANNELS

The low limit defines the temperature at which the T starts to be increased, if temperature falls below this value. This has the net effect of reducing the fan speed, allowing the system to get hotter. An interrupt can be generated when the temperature drops below the low limit.

The high limit defines the temperature at which the T starts to be reduced, if temperature increases above this value. This has the net effect of increasing fan speed to cool down the system. An interrupt can be generated when the temperature rises above the high limit.

Programming High and Low Limits

There are six limit registers; a high limit and low limit are associated with each temperature channel. These 8-bit registers allow the high and low limit temperatures to be programmed with 1°C resolution.

Temperature Limit Registers

Reg. 0x4E, Remote 1 Temperature Low Limit = 0x01

Reg. 0x4F,

Reg. 0x50,

Reg. 0x51,

Remote 1 Temperature High Limit = 0x7F

Local Temperature Low Limit = 0x01

Local Temperature High Limit = 0x7F

MIN

value

POINT

PWM

MIN

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 1 MEASUREMENT

PWM

MIN

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 2 MEASUREMENT

PWM

MIN

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 3

AND 4

MEASUREMENT

How Dynamic T

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

Control Works

MIN

PWM1

TACH1

PWM2

TACH2

FRONT CHASSIS

PWM3

TACH3

REAR CHASSIS

CPU FAN SINK

04499-0-075

The basic premise is as follows:

Set the target temperature for the temperature zone, which

1. could be, for example, the Remote 1 thermal diode. This value is programmed to the Remote 1 operating temperature register.

As the temperature in that zone (Remote 1 temperature)

rises toward and exceeds the operating point temperature,

is reduced and the fan speed increases.

MIN

As the temperature drops below the operating point

3. temperature, T

is increased and the fan speed is reduced.

MIN

However, the loop operation is not as simple as described in these steps. A number of conditions govern the situations in which T

can increase or decrease.

MIN

Short Cycle and Long Cycle

The ADT7468 implements two loops: a short cycle and a long cycle. The short cycle takes place every n monitoring cycles. The long cycle takes place every 2n monitoring cycles. The value of n is programmable for each temperature channel. The bits are located at the following register locations:

Remote 1 = CYR1 = Bits <2:0> of Calibration Control Register 2 (Address = 0x37).

Reg. 0x52,

Reg. 0x53,

Remote 2 Temperature Low Limit = 0x01

Remote 2 Temperature High Limit = 0x7F

Rev. 0 | Page 52 of 80

Page 53

ADT7468

Local = CYL = Bits <5:3> of Calibration Control Register 2 (Address = 0x37).

Remote 2 = CYR2 = Bits <7:6> of Calibration Control Register 2 and Bit 0 of Calibration Control Register 1 (Address = 0x36).

Table 15. Cycle Bit Assignments

Code Short Cycle Long Cycle

000 8 cycles (1 s) 16 cycles (2 s) 001 16 cycles (2 s) 32 cycles (4 s) 010 32 cycles (4 s) 64 cycles (8 s) 011 64 cycles (8 s) 128 cycles (16 s) 100 128 cycles (16 s) 256 cycles (32 s) 101 256 cycles (32 s) 512 cycles (64 s) 110 512 cycles (64 s) 1024 cycles (128 s) 111 1024 cycles (128 s) 2048 cycles (256 s)

Care should be taken when choosing the cycle time. A long cycle time means that T has very fast temperature transients, the dynamic T

is updated less often. If your system

MIN

control

MIN

loop will always be lagging. If you choose a cycle time that is too fast, the full benefit of changing T

might not be realized and

MIN

needs to change again on the next cycle; in effect, it is overshooting. It is necessary to carry out some calibration to identify the most suitable response time.

Figure 71 shows the steps taken during the short cycle.

WAIT n

MONITORING

CYCLES

CURRENT

TEMPERATURE

MEASUREMENT

T1(n)

OPERATING

POINT

TEMPERATURE

OP1

TEMPERATURE

MEASUREMENT

T1 (n – 1)

IS T1(n) >

(OP1 – HYS)

IS T1(n) – T1(n – 1)

≤ 0.25°C

IS T1(n) – T1(n – 1) = 0.5 – 0.75°C IS T1(n) – T1(n – 1) = 1.0 – 1.75°C IS T1(n) – T1(n – 1) > 2.0°C

YES

DO NOTHING

(SYSTEM IS

COOLING OF

FOR CONSTANT)

DECREASE T DECREASE T DECREASE T

MIN

MIN MIN

BY 1°C

BY 2°C BY 4°C

Figure 71. Short Cycle Steps

Figure 72 shows the steps taken during the long cycle.

The following examples illustrate some of the circumstances that might cause T

Example: Normal Operation—No T

to increase, decrease, or stay the same.

MIN

Adjustment

MIN

1. If measured temperature never exceeds the programmed

operating point minus the hysteresis temperature, then

is not adjusted, that is, remains at its current setting.

MIN

If measured temperature never drops below the low

2. temperature limit, then T

is not adjusted.

MIN

04499-0-077

CURRENT

TEMPERATURE

MEASUREMENT

T1(n)

OPERATING

POINT

TEMPERATURE

OP1

THERM LIMIT

HIGH TEMP

LIMIT

OPERATING

POINT

LOW TEMP

LIMIT

MIN

Figure 73. Temperature between Operating Point and Low Temperature Limit

Because neither the operating point minus the hysteresis temperature nor the low temperature limit has been exceeded, the T

value is not adjusted, and the fan runs at a speed

MIN

determined by the fixed T automatic fan speed control mode.

Example: Operating Point Exceeded—T

When the measured temperature is below the operating point temperature minus the hysteresis, T

Once the temperature exceeds the operating temperature minus the hysteresis (OP − Hyst), T during the short cycle (see Figure 71). The rate at which T decreases depends on the programmed value of n. It also depends on how much the temperature has increased between this monitoring cycle and the last monitoring cycle, that is, if the temperature has increased by 1°C, then T 2°C. Decreasing T thus providing more cooling to the system.

If the temperature is slowly increasing only in the range (OP − Hyst), that is, ≤0.25°C per short monitoring cycle, then T

does not decrease. This allows small changes in

MIN

temperature in the desired operating zone without changing

. The long cycle makes no change to T

MIN

WAIT 2n

MONITORING

CYCLES

IS T1(n) > OP1

IS T1(n) < LOW TEMP LIMIT

AND

< HIGH TEMP LIMIT

MIN

AND

< OP1

MIN

AND

T1(n) > T

YES

MIN

YES

DECREASE T

BY 1°C

INCREASE

BY 1°C

MIN

DO NOT

CHANGE

Figure 72. Long Cycle Steps

HYSTERESIS

ACTUAL

TEMP

and T

MIN

starts to decrease. This occurs

MIN

has the effect of increasing the fan speed,

MIN

values defined in the

RANGE

Reduced

MIN

remains the same.

MIN

is reduced by

MIN

in the

MIN

04499-0-078

04499-0-079

Rev. 0 | Page 53 of 80

Page 54

ADT7468

temperature range (OP − Hyst), because the temperature has not exceeded the operating temperature.

Once the temperature exceeds the operating temperature, the long cycle causes T while the temperature remains above the operating temperature. This takes place in addition to the decrease in T occur due to the short cycle. In Figure 74, because the temperature is increasing at a rate ≤0.25°C per short cycle, no reduction

takes place during the short cycle.

in T

MIN

Once the temperature has fallen below the operating temperature, T starts to increase slowly, T temperature increases at a rate ≤0.25°C per cycle.

Example: Increase T

When the temperature drops below the low temperature limit,

can increase in the long cycle. Increasing T

MIN

effect of running the fan slower and, therefore, quieter. The long cycle diagram in Figure 74 shows the conditions that need to be true for T

to increase. Here is a quick summary of those

MIN

to be reduced by 1°C every long cycle

MIN

that would

MIN

stays the same. Even when the temperature

MIN

stays the same, because the

MIN

Cycle

MIN

has the

MIN

THERM

LIMIT

HIGH TEMP

LIMIT

PERATING

POINT

HYSTERESIS

conditions and the reasons they need to be true.

can increase, if

MIN

The measured temperature has fallen below the low

•

temperature limit. This means the user must choose the low limit carefully. It should not be so low that the temperature never falls below it, because T increase and the fans would run faster than necessary.

•

is below the high temperature limit. T

MIN

allowed to increase above the high temperature limit. As a result, the high limit should be sensibly chosen, because it determines how high T

•

is below the operating point temperature. T

MIN

can go.

MIN

never be allowed to increase above the operating point temperature, because the fans would not switch on until the temperature rose above the operating point.

•

The temperature is above T

is turned off below T

MIN

. The dynamic T

MIN

would never

MIN

is never

MIN

control

MIN

should

MIN

LOW TEMP

LIMIT

ACTUAL

TEMP

DECREASE HERE DUE TO

SHORT CYCLE ONLY

T1(n) – T1 (n – 1) = 0.5°C

OR 0.75°C = > T

DECREASES BY 1°C

EVERY SHORT CYCLE

MIN

DECREASE HERE DUE TO

LONG CYCLE ONLY

T1(n) – T1 (n – 1)

AND T1(n) > OP = > T

DECREASES BY 1°C

EVERY LONG CYCLE

NO CHANGE IN T

DUE TO ANY CYCLE, BECAUSE

T1(n) – T1 (n – 1)

AND T1(n) < OP = > T

STAYS THE SAME

≤

0.25°C

MIN

Figure 74. Effect of Exceeding Operating Point Minus Hysteresis Temperature

MIN

≤

0.25°C

HERE

MIN

04499-0-080

Rev. 0 | Page 54 of 80

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ADT7468

Figure 75 shows how T ture is above T T

is below the high temperature limit and below the

MIN

and below the low temperature limit, and

MIN

increases when the current tempera-

MIN

operating point. Once the temperature rises above the low temperature limit, T

THERM

LIMIT

HIGH TEMP

LIMIT

OPERATING

POINT

HYSTERESIS

LOW TEMP

LIMIT

ACTUAL

MIN

Figure 75. Increasing T

Example: Preventing T

Because T

is dynamically adjusted, it is undesirable for T

MIN

TEMP

stays the same.

for Quieter Operation

MIN

from Reaching Full Scale

MIN

04499-0-081

MIN

to reach full scale (127°C), because the fan would never switch on. As a result, T

is allowed to vary only within a specified

MIN

range:

The lowest possible value for T

is –127°C (twos

MIN

complement mode) or −64°C (Offset 64 mode).

cannot exceed the high temperature limit.

MIN

If the temperature is below T

, the fan is switched off or

MIN

is running at minimum speed, and dynamic T

control is

MIN

disabled.

THERM

LIMIT

PERATING

POINT

LOW TEMP

HIGH TEMP

Figure 76. T

LIMIT

MIN

HYSTERESIS

ACTUAL

TEMP

PREVENTED

MIN

FROM INCREASING

Adjustments Limited by the High Temperature Limit

MIN

04499-0-082

STEP 11: MONITORING THERM

Using the operating point limit ensures that the dynamic T control mode is operating in the best possible acoustic position while ensuring that the temperature never exceeds the maximum operating temperature. Using the operating point limit allows T

to be independent of system-level issues because of

MIN

its self-corrective nature. In PC design, the operating point for the chassis is usually the worst-case internal chassis temperature.

MIN

The optimal operating point for the processor is determined by monitoring the thermal monitor in the Intel Pentium 4 processor. To do this, the connected to the

PROCHOT

THERM

output of the Pentium 4 is

input of the ADT7468.

The operating point for the processor can be determined by allowing the current temperature to be copied to the operating point register when the

PROCHOT

output pulls the

THERM input low on the ADT7468. This gives the maximum temperature at which the Pentium 4 can run before clock

modulation occurs.

