Datasheet ADM1031 Datasheet (Analog Devices)

Page 1

Intelligent Temperature Monitor

FEATURES Optimized for Pentium® III: Allows Reduced Guardbanding Software and Automatic Fan Speed Control Automatic Fan Speed Control Allows Control Indepen-

dent of CPU Intervention after Initial Setup

Control Loop Minimizes Acoustic Noise and Battery

Consumption

Remote Temperature Measurement Accurate to 1ⴗC

Using Remote Diode (Two Channels)

0.125ⴗC Resolution on External Temperature Channels Local Temperature Sensor with 0.25ⴗC Resolution Pulsewidth Modulation Fan Control (PWM) for Two Fans Programmable PWM Frequency Programmable PWM Duty Cycle Tach Fan Speed Measurement (Two Channels) Analog Input To Measure Fan Speed of 2-Wire Fans

(Using Sense Resistor)

2-Wire System Management Bus (SMBus) with ARA

Support

Overtemperature THERM Output Pin for CPU Throttling Programmable INT Output Pin Configurable Offsets for Temperature Channels 3 V to 5.5 V Supply Range Shutdown Mode to Minimize Power Consumption Limit Comparison of All Monitored Values

APPLICATIONS Notebook PCs, Network Servers and Personal Computers Telecommunications Equipment

and Dual PWM Fan Controller

ADM1031

PRODUCT DESCRIPTION

The ADM1031 is an ACPI-compliant three-channel digital thermometer and under/over temperature alarm, for use in personal computers and thermal management systems. Optimized for the Pentium III, the higher 1°C accuracy offered allows systems designers to safely reduce temperature guardbanding and increase system performance. Two Pulsewidth Modulated (PWM) Fan Control outputs control the speed of two cooling fans by varying output duty cycle. Duty cycle values between 33%–100% allow smooth control of the fans. The speed of each fan can be monitored via TACH inputs. The TACH inputs may be reprogrammed as analog inputs, allowing fan speeds for 2-wire fans to be measured via sense resistors. The device will also detect a stalled fan. A dedicated Fan Speed Control Loop provides control even without the intervention of CPU software. It also ensures that if the CPU or system locks up, each fan can still be controlled based on temperature measurements, and the fan speed adjusted to correct any changes in system temperature. Fan speed may also be controlled using existing ACPI software. Two inputs (four pins) are dedicated to remote temperature-sensing diodes with an accuracy of ±1°C, and an on-chip temperature sensor allows ambient temperature to be monitored. The device has a programmable INT output to indicate error conditions. There is a dedicated FAN_FAULT output to signal fan failure. The THERM pin is a fail-safe output for overtemperature conditions that can be used to throttle a CPU clock.

FUNCTIONAL BLOCK DIAGRAM

SLAVE

ADDRESS

FAN FILTER

FA N

CHARACTERISTICS

REGISTERS

FAN SPEED

CONFIG

FAN SPEED

COUNTER

ANALOG

MULTIPLEXER

*Patents pending.

PWM_OUT1

PWM_OUT2

TACH2 /AIN2

TACH1 /AIN1

D1+

D1–

D2+

D2–

ADM1031

PWM

CONTROLLERS

TACH SIGNAL

CONDITIONING

BANDGAP

TEMPERATURE

SENSOR

REV. A

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. 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 companies.

SERIAL BUS

INTERFACE

ADDRESS

POINTER

INTERRUPT

STATUS

REGISTERS

LIMIT

COMPARATOR

VA LUE AND LIMIT

REGISTERS

OFFSET

ADC

2.5V

BANDGAP

REFERENCE

GND

REGISTERS

CONFIGURATION

REGISTERS

ADD

SDA

SCL

INT (SMBALERT)

THERM

FAN_FAULT

Page 2

ADM1031–SPECIFICATIONS

(TA = T

MIN

to T

, VCC = V

MAX

MIN

to V

, unless otherwise noted.)

MAX

Parameter Min Typ Max Unit Test Conditions/Comments

POWER SUPPLY

Supply Voltage, V Supply Current, I

3.0 3.30 5.5 V

1.4 3 mA Interface Inactive, ADC Active 32 50 µA Standby Mode

TEMPERATURE-TO-DIGITAL CONVERTER

Local Sensor Accuracy ± 1 ± 3 °C Resolution 0.25 °C Remote Diode1 Sensor Accuracy ± 0.5 ± 1 °C60°C ≤ T Remote Diode2 Sensor Accuracy ± 0.5 ± 1.75 °C60°C ≤ T

≤ 100°C

Resolution 0.125 °C Remote Sensor Source Current 180 µA High Level

11 µA Low Level

OPEN-DRAIN DIGITAL OUTPUTS (THERM, INT, FAN_FAULT, PWM_OUT)

Output Low Voltage, V High-Level Output Leakage Current, I

0.4 V I

0.1 1 µAV

= –6.0 mA; V

OUT

= VCC; V

OUT

= 3 V

OPEN-DRAIN SERIAL DATA BUS OUTPUT (SDA)

Output Low Voltage, V High-Level Output Leakage Current, I

0.4 V I

0.1 1 µAV

= –6.0 mA; V

OUT

= V

OUT

= 3 V

SERIAL BUS DIGITAL INPUTS (SCL, SDA)

Input High Voltage, V Input Low Voltage, V

2.1 V

0.8 V

Hysteresis 500 mV

DIGITAL INPUT LOGIC LEVELS

(ADD, THERM, TACH1/2)

Input High Voltage, V Input Low Voltage, V

2.1 V

0.8 V

DIGITAL INPUT LEAKAGE CURRENT

Input High Current, I Input Low Current, I Input Capacitance, C

–1 µAV

1 µAV

5pF

= V = 0

FAN RPM-TO-DIGITAL CONVERTER

Accuracy ± 6% 60°C ≤ T

≤ 100°C

Full-Scale Count 255 TACH Nominal Input RPM 4400 RPM Divisor N = 1, Fan Count = 153

2200 RPM Divisor N = 2, Fan Count = 153 1100 RPM Divisor N = 4, Fan Count = 153 550 RPM Divisor N = 8, Fan Count = 153

Conversion Cycle Time 637 ms

SCLK

BUF

SU;STA

HD;STA

LOW

HIGH

SU;DAT

HD;DAT

10 100 kHz See Figure 1

50 ns See Figure 1

4.7 µs See Figure 1

4.7 µs See Figure 1 4 µs See Figure 1

SU;STO

4 µs See Figure 1

1.3 µs See Figure 1 450µs See Figure 1

1000 ns See Figure 1

300 ns See Figure 1 250 ns See Figure 1 300 ns See Figure 1

= 0.8 V for a falling edge and V

= 2.2 V for a rising edge.

SERIAL BUS TIMING

Clock Frequency, f Glitch Immunity, t Bus Free Time, t Start Setup Time, t Start Hold Time, t Stop Condition Setup Time t SCL Low Time, t SCL High Time, t SCL, SDA Rise Time, t SCL, SDA Fall Time, t Data Setup Time, t Data Hold Time, t

NOTES

Typicals are at TA = 25°C and represent most likely parametric norm. Shutdown current typ is measured with VCC = 3.3 V.

ADD is a three-state input that may be pulled high, low or left open-circuit.

Timing specifications are tested at logic levels of V

Specifications subject to change without notice.

–2–

REV. A

Page 3

ADM1031

ABSOLUTE MAXIMUM RATINGS*

Positive Supply Voltage (VCC) . . . . . . . . . . . . . . . . . . . . .6.5 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

) . . . . . . . . . . 150°C

JMAX

Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C

Lead Temperature, Soldering

Vapor Phase 60 sec . . . . . . . . . . . . . . . . . . . . . . . . . . 215°C

Infrared 15 sec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200°C

ESD Rating All Pins . . . . . . . . . . . . . . . . . . . . . . . . . . 2000 V

*Stresses above those listed under Absolute Maximum Ratings may cause perma-

nent 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

16-Lead QSOP Package

= 105°C/W, θ

SCL

= 39°C/W

HD:STA

LOW

HD:DAT

HIGH

SU:DAT

ORDERING GUIDE

Temperature Package Package

Model Range Description Option

ADM1031ARQ 0°C to 100°C 16-Lead QSOP RQ-16

HD:STA

SU:STA

SU:STO

SDA

BUF

Figure 1. Diagram for Serial Bus Timing

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 the ADM1031 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.