Enabling the

Bits <4:2> of dynamic T enable/disable

THERM

Trip Point as the Operating Point

control Register 1 (Reg. 0x36)

MIN

THERM

monitoring to program the operating

point.

Dynamic T

<2> PHTR2 = 1,

the Remote 2 operating point register, if The operating point contains the temperature at which

Control Register 1 (0x36)

MIN

copies the Remote 2 current temperature to

THERM

is asserted.

THERM

is asserted. This allows the system to run as quietly as possible without affecting system performance.

PHTR2 = 0, ignores any

THERM

assertions. The Remote 2

operating point register reflects its programmed value.

<3> PHTL = 1, copies the local current temperature to the local

temperature operating point register, if operating point contains the temperature at which

THERM

is asserted. The

THERM

is asserted. This allows the system to run as quietly as possible without affecting system performance.

PHTL = 0, ignores any

THERM

assertions. The local temperature operating point register reflects its programmed value.

<4> PHTR1 = 1, copies the Remote 1 current temperature to

the Remote 1 operating point register, if The operating point contains the temperature at which

THERM

is asserted.

THERM

is asserted. This allows the system to run as quietly as possible without affecting system performance.

PHTR1 = 0, ignores any

THERM

assertions. The Remote 1

operating point register reflects its programmed value.

Enabling Dynamic T

Bits <7:5>

of dynamic T

enable/disable dynamic T

Control Mode

MIN

control Register 1 (Reg. 0x36)

MIN

control on the temperature

MIN

channels.

Dynamic

<5> R2T = 1,

temperature channel. The chosen T

Control Register 1 (0x36)

TMIN

enables dynamic T

control on the Remote 2

MIN

value is dynamically

MIN

adjusted based on the current temperature, operating point, and high and low limits for this zone.

Rev. 0 | Page 55 of 80

Page 56

ADT7468

R2T = 0, disables dynamic T

is not adjusted and the channel behaves as described in the Automatic Fan Control Overview section.

<6> LT = 1, enables dynamic T

temperature channel. The chosen T adjusted based on the current temperature, operating point, and high and low limits for this zone.

LT = 0 , disables dynamic T

not adjusted and the channel behaves as described in the Automatic Fan Control Overview section.

<7> R1T = 1, enables dynamic T

temperature channel. The chosen T adjusted based on the current temperature, operating point, and high and low limits for this zone.

R1T = 0, disables dynamic T

is not adjusted and the channel behaves as described in the Automatic Fan Control Overview section.

control. The T

MIN

control on the local

MIN

value is dynamically

MIN

control. The T

MIN

control on the Remote 1

MIN

value is dynamically

MIN

control. The T

MIN

value chosen

MIN

value chosen is

MIN

value chosen

MIN

ENHANCING SYSTEM ACOUSTICS

Automatic fan speed control mode reacts instantaneously to changes in temperature, that is, the PWM duty cycle responds immediately to temperature change. Any impulses in temperature can cause an impulse in fan noise. For psychoacoustic reasons, the ADT7468 can prevent the PWM output from reacting instantaneously to temperature changes. Enhanced acoustic mode controls the maximum change in PWM duty cycle at a given time. The objective is to prevent the fan from cycling up and down, annoying the user.

Acoustic Enhancement Mode Overview

Figure 77 gives a top-level overview of the automatic fan control circuitry on the ADT7468 and shows where acoustic enhancement fits in. Acoustic enhancement is intended as a postdesign tweak made by a system or mechanical engineer evaluating best settings for the system. Having determined the optimal settings for the thermal solution, the engineer can adjust the system acoustics. The goal is to implement a system that is acoustically pleasing without causing user annoyance due to fan cycling. It is important to realize that although a system might pass an acoustic noise requirement specification (for example, 36 dB), if the fan is annoying, it fails the consumer test.

ACOUSTIC

ENHANCEMENT

REMOTE 2 =

CPU TEMP

LOCAL =

VRM TEMP

REMOTE 1 =

AMBIENT TEMP

THERMAL CALIBRATION

MIN

THERMAL CALIBRATION

RANGE

100%

MUX

MIN

THERMAL CALIBRATION

MIN

RANGE

100%

Figure 77. Acoustic Enhancement Smoothes Fan Speed Variations under Automatic Fan Speed Control

PWM

MIN

PWM

MIN

PWM

MIN

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 1 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 2 MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 3

AND 4

MEASUREMENT

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

PWM1

TACH1

CPU FAN SINK

PWM2

TACH2

FRONT CHASSIS

PWM3

TACH3

REAR CHASSIS

04499-0-083

Rev. 0 | Page 56 of 80

Page 57

ADT7468

Approaches to System Acoustic Enhancement

There are two different approaches to implementing system acoustic enhancement: temperature-centric and fan-centric.

The temperature-centric approach involves smoothing transient temperatures as they are measured by a temperature source (for example, Remote 1 temperature). The temperature values used to calculate the PWM duty cycle values are smoothed, reducing fan speed variation. However, this approach causes an inherent delay in updating fan speed and causes the thermal characteristics of the system to change. It also causes the system fans to stay on longer than necessary, because the fan’s reaction is merely delayed. The user has no control over noise from different fans driven by the same temperature source. Consider, for example, a system in which control of a CPU cooler fan (on PWM1) and a chassis fan (on PWM2) use Remote 1 temperature. Because the Remote 1 temperature is smoothed, both fans are updated at exactly the same rate. If the chassis fan is much louder than the CPU fan, there is no way to improve its acoustics without changing the thermal solution of the CPU cooling fan.

The fan-centric approach to system acoustic enhancement controls the PWM duty cycle, driving the fan at a fixed rate (for example, 6%). Each time the PWM duty cycle is updated, it is incremented by a fixed 6%. As a result, the fan ramps smoothly to its newly calculated speed. If the temperature starts to drop, the PWM duty cycle immediately decreases by 6% at every update. Therefore, the fan ramps smoothly up or down without inherent system delay. Consider, for example, controlling the same CPU cooler fan (on PWM1) and chassis fan (on PWM2) using Remote 1 temperature. The T

MIN

and T

settings have

RANGE

already been defined in automatic fan speed control mode, that is, thermal characterization of the control loop has been optimized. Now the chassis fan is noisier than the CPU cooling fan. Using the fan-centric approach, PWM2 can be placed into acoustic enhancement mode independently of PWM1. The acoustics of the chassis fan can, therefore, be adjusted without affecting the acoustic behavior of the CPU cooling fan, even though both fans are controlled by Remote 1 temperature. The fan-centric approach is how acoustic enhancement works on the ADT7468.

Enabling Acoustic Enhancement for Each PWM Output

Enhance Acoustics Register 1 (Reg. 0x62)

<3> = 1,

enables acoustic enhancement on PWM1 output.

Enhance Acoustics Register 2 (Reg. 0x63)

<7> = 1,

enables acoustic enhancement on PWM2 output.

<3> = 1, enables acoustic enhancement on PWM3 output.

Effect of Ramp Rate on Enhanced Acoustics Mode

The PWM signal driving the fan has a period, T, given by the PWM drive frequency, f, b ecause T = 1/f. For a given PWM

period, T, the PWM period is subdivided into 255 equal time slots. One time slot corresponds to the smallest possible increment in the PWM duty cycle. A PWM signal of 33% duty cycle is, therefore, high for 1/3 × 255 time slots and low for 2/3 × 255 time slots. Therefore, a 33% PWM duty cycle corresponds to a signal that is high for 85 time slots and low for 170 time slots.

PWM_OUT

33% DUTY

CYCLE

Figure 78. 33% PWM Duty Cycle Represented in Time Slots

TIME SLOTS

PWM OUTPUT (ONE PERIOD)

= 255 TIME SLOTS

170

TIME SLOTS

The ramp rates in the enhanced acoustics mode are selectable from the values 1, 2, 3, 5, 8, 12, 24, and 48. The ramp rates are discrete time slots. For example, if the ramp rate is 8, then eight time slots are added to the PWM high duty cycle each time the PWM duty cycle needs to be increased. If the PWM duty cycle value needs to be decreased, it is decreased by eight time slots. Figure 79 shows how the enhanced acoustics mode algorithm operates.

READ

TEMPERATURE

CALCULATE

NEW PWM

DUTY CYCLE

IS NEW PWM

VALUE >

VALUE?

YES

INCREMENT

PWM VALUE

BY RAMP RATE

Figure 79. Enhanced Acoustics Algorithm

BY RAMP RATE

DECREMENT

PWM VALUE

04499-0-085

The enhanced acoustics mode algorithm calculates a new PWM duty cycle based on the temperature measured. If the new PWM duty cycle value is greater than the previous PWM value, then the previous PWM duty cycle value is incremented by either 1, 2, 3, 5, 8, 12, 24, or 48 time slots, depending on the settings of the enhance acoustics registers. If the new PWM duty cycle value is less than the previous PWM value, then the previous PWM duty cycle is decremented by 1, 2, 3, 5, 8, 12, 24, or 48 time slots. Each time the PWM duty cycle is incremented or decremented, its value is stored as the previous PWM duty cycle for the next comparison.

A ramp rate of 1 corresponds to one time slot, which is 1/255 of the PWM period. In enhanced acoustics mode, incrementing or decrementing by 1 changes the PWM output by 1/255 × 100%.

04499-0-084

Rev. 0 | Page 57 of 80

Page 58

ADT7468

STEP 12: RAMP RATE FOR ACOUSTIC ENHANCEMENT

The optimal ramp rate for acoustic enhancement can be found through system characterization after the thermal optimization has been finished. The effect of each ramp rate should be logged, if possible, to determine the best setting for a given solution.

Enhanced Acoustics Register 1 (Reg. 0x62)

<2:0> ACOU,

000 = 1 time slot = 35 s

001 = 2 time slots = 17.6 s

010 = 3 time slots = 11.8 s

011 = 5 time slots = 7 s

100 = 8 time slots = 4.4 s

101 = 12 time slots =3 s

110 = 24 time slots = 1.6 s

111 = 48 time slots = 0.8 s

Enhance Acoustics Register 2 (Reg. 0x63)

<2:0> ACOU3,

000 = 1 time slot = 35 s

001 = 2 time slots = 17.6 s

010 = 3 time slots = 11.8 s

011 = 5 time slots = 7 s

100 = 8 time slots = 4.4 s

101 = 12 time slots = 3 s

110 = 24 time slots = 1.6 s

111 = 48 time slots = 0.8 s

<6:4> ACOU2, selects the ramp rate for PWM2.

000 = 1 time slot = 35 s

001 = 2 time slots = 17.6 s

010 = 3 time slots = 11.8 s

011 = 5 time slots = 7 s

100 = 8 time slots = 4.4 s

101 = 12 time slots = 3 s

110 = 24 time slots = 1.6 s

111 = 48 time slots = 0.8 s

Another way to view the ramp rates is to measure the time it takes for the PWM output to ramp up from 0% to 100% duty cycle for an instantaneous change in temperature. This can be tested by putting the ADT7468 into manual mode and changing the PWM output from 0% to 100% PWM duty cycle. The PWM output takes 35 s to reach 100%, when a ramp rate of 1 time slot is selected.

Figure 80 shows remote temperature plotted against PWM duty cycle for enhanced acoustics mode. The ramp rate is set to 48, which corresponds to the fastest ramp rate. Assume that a new

selects the ramp rate for PWM1.

selects the ramp rate for PWM3.

temperature reading is available every 115 ms. With these settings, it takes approximately 0.76 s to go from 33% duty cycle to 100% duty cycle (full speed). Even though the temperature increases very rapidly, the fan ramps up to full speed gradually.

140

(°C)

120

100

TEMP

PWM CYCLE (%)

0 0.76

TIME (s)

Figure 80. Enhanced Acoustics Mode with Ramp Rate = 48

120

100

04499-0-086

Figure 81 shows how changing the ramp rate from 48 to 8 affects the control loop. The overall response of the fan is slower. Because the ramp rate is reduced, it takes longer for the fan to achieve full running speed. In this case, it takes approximately 4.4 s for the fan to reach full speed.