PSP

REV. A

–3–

Page 4

ADM1031

PIN FUNCTION DESCRIPTIONS

Pin No. Mnemonic Description

1 PWM_OUT1 Digital Output (Open-Drain). Pulsewidth modulated output to control fan speed. Requires pull-

up resistor (10 kΩ typical).

2 TACH1/AIN1 Digital/Analog Input. Fan tachometer input to measure FAN1 fan speed. May be reprogrammed as

an analog input to measure speed of a 2-wire fan via a sense resistor (2 Ω typical).

3 PWM_OUT2 Digital Output (Open-Drain). Pulsewidth Modulated output to control FAN2 fan speed.

Requires pull-up resistor (10 kΩ typical).

4 TACH2/AIN2 Digital/Analog Input. Fan tachometer input to measure FAN2 fan speed. May be repro-

grammed as an analog input to measure speed of a 2-wire fan via a sense resistor (2 Ω typical). 5GND System Ground. 6V

7 THERM Digital I/O (Open-Drain). An active low thermal overload output that indicates a violation of a

8 FAN_FAULT Digital Output (Open-Drain). Can be used to signal a fan fault. Drives second fan to full speed

9 D1– Analog Input. Connected to cathode of first remote temperature-sensing diode. The temperature-

10 D1+ Analog Input. Connected to anode of first remote temperature-sensing diode. 11 D2– Analog Input. Connected to cathode of second remote temperature-sensing diode. 12 D2+ Analog Input. Connected to anode of second remote temperature-sensing diode. 13 ADD Three-State Logic Input. Sets two lower bits of device SMBus address. 14 INT (SMBALERT)Digital Output (Open-Drain). Can be programmed as an interrupt (SMBus ALERT) output for

15 SDA Digital I/O. Serial Bus Bidirectional Data. Open-drain output. Requires pull-up resistor

16 SCL Digital Input. Serial Bus Clock. Requires pull-up resistor (2.2 kΩ typical).

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

temperature set point (overtemperature). Also acts as an input to provide external fan control.

When this pin is pulled low by an external signal, a status bit is set, and the fan speed is set to

full-on. Requires pull-up resistor (10 kΩ).

if one fan fails. Requires pull-up resistor (typically 10 kΩ).

sensing element is either a Pentium III substrate transistor or a general-purpose 2N3904.

temperature/fan speed interrupts. Requires pull-up resistor (10 kΩ typical).

(2.2 kΩ typical).

PIN CONFIGURATION

GND

THERM

ADM1031

TOP VIEW

(Not to Scale)

PWM_OUT1

TACH1/AIN1

PWM_OUT2

TACH2/AIN2

FAN_FAULT

SCL

SDA

INT(SMBALERT)

ADD

D2+

D2–

D1+

D1–

–4–

REV. A

Page 5

Typical Performance Characteristics–ADM1031

DXP – DXN CAPACITANCE – nF

–2

–10

1472.2

REMOTE TEMPERATURE ERROR – ⴗC

3.3

4.7

10 22

–3

–5

–7

–9

–6

–11 –12 –13 –14 –15 –16

–1

–4

–8

–5

–10

–15

REMOTE TEMPERATURE ERROR – ⴗC

–20

3.3 LEAKAGE RESISTANCE – M⍀

DXP TO GND

DXP TO VCC (3.3V)

10 30

100

TPC 1. Temperature Error vs. PCB Track Resistance

ⴗ

REMOTE TEMPERATURE ERROR –

–1

VIN = 200mV p-p

500k 2M

VIN = 100mV p-p

4M 6M 10M 100M 400M

FREQUENCY – Hz

110

100

READING – ⴗC

06010

40 50

PIII TEMPERATURE – ⴗC

70 80 90 100 110

TPC 4. Pentium III Temperature Measurement vs. ADM1031 Reading

TPC 2. Temperature Error vs. Power Supply Noise Frequency

ⴗ

REMOTE TEMPERATURE ERROR –

–1

0 400M100k 1M

VIN = 40mV p-p

200M 300M

100M

FREQUENCY – Hz

VIN = 20mV p-p

500M

TPC 3. Temperature Error vs. Common-Mode Noise Frequency

REV. A

TPC 5. Temperature Error vs. Capacitance between D+ and D–

110

100

␮

SUPPLY CURRENT –

0751

25 50

SCLK FREQUENCY – kHz

VCC = 5V

VCC = 3.3V

100 250 500 750 1000

TPC 6. Standby Current vs. Clock Frequency

–5–

Page 6

ADM1031

REMOTE TEMPERATURE ERROR – ⴗC

–1

0 400M100k

VIN = 30mV p-p

VIN = 20mV p-p

100M

FREQUENCY – Hz

200M 300M

500M

TPC 7. Temperature Error vs. Differential-Mode Noise Frequency

200

180

160

140

120

100

SUPPLY CURRENT – ␮A

–20

0 1.1 1.3 1.5 1.7 1.9 2.1

ADD = V

SUPPLY VOLTAGE – V

ADD = GND

ADD = Hi-Z

2.9 4.5

2.5

0.08

–0.08

–0.16

–0.24

ⴗ

–0.32

–0.40

ERROR –

–0.48

–0.56

–0.64

–0.72

–0.80

20 40 60 80 85 100 105 120

TEMPERATURE – ⴗC

TPC 10. Remote Temperature Sensor Error

1.30

1.25

1.20

1.15

1.10

1.05

1.00

0.95

SUPPLY CURRENT – mA

0.90

0.85

0.80

2.0

2.8 3.2 3.6 4.0 4.4 4.82.2 2.6 3.0 3.4 3.8 4.2 4.6 5.0

2.4 SUPPLY VOLTAGE – V

TPC 8. Standby Supply Current vs. Supply Voltage

0.08

–0.08

–0.16

–0.24

ⴗ

–0.32

–0.40

ERROR –

–0.48

–0.56

–0.64

–0.72

–0.80

20 40 60 80 85 100 105 120

TEMPERATURE – ⴗC

TPC 9. Local Sensor Temperature Error

TPC 11. Supply Current vs. Supply Voltage

120

110

100

TEMPERATURE – ⴗC

4681013579

TIME – Sec

TPC 12. Response to Thermal Shock

–6–

REV. A

Page 7

ADM1031

GENERAL DESCRIPTION

The ADM1031 is a temperature monitor and dual PWM fan controller for microprocessor-based systems. The device communicates with the system via a serial System Management Bus. The serial bus controller has a hardwired address pin for device selection (Pin 13), a serial data line for reading and writing addresses and data (Pin 15), and an input line for the serial clock (Pin 16). All control and programming functions of the ADM1031 are performed over the serial bus. The device also supports Alert Response Address (ARA).

INTERNAL REGISTERS OF THE ADM1031

A brief description of the ADM1031’s principal internal registers is given below. More detailed information on the function of each register is given in Table XII to Table XXIX.

Configuration Register

Provides control and configuration of various functions on the device.

Address Pointer Register

This register contains the address that selects one of the other internal registers. When writing to the ADM1031, the first byte of data is always a register address, which is written to the Address Pointer Register.

Status Registers

These registers provide status of each limit comparison.

Value and Limit Registers

The results of temperature and fan speed measurements are stored in these registers, along with their limit values.

Fan Speed Config Register

This register is used to program the PWM duty cycle for each fan.

Offset Registers

Allows the temperature channel readings to be offset by a 5-bit two’s complement value written to these registers. These values will automatically be added to the temperature values (or subtracted from if negative). This allows the systems designer to optimize the system if required, by adding or subtracting up to 15°C from a temperature reading.

Fan Characteristics Registers

These registers are used to select the spin-up time, PWM frequency, and speed range for the fans used.

THERM Limit Registers

These registers contain the temperature values at which THERM will be asserted.

MIN/TRANGE

Registers

These registers are read/write registers that hold the minimum temperature value below which the fan will not run when the device is in Automatic Fan Speed Control Mode. These registers also hold the temperature range value that defines the range over which auto fan control will be provided, and hence determines the temperature at which the fan will run at full speed.

SERIAL BUS INTERFACE

Control of the ADM1031 is carried out via the SMBus. The ADM1031 is connected to this bus as a slave device, under the control of a master device, e.g., the 810 chipset.

The ADM1031 has a 7-bit serial bus address. When the device is powered up, it will do so with a default serial bus address. The five MSBs of the address are set to 01011, the two LSBs are determined by the logical state of Pin 13 (ADD). This is a

three-state input that can be grounded, connected to V

CC,

or left open-circuit to give three different addresses. The state of the ADD pin is only sampled at power-up, so changing ADD with power on will have no effect until the device is powered off, then on again.