120

(°C)

100

TEMP

PWM DUTY CYCLE (%)

TIME (s)

Figure 81. Enhanced Acoustics Mode with Ramp Rate = 8

140

120

100

4.4

04499-0-087

Figure 82 shows the PWM output response for a ramp rate of 2. In this instance, the fan took about 17.6 s to reach full running speed.

140

(°C)

TEMP

120

100

PWM DUTY CYCLE (%)

TIME (s)

17.6

Figure 82. Enhanced Acoustics Mode with Ramp Rate = 2

120

100

04499-0-088

Rev. 0 | Page 58 of 80

Page 59

ADT7468

908

Figure 83 shows how the control loop reacts to temperature with the slowest ramp rate. The ramp rate is set to 1, while all other control parameters remain the same. With the slowest ramp rate selected, it takes 35 s for the fan to reach full speed.

120

100

(°C)

TEMP

PWM DUTY CYCLE (%)

TIME (s)

Figure 83. Enhanced Acoustics Mode with Ramp Rate = 1

140

120

100

04499-0-089

As Figure 80 to Figure 83 show, the rate at which the fan reacts to temperature change is dependent on the ramp rate selected in the enhanced acoustics registers. The higher the ramp rate, the faster the fan reaches the newly calculated fan speed.

Figure 84 shows the behavior of the PWM output as temperature varies. As the temperature increases, the fan speed ramps up. Small drops in temperature do not affect the ramp-up function, because the newly calculated fan speed is still higher than the previous PWM value. Enhanced acoustics mode allows the PWM output to be made less sensitive to temperature variations. This is dependent on the ramp rate selected and programmed into the enhanced acoustics registers.

PWM DUTY CYCLE (%)

(°C)

TEMP

04499-0-090

Figure 84. How Fan Reacts to Temperature Variation

in Enhanced Acoustics Mode

Slower Ramp Rates

The ADT7468 can be programmed for much longer ramp times by slowing the ramp rates. Each ramp rate can be slowed by a factor of 4.

PWM1 Configuration Register (Reg. 0x5C)

<3> SLOW,

1 slows the ramp rate for PWM1 by 4.

PWM2 Configuration Register (Reg. 0x5D)

<3> SLOW,

1 slows the ramp rate for PWM2 by 4.

PWM3 Configuration Register (Reg. 0x5E)

<3> SLOW,

1 slows the ramp rate for PWM3 by 4.

The following sections list the ramp-up times when the SLOW bit is set for each PWM output.

Enhanced Acoustics Register 1 (Reg. 0x62)

<2:0> ACOU,

selects the ramp rate for PWM1.

000 = 140 s

001 = 70.4 s

010 = 47.2 s

011 = 28 s

100 = 17.6 s

101 = 12 s

110 = 6.4 s

111 = 3.2 s

Enhance Acoustics Register 2 (Reg. 0x63)

<2:0> ACOU3,

selects the ramp rate for PWM3.

000 = 140 s

001 = 70.4 s

010 = 47.2 s

011 = 28 s

100 = 17.6 s

101 = 12 s

110 = 6.4 s

111 = 3.2 s

<6:4> ACOU2, selects the ramp rate for PWM2.

000 = 140 s

001 = 70.4 s

010 = 47.2 s

011 = 28 s

100 = 17.6 s

101 = 12 s

110 = 6.4 s

111 = 3.2 s

Rev. 0 | Page 59 of 80

Page 60

ADT7468

REGISTER TABLES

Table 16. ADT7468 Registers

Address R/W Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable?

0x20 R 2.5 V measurement 9 8 7 6 5 4 3 2 0x00 0x21 R V 0x22 R VCC measurement 9 8 7 6 5 4 3 2 0x00 0x23 R 5 V measurement 9 8 7 6 5 4 3 2 0x00 0x24 R 12 V measurement 9 8 7 6 5 4 3 2 0x00 0x25 R

0x26 R Local Temperature 9 8 7 6 5 4 3 2 0x01 0x27 R

0x28 R TACH1 Low Byte 7 6 5 4 3 2 1 0 0x00 0x29 R TACH1 High Byte 15 14 13 12 11 10 9 8 0x00 0x2A R TACH2 Low Byte 7 6 5 4 3 2 1 0 0x00 0x2B R TACH2 High Byte 15 14 13 12 11 10 9 8 0x00 0x2C R TACH3 Low Byte 7 6 5 4 3 2 1 0 0x00 0x2D R TACH3 High Byte 15 14 13 12 11 10 9 8 0x00 0x2E R TACH4 Low Byte 7 6 5 4 3 2 1 0 0x00 0x2F R TACH4 High Byte 15 14 13 12 11 10 9 8 0x00 0x30 R/W

0x31 R/W

0x32 R/W

0x33 R/W

0x34 R/W

0x35 R/W

0x36 R/W

0x37 R/W

0x38 R/W

0x39 R/W

0x3A R/W

0x3D R Device ID Register 7 6 5 4 3 2 1 0 0x68 0x3E R

0x3F R Revision Number VER VER VER VER STP STP STP STP 0x70 0x40 R/W Configuration 1

0x41 R Interrupt Status 1 OOL R2T LT R1T

0x42 R Interrupt Status 2

0x43 R/W VID Config VIDSEL THLD VID 5 VID 4 VID 3 VID 2 VID 1 VID 0 0x00 0x44 R/W 2.5 V Low Limit 7 6 5 4 3 2 1 0 0x00 0x45 R/W 2.5 V High Limit 7 6 5 4 3 2 1 0 0xFF 0x46 R/W V 0x47 R/W V 0x48 R/W VCC Low Limit 7 6 5 4 3 2 1 0 0x00 0x49 R/W VCC High Limit 7 6 5 4 3 2 1 0 0xFF 0x4A R/W 5 V Low Limit 7 6 5 4 3 2 1 0 0x00

measurement 9 8 7 6 5 4 3 2 0x00

CCP

Remote 1

9 8 7 6 5 4 3 2 0x01

Temperature

Remote 2

9 8 7 6 5 4 3 2 0x01

Temperature

PWM1 Current Duty

7 6 5 4 3 2 1 0 0x00

Cycle PWM2 Current Duty

7 6 5 4 3 2 1 0 0x00

Cycle PWM3 Current Duty

7 6 5 4 3 2 1 0 0x00

Cycle Remote 1

7 6 5 4 3 2 1 0 0xA4 Yes

Operating Point Local Temp

7 6 5 4 3 2 1 0 0xA4 Yes

Operating Point Remote 2

7 6 5 4 3 2 1 0 0xA4 Yes

Operating Point Dynamic T

Control Reg. 1 Dynamic T

Control Reg. 2

MIN

Max PWM 1 Duty

R2T LT R1T PHTR2 PHTL PHTR1 V

CYR2 CYR2 CYL CYL CYL CYR1 CYR1 CYR1 0x00 Yes

7 6 5 4 3 2 1 0 0xFF Yes

LO CYR2 0x00 Yes

CCP

Cycle Max PWM 2 Duty

7 6 5 4 3 2 1 0 0xFF Yes

Cycle Max PWM 3 Duty

7 6 5 4 3 2 1 0 0xFF Yes

Cycle

Company ID

7 6 5 4 3 2 1 0 0x41

Number

TODIS FSPDIS VxI FSPD RDY LOCK STRT 0x01 Yes

5 V

5 V/

THERM

2.5 V 0x00

CCP

Timer Limit

D2 FAU LT

D1 FAU LT

FAN 4 / THERM

FAN 3 FA N 2 FAN1

THERM Tem p

12 V/VC 0x00

Limit

Low Limit 7 6 5 4 3 2 1 0 0x00

CCP

High Limit 7 6 5 4 3 2 1 0 0xFF

CCP

Rev. 0 | Page 60 of 80

Page 61

ADT7468

Address R/W Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable?

0x4B R/W 5 V High Limit 7 6 5 4 3 2 1 0 0xFF 0x4C R/W 12 V Low Limit 7 6 5 4 3 2 1 0 0x00 0x4D R/W 12 V High Limit 7 6 5 4 3 2 1 0 0xFF 0x4E R/W

Remote 1 Temp Low Limit

0x4F R/W

Remote 1 Temp High Limit

0x50 R/W

Local Temp Low Limit

0x51 R/W

Local Temp High Limit

0x52 R/W

Remote 2 Temp Low Limit

0x53 R/W

Remote 2 Temp High Limit

0x54 R/W

TACH1 Minimum Low Byte

0x55 R/W

TACH1 Minimum High Byte

0x56 R/W

TACH2 Minimum Low Byte

0x57 R/W

TACH2 Minimum High Byte

0x58 R/W

TACH3 Minimum Low Byte

0x59 R/W

TACH3 Minimum High Byte

0x5A R/W

TACH4 Minimum Low Byte

0x5B R/W

TACH4 Minimum High Byte

0x5C R/W

PWM1 Configuration Register

0x5D R/W

PWM2 Configuration Register

0x5E R/W

PWM3 Configuration Register

0x5F R/W

Remote 1

/PWM 1

RANGE

Frequency

0x60 R/W

0x61 R/W

Local T

RANGE

Frequency Remote 2

/PWM3

RANGE

/PWM 2

Frequency

0x62 R/W

Enhance Acoustics Reg. 1

0x63 R/W

Enhance Acoustics Reg. 2

0x64 R/W

PWM1 Min Duty Cycle

0x65 R/W

PWM2 Min Duty Cycle

0x66 R/W

PWM3 Min Duty

Cycle 0x67 R/W Remote 1 Temp T 0x68 R/W Local Temp T

MIN

0x69 R/W Remote 2 Temp T 0x6A R/W

Remote 1

THERM

Temp Limit 0x6B R/W

Local

THERM

Tem p

Limit

7 6 5 4 3 2 1 0 0x01

7 6 5 4 3 2 1 0 0x7F

7 6 5 4 3 2 1 0 0x01

7 6 5 4 3 2 1 0 0x7F

7 6 5 4 3 2 1 0 0x01

7 6 5 4 3 2 1 0 0x7F

7 6 5 4 3 2 1 0 0xFF

15 14 13 12 11 10 9 8 0xFF

7 6 5 4 3 2 1 0 0xFF

15 14 13 12 11 10 9 8 0xFF

7 6 5 4 3 2 1 0 0xFF

15 14 13 12 11 10 9 8 0xFF

7 6 5 4 3 2 1 0 0xFF

15 14 13 12 11 10 9 8 0xFF

BHVR BHVR BHVR INV SLOW SPIN SPIN SPIN 0x82 Yes

RANGE RANGE RANGE RANGE THRM FREQ FREQ FREQ 0XC4 Yes

MIN3 MIN2 MIN1 SYNC EN1 ACOU ACOU ACOU 0X00 Yes

EN2 ACOU2 ACOU2 ACOU2 EN3 ACOU3 ACOU3 ACOU3 0X00 Yes

7 6 5 4 3 2 1 0 0X80 Yes

7 6 5 4 3 2 1 0 0X9A Yes

MIN

7 6 5 4 3 2 1 0 0X9A Yes

MIN

7 6 5 4 3 2 1 0 0XA4 Yes

Rev. 0 | Page 61 of 80

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ADT7468

Address R/W Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable?

0x6C R/W

Remote 2

THERM

Temp Limit

0x6D R/W

0x6E R/W

0x6F R/W

Remote 1 and Local Tem p/ T Hysteresis

MIN

Remote 2 Tem p/ T Hysteresis

MIN

XNOR Tree Test Enable

0x70 R/W

Remote 1 Temperature Offset

0x71 R/W

Local Temperature Offset

0x72 R/W

Remote 2 Temperature Offset

0x73 R/W

Configuration Register 2

0x74 R/W

Interrupt Mask 1 Register

0x75 R/W

Interrupt Mask 2 Register

0x76 R/W

Extended Resolution 1

0x77 R/W

Extended Resolution 2

0x78 R/W

Configuration Register 3

0x79 R

THERM

Timer Status

0x7A R/W

THERM

Timer Limit

0x7B R/W

TACH Pulses per Revolution

0x7C R/W

Configuration Register 5

0x7D R/W

Configuration

Register 4 0x7E R Test Register 1 DO NOT WRITE TO THESE REGISTERS 0X00 Yes 0x7F R Test Register 2 DO NOT WRITE TO THESE REGISTERS 0X00 Yes

Table 17. Voltage Reading Registers (Power-On Default = 0x00)1

0x20 Read-only Reflects the voltage measurement at the 2.5 V input on Pin 22 (8 MSBs of reading). 0x21 Read-only Reflects the voltage measurement2 at the V 0x22 Read-only Reflects the voltage measurement3 at the VCC input on Pin 4 (8 MSBs of reading). 0x23 Read-only Reflects the voltage measurement at the 5 V input on Pin 20 (8 MSBs of reading. 0x24 Read-only Reflects the voltage measurement at the 12 V input on Pin 21 (8 MSBs of reading).

If the extended resolution bits of these readings are also being read, the extended resolution registers (Reg. 0x76, 0x77) must be read first. Once the extended

resolution registers have been read, the associated MSB reading registers are frozen until read. Both the extended resolution registers and the MSB registers are frozen.

If V

Low (Bit 1 of the Dynamic T

CCP

VCC (Pin 4) is the supply voltage for the ADT7468.

MIN

7 6 5 4 3 2 1 0 0XA4 Yes

HYSR1 HYSR1 HYSR1 HYSR1 HYSL HYSL HYSL HYSL 0X44 Yes

HYSR2 HYSR2 HYSR2 HYRS RES RES RES RES 0X40 Yes

RES RES RES RES RES RES RES XEN 0X00 Yes

7 6 5 4 3 2 1 0 0X00 Yes

SHDN CONV ATTN AVG AIN4 AIN3 AIN2 AIN1 0X00 Yes

OOL R2T LT RIT 5 V V

2.5 V 0X00

CCP

D2 D1 F4P FAN3 FAN2 FAN1 OV T 12 V / VC 0X00

5 V 5 V V

CCP

2.5 V 2.5 V 0X00

CCP

TDM2 TDM2 LTMP LTMP TDM1 TDM1 12 V 12 V 0X00

DC4 DC3 DC2 DC1 FAST BOOST

THERM

ALERT Enable

0X00 Yes

TMR TMR TMR TMR TMR TMR TMR ASRT/TMRO 0X00

LIMT LIMT LIMT LIMT LIMT LIMT LIMT LIMT 0X00

FAN 4 FA N 4 FAN3 FAN3 FA N 2 FAN2 FAN1 FA N 1 0X55

RES RES RES RES GPIOP GPIOD LF/HF

TWOS

0X00 Yes

COMPL

BpAtt 12 V

BpAtt 5 V

Control Register 1, 0x36) is set, V

BpAtt V

CCP

BpAtt

2.5 V

can control the sleep state of the ADT7468.

CCP

AINL AINL

Pin 14 Func

input on Pin 23 (8 MSBs of reading).

CCP

Pin 14 Func 0X00 Yes

Rev. 0 | Page 62 of 80

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ADT7468

Table 18. Temperature Reading Registers (Power-On Default = 0x01)

1, 2, 3

0x25

Read-only

Remote 1 temperature reading

3, 4

(8 MSB of reading). 0x26 Read-only Local temperature reading (8 MSB of reading). 0x27 Read-only Remote 2 temperature reading

If the extended resolution bits of these readings are also being read, the extended resolution registers (Reg. 0x76, 0x77) must be read first. Once the extended

resolution registers have been read, all associated MSB reading registers are frozen until read. Both the extended resolution registers and the MSB registers are frozen.

These temperature readings can be in twos complement or Offset 64 format; this interpretation is determined by Bit 0 of Configuration Register 5 (0x7C).

In twos complement mode, a temperature reading of −128°C (0x80) indicates a diode fault (open or short) on that channel.

In Offset 64 mode, a temperature reading of −64°C (0x00) indicates a diode fault (open or short) on that channel.

3, 4

(8 MSB of reading).

Table 19. Fan Tachometer Reading Registers (Power-On Default = 0x00)1

0x28 Read-only TACH1 low byte. 0x29 Read-only TACH1 high byte. 0x2A Read-only TACH2 low byte. 0x2B Read-only TACH2 high byte. 0x2C Read-only TACH3 low byte. 0x2D Read-only TACH3 high byte. 0x2E Read-only TACH4 low byte. 0x2F Read-only TACH4 high byte.

These registers count the number of 11.11 µs periods (based on an internal 90 kHz clock) that occur between a number of consecutive fan TACH pulses (default = 2). The number of TACH pulses used to count can be changed using the fan pulses per revolution register (Reg. 0x7B). This allows the fan speed to be accurately measured. Because a valid fan tachometer reading requires that two bytes are read, the low byte must be read first. Both the low and high bytes are then frozen until read. At power-on, these registers contain 0x0000 until such time as the first valid fan TACH measurement is read into these registers. This prevents false interrupts from occurring while the fans are spinning up. A count of 0xFFFF indicates that a fan is one of the following:

• Stalled or blocked (object jamming the fan).

• Failed (internal circuitry destroyed).

• Not populated. (The ADT7468 expects to see a fan connected to each TACH. If a fan is not connected to that TACH, its TACH minimum high and low bytes should

be set to 0xFFFF.)

• Alternate function, for example, TACH4 reconfigured as

• 2-wire instead of 3-wire fan.

THERM

pin.

Table 20. Current PWM Duty Cycle Registers (Power-On Default = 0x00)

0x30 Read/write PWM1 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF). 0x31 Read/write PWM2 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF). 0x32 Read/write PWM3 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF).

These registers reflect the PWM duty cycle driving each fan at any given time. When in automatic fan speed control mode, the ADT7468 reports the PWM duty cycles back through these registers. The PWM duty cycle values vary according to temperature in automatic fan speed control mode. During fan startup, these registers report back 0x00. In software mode, the PWM duty cycle outputs can be set to any duty cycle value by writing to these registers.

Table 21. Operating Point Registers (Power-On Default = 0x64)

1, 2, 3

0x33 Read/write Remote 1 operating point register (default = 100°C). 0x34 Read/write Local temperature operating point register (default = 100°C). 0x35 Read/write Remote 2 operating point register (default = 100°C).

These registers set the target operating point for each temperature channel when the dynamic T

The fans being controlled are adjusted to maintain temperature about an operating point.

These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to these registers fail.

control feature is enabled.

MIN

Rev. 0 | Page 63 of 80

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ADT7468

Table 22. Register 0x36—Dynamic T

Bit Name R/W Description

<0> CYR2 Read/write

MSB of 3-bit remote 2 cycle value. The other two bits of the code reside in Dynamic T (Reg. 0x37). These three bits define the delay time between making subsequent T control loop, in terms of the number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop.

<1> V

LO Read/write

CCP

low limit value (Reg. 0x46), the following occurs:

• Status Bit 1 in Status Register 1 is set.

• SMBALERT

• PROCHOT

• Dynamic T

• The device is prevented from entering shutdown.

• Everything is re-enabled once V

<2> PHTR1 Read/write

PHTR1 = 1 copies the Remote 1 current temperature to the Remote 1 operating point register, if THERM asserted. The operating point contains the temperature at which THERM to run as quietly as possible without affecting system performance. PHTR1 = 0 ignores any THERM its programmed value.

<3> PHTL Read/write

PHTL = 1 copies the local channel’s current temperature to the local operating point register, if THERM asserted. The operating point contains the temperature at which THERM to run as quietly as possible without affecting system performance. PHTL = 0 ignores any THERM reflects its programmed value.

<4> PHTR2 Read/write

PHTR2 = 1 copies the Remote 2 current temperature to the Remote 2 operating point register, if THERM asserted. The operating point contains the temperature at which THERM run as quietly as possible without affecting system performance. PHTR2 = 0 ignores any THERM its programmed value.

<5> R1T Read/write

R1T = 1 enables dynamic T dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone.

R1T = 0 disables dynamic T described in the Fan Speed Control section.

<6> LT Read/write

LT=1 enables dynamic T adjusted based on the current temperature, operating point, and high and low limits for this zone.

LT = 0 disables dynamic T described in the Fan Speed Control section.

<7> R2T Read/write

R2T = 1 enables dynamic T dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone.

R2T = 0 disables dynamic T

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to this register fail.

described in the Fan Speed Control section.

Control Register 1 (Power-On Default = 0x00)1

MIN

LO = 1. When the power is supplied from 3.3 V STANDBY and the core voltage (V

is generated, if enabled.

monitoring is disabled.

control is disabled.

MIN

increases above the V

CCP

low limit.

CCP

is asserted, which allows the system

assertions on the THERM pin. The Remote 1 operating point register reflects

is asserted, which allows the system

assertions on the THERM pin. The local operating temperature point register

is asserted. This allows the system to

assertions on the THERM pin. The Remote 2 operating point register reflects

control on the Remote 1 temperature channel. The chosen T

MIN

control. The T

MIN

control on the local temperature channel. The chosen T

MIN

control. The T

MIN

control on the Remote 2 temperature channel. The chosen T

MIN

control. The T

MIN

value chosen is not adjusted, and the channel behaves as

MIN

value chosen is not adjusted, and the channel behaves as

MIN

value chosen is not adjusted, and the channel behaves as

MIN

Control Register 2

MIN

adjustments in the

) drops below its V

CCP

value is

MIN

value is dynamically

value is

MIN

CCP

Rev. 0 | Page 64 of 80

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ADT7468

Table 23. Register 0x37—Dynamic T

Bit Name R/W Description

<2:0> CYR1 Read/write

3-Bit Remote 1 Cycle Value. These three bits define the delay time between making subsequent T adjustments in the control loop for the Remote 1 channel, in terms of number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop.

Bits Decrease Cycle Increase Cycle

<5:3> CYL Read/write

3-bit local temperature cycle value. These three bits define the delay time between making subsequent T adjustments in the control loop for the local temperature channel, in terms of number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop.

Bits Decrease Cycle Increase Cycle

<7:6> CYR2 Read/write

2 LSBs of 3-bit Remote 2 cycle value. The MSB of the 3-bit code resides in Dynamic T (Reg. 0x36). These three bits define the delay time between making subsequent T control loop for the Remote 2 channel, in terms of number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop.

Control Register 2 (Power-On Default = 0x00)1

MIN

Control Register 1

MIN

adjustments in the

MIN

Bits Decrease Cycle Increase Cycle

000 8 cycles (1 s) 16 cycles (2 s) 001 16 cycles (2 s) 32 cycles (4 s) 010 32 cycles (4 s) 64 cycles (8 s) 011 64 cycles (8 s) 128 cycles (16 s) 100 128 cycles (16 s) 256 cycles (32 s) 101 256 cycles (32 s s) 512 cycles (64 s) 110 512 cycles (64 s) 1024 cycles (128 s)

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to this register fail.

111 1024 cycles (128 s) 2048 cycles (256 s)

1, 2

Table 24. Maximim PWM Duty Cycle (Power-On Default = 0xFF)

0x38 Read/write Maximum duty cycle for PWM1 output, default = 100% (0xFF.) 0x39 Read/write Maximum duty cycle for PWM2 output, default = 100% (0xFF). 0x3A Read/write Maximum duty cycle for PWM3 output, default = 100% (0xFF).

These registers set the maximum PWM duty cycle of the PWM output .

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to this register fail.