Table I. ADD Pin Truth Table

ADD Pin A1 A0 GND 0 0 No Connect 1 0 V

If ADD is left open-circuit, the default address will be 0101110.

The facility to make hardwired changes at the ADD pin allows the user to avoid conflicts with other devices sharing the same serial bus; for example, if more than one ADM1031 is used in a system.

The serial bus protocol operates as follows:

1. The master initiates data transfer by establishing a START

condition, defined as a high-to-low transition on the serial data line SDA while the serial clock line SCL remains high. This indicates that an address/data stream will follow. All slave peripherals connected to the serial bus respond to the START condition, and shift in the next 8 bits, consisting of a 7-bit address (MSB first) plus an R/W bit that determines the direction of the data transfer, i.e., whether data will be written to or read from the slave device.

The peripheral whose address corresponds to the transmitted address responds by pulling the data line low during the low period before the ninth clock pulse, known as the Acknowledge Bit. All other devices on the bus now remain idle while the selected device waits for data to be read from or written to it. If the R/W bit is a 0, the master will write to the slave device. If the R/W bit is a 1, the master will read from the slave device.

2. 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, as a low-to-high transition when the clock is high may 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.

3. When all data bytes have been read or written, stop condi-

tions are established. In WRITE mode, the master will pull the data line high during the tenth clock pulse to assert a STOP condition. In READ mode, the master device will override 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 will then take the data line low during the low period before the tenth clock pulse, then high during the tenth clock pulse to assert a STOP condition.

Any number of bytes of data may 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.

REV. A

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ADM1031

In the case of the ADM1031, 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; data can then 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, the write operation contains a second data byte that is written to the register selected by the address pointer register.

This is illustrated in Figure 2a. The device address is sent over the bus followed by R/W 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:

1. If the ADM1031’s Address Pointer Register value is unknown or not the desired value, it is first necessary to set it to the correct value before data can be read from the desired data register. This is done by performing a write to the ADM1031

SCL

as before, but only the data byte containing the register address is sent, as data is not to be written to the register. This is shown in Figure 2b.

A read operation is then performed consisting of the serial bus address, R/W bit set to 1, followed by the data byte read from the data register. This is shown in Figure 2c.

2. 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, so Figure 2b can be omitted.

NOTES

1. Although 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, 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.

2. In Figures 2a to 2c, the serial bus address is shown as the default value 01011(A1)(A0), where A1 and A0 are set by the three-state ADD pin.

3. The ADM1031 also supports the Read Byte protocol, as described in the System Management Bus specification.

SDA

START BY

MASTER

1011

SERIAL BUS ADDRESS BYTE

FRAME 1

SCL (CONTINUED)

SDA (CONTINUED)

R/W

ACK. BY

ADM1031

ADDRESS POINTER REGISTER BYTE

FRAME 2

FRAME 3

DATA BYTE

ACK. BY

ADM1031

ACK. BY

ADM1031

STOP BY

MASTER

Figure 2a. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

ACK. BY ADM1031

STOP BY MASTER

SCL

SDA

START BY

MASTER

1011

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

ACK. BY

ADM1031

ADDRESS POINTER REGISTER BYTE

FRAME 2

Figure 2b. Writing to the Address Pointer Register Only

SCL

SDA

START BY

MASTER

1011

SERIAL BUS ADDRESS BYTE

FRAME 1

R/W

ACK. BY

ADM1031

FRAME 2

DATA BYTE FROM ADM1031

Figure 2c. Reading Data from a Previously Selected Register

–8–

NO ACK.

BY MASTER

STOP BY MASTER

REV. A

Page 9

ADM1031

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.

The INT output can be used as an interrupt output or can be used as an SMBALERT. One or more INT outputs can be connected to a common SMBALERT line connected to the master. If a device’s INT line goes low, the following procedure occurs:

1. SMBALERT pulled low.

2. 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 INT 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 INT output is low, the one with the lowest device address will have priority, in accordance with normal SMBus arbitration.

5. Once the ADM1031 has responded to the Alert Response Address, it will reset its INT output; however, if the error condition that caused the interrupt persists, INT will be reasserted on the next monitoring cycle.

TEMPERATURE MEASUREMENT SYSTEM Internal Temperature Measurement

The ADM1031 contains an on-chip bandgap temperature sensor. The on-chip ADC performs conversions on the output of this sensor and outputs the temperature data in 10-bit two’s complement format. The resolution of the local temperature sensor is 0.25°C. The format of the temperature data is shown in Table II.

External Temperature Measurement

The ADM1031 can measure the temperatures of two external diode sensors or diode-connected transistors, connected to Pins 9 and 10 and Pins 11 and 12.

These pins are dedicated temperature input channels. The function of Pin 7 is as a THERM input/output and is used to flag overtemperature conditions.

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 of V

, varies from device to device, and individual

calibration is required to null this out, so the technique is unsuitable for mass production.

The technique used in the ADM1031 is to measure the change in V

when the device is operated at two different currents.

This is given by:

∆V

= KT/q × ln (N)

where:

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

Figure 3 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, provided for temperature monitoring on some microprocessors, but it could equally well be a discrete transistor.

REMOTE

SENSING

TRANSISTOR

IN ⴛ II

D+

D–

BIAS

DIODE

BIAS

LOW-PASS

FILTER

= 65kHz

OUT+

OUT–

ADC

Figure 3. Signal Conditioning

If a discrete transistor is used, the collector will not be 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.

One LSB of the ADC corresponds to 0.125°C, so the ADM1031 can theoretically measure temperatures from –127°C to +127.75°C, although –127°C is outside the operating range for the device. The extended temperature resolution data format is shown in Tables III and IV.

Table II. Temperature Data Format (Local Temperature and Remote Temperature High Bytes)

Temperature (ⴗC) Digital Output

–128°C 1000 0000 –125°C 1000 0011 –100°C 1001 1100 –75°C 1011 0101 –50°C 1100 1110 –25°C 1110 0111 –1°C 1111 1111 0°C 0000 0000 +1°C 0000 0001 +10°C 0000 1010 +25°C 0001 1001 +50°C 0011 0010 +75°C 0100 1011 +100°C 0110 0100 +125°C 0111 1101 +127°C 0111 1111

REV. A

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ADM1031

Table III. Remote Sensor Extended Temperature Resolution

Extended Remote Temperature Resolution (ⴗC) Low Bits

0.000 000

0.125 001

0.250 010

0.375 011

0.500 100

0.625 101

0.750 110

0.875 111

The extended temperature resolution for the local and remote channels is stored in the Extended Temperature Resolution Register (Register 0x06), and is outlined in Table XVIII.

Table IV. Local Sensor Extended Temperature Resolution

Extended Local Temperature Resolution (ⴗC) Low Bits

0.00 00

0.25 01

0.50 10

0.75 11

To prevent ground noise interfering with the measurement, the more negative terminal of the sensor is not referenced to ground, but biased above ground by an internal diode at the D– input. If the sensor is used in a very noisy environment, a capacitor of value up to 1000 pF may be placed between the D+ and D– inputs to filter the noise.

To measure ∆V

, the sensor is switched between operating

ΒΕ

currents of I and N × I. The resulting waveform is passed through a 65 kHz low-pass filter to remove noise, then to a chopperstabilized amplifier that performs the functions of amplification and rectification of the waveform to produce a dc voltage proportional to ∆V

. This voltage is measured by the ADC to give

a temperature output in 11-bit two’s complement format. To further reduce the effects of noise, digital filtering is performed by averaging the results of 16 measurement cycles. An external temperature measurement nominally takes 9.6 ms.

LAYOUT CONSIDERATIONS

Digital boards can be electrically noisy environments and care must be taken to protect the analog inputs from noise, particularly when measuring the very small voltages from a remote diode sensor. The following precautions should be taken:

1. Place the ADM1031 as close as possible to the remote sensing diode. Provided that the worst noise sources such as clock generators, data/address buses, and CRTs are avoided, this distance can be 4 to 8 inches.

2. Route the D+ and D– tracks close together, in parallel, with grounded guard tracks on each side. Provide a ground plane under the tracks if possible.

3. Use wide tracks to minimize inductance and reduce noise pickup. 10 mil track minimum width and spacing is recommended.