Rev. 0 | Page 65 of 80

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ADT7468

Table 25. Register 0x40—Configuration Register 1 (Power-On Default = 0x01)

Bit Name R/W Description

<0> STRT Read/write Logic 1 enables monitoring and PWM control outputs based on the limit settings programmed.

Logic 0 disables monitoring and PWM control based on the default power-up limit settings. Note that the limit values programmed are preserved even if a Logic 0 is written to this bit and the

default settings are enabled. This bit becomes read-only and cannot be changed once Bit 1 (LOCK bit) has been written. All limit registers should be programmed by BIOS before setting this bit to 1. (Lockable.)

<1> LOCK Write once

<2> RDY Read-only

<3> FSPD Read/write When set to 1, this bit runs all fans at full speed. Power-on default = 0. This bit never gets locked.

<4> VxI Read/write

<5> FSPDIS Read/write

<6> TODIS Read/write

<7> VCC Read/write

Table 26. Register 0x41—Interrupt Status Register 1 (Power-On Default = 0x00)

Bit Name R/W Description

<0> 2.5 V Read-only

<1> V

Read-only

CCP

<2> VCC Read-only

<3>

5 V/ THERM

Read-only

timer

<4> R1T Read-only

<5> LT Read-only

<6> R2T Read-only

<7> OOL Read-only

Logic 1 locks all limit values to their current settings. Once this bit is set, all lockable registers become read-only and cannot be modified until the ADT7468 is powered down and powered up again. This prevents rogue programs such as viruses from modifying critical system limit settings. (Lockable.)

This bit is set to 1 by the ADT7468 to indicate only that the device is fully powered-up and ready to begin system monitoring.

BIOS should set this bit to a 1 when the ADT7468 is configured to measure current from an ADI ADOPT™ VRM controller and to measure the CPU’s core voltage. This bit allows monitoring software to display CPU watts usage. (Lockable.)

Logic 1 disables fan spin-up for two TACH pulses. Instead, the PWM outputs go high for the entire fan spin-up timeout selected.

When this bit is set to 1, the SMBus timeout feature is enabled. This allows the ADT7468 to be used with SMBus controllers that cannot handle SMBus timeouts. (Lockable.)

When this bit is set to 1, the ADT7468 rescales its V ADT7468 measures V

as a 3.3 V supply. (Lockable.)

pin to measure 5 V supply. If this bit is 0, the

2.5 V = 1 indicates that the 2.5 V high or low limit has been exceeded. This bit is cleared on a read of the status register only if the error condition has subsided.

= 1 indicates that the V

CCP

high or low limit has been exceeded. This bit is cleared on a read of the

CCP

status register only if the error condition has subsided.

= 1 indicates that the VCC high or low limit has been exceeded. This bit is cleared on a read of the

status register only if the error condition has subsided. A one indicates the 5 V high or low limit has been exceeded. This bit is cleared on a read of the status

, this bit is asserted when

the Timer Limit has been exceeded. R1T = 1 indicates that the Remote 1 low or high temperature has been exceeded. This bit is cleared on a

read of the status register only if the error condition has subsided. LT =1 indicates that the local low or high temperature has been exceeded. This bit is cleared on a read of

the status register only if the error condition has subsided. R2T = 1 indicates that the Remote 2 low or high temperature has been exceeded. This bit is cleared on a

read of the status register only if the error condition has subsided. OOL = 1 indicates that an out-of-limit event has been latched in Status Register 2. This bit is a logical OR

of all status bits in Status Register 2. Software can test this bit in isolation to determine whether any of the voltage, temperature, or fan speed readings represented by Status Register 2 are out-of-limit, which saves the need to read Status Register 2 during every interrupt or polling cycle.

Rev. 0 | Page 66 of 80

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ADT7468

Table 27. Register 0x42—Interrupt Status Register 2 (Power-On Default = 0x00)

Bit Name R/W Description

<0> 12V/VC Read-only

<1> OVT Read-only

<2> FAN1 Read-only

<3> FAN2 Read-only

<4> FAN3 Read-only

<5> F4P Read-only

Read/write When Pin 14 is programmed as a GPIO output, writing to this bit determines the logic output of the GPIO. Read-only

<6> D1 Read-only D1 = 1 indicates either an open or short circuit on the Thermal Diode 1 inputs. <7> D2 Read-only D2 = 1 indicates either an open or short circuit on the Thermal Diode 2 inputs.

Table 28. Register 43H—VID Register (Power-On Default = 0x00 )

Bit Name R/W Description

<4:0> VID[4:0] Read-only

<5> VID5 Read-only

<6> THLD Read/write Selects the input switching threshold for the VID inputs.

<7> VIDSEL Read/write VIDSEL = 0 configures Pin 21 as the 12 V measurement input (default).

Table 29. Voltage Limit Registers

0x44 Read/write 2.5 V. 0x00 0x45 Read/write 2.5 V. 0xFF 0x46 Read/write V 0x47 Read/write V 0x48 Read/write VCC low limit. 0x00 0x49 Read/write VCC high limit. 0xFF 0x4A Read/write 5 V low limit. 0x00 0x4B Read/write 5 V high limit. 0xFF 0x4C Read/write 12 V low limit. 0x00 0x4D Read/write 12 V high limit. 0xFF

Setting the Configuration Register 1 lock bit has no effect on these registers.

High Limits: An interrupt is generated when a value exceeds its high limit (> comparison). Low Limits: An interrupt is generated when a value is equal to or below its

low limit (≤ comparison).

A one indicates that the 12 V high or low limit has been exceeded. This bit is cleared on a read of the status register only if the error condition has subsided. If Pin 21 is configured as VID5, this bit is the VID change bit. This bit is set when the levels on VID0 to VID5 are different than they were 11 µs previously. This pin can be used to generate an SMBALERT

OVT = 1 indicates that one of the THERM read of the status register when the temperature drops below THERM − T

whenever the VID code changes.

overtemperature limits has been exceeded. This bit is cleared on a

HYST

FAN1 = 1 indicates that Fan 1 has dropped below minimum speed or has stalled. This bit is not set when the PWM 1 output is off.

FAN2 = 1 indicates that Fan 2 has dropped below minimum speed or has stalled. This bit is not set when the PWM 2 output is off.

FAN3 = 1 indicates that Fan 3 has dropped below minimum speed or has stalled. This bit is not set when the PWM 3 output is off.

When Pin 14 is programmed as a TACH4 input, F4P = 1 indicates that Fan 4 has dropped below minimum speed or has stalled. This bit is not set when the PWM3 output is off.

If Pin 14 is configured as the

THERM

timer input for

assertion time exceeds the limit programmed in the

THERM

monitoring, then this bit is set when the

THERM

limit register (Reg. 0x7A).

THERM

The VID[4:0] inputs from the CPU indicate the expected processor core voltage. On power-up, these bits reflect the state of the VID pins, even if monitoring is not enabled.

Reads VID5 from the CPU when Bit 7 = 1. If Bit 7 = 0, then the VID5 bit always reads back 0 (power-on default).

THLD = 0 selects a threshold of 1 V (V THLD = 1 lowers the switching threshold to 0.6 V (V

low limit. 0x00

CCP

high limit. 0xFF

CCP

< 0.8 V, VIH > 1.7 V).

< 0.4 V, VIH > 0.8 V).

Rev. 0 | Page 67 of 80

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ADT7468

Table 30. Temperature Limit Registers1

0x4E Read/write Remote 1 temperature low limit. 0x81 0x4F Read/write Remote 1 temperature high limit. 0x7F 0x50 Read/write Local temperature low limit. 0x81 0x51 Read/write Local temperature high limit. 0x7F 0x52 Read/write Remote 2 temperature low limit. 0x81 0x53 Read/write Remote 2 temperature high limit. 0x7F

Exceeding any of these temperature limits by 1°C causes the appropriate status bit to be set in the interrupt status register. Setting the Configuration Register 1 lock bit

has no effect on these registers.

High Limits: An interrupt is generated when a value exceeds its high limit (> comparison). Low Limits: An interrupt is generated when a value is equal to or below its

low limit (≤ comparison).

Table 31. Fan Tachometer Limit Registers

0x54 Read/write TACH1 minimum low byte. 0xFF

0x55 Read/write

0x56 Read/write TACH2 minimum low byte. 0xFF 0x57 Read/write TACH2 minimum high byte. 0xFF 0x58 Read/write TACH3 minimum low byte. 0xFF 0x59 Read/write TACH3 minimum high byte. 0xFF 0x5A Read/write TACH4 minimum low byte. 0xFF 0x5B Read/write TACH4 minimum high byte. 0xFF

Exceeding any of the TACH limit registers by 1 indicates that the fan is running too slowly or has stalled. The appropriate status bit is set in Interrupt Status Register 2 to

indicate the fan failure. Setting the Configuration Register 1 lock bit has no effect on these registers.

Table 32. Register 0x55—TACH 1 Minimum High Byte (Power-On Default = 0xFF)

Bits Name R/W Description

<4:0> Reserved Read-only

These bits are reserved when Bit 6 of Config 2 Register (0x73) is set (single-channel ADC mode). Otherwise, these bits represent Bits <4:0> of the TACH1 minimum high byte.

<7:5> SCADC Read/write

When Bit 6 of Config 2 Register (0x73) is set (single channel ADC mode), these bits are used to select the only channel from which the ADC makes measurements. Otherwise, these bits represent Bits <7:5> of the TACH1 minimum high byte.

TACH1 minimum high byte/Single channel ADC channel select.

0xFF

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ADT7468

Table 33. PWM Configuration Registers

0x5C Read/write PWM1 configuration. 0x82 0x5D Read/write PWM2 configuration. 0x82 0x5E Read/write PWM3 configuration. 0x82

Bit Name R/W Description

<2:0> SPIN Read/write

000 = No startup timeout 001 = 100 ms 010 = 250 ms (default) 011 = 400 ms 100 = 667 ms 101 = 1 s 110 = 2 s 111 = 4 s <3> SLOW Read/write SLOW = 1 makes the ramp rates for acoustic enhancement four times longer. <4> INV Read/write

<7:5> BHVR Read/write These bits assign each fan to a particular temperature sensor for localized cooling. 000 = Remote 1 temperature controls PWMx (automatic fan control mode). 001 = local temperature controls PWMx (automatic fan control mode). 010 = Remote 2 temperature controls PWMx (automatic fan control mode). 011 = PWMx runs full speed. 100 = PWMx disabled (default). 101 = fastest speed calculated by local and Remote 2 temperature controls PWMx. 110 = fastest speed calculated by all three temperature channel controls PWMx.

These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to these registers fail.

These bits control the startup timeout for PWMx. The PWM output stays high until two valid TACH rising edges are seen from the fan. If there is not a valid TACH signal during the fan TACH measurement directly after the fan startup timeout period, then the TACH measurement reads 0xFFFF and Status Register 2 reflects the fan fault. If the TACH minimum high and low bytes contain 0xFFFF or 0x0000, then the Status Register 2 bit is not set, even if the fan has not started.

This bit inverts the PWM output. The default is 0, which corresponds to a logic high output for 100% duty cycle. Setting this bit to 1 inverts the PWM output, so 100% duty cycle corresponds to a logic low output.

111 = manual mode. PWM duty cycle registers (Reg. 0x30 to Reg. 0x32) become writable.

Rev. 0 | Page 69 of 80

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ADT7468

Table 34. TEMP T

0x5F Read/write Remote 1 T 0x60 Read/write Local temperature T 0x61 Read/write Remote 2 T

Bit Name R/W Description

<2:0> FREQ Read/write These bits control the PWMx frequency. 000 = 11.0 Hz 001 = 14.7 Hz 010 = 22.1 Hz 011 = 29.4 Hz 100 = 35.3 Hz (default) 101 = 44.1 Hz 110 = 58.8 Hz 111 = 88.2 Hz <3> THRM Read/write

<7:4> RANGE Read/write

0000 = 2°C 0001 = 2.5°C 0010 = 3.33°C 0011 = 4°C 0100 = 5°C 0101 = 6.67°C 0110 = 8°C 0111 = 10°C 1000 = 13.33°C 1001 = 16°C 1010 = 20°C 1011 = 26.67°C 1100 = 32°C (Default) 1101 = 40°C 1110 = 53.33°C 1111 = 80°C

These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers have no effect.

/PWM Frequency Registers

RANGE

/PWM1 frequency. 0xC4

RANGE

/PWM2 frequency. 0xC4

RANGE

/PWM3 frequency. 0xC4

RANGE

THRM = 1 causes the temperature channel’s remains asserted until the temperature is equal to or below the minimum time that

THERM

pin (Pin 14/20) to assert low as an output when this

THERM

limit has been exceeded by 0.25°C. The

THERM

asserts is one monitoring cycle. This allows clock

THERM

limit. The

modulation of devices that incorporate this feature. THRM = 0 makes the

PROCHOT

monitoring, when Pin 14/20 is configured as

THERM

pin act as an input only, for example, for Pentium 4

THERM

These bits determine the PWM duty cycle vs. the temperature slope for automatic fan control.

Rev. 0 | Page 70 of 80

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ADT7468

Table 35. Register 0x62—Enhanced Acoustics Register 1 (Power-On Default = 0x00)

Bit Name R/W1 Description

<2:0> ACOU Read/write

<3> EN1 Read/write When this bit is 1, acoustic enhancement is enabled on PWM1 output. <4> SYNC Read/write

<5> MIN1 Read/write

<6> MIN2 Read/write

<7> MIN3 Read/write

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.

These bits select the ramp rate applied to the PWM1 output. Instead of PWM1 jumping instantaneously to its newly calculated speed, PWM1 ramps gracefully at the rate determined by these bits. This feature enhances the acoustics of the fan being driven by the PWM1 output.

Time Slot Increase Time for 33% to 100%

000 = 1 35 s 001 = 2 17.6 s 010 = 3 11.8 s 011 = 4 7 s 100 = 8 4.4 s 101 = 12 3 s 110 = 24 1.6 s 111 = 48 0.8 s

SYNC = 1 synchronizes fan speed measurements on TACH2, TACH3, and TACH4 to PWM3. This allows up to three fans to be driven from PWM3 output and their speeds to be measured.

SYNC = 0 synchronizes only TACH3 and TACH4 to PWM3 output. When the ADT7468 is in automatic fan control mode, this bit defines whether PWM1 is off (0% duty cycle) or

at PWM1 minimum duty cycle when the controlling temperature is below its T 0 = 0% duty cycle below T 1 = PWM1 minimum duty cycle below T

– hysteresis.

MIN

– hysteresis.

MIN

– hysteresis value.

MIN

When the ADT7468 is in automatic fan speed control mode, this bit defines whether PWM2 is off (0% duty cycle) or at PWM2 minimum duty cycle when the controlling temperature is below its T

0 = 0% duty cycle below T 1 = PWM 2 minimum duty cycle below T

– hysteresis.

MIN

– hysteresis.

MIN

– hysteresis value.

MIN

When the ADT7468 is in automatic fan speed control mode, this bit defines whether PWM3 is off (0% duty cycle) or at PWM3 minimum duty cycle when the controlling temperature is below its T

0 = 0% duty cycle below T 1 = PWM3 minimum duty cycle below T

– hysteresis.

MIN

– hysteresis.

MIN

– hysteresis value.

MIN

Rev. 0 | Page 71 of 80

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ADT7468

Table 36. Register 0x63 – Enhanced Acoustics Register 2 (Power-On Default = 0x00)

Bit Name R/W1 Description

<2:0> ACOU3 Read/write

< 3 > EN3 Read/write When this bit is 1, acoustic enhancement is enabled on PWM3 output. <6:4> ACOU2 Read/write

<7> EN2 Read/write When this bit is 1, acoustic enhancement is enabled on PWM2 output.

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.

Table 37. PWM Minimum Duty Cycle Registers

0x64 Read/write PWM1 minimum duty cycle. 0x80 (50% duty cycle) 0x65 Read/write PWM2 minimum duty cycle. 0x80 (50% duty cycle) 0x66 Read/write PWM3 minimum duty cycle. 0x80 (50% duty cycle)

Bit Name R/W1 Description

<7:0> PWM duty cycle Read/write These bits define the PWM 0x00 = 0% duty cycle (fan off). 0x40 = 25% duty cycle. 0x80 = 50% duty cycle. 0xFF = 100% duty cycle (fan full speed).

These registers become read-only when the ADT7468 is in automatic fan control mode.

Table 38. T

Registers1

MIN

0x67 Read/write Remote 1 temperature T 0x68 Read/write Local temperatue T 0x69 Read/write Remote 2 temperature T

These are the T

with temperature according to T

These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers have no effect.

registers for each temperature channel. When the temperature measured exceeds T

MIN

These bits select the ramp rate applied to the PWM3 output. Instead of PWM3 jumping instantaneously to its newly calculated speed, PWM3 ramps gracefully at the rate determined by these bits. This effect enhances the acoustics of the fan being driven by the PWM3 output.

Time Slot Increase Time for 33% to 100%

000 = 1 35 s 001 = 2 17.6 s 010 = 3 11.8 s 011 = 5 7 s 100 = 8 4.4 s 101 = 12 3 s 110 = 24 1.6 s 111 = 48 0.8 s

These bits select the ramp rate applied to the PWM2 output. Instead of PWM2 jumping instantaneously to its newly calculated speed, PWM2 ramps gracefully at the rate determined by these bits. This effect enhances the acoustics of the fans being driven by the PWM2 output.

Time Slot Increase Time for 33% to 100%

000 = 1 35 s 001 = 2 17.6 s 010 = 3 11.8 s 011 = 5 7 s 100 = 8 4.4 s 101 = 12 3 s 110 = 24 1.6 s

duty cycle for PWMx.

MIN

. 0x5A (90°C)

MIN

. 0x5A (90°C)

MIN

. 0x5A (90°C)

MIN

, the appropriate fan runs at minimum speed and increases

RANGE

MIN

Rev. 0 | Page 72 of 80

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ADT7468

Table 39.

0x6A Read/write 0x6B Read/write 0x6C Read/write

If any temperature measured exceeds its system in the event of a critical overtemperature. It also ensures some level of cooling in the event that software or hardware locks up. If set to 0x80, this feature is disabled. The PWM output remains at 100% until the temperature drops below these limits by 0.25°C can cause the

These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to these registers have no effect.

Table 40. Temperature/T

0x6D Read/write Remote 1 and local temperature hysteresis. 0x44 <3:0> HYSL

<7:4> HYSR1

0x6E Read/write Remote 2 temperature hysteresis. 0x40 <7:4> HYSR2

Each 4-bit value controls the amount of temperature hysteresis applied to a particular temperature channel. Once the temperature for that channel falls below its T value, the fan remains running at PWM hysteresis value chosen also applies to that temperature channel, if its

exceeded and remains at 100% until the temperature drops below programmed less than 4°C. Setting the hysteresis value lower than 4°C causes the fan to switch on and off regularly when the temperature is close to T

These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to these registers have no effect.

Table 41. XNOR Tree Test Enable

0x6F Read/write XNOR tree test enable register. 0x00 <0> XEN

<7:1> Reserved Unused. Do not write to these bits.

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.

Table 42. Remote 1 Temperature Offset

0x70 Read/write Remote 1 temperature offset. 0x00 <7:0> Read/write

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.

THERM

Limit Registers1

THERM

Hysteresis Registers1

MIN

duty cycle until the temperature = T

MIN

Remote 1 THERM Local THERM Remote 2 THERM

THERM

limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail-safe mechanism incorporated to cool the

THERM

pin to assert low as an output.

Local temperature hyseresis. 0°C to 15°C of

limit.

limit – hysteresis. If the

0x64 (100°C) 0x64 (100°C) 0x64 (100°C)

THERM

pin is programmed as an output, then exceeding

hysteresis can be applied to the local temperature AFC and dynamic T

Remote 1 temperature hyseresis. 0°C to 15°C of

control loops.

MIN

hysteresis can be applied to the Remote 1 temperature AFC and dynamic T

Local temperature hyseresis. 0°C to 15°C of

control loops.

MIN

hysteresis can be applied to the local temperature AFC and dynamic T

– hysteresis. Up to 15°C of hysteresis can be assigned to any temperature channel. The

MIN

THERM

limit is exceeded. The PWM output being controlled goes to 100%, if the

– hysteresis. For acoustic reasons, it is recommended that the hysteresis value not be

If the XEN bit is set to 1, the device enters the XNOR

control loops.

MIN

tree test mode. Clearing the bit removes the device from the XNOR tree test mode.

Allows a twos complement offset value to be automatically added to or subtracted from the Remote 1 temperature reading. This is to compensate for any inherent system offsets such as PCB trace resistance. LSB value = 0.5°C.

THERM

MIN

limit is

MIN

Rev. 0 | Page 73 of 80

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ADT7468

Table 43. Local Temperature Offset

0x71 Read/write Local temperature offset. 0x00 <7:0> Read/write

Allows a twos complement offset value to be automatically added to or subtracted from the local

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.

temperature reading. LSB value = 0.5°C.

Table 44. Remote 2 Temperature Offset

0x72 Read/write Remote 2 temperature offset. 0x00 <7:0> Read/write

Allows a twos complement offset value to be automatically added to or subtracted from the Remote 2 temperature reading. This is to compensate for any inherent system offsets such as

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.

PCB trace resistance. LSB value = 0.5°C.

Table 45. Register 0x73—Configuration Register 2 (Power-On Default = 0x00)

Bit Name R/W1 Description

0 AIN1 Read/write

AIN1 = 0, speed of 3-wire fans measured using the TACH output from the fan. AIN1 = 1, Pin 6 is reconfigured to measure the speed of 2-wire fans using an external sensing resistor and coupling capacitor. AIN voltage threshold is set via Configuration Register 4 (Reg. 0x7D). Only relevant in low frequency mode.

1 AIN2 Read/write

AIN2 = 0, speed of 3-wire fans measured using the TACH output from the fan. AIN2 = 1, Pin 7 is reconfigured to measure the speed of 2-wire fans using an external sensing resistor and coupling capacitor. AIN voltage threshold is set via Configuration Register 4 (Reg. 0x7D). Only relevant in low frequency mode.

2 AIN3 Read/write

AIN3 = 0, speed of 3-wire fans measured using the TACH output from the fan. AIN3 = 1, Pin 4 is reconfigured to measure the speed of 2-wire fans using an external sensing resistor and coupling capacitor. AIN voltage threshold is set via Configuration Register 4 (Reg. 0x7D). Only relevant in low frequency mode.

3 AIN4 Read/write

AIN4 = 0, speed of 3-wire fans measured using the TACH output from the fan. AIN4 = 1, Pin 9 is reconfigured to measure the speed of 2-wire fans using an external sensing resistor and coupling capacitor. AIN voltage threshold is set via Configuration Register 4 (Reg. 0x7D). Only relevant in low frequency mode.

4 AVG Read/write

AVG = 1, averaging on the temperature and voltage measurements is turned off. This allows measurements on each channel to be made much faster.

5 ATTN Read/write

ATTN = 1, the ADT7468 removes the attenuators from the 2.5 V, V inputs. These inputs can be used for other functions such as connecting up external sensors. It is possible to remove attenuators from individual channels using Bits <7:4> of Configuration Register 4 (0x7D).

6 CONV Read/write

CONV = 1, the ADT7468 is put into a single-channel ADC conversion mode. In this mode, the ADT7468 can be made to read continuously from one input only, for example, Remote 1 temperature. The appropriate ADC channel is selected by writing to Bits <7:5> of TACH1 minimum high byte register (0x55).