GND

D+

D–

GND

10MIL

Figure 4. Arrangement of Signal Tracks

4. Try to minimize the number of copper/solder joints, which can cause thermocouple effects. Where copper/solder joints are used, make sure that they are in both the D+ and D– path and at the same temperature.

Thermocouple effects should not be a major problem as 1°C corresponds to about 200 µV, and thermocouple voltages are about 3 µV/°C of temperature difference. Unless there are two thermocouples with a big temperature differential between them, thermocouple voltages should be much less than 200 µV.

5. Place a 0.1 µF bypass capacitor close to the ADM1031.

6. If the distance to the remote sensor is more than 8 inches, the use of twisted pair cable is recommended. This will work up to about 6 to 12 feet.

7. For really long distances (up to 100 feet) use shielded twisted pair such as Belden #8451 microphone cable. Connect the twisted pair to D+ and D– and the shield to GND close to the ADM1031. Leave the remote end of the shield unconnected to avoid ground loops.

Because the measurement technique uses switched current sources, excessive cable and/or filter capacitance can affect the measurement. When using long cables, the filter capacitor C1 may be reduced or removed. In any case the total shunt capacitance should not exceed 1000 pF.

Cable resistance can also introduce errors. 1 Ω series resistance introduces about 0.5°C error.

ADDRESSING THE DEVICE

ADD (Pin 13) is a three-state input. It is sampled, on power-up to set the lowest two bits of the serial bus address. Up to three addresses are available to the systems designer via this address pin. This reduces the likelihood of conflicts with other devices attached to the System Management Bus.

THE ADM1031 INTERRUPT SYSTEM

The ADM1031 has two interrupt outputs, INT and THERM. These have different functions. INT responds to violations of software programmed temperature limits and is maskable (described in more detail later).

THERM is intended as a “fail-safe” interrupt output that cannot be masked. If the temperature is below the low temperature limit, the INT pin will be asserted low to indicate an out-of-limit condition. If the temperature exceeds the high temperature limit, the INT pin will also be asserted low. A third limit; THERM limit, may be programmed into the device to set the temperature limit above which the overtemperature THERM pin will be

–10–

REV. A

Page 11

ADM1031

asserted low. The behavior of the high limit and THERM limit is as follows:

1. Whenever the temperature measured exceeds the high tem-

perature limit, the INT pin is asserted low.

2. If the temperature exceeds the THERM limit, the THERM

output asserts low. This can be used to throttle the CPU clock. If the THERM-to-Fan Enable bit (Bit 7 of THERM behavior/revision register) is cleared to 0, the fans will not run full-speed. The THERM limit may be programmed at a lower temperature than the high temperature limit. This allows the system to run in silent mode, where the CPU can be throttled while the cooling fan is off. If the temperature continues to increase, and exceeds the high temperature limit, an INT is generated. Software may then decide whether the fan should run to cool the CPU. This allows the system to run in SILENT MODE.

3. If the THERM-to-Fan Enable bit is set to 1, the fan will run full-speed whenever THERM is asserted low. In this case, both throttling and active cooling take place. If the high temperature limit is programmed to a lower value than the THERM limit, exceeding the high temperature limit will assert INT low. Software could change the speed of the fan depending on temperature readings. If the temperature continues to increase and exceeds the THERM limit, THERM asserts low to throttle the CPU and the fan runs full-speed. This allows the system to run in PERFORMANCE MODE, where active cooling takes place and the CPU is only throttled at high temperature.

Using the high temperature limit and the THERM limit in this way allows the user to gain maximum performance from the system by only slowing it down, should it be at a critical temperature.

Although the ADM1031 does not have a dedicated Interrupt Mask Register, clearing the appropriate enable bits in Configuration Register 2 will clear the appropriate interrupts and mask out future interrupts on that channel. Disabling interrupt bits will prevent out-of-limit conditions from generating an interrupt or setting a bit in the Status Registers.

USING THERM AS AN INPUT

The THERM pin is an open-drain input/output pin. When used as an output, it signals overtemperature conditions. When asserted low as an output, the fan will be driven full-speed if the THERM-to-Fan Enable bit is set to 1 (Bit 7 of Register 0x3F). When THERM is pulled low as an input, the THERM bit (Bit 7) of Status Register 2 is set to 1, and the fans are driven full-speed. Note that the THERM-to-Fan Enable bit has no effect whenever THERM is used as an input. If THERM is pulled low as an input, and the THERM-to-Fan Enable bit = 0, the fans will still be driven full-speed. The THERM-to-Fan Enable bit only affects the behavior of THERM when used as an output.

STATUS REGISTERS

All out-of-limit conditions are flagged by status bits in Status Registers 1 and 2 (0x02, 0x03). Bits 0 and 1 (Alarm Speed, Fan Fault) of Status Register 1, once set, may be cleared by reading Status Register 1. Once the Alarm Speed bit is cleared, this bit will not be reasserted on the next monitoring cycle even if the condition still persists. This bit may be reasserted only if the

fan is no longer at Alarm Speed. Bit 1 (Fan Fault) is set whenever a fan tach failure is detected.

Once cleared, it will reassert on subsequent fan tach failures.

Bits 2 and 3 of Status Registers 1, 2 are the Remote 1, 2 Temperature High and Low status bits. Exceeding the high or low temperature limits for the external channel sets these status bits. Reading the status register clears these bits. However, these bits will be reasserted if the out-of limit condition still exists on the next monitoring cycle. Bits 6 and 7 are the Local Temperature High and Low status bits. These behave exactly the same as the Remote Temperature High and Low status bits. Bit 4 of Status Register 1 indicates that the Remote Temperature THERM limit has been exceeded. This bit gets cleared on a read of Status Register 1 (see Figure 5). Bit 5 indicates a Remote Diode Error. This bit will be a 1 if a short or open is detected on the Remote Temperature channel on power-up. If this bit is set to 1 on power-up, it cannot be cleared. Bit 6 of Status Register 2 (0x03) indicates that the Local THERM limit has been exceeded. This bit is cleared on a read of Status Register 2. Bit 7 indicates that THERM has been pulled low as an input. This bit can also be cleared on a read of Status Register 2.

THERM LIMIT

5ⴗ

TEMP

THERM

INT REARMED

INT

STATUS REG. READ

Figure 5. Operation of

THERM

and

INT

Signals

Figure 5 shows the interaction between INT and THERM. Once a critical temperature THERM limit is exceeded, both INT and THERM assert low. Reading the Status Registers clears the interrupt and the INT pin goes high. However, the THERM pin remains asserted until the measured temperature falls 5

C below the exceeded THERM limit. This feature can be

used to CPU throttle or drive a fan full speed for maximum cooling. Note, that the INT pin for that interrupt source is not rearmed until the temperature has fallen below the THERM limit –5

C. This prevents unnecessary interrupts from tying up

valuable CPU resources.

MODES OF OPERATION

The ADM1031 has four different modes of operation. These modes determine the behavior of the system.

1. Automatic Fan Speed Control Mode.

2. Filtered Automatic Fan Speed Control Mode.

3. PWM Duty Cycle Select Mode (directly sets fan speed under software control).

4. RPM Feedback Mode.

REV. A

–11–

Page 12

ADM1031

AUTOMATIC FAN SPEED CONTROL

The ADM1031 has a local temperature channel and two remote temperature channels, which may be connected to an on-chip diode-connected transistor on a CPU. These three temperature channels may be used as the basis for an automatic fan speed control loop to drive fans using Pulsewidth Modulation (PWM).

HOW DOES THE CONTROL LOOP WORK?

The Automatic Fan Speed Control Loop is shown in Figure 6.

MAX

FA N

SPEED

SPIN-UP FOR TWO SECONDS

100

ⴗ

= 5

PWM DUTY CYCLE – %

MIN

ⴗ

RANGE

= 10

RANGE

ⴗ

= 20

510 20 40 60 80

ⴗ

= 40

RANGE

ⴗ

= 80

RANGE

TEMPERATURE – ⴗC

MAX

= T

MIN

+ T

RANGE

MIN

= T

MIN

TEMPERATURE

MAX

MIN

+ T

RANGE

Figure 6. Automatic Fan Speed Control

In order for the fan speed control loop to work, certain loop parameters need to be programmed into the device.

1. T

. The temperature at which the fan should switch on

MIN

and run at minimum speed. The fan will only turn on once the temperature being measured rises above the T

MIN

value programmed. The fan will spin up for a predetermined time (default = 2 secs). See Fan Spin-Up section for more details.

2. T

. The temperature range over which the ADM1031

RANGE

will automatically adjust the fan speed. As the temperature increases beyond T increased accordingly. The T

, the PWM_OUT duty cycle will be

MIN

parameter actually defines

RANGE

the fan speed versus temperature slope of the control loop.

3. T

The temperature at which the fan will be at its maxi-

MAX.

mum speed. At this temperature, the PWM duty cycle driving the fan will be 100%. T

is given by T

MAX

Since this parameter is the sum of the T

MIN

+ T

and T

RANGE

parameters, it does not need to be programmed into a register on-chip.

4. A hysteresis value of 5

C is included in the control loop to prevent the fan continuously switching on and off if the temperature is close to T such time as the temperature drops 5

. The fan will continue to run until

MIN

C below T

MIN

Figure 7 shows the different control slopes determined by the T

value chosen, and programmed into the ADM1031.

RANGE

was set to 0°C to start all slopes from the same point. It

MIN

can be seen how changing the T

value affects the PWM

RANGE

duty cycle versus temperature slope.

Figure 7. PWM Duty Cycle vs. Temperature Slopes (T

Figure 8 shows how, for a given T value affects the loop. Increasing the T the T since T

(temperature at which the fan runs full speed) value,

MAX

= T

MIN

+ T

. Note, however, that the PWM

RANGE

, changing the T

RANGE

value will increase

MIN

RANGE

MIN

)

Duty Cycle vs Temperature slope remains exactly the same. Changing the T

may be changed in increments of 4°C.

MIN

100

PWM DUTY CYCLE – %

MIN

Figure 8. Effect of Increasing T

value merely shifts the control slope. The

MIN

ⴗ

= 40

RANGE

20 40 60 80

TEMPERATURE – ⴗC

ⴗ

= 40

RANGE

Value on Control Loop

MIN

MAX

= 40

RANGE

= T

MIN

ⴗ

+ T

RANGE

FAN SPIN-UP

As was previously mentioned, once the temperature being measured exceeds the T

value programmed, the fan will turn on

MIN

at minimum speed (default = 33% duty cycle). However, the problem with fans being driven by PWM is that 33% duty cycle is not enough to reliably start the fan spinning. The solution is to spin the fan up for a predetermined time, and once the fan has spun up, its running speed may be reduced in line with the temperature being measured.

The ADM1031 allows fan spin-up times between 200 ms and 8 seconds. Bits <2:0> of Fan Characteristics Registers 1 and 2 (Register 0x20, 0x21) program the fan spin-up times.

–12–

REV. A

Page 13

Once the Automatic Fan Speed Control Loop parameters have been

LOCAL TEMPERATURE – ⴗC

PWM DUTY CYCLE – %

100

MIN

20 40 60

RANGE

= 40

ⴗ

MAX

= T

MIN

+ T

RANGE

chosen, the ADM1031 device may be programmed. The ADM1031 is placed into Automatic Fan Speed Control Mode by setting Bit 7 of Configuration Register 1 (Register 0x00). The device powers up in Automatic Fan Speed Control Mode by default. The control mode offers further flexibility in that the user can decide which temperature channel/channels control each fan.

Bits 6, 5 Control Operation (Config Register 1)

00 Remote Temp 1 Controls Fan 1. Remote Temp 2

01 Remote Temp 1 Controls Fans 1 and 2. 10 Remote Temp 2 Controls Fans 1 and 2. 11 Maximum Speed Calculated by Local and Remote

When Bits 5 and 6 of Config Register 1 are both set to 1, it offers increased flexibility. The local and remote temperature channels can have independently programmed control loops with different control parameters. Whichever control loop calculates the fastest fan speed based on the temperature being measured, drives the fans.

Figure 9 shows how the fan’s PWM duty cycle is determined by two independent control loops. This is the type of Auto Mode Fan Behavior seen when Bits 5 and 6 of Config Register 1 are set to 11. Figure 9a shows the control loop for the Local Temperature channel. Its T value is 40°C. The local temperature’s T Figure 9b shows the control loop for the Remote Temperature channel. Its T Therefore, the Remote Temperature’s T

Consider if both temperature channels measure 40°C. Both control loops will calculate a PWM duty cycle of 66%. Therefore, the fan will be driven at 66% duty cycle.

If both temperature channels measure 20°C, the local channel will calculate 33% PWM duty cycle, while the Remote 1 channel will calculate 50% PWM duty cycle. Thus, the fans will be driven at 50% PWM duty cycle. Consider the local temperature measuring 60°C while the Remote 1 temperature is measuring 70°C. The PWM duty cycle calculated by the local temperature control loop will be 100% (since the temperature = T calculated by the Remote 1 temperature control loop at 70°C will be approximately 90%. So the fan will run full-speed (100% duty cycle). Remember, that the fan speed will be based on the fastest speed calculated, and is not necessarily based on the highest temperature measured. Depending on the control loop parameters programmed, a lower temperature on one channel, may actually calculate a faster speed, than a higher temperature on the other channel.

REV. A

Table V. Fan Spin-Up Times

Spin-Up Time

Bits 2:0 (Fan Characteristics Registers 1, 2)

000 200 ms 001 400 ms 010 600 ms 011 800 ms 100 1 sec 101 2 secs (Default) 110 4 secs 111 8 secs

Table VI. Auto Mode Fan Behavior

Controls Fan 2.

Temperature Channels Controls Fans 1 and 2.

value has been programmed to 20°C, and its T

MIN

value has been set to 0°C, while its T

MIN

will thus be 60°C.

MAX

RANGE

value will be 80°C.

MAX

). The PWM duty cycle

MAX

RANGE

= 80°C.

ADM1031

100

PWM DUTY CYCLE – %

MIN

20 40 8070

REMOTE TEMPERATURE – ⴗC

b. Figure 9. Max Speed Calculated by Local and Remote Temperature Control Loops Drives Fan

PROGRAMMING THE AUTOMATIC FAN SPEED CONTROL LOOP

1. Program a value for T

2. Program a value for the slope T

3. T

MAX

= T

MIN

+ T

MIN

RANGE

4. Program a value for Fan Spin-up Time.

5. Program the desired Automatic Fan Speed Control Mode Behavior, i.e., which temperature channel controls the fan.

6. Select Automatic Fan Speed Control Mode by setting Bit 7 of Configuration Register 1.

OTHER CONTROL LOOP PARAMETERS

Having programmed all the above loop parameters, are there any other parameters to worry about?

was defined as the temperature at which the fan switched

MIN

on and ran at minimum speed. This minimum speed is 33% duty cycle by default. If the minimum PWM duty cycle is programmed to 33%, the fan control loops will operate as previously described.

–13–

RANGE

= 80

ⴗ

= T

MAX

MIN

+ T

RANGE

Page 14

ADM1031

It should be noted however, that changing the minimum PWM duty cycle affects the control loop behavior.

Slope 1 of Figure 10 shows T

set to 0°C and the T

MIN

RANGE

chosen is 40°C. In this case, the fan’s PWM duty cycle will vary over the range 33% to 100%. The fan will run full-speed at 40°C. If the minimum PWM duty cycle at which the fan runs at T

is changed,

MIN

its effect can be seen on Slopes 2 and 3. Take Case 2, where the minimum PWM duty cycle is reprogrammed from 33% (default) to 53%.

100

PWM DUTY CYCLE – %

MIN

16 28 40 600

TEMPERATURE – ⴗC

RANGE

= 40

ⴗ

Figure 10. Effect of Changing Minimum Duty Cycle on Control Loop with Fixed T

MIN

and T

RANGE

Values

The fan will actually reach full speed at a much lower temperature; 28°C. Case 3 shows that when the minimum PWM duty cycle was increased to 73%, the temperature at which the fan ran full speed was 16°C. So the effect of increasing the minimum PWM duty cycle, with a fixed T

MIN

reach full speed (T How can T

be calculated?

MAX

and fixed T

) at a lower temperature than T

MAX

, is that the fan will actually

RANGE

MIN

+ T

RANGE

In Automatic Fan Speed Control Mode, the register that holds the minimum PWM duty cycle at T

, is the Fan Speed Config

MIN

Register (Register 0x22). Table VII shows the relationship between the decimal values written to the Fan Speed Config Register and PWM duty cycle obtained.