Bits <7:5> Reg. 0x55

000 2.5 V 001 V

CCP

010 VCC (3.3 V) 011 5 V 100 12 V 101 Remote 1 temperature 110 Local temperature 111 Remote 2 temperature 7 SHDN Read/write

SHDN = 1, ADT7468 goes into shutdown mode. All PWM outputs assert low (or high depending on state of INV bit) to switch off all fans. The PWM current duty

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.

cycle registers read 0x00 to indicate that the fans are not being driven.

, 5 V, and 12 V

CCP

Rev. 0 | Page 74 of 80

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ADT7468

Table 46. Register 0x74—Interrupt Mask Register 1 (Power-On Default <7:0> = 0x00)

Bit Name R/W Description

0 2.5V Read/write 1 V

Read/write

CCP

2 VCC Read/write 3 5V Read/write 4 RIT Read/write 5 LT Read/write 6 R2T Read/write 7 OOL Read/write

2.5 V = 1, masks SMBALERT = 1, masks SMBALERT for out-of-limit conditions on the V

CCP

= 1, masks SMBALERT for out-of-limit conditions on the VCC channel.

5 V = 1, masks SMBALERT RIT = 1, masks SMBALERT LT = 1, masks SMBALERT R2T = 1, masks SMBALERT OOL = 1, masks SMBALERT

Table 47. Register 0x75—Interrupt Mask Register 2 (Power-On Default <7:0> = 0x00)

Bit Name R/W Description

When Pin 21 is configured as a 12 V input, 12V/VC = 1 masks SMBALERT

0 12V/VC Read/write

on the 12 V channel. When Pin 21 is programmed as VID5, this bit masks an SMBALERT

VID code bit changes. 1 OVT Read only

2 FAN1 Read/write 3 FAN2 Read/write 4 FAN3 Read/write 5 F4P Read/write

OVT = 1, masks SMBALERT

FAN1 = 1, masks SMBALERT

FAN2 = 1, masks SMBALERT

FAN3 = 1, masks SMBALERT

If Pin 14 is configured as TACH 4, F4P = 1 masks SMBALERT

If Pin 14 is configured as

If Pin 14 is configured as GPIO, F4P = 1 masks SMBALERT when GPIO is an input and GPIO is

asserted. 6 D1 Read/write 7 D2 Read/write

D1 = 1 masks SMBALERT

D2 = 1 masks SMBALERT

for out-of-limit conditions on the 2.5 V channel.

channel.

CCP

for out-of-limit conditions on the 5 V channel.

for out-of-limit conditions on the Remote 1 temperature channel.

for out-of-limit conditions on the local temperature channel.

for out-of-limit conditions on the Remote 2 temperature channel.

for any out-of-limit condition in Status Register 2.

for out-of-limit conditions

, if the VID5

for overtemperature

THERM

conditions. for a Fan 1 fault. for a Fan 2 fault. for a Fan 3 fault.

for a Fan 4 fault.

THERM

, F4P = 1 masks SMBALERT for an exceeded

THERM

timer limit.

for a diode open or short on a Remote 1 channel. for a diode open or short on a Remote 2 channel.

Table 48. Register 0x76—Extended Resolution Register 11

Bit Name R/W Description

<1:0> 2.5V Read-only 2.5 V LSBs. Holds the 2 LSBs of the 10-bit 2.5 V measurement. <3:2> V

Read-only V

CCP

LSBs. Holds the 2 LSBs of the 10-bit V

CCP

measurement.

CCP

<5:4> VCC Read-only VCC LSBs. Holds the 2 LSBs of the 10-bit VCC measurement. <7:6> 5 V Read-only 5 V LSBs. Holds the 2 LSBs of the 10-bit 5 V measurement.

If this register is read, this register and the registers holding the MSB of each reading are frozen until read.

Table 49. Register 0x77—Extended Resolution Register 21

Bit Name R/W Description

<1:0> 12V Read-only 12 V LSBs. Holds the 2 LSBs of the 10-bit 12 V measurement. <3:2> TDM1 Read-only Remote 1 temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 1 temperature measurement. <5:4> LTMP Read-only Local temperature LSBs. Holds the 2 LSBs of the 10-bit local temperature measurement. <7:6> TDM2 Read-only Remote 2 temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 2 temperature measurement.

If this register is read, this register and the registers holding the MSB of each reading are frozen until read.

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ADT7468

Table 50. Register 0x78—Configuration Register 3 (Power-On Default = 0x00)

Bit Name R/W1 Description

<0> ALERT Read/write

<1>

<2> BOOST Read/write

<3> FAST Read/write

<4> DC1 Read/write

<5> DC2 Read/write

<6> DC3 Read/write

<7> DC4 Read/write

THERM

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.

Read/write

ALERT = 1, Pin 10 (PWM2/SMBALERT) is configured as an out-of-limit error conditions.

ALERT = 0, Pin 10 (PWM2/SMBALERT THERM Enable = 1 enables THERM functionality on Pin 20 and Pin 14, if Pin 14 is configured as

THERM

, determined by Bits 0 and 1 (PIN14FUNC) of Configuration Register 4. When THERM is

asserted, if the fans are running and the boost bit is set, the fans run at full speed. Alternatively,

can be programmed so that a timer is triggered to time how long THERM has been asserted.

THERM When THERM

programmed duty cycle for fail-safe cooling. FAST = 1, enables fast TACH measurements on all channels. This increases the TACH measurement

rate from once per second to once every 250 ms (4 ×). DC1 = 1, enables TACH measurements to be continuously made on TACH1. Fans must be driven by

dc. Setting this bit prevents pulse stretching, because it is not required for dc-driven motors. DC2 = 1, enables TACH measurements to be continuously made on TACH2. Fans must be driven by

dc. Setting this bit prevents pulse stretching, because it is not required for dc-driven motors. DC3 = 1, enables TACH measurements to be continuously made on TACH3. Setting this bit prevents

pulse stretching, because it is not required for dc-driven motors. DC4 = 1, enables TACH measurements to be continuously made on TACH4. Setting this bit prevents

pulse stretching, because it is not required for dc-driven motors.

is an input and BOOST = 1, assertion of THERM causes all fans to run at the maximum

) is configured as the PWM2 output.

Table 51. Register 0x79—

Bit Name R/W Description

<7:1> TMR Read-only

<0>

ASRT/ TMR0

THERM

Read-only

Timer Status Register (Power-On Default = 0x00)

Times how long THERM exceeds 45.52 ms.

This bit is set high on the assertion of the THERM assertion time exceeds 45.52 ms, this bit is set and becomes the LSB of the 8-bit TMR reading. This allows THERM

22.76 ms.

assertion times from 45.52 ms to 5.82 s to be reported back with a resolution of

input is asserted. These seven bits read zero until the THERM assertion time

Table 52. Register 0x7A—

Bit Name R/W Description

<7:0> LIMT Read/write

THERM

Timer Limit Register (Power-On Default = 0x00)

Sets maximum limit with a resolution of 22.76 ms allowing programmed. If the

2 (Reg. 0x42) is set. If the limit value is 0x00, then an interrupt is generated immediately on the assertion of the

THERM

assertion length allowed before an interrupt is generated. This is an 8-bit

THERM

assertion time exceeds this limit, Bit 5 (F4P) of Interrupt Status Register

THERM

input.

SMBALERT

input and is cleared on read. If the THERM

assertion limits of 45.52 ms to 5.82 s to be

interrupt output to indicate

Rev. 0 | Page 76 of 80

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ADT7468

Table 53. Register 0x7B—TACH Pulses per Revolution Register (Power-On Default = 0x55)

Bit Name R/W Description

<1:0> FAN1 Read/write

00 = 1 01 = 2 (default) 10 = 3 11 = 4 <3:2> FAN2 Read/write

00 = 1 01 = 2 (default) 10 = 3 11 = 4 <5:4> FAN3 Read/write

00 = 1 01 = 2 (default) 10 = 3 11 = 4 <7:6> FAN4 Read/write

00 = 1 01 = 2 (default) 10 = 3 11 = 4

Table 54. Register 0x7C—Configuration Register 5 (Power-On Default = 0x00)

Bit Name R/W1 Description

<0> 2sC Read/write 2sC = 1, sets the temperature range to twos complement temperature range.

<1> HF/LF Sets the PWM drive frequency to high frequency mode (0) or low frequency mode (1). <2> GPIOD

<3> GPIOP

<4:7> RES Unused.

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.

Sets number of pulses to be counted when measuring Fan 1 speed. Can be used to determine fan pulses per revolution for unknown fan type.

Pulses Counted

Sets number of pulses to be counted when measuring Fan 2 speed. Can be used to determine fan pulses per revolution for unknown fan type.

Pulses Counted

Sets number of pulses to be counted when measuring Fan 3 speed. Can be used to determine fan pulses per revolution for unknown fan type.

Pulses Counted

Sets number of pulses to be counted when measuring Fan 4 speed. Can be used to determine fan pulses per revolution for unknown fan type.

Pulses Counted

2sC = 0, changes the temperature range to Offset 64. When this bit is changed, the ADT7468 interprets all relevant temperature register values as defined by this bit.

GPIO direction. When GPIO function is enabled, this determines whether the GPIO is an input (0) or an output (1).

GPIO polarity. When the GPIO function is enabled and is programmed as an output, this bit determines whether the GPIO is active low (0) or high (1).

Rev. 0 | Page 77 of 80

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ADT7468

Table 55. Register 0x7D—Configuration Register 4 (Power-On Default = 0x00)

Bit Name R/W1 Description

<1:0> PIN14FUNC Read/write These bits set the functionality of Pin 14: 00 = TACH4 (default)

01 = Bidirectional

10 = SMBALERT 11 = GPIO <3:2> AINL Read/write

These two bits define the input threshold for 2-wire fan speed measurements (low frequency mode

only): 00 = ±20 mV 01 = ±40 mV 10 = ±80 mV 11 = ±130 mV <4> BpAtt2.5V

Bypass 2.5 V attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to

2.2965 V (0xFF).

<5> BpAttV

CCP

Bypass V

attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to

CCP

2.2965 V (0xFF).

<6> BpAtt5V

Bypass 5 V attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to

2.2965 V (0xFF).

<7> BpAtt12V

This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.

Bypass 12 V attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to

2.2965 V (0xFF).

Table 56. Register 0x7E—Manufacturer’s Test Register 1 (Power-On Default = 0x00)

Bit Name R/W Description

<7:0> Reserved Read-only

Manufacturer’s test register. These bits are reserved for manufacturer’s test purposes and should not

be written to under normal operation.

Table 57. Register 0x7F—Manufacturer’s Test Register 2 (Power-On Default = 0x00)

Bit Name R/W Description

<7:0> Reserved Read-only

Manufacturer’s test register. These bits are reserved for manufacturer’s test purposes and should not

be written to under normal operation.

THERM

Rev. 0 | Page 78 of 80

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ADT7468

ADT7468 PROGRAMMING BLOCK DIAGRAM

PWM DUTY CYCLE/RELATIVE FAN SPEED

TEMPERATURE

F4P

THERM

HYST

MIN

HYST

MIN PWM

0% DUTY CYCLE

AUTOMATIC FAN CONTROL

TEMPERATURE

HEATINGCOOLING

= SLOPE

RANGE

MAX PWM

100% DUTY CYCLE

OFFSET 64

(0x41, 0x42)

MASK INTERRUPT?

INTERRUPT STATUS

THERM

FAN FAULT

FOR REMOTE

DIODE FAULT.