Table VII. Programming PWM Duty Cycle

Decimal Value PWM Duty Cycle

00 0% 01 7% 02 14% 03 20% 04 27% 05 33% (Default) 06 40% 07 47% 08 53% 09 60% 10 (0x0A) 67% 11 (0x0B) 73% 12 (0x0C) 80% 13 (0x0D) 87% 14 (0x0E) 93% 15 (0x0F) 100%

The temperature at which the fan will run full-speed (100% duty cycle) is given by:

MAX

= T

+ ((Max DC – Min DC) × T

MIN

RANGE

/10)

where,

MAX

MIN

=Temperature at which fan runs full-speed.

=Temperature at which fan will turn on.

Max DC =Maximum Duty Cycle (100%) = 15 decimal.

Min DC =Duty Cycle at T

, programmed in to Fan Speed

MIN

Config Register (default = 33% = 5 decimal).

RANGE

=PWM Duty Cycle versus Temperature Slope.

Example 1

MIN

=0°C, T

RANGE

= 40°C

Min DC = 53% = 8 Decimal (Table VII)

Calculate T

MAX

+ ((Max DC – Min DC) × T

MIN

RANGE

=0 + ((100% DC – 53% DC) × 40/10)

=0 + ((15 – 8) × 4) = 28

=28ⴗC (As seen on Slope 2 of Figure 10)

/10)

Example 2

MIN

=0°C, T

RANGE

= 40°C

Min DC = 73% = 11 Decimal (Table VII)

Calculate T

MAX

+ ((Max DC – Min DC) × T

MIN

RANGE

=0 + ((100% DC – 73% DC) × 40/10)

=0 + ((15 – 11) × 4) = 16

=16ⴗC (As seen on Slope 3 of Figure 10)

/10)

Example 3

MIN

=0°C, T

RANGE

= 40°C

Min DC = 33% = 5 Decimal (Table VII)

Calculate T

MAX

+ ((Max DC – Min DC) × T

MIN

RANGE

=0 + ((100% DC – 33% DC) × 40/10)

=0 + ((15 – 5) × 4) = 40

=40ⴗC (As seen on Slope 1 of Figure 10)

/10)

In this case, since the Minimum Duty Cycle is the default 33%, the equation for T

MAX

reduces to:

MAX

+ ((Max DC – Min DC) × T

MIN

+ ((15 – 5) × T

MIN

+ (10 × T

MIN

+ T

MIN

RANGE

/10)

RANGE

/10)

–14–

REV. A

Page 15

ADM1031

RELEVANT REGISTERS FOR AUTOMATIC FAN SPEED CONTROL MODE Register 0x00 Configuration Register 1

<7> Logic 1 selects Automatic Fan Speed Control, Logic 0

selects software control (Default = 1).

<6:5> 00 = Remote Temp 1 controls Fan 1, Remote Temp 2

controls Fan 2. 01 = Remote Temp 1 controls Fans 1 and 2 10 = Remote Temp 2 controls Fans 1 and 2 11 = Fastest Calculated Speed controls Fans 1 and 2

Register 0x20, 0x21 Fan Characteristics Registers 1, 2

<2:0> Fan X Spin-Up Time

000 = 200 ms 001 = 400 ms 010 = 600 ms 011 = 800 ms 100 = 1 sec 101 = 2 secs (Default) 110 = 4 secs 111 = 8 secs

<5:3> PWM Frequency Driving the Fan

000 = 11.7 Hz 001 = 15.6 Hz 010 = 23.4 Hz 011 = 31.25 Hz (Default) 100 = 37.5 Hz 101 = 46.9 Hz 110 = 62.5 Hz 111 = 93.5 Hz

<7:6> Speed Range N; defines the lowest fan speed that can be

measured by the device. 00 = 1: Lowest Speed = 2647 RPM 01 = 2: Lowest Speed = 1324 RPM 10 = 4: Lowest Speed = 662 RPM 11 = 8: Lowest Speed = 331 RPM

Register 0x22 Fan Speed Configuration Register

<3:0> Min Speed: This nibble contains the speed at which the

fan will run when the temperature is at T

. The default is

MIN

0x05, meaning that the fan will run at 33% duty cycle when the temperature is at T

MIN

<7:4> Min Speed: Determines the minimum PWM cycle for

Fan 2 in Automatic Fan Speed Control Mode.

<7:3> Local Temperature T

MIN

MIN/TRANGE

. These bits set the temperature at which the fan will turn on when under Auto Fan Speed Control. T

can be programmed in 4°C increments.

MIN

00000 = 0°C 00001 = 4°C 00010 = 8°C 00011 = 12°C | | 01000 = 32°C (Default) | | 11110 = 120°C 11111 = 124°C

<2:0> Local Temperature T

. This nibble sets the tem-

RANGE

perature range over which Automatic Fan Speed Control takes place. 000 = 5°C 001 = 10°C 010 = 20°C 011 = 40°C 100 = 80°C

<7:3> Remote Temperature T

. Sets the temperature at

MIN

MIN/TRANGE

which the fan will switch on based on Remote X Temperature Readings. 00000 = 0°C 00001 = 4°C 00010 = 8°C 00011 = 12°C | |

01100 = 48°C | |

11110 = 120 11111 = 124

<2:0> Remote Temperature T

. This nibble sets the tem-

RANGE

perature range over which the fan will be controlled based on Remote Temperature readings. 000 = 5°C 001 = 10°C 010 = 20°C 011 = 40°C 100 = 80°C

REV. A

–15–

Page 16

ADM1031

FILTERED CONTROL MODE

The Automatic Fan Speed Control Loop reacts instantaneously to changes in temperature, i.e., the PWM duty cycle will respond immediately to temperature change. In certain circumstances, we may not want the PWM output to react instantaneously to temperature changes. If significant variations in temperature were found in a system, this would have the effect of changing the fan speed, which could be obvious to someone in close proximity. One way to improve the system’s acoustics would be to slow down the loop so that the fan ramps slowly to its newly calculated fan speed. This also ensures that temperature transients will effectively be ignored, and the fan’s operation will be smooth.

There are two means by which to apply filtering to the Automatic Fan Speed Control Loop. The first method is to ramp the fan speed at a predetermined rate, to its newly calculated value instead of jumping directly to the new fan speed. The second approach involves changing the on-chip ADC sample rate, to change the number of temperature readings taken per second.

The filtered mode on the ADM1031 is invoked by setting Bit 0 of the Fan Filter Register (Register 0x23) for Fan 1 and Bit 1 for Fan 2. Once the Fan Filter Register has been written to, and all other control loop parameters (T been programmed, the device may be placed into Automatic Fan Speed Control Mode by setting Bit 7 of Configuration Register 1 (Register 0x00) to 1.

Effect of Ramp Rate on Filtered Mode

Bits <6:5> of the Fan Filter Register determine the ramp rate in Filtered Mode. The PWM_OUT signal driving the fan will have a period, T, given by the PWM_OUT drive frequency, f, since T = 1/f. For a given PWM period, T, the PWM period is subdivided in to 240 equal time slots. One time slot corresponds to the smallest possible increment in PWM duty cycle. A PWM signal of 33% duty cycle will thus be high for 1/3 × 240 time slots and low for 2/3 × 240 time slots. Therefore, 33% PWM duty cycle corresponds to a signal which is high for 80 time slots and low for 160 time slots.

MIN

, T

RANGE

, etc.) have

READ

TEMPERATURE

CALCULATE

NEW PWM

DUTY CYCLE

DECREMENT

YES

PWM VALUE

BY RAMP

RATE

IS NEW

PWM VALUE >

VALUE?

INCREMENT

PREVIOUS PWM

VALUE BY RAMP

RATE

Figure 12. Filtered Mode Algorithm

The Filtered 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, the previous PWM duty cycle value is incremented by either 1, 2, 4, or 8 time slots (depending on the setting of bits <6:5> of the Fan Filter Register). If the new PWM duty cycle value is less than the previous PWM value, the previous PWM duty cycle is decremented by 1, 2, 4, or 8 time slots. Each time the PWM duty cycle is incremented or decremented, it is stored as the previous PWM duty cycle for the next comparison.

So what does an increase of 1, 2, 4, or 8 time slots actually mean in terms of PWM duty cycle?

A Ramp Rate of 1 corresponds to one time slot, which is 1/240 of the PWM period. In Filtered Auto Fan Speed Control Mode, incrementing or decrementing by 1 changes the PWM output duty cycle by 0.416%.

PWM_OUT 33% DUTY

CYCLE

80 TIME

SLOTS

160 TIME

PWM OUTPUT (ONE PERIOD) = 240 TIME SLOTS

SLOTS

Figure 11. 33% PWM Duty Cycle Represented in Time Slots

The ramp rates in Filtered Mode are selectable between 1, 2, 4, and 8. The ramp rates are actually discrete time slots. For example, if the ramp rate = 8, then eight time slots will be added to the PWM_OUT high duty cycle each time the PWM_OUT duty cycle needs to be increased. Figure 12 shows how the Filtered Mode algorithm operates.

–16–

Table VIII. Effect of Ramp Rates on PWM_OUT

Ramp Rate PWM Duty Cycle Change

1 0.416% 2 0.833% 4 1.66% 8 3.33%

So programming a ramp rate of 1, 2, 4, or 8 simply increases or decreases the PWM duty cycle by the amounts shown in Table VIII, depending on whether the temperature is increasing or decreasing.

Figure 13 shows remote temperature plotted against PWM duty cycle for Filtered Mode. The ADC sample rate is the highest sample rate; 11.25 kHz. The ramp rate is set to 8 which would correspond to the fastest ramp rate. With these settings it took approximately 12 seconds to go from 0% duty cycle to 100% duty cycle (full-speed). The T

value = 32°C and the T

MIN

RANGE

= 80°C. It can be seen that even though the temperature increased very rapidly, the fan gradually ramps up to full speed.

REV. A

Page 17

ADM1031

ⴗ

TIME – s

0 112

120

140

110

120

100

PWM DUTY CYCLE – %

TEMP

– ⴗC

TEMP

PWM DUTY CYCLE

140

120

100

ⴗ

–

TEMP

012

Figure 13. Filtered Mode with Ramp Rate = 8

Figure 14 shows how changing the ramp rate from 8 to 4 affects the control loop. The overall response of the fan is slower. Since the ramp rate is reduced, it takes longer for the fan to achieve full running speed. In this case, it took approximately 22 seconds for the fan to reach full speed.

120

110

ⴗ

–

TEMP

022

TEMP

Figure 14. Filtered Mode with Ramp Rate = 4

Figure 15 shows the PWM output response for a ramp rate of

2. In this instance the fan took about 54 seconds to reach full running speed.

140

120

100

–

TEMP

054

Figure 15. Filtered Mode with Ramp Rate = 2

REV. A

TEMP

PWM DUTY CYCLE

TIME – s

PWM DUTY CYCLE

TIME – s

PWM DUTY CYCLE

TIME – s

120

100

PWM DUTY CYCLE – %

140

120

100

PWM DUTY CYCLE – %

120

100

PWM DUTY CYCLE – %

–17–

Finally, Figure 16 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 took 112 seconds for the fan to reach full speed.

Figure 16. Filtered Mode with Ramp Rate = 1

As can be seen from Figures 13 through 16, the rate at which the fan will react to temperature change is dependent on the ramp rate selected in the Fan Filter Register. The higher the ramp rate, the faster the fan will reach the newly calculated fan speed.

Figure 17 shows the behavior of the PWM output as temperature varies. As the temperature is rising, the fan speed will ramp up. Small drops in temperature will not affect the ramp-up function since the newly calculated fan speed will still be higher than the previous PWM value. The Filtered Mode allows the PWM output to be made less sensitive to temperature variations. This will be dependent on the ramp rate selected and the ADC sample rate programmed into the Fan Filter Register.

90 90

80 80

70 70

60 60

50 50

40 40

30 30

PWM DUTY CYCLE – %

20 20

10 10

PWM DUTY CYCLE

TEMP

TIME – s

ⴗ

–

TEMP

Figure 17. How Fan Reacts to Temperature Variation in Filtered Mode

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ADM1031

Effect of ADC Sample Rate on Filtered Mode

The second means by which to change the Filtered Mode characteristics is to adjust the ADC sample rate. The faster the ADC sample rate, the more temperature samples are obtained per second. One way to apply filtering to the control loop is to slow down the ADC sampling rate. This means that the number of iterations of the Filtered Mode algorithm per second is effectively reduced. If the number of temperature measurements per second is reduced, how often the PWM_OUT signal controlling the fan is updated is also reduced.

Bits <4:2> of the Fan Filter Register (Reg 0x23) set the ADC sample rate. The default ADC sample rate is 1.4 kHz. The ADC sample rate is selectable from 87.5 Hz to 11.2 kHz. Table IX shows how many temperature samples are obtained per second, for each of the ADC sample rates.

Table IX. Temperature Updates per Second

ADC Sample Rate Temperature Updates/Sec

87.5 Hz 0.0625 175 Hz 0.125 350 Hz 0.25 700 Hz 0.5

1.4 kHz 1 (Default)

2.8 kHz 2

5.6 kHz 4

11.2 kHz 8

RELEVANT REGISTERS FOR FILTERED AUTOMATIC FAN SPEED CONTROL MODE

In addition to the registers used to program the normal Automatic Fan Speed Control Mode, the following register needs to be programmed.

Register 0x23 Fan Filter Register

<7> Spin-up Disable :- when this bit is set to 1, fan spin-up

is disabled. (Default = 0)

<6:5> Ramp Rate: these bits set the ramp rate for filtered mode.

00 = 1 (0.416% Duty Cycle Change) 01 = 2 (0.833% Duty Cycle Change) 10 = 4 (1.66% Duty Cycle Change) 11 = 8 (3.33% Duty Cycle Change)

<4:2> ADC Sample Rate

000 = 87.5 Hz 001 = 175 Hz 010 = 350 Hz 011 = 700 Hz 100 = 1.4 kHz (Default) 101 = 2.8 kHz 110 = 5.6 kHz 111 = 11.2 kHz

<1> Fan 2 Filter Enable: when this bit is set to 1, it enables

filtering on Fan 2. Default = 0.

<0> Fan 1 Filter Enable: when this bit is set to 1, it enables

filtering on Fan 1. Default = 0.

PROGRAMMING THE FILTERED AUTOMATIC FAN SPEED CONTROL LOOP

1. Program a value for T

2. Program a value for the slope T

3. T

MAX

= T

MIN

+ T

MIN

RANGE

4. Program a value for Fan Spin-up Time.

5. Program the desired Automatic Fan Speed Control Mode Behavior, i.e., which temperature channel controls the fan.

6. Program a ramp rate for the filtered mode.

7. Program the ADC sample rate in the Fan Filter Register.

8. Set Bit 0 to enable fan filtered mode for Fan 1.

9. Set Bit 1 to enable the fan filtered mode for Fan 2.

10. Select Automatic Fan Speed Control Mode by setting Bit 7 of Configuration Register 1.

PWM DUTY CYCLE SELECT MODE

The ADM1031 may be operated under software control by clearing Bit 7 of Configuration Register 1 (Register 0x00). This allows the user to directly control PWM duty cycle for each fan.

Clearing Bits 5, 6 of Configuration Register 1 allows fan control by varying PWM duty cycle. Values of duty cycle between 0% to 100% may be written to the Fan Speed Config Register (0x22) to control the speed of each fan. Table X shows the relationship between hex values written to the Fan Speed Configuration Register and PWM duty cycle obtained.

Table X. PWM Duty Cycle Select Mode

Hex Value PWM Duty Cycle

00 0% 01 7% 02 14% 03 20% 04 27% 05 33% 06 40% 07 47% 08 53% 09 60% 0A 67% 0B 73% 0C 80% 0D 87% 0E 93% 0F 100%

Bits <3:0> set the PWM duty cycle for Fan 1; Bits <7:4> set the PWM duty cycle for Fan 2.

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ADM1031

RPM FEEDBACK MODE

The second method of fan speed control under software is RPM Feedback Mode. This involves programming the desired fan RPM value to the device to set fan speed. The advantages include a very tightly maintained fan RPM over the fan’s life, and virtually no acoustic pollution due to fan speed variation.

Fans typically have manufacturing tolerances of ±20%, meaning a wide variation in speed for a typical batch of identical fan models. If it is required that all fans run at exactly 5000 RPM, it may be necessary to specify fans with a nominal fan speed of 6250 RPM. However, many of these fans will run too fast and make excess noise. A fan with nominal speed of 6250 RPM could run as fast as 7000 RPM at 100% PWM duty cycle. RPM Mode will allow all of these fans to be programmed to run at the desired RPM value.

Clearing Bit 7 of Configuration Register 1 (Reg 0x00) to 0 places the ADM1031 under software control. Once under software control, the device may be placed in to RPM Feedback Mode by writing to Bits 5, 6 of Configuration Register 1. Writing a 1 to Bits 5, 6 selects RPM Feedback Mode for each fan. Once RPM Feedback Mode has been selected, the required fan RPM may be written to the Fan Tach High Limit Registers (0x10, 0x11). The RPM Feedback Mode function allows a fan RPM value to be programmed into the device, and the ADM1031 will maintain the selected RPM value by monitoring the fan tach and speeding up the fan as necessary, should the fan start to slow down. Conversely, should the fan start to speed up due to aging, the RPM feedback will slow the fan down to maintain the correct RPM speed. The value to be programmed into each Fan Tach High Limit Register is given by:

Count = (f × 60)/R × N

where:

f = 11.25 kHz

R = desired RPM value

N = Speed Range; MUST be set to 2

The speed range, N, really determines what the slowest fan speed measured can be before generating an interrupt. The slowest fan speed will be measured when the Count value reaches 255.

Since speed range, N, = 2,

Count = (f × 60)/R × N

R = (f × 60)/Count × N

R = (11250 × 60)/255 × 2

R = (675000)/510

R = 1324 RPM, fan fail detect speed.

Programming RPM Values in RPM Feedback Mode

Rather than writing a value such as 5000 to a 16-bit register, an 8-bit count value is programmed instead. The count to be programmed is given by:

Count = (f × 60)/R × N

where:

f = 11.25 kHz

R = desired RPM value

N = Speed Range = 2

Example 1:

If the desired value for RPM Feedback Mode is 5000 RPM, what value needs to be programmed for Count?

Count = (f × 60)/R × N

Since the desired RPM value, R, is 5000 RPM, the value for Count is:

N = 2:

Count = (11250 × 60)/5000 × 2

Count = 675000/10000

Count = 67 (assumes 2 tach pulses/rev).

Example 2:

If the desired value for RPM Feedback Mode is 3650 RPM, what value needs to be programmed for Count?

Count = (f × 60)/R × N

Since the desired RPM value, R, is 3650 RPM, the value for Count is:

N = 2:

Count = (11250 × 60)/3650 × 2

Count = 675000/7300

Count = 92 (assumes 2 tach pulses/rev).

Once the count value has been calculated, it should be written to the Fan Tach High Limit Register. It should be noted that in RPM Feedback Mode, there is no high limit register for underspeed detection that can be programmed as there are in the other fan speed control modes. The only time each fan will indicate a fan failure condition is whenever the count reaches

255. Since the speed range, N, = 2, the fan will fail if its speed drops below 1324 RPM.

Programming RPM Values

1. Choose the RPM value to be programmed.

2. Set speed range value, N, = 2.

3. Calculate count value based on RPM and speed range values chosen. Use Count Equation to calculate Count Value.

4. Clear Bit 7 of Configuration Register 1 (Reg. 0x00) to place the ADM1031 under software control.

5. Write a 1 to Bit 5 of Configuration Register 1 to place the device in RPM Feedback Mode.

6. Write the calculated Count value to the Fan Tach High Limit Register (Reg. 0x10). The fan speed will now go to the desired RPM value and maintain that fan speed.

RPM Feedback Mode Limitations

RPM feedback mode only controls Fan RPM over a limited fan speed range of about 75% to 100%. However, this should be enough range to overcome fan manufacturing tolerance. In practice, however, the program must not function at too low an RPM value for the fan to run at, or the RPM Mode will not operate.

To find the lowest RPM value allowed for a given fan, do the following:

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ADM1031

1. Run the fan at 53% PWM duty cycle in Software Mode. Clear Bits 5 and 7 of Configuration Register 1 (Reg 0x00) to enter PWM duty cycle mode. Write 0x08 to the Fan Speed Config Register (Reg 0x22) to set the PWM output to 53% duty cycle.

2. Measure the fan RPM. This represents the fan RPM below which the RPM mode will fail to operate. Do NOT program a lower RPM than this value when using RPM Feedback mode.

3. Ensure that Speed Range, N, = 2 when using RPM Feedback mode.

Fans come in a variety of different options. One distinguishing feature of fans is the number of poles that a fan has internally. The most common fans available have four, six, or eight poles. The number of poles the fan has generally affects the number of pulses per revolution the fan outputs.

If the ADM1031 is used to drive fans other than 4-pole fans that output 2 tach pulses/revolution, then the fan speed measurement equation needs to be adjusted to calculate and display the correct fan speed, and also to program the correct count value in RPM Feedback Mode.

FAN SPEED MEASUREMENT EQUATIONS

For a 4-pole fan (2 tach pulses/rev):

Fan RPM = (f × 60)/Count × N

For a 6-pole fan (3 tach pulses/rev):

Fan RPM = (f × 60)/(Count × N × 1.5)

For an 8-pole fan (4 tach pulses/rev):

Fan RPM = (f × 60)/(Count × N × 2)

If in doubt as to the number of poles the fans used have, or the number of tach output pulses/rev, consult the fan manufacturer’s data sheet, or contact the fan vendor for more information.

FAN DRIVE USING PWM CONTROL

The external circuitry required to drive a fan using PWM control is extremely simple. A single NMOS FET is the only drive transistor required. The specifications of the MOSFET depend on the maximum current required by the fan being driven. Typical notebook fans draw a nominal 170 mA, and so SOT devices can be used where board space is a constraint. If driving several fans in parallel from a single PWM output, or driving larger server fans, the MOSFET will need to handle the higher current requirements. The only other stipulation is that the MOSFET should have a gate voltage drive, V

< 3.3 V, for

direct interfacing to the PWM_OUT pin. The MOSFET should also have a low on-resistance to ensure that there is not significant voltage drop across the FET. This would reduce the maximum operating speed of the fan.

Figure 18 shows how a 3-wire fan may be driven using PWM control.

TACH/AIN

ADM1031

PWM_OUT

3.3V

10k⍀ TYPICAL

TACH

5V OR 12V FAN

Q1 NDT3055L

Figure 18. Interfacing the ADM1031 to a 3-Wire Fan

The NDT3055L n-type MOSFET was chosen since it has 3.3 V gate drive, low on-resistance, and can handle 3.5 A of current. Other MOSFETs may be substituted based on the system’s fan drive requirements.

5V OR 12V FAN

Q1 NDT3055L

SENSE

(2⍀ TYPICAL)

PWM_OUT

ADM1031

TACH/AIN

3.3V

10k⍀ TYPICAL

0.01␮F

TACH

Figure 19. Interfacing the ADM1031 to a 2-Wire Fan

Figure 19 shows how a 2-wire fan may be connected to the ADM1031. This circuit allows the speed of the 2-wire fan to be measured even though the fan has no dedicated Tach signal. A series R

resistor in the fan circuit converts the fan commu-

SENSE

tation pulses into a voltage. This is ac-coupled into the ADM1031 through the 0.01 µF capacitor. On-chip signal conditioning allows accurate monitoring of fan speed. For typical notebook fans drawing approximately 170 mA, a 2 Ω R

SENSE

value is suitable. For fans such as desktop or server fans that draw more current, R

may be reduced. The smaller R

SENSE

is, the better, since more voltage will be developed across the fan, and the fan will spin faster. Figure 20 shows a typical plot of the sensing waveform at the TACH/AIN pin. The most important thing is that the negative-going spikes are more than 250 mV in amplitude. This will be the case for most fans when R = 2 Ω. The value of R

can be reduced as long as the volt-

SENSE

age spikes at the TACH/AIN pin are greater than 250 mV. This allows fan speed to be reliably determined.

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CLOCK

CONFIG 2

REG. BIT 2

FAN

INPUT

ADM1031

Figure 20. Fan Speed Sensing Waveform at TACH/AIN Pin

FAN SPEED MEASUREMENT

The fan counter does not count the fan tach output pulses directly, because the fan speed may be less than 1000 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 11.25 kHz oscillator into the input of an 8-bit counter. The fan speed measuring circuit is initialized on the rising edge of a PWM high output if fan speed measurement is enabled (Bit 2, 3 of Configuration Register 2 = 1). It then starts counting on the rising edge of the second tach pulse and counts for two fan tach periods, until the rising edge of the fourth tach pulse, or until the counter overranges if the fan tach period is too long. The measurement cycle will repeat until monitoring is disabled. The fan speed measurement is stored in the Fan Speed Reading register at address 0x08, 0x09.

The fan speed count is given by:

Count = (f × 60)/R × N

where:

f = 11.25 kHz

R =Fan Speed