MEASURED IS

OUT OF LIMITS

CHANNELS ONLY

HARDWARE INTERRUPTS

TACH 4

THERM

SET PIN 14/20

GPIO

SMBALERT

FUNCTIONALITY

SMBALERT

(0x74,0x75)

TWOS COMPLEMENT

MODE

RANGE

HIGH/LOW

FAN DRIVE

FREQUENCY

TEMPERATURE

(0X7C)

CONFIGURATION 5

GPIO POLARITY

GPIO DIRECTION

±20mV

±40mV

±80mV

±130mV

CONFIGURATION 2

(0X73)

MEASURE

TEMPERATURE

FROM 2- OR 3-

WIRE FANS

OFFSET

AND VOLTAGE

AVERAGE TEMP

MEASUREMENTS

(0x70-0x72)

TEMPERATURE

MEASUREMENT

CCP

RESCALE V

INPUT (5V/3.3V)

LOW LIMIT

HIGH LIMIT

ADC MODE

SINGLE CHANNEL

(0X4E-0X53)

SHUTDOWN

OUTPUTS

HIGH/LOW

DRIVE PWM

ON STATUS

INTERRUPTS

EXCEEDED

THERM TIMER

LIMIT HAS BEEN

SOFTWARE INTERRUPTS

MEASUREMENT

(ONLY USED WHEN FANS ARE

CYXX

THERM TIMER

FOR 2-WIRE FANS

INPUT THRESHOLD

CHANGE

CYCLE TIME

ADJUSTMENT

CYCLE TIME

MIN

LIMIT (0x7A)

THERM TIMER

(AINL)

LOW

CCP

STATUS (0x79)

CCP

ATTENUATOR

BYPASS V

8 CYCLES (1s)

DECREASE

CYCLE TIME

INCREASE

CYCLE TIME

(SLEEP)

16 CYCLES (2s)

32 CYCLES (4s)

LOW LIMIT

CCP

64 CYCLES (8s)

16 CYCLES (2s)

(0x46)

(0x47)

MEASUREMENT

CCP

128 CYCLES (16s)

32 CYCLES (4s)

(0x47)

HIGH LIMIT

CCP

256 CYCLES (32s)

64 CYCLES (8s)

512 CYCLES (64s)

128 CYCLES (16s)

AND VOLTAGE

AVERAGE TEMP

LIMITS

THERM TEMP

1024 CYCLES (128s)

256 CYCLES (32s)

512 CYCLES (64s)

MEASUREMENTS

(SEE CONFIGURATION 2,

(0x6A, 0x6B, 0x6C)

0x73)

XNOR Test

1024 CYCLES (128s)

(0x6F)

2048 CYCLES (256s)

TEMPERATURE

FANS

THERM

GENERAL

VOLTAGES

INTERRUPT

TEMPERATURE

MEASUREMENT

(0X25, 0X26,0X27)

(0x49)

(0x48)

LOW LIMIT

HIGH LIMIT

(0x22)

MEASUREMENT

OUTPUT

INVERT PWM

(0X54-0X5B)

MINIMUM LIMIT

FANTACH 16-BIT

SLOW IMPROVED

PWM CONFIGURATION

(0x25-0x27)

MEASUREMENT MSBs

REMOTE 1 TEMP CONTROLS

SELECTED PWM DRIVE (AFC MODE)

FAN BEHAVIOR

ACOUSTIC RAMP-UP

(0x5C-0x5E)

(0X77)

MEASUREMENT LSBs

PWM DRIVE (AFC MODE)

LOCAL TEMP CONTROLS SELECTED

NO TIMEOUT

UNTIL ALL TEMPERATURE

MSB REGISTERS ARE FROZEN

IF THESE REGISTERS ARE USED,

MEASUREMENT MSB REGISTERS

ALL TEMPERATURE MEASUREMENT

SELECTED PWM DRIVE

REMOTE 2 TEMP CONTROLS

SELECTED PWM DRIVE (AFC MODE)

100ms

400ms

250ms (DEFAULT)

TIMEOUT

FAN SPINUP

ARE READ.

RUNS FULL SPEED

667ms

1 PULSE PER REV

FAN TACH

PULSES PER REV

(0X40)

CONFIGURATION 1

DISABLED (DEFAULT)

SELECTED PWM DRIVE

1s2s4s

2 PULSE PER REV

(0x7B)

LOCK

START

MONITORING

FASTEST SPEED CALCULATED

BY LOCAL AND REMOTE 2 TEMP

CONTROLS SELECTED PWM DRIVE

FASTEST SPEED CALCULATED BY ALL

3 PULSE PER REV

4 PULSE PER REV

MAX FAN SPEED

READY

SETTINGS

(MAX PWM DUTY CYCLE)

(5V/3.3V)

FULLSPEED

RUN FANS AT

RESCALE V

MANUAL MODE. PWM DUTY CYCLE

3 TEMPERATURE CHANNEL CONTROLS

REGISTERS (0x30-0x32) BECOME WRITABLE

(0x30-0x32)

(0x38-0x3A)

PWM DUTY CYCLE

(MANUAL MODE ONLY)

(0x78)

CONFIGURATION 3

DUTY CYCLE

MIN

PWM

(AUTOMATIC MODE ONLY)

(0x7D)

CONFIGURATION 4

ENABLE THERM

(0X64-0X66)

(FAN MUST BE RUNNING)

THERM BOOST

PHTXX

DYNAMIC T

CURRENT TEMPERATURE OF SELECTED

MIN

CONTROL

PWM 2

FAST TACH

CONFIGURE

MEASUREMENTS

POINT REGISTER ON ASSERTION OF THERM

ENABLE DYNAMIC T

CHANNEL IS COPIED TO RELEVANT OPERATING

(0x36, 0x37)

MIN

SMBALERT

PIN 10

CONTROL ON INDIVIDUAL

FAN SPEED

ENABLE CONTINUOUS

CHANNEL

CONTROL

. MIN TEMP THAT CAUSES

SELECTED FANS TO RUN

MIN

AUTOMATIC FAN

(0x67-0x69)

TEMPERATURE HYSTERES IS

(THYST)

(0x6D, 0x6E)

OPERATING

POINT

(0x33-0x35)

(0x28-0x2F)

WHEN THE LOW BYTE IS READ,

FAN 16-BIT MEASUREMENT

LOW BYTE MUST BE READ FIRST.

ASSOCIATED HIGH BYTE IS READ.

REGISTERS ARE LOCKED UNTIL THE

CCP

LOCAL TEMP

REMOTE TEMP1

REMOTE TEMP2

35s (33%-100%)

SELECTED PWM

17.6s (33%-100%)

RAMP-UP SPEED

ENHANCE

ACOUSTICS

7s (33%-100%)

18s (33%-100%)

ENABLE

SELECTED PWM

RAMP-UP SPEED

(0x62,0x63)

3s (33%-100%)

4.4s (33%-100%)

1.6s (33%-100%)

0.8s (33%-100%)

–HYST

MIN

MEASUREMENTS

SYNC FAN SPEED

ALLOW SELECTED

PWM TO TURN OFF

WHEN TEMP IS BELOW

THERM IS

INPUT/OUTPUT

,PWM

ENABLE

RANGE

(0x5F, 0x60, 0x61)

TEMP T

FREQ,THERM

THERM AS

(TIMER) INPUT

2°C

4°C

5°C

2.5°C

3.33°C

RANGE

11.0Hz

14.7Hz

22.1Hz

OUTPUT

THERM AS

OVERTEMP

8°C

10°C

16°C

20°C

32°C

40°C

6.67°C

13.33°C

26.67°C

29.4Hz

35.3Hz

44.1Hz

58.8Hz

88.2Hz

80°C

53.33°C

ADT7467/ADT7468 PROGRAMMING BLOCK DIAGRAM

PWM

FREQUENCY

04498-0-044

Figure 85.

Rev. 0 | Page 79 of 80

Page 80

ADT7468

OUTLINE DIMENSIONS

0.341 BSC

PIN 1

0.010

0.004

COPLANARITY

0.004

24 13

0.065

0.049

0.025 BSC

COMPLIANT TO JEDEC STANDARDS MO-137AE

0.012

0.008

0.069

0.053

0.154 BSC

SEATING PLANE

0.236 BSC

0.010

0.006

8° 0°

0.050

0.016

Figure 86. 24-Lead Shrink Small Outline Package [QSOP]

(RQ-24)

Dimensions shown in inches

ORDERING GUIDE

Model Temperature Range Package Description Package Option

ADT7468ARQ –40°C to +120°C 24-Lead QSOP RQ-24 ADT7468ARQ-REEL –40°C to +120°C 24-Lead QSOP RQ-24 ADT7468ARQ-REEL7 –40°C to +120°C 24-Lead QSOP RQ-24

D04499–0–4/04(0)

Rev. 0 | Page 80 of 80

Datasheet ADT7468 Datasheet (Analog Devices)

Specifications and Main Features

Frequently Asked Questions

User Manual

FEATURES

GENERAL DESCRIPTION

FUNCTIONAL BLOCK DIAGRAM

SPECIFICATIONS

ABSOLUTE MAXIMUM RATINGS

ESD CAUTION

THERMAL CHARACTERISTICS

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

TYPICAL PERFORMANCE CHARACTERISTICS

PRODUCT DESCRIPTION

COMPARISON BETWEEN ADT7463 AND ADT7468

Configuration Register 5

RECOMMENDED IMPLEMENTATION

HOW TO SET THE FUNCTIONALITY OF PIN 14

SERIAL BUS INTERFACE

WRITE OPERATIONS

Write Byte

Send Byte

READ OPERATIONS

Receive Byte

Alert Response Address

SMBUS TIMEOUT

Configuration Register 1(Reg. 0x40)

VOLTAGE MEASUREMENT INPUT

ANALOG-TO-DIGITAL CONVERTER

INPUT CIRCUITRY

VID CODE MONITORING

VID Code Register (Reg. 0x43)

VOLTAGE MEASUREMENT REGISTERS

VOLTAGE LIMIT REGISTERS

VID CODE INPUT THRESHOLD VOLTAGE

VID CODE REGISTER (Reg. 0x43)

Reconfiguring Pin 21 as VID5 Input

VID Code Register (Reg. 0x43)

VID CODE CHANGE DETECT FUNCTION

Status Register 2 (Reg. 0x42)

ADDITIONAL ADC FUNCTIONS FOR VOLTAGE MEASUREMENTS

Turn-Off Averaging

Bypass Voltage Input Attenuator

Single-Channel ADC Conversion

Configuration Register 2 (Reg. 0x73)

TACH1 Minimum High Byte (Reg. 0x55)

TEMPERATURE MEASUREMENT METHOD

Local Temperature Measurement

Remote Temperature Measurement

Noise Filtering

SERIES RESISTANCE CANCELLATION

FACTORS AFFECTING DIODE ACCURACY

Remote Sensing Diode

Nulling Out Temperature Errors

Temperature Offset Registers

ADT7463/ADT7468 Backwards Compatible Mode

Temperature Measurement Registers

Temperature Measurement Limit Registers

Reading Temperature from the ADT7468

Single-Channel ADC Conversions

Configuration Register 2 (Reg. 0x73)

ADDITIONAL ADC FUNCTIONS FOR TEMPERATURE MEASUREMENT

Turn-Off Averaging

TACH1 Minimum High Byte (Reg. 0x55)

Overtemperature Events

LIMITS, STATUS REGISTERS, AND INTERRUPTS

LIMIT VALUES

8-Bit Limits

16-Bit Limits

Fan Limit Registers

Status Register 1 (Reg. 0x41)

Status Register 2 (Reg. 0x42)

STATUS REGISTERS

Interrupt Mask Register 1 (Reg. 0x74)

Masking Interrupt Sources

Interrupt Mask Register 2 (Reg. 0x75)

FAN DRIVE USING PWM CONTROL

Driving Two Fans from PWM3

Driving up to Three Fans from PWM3

<4> (SYNC) Enhance Acoustics Register 1 (Reg. 0x62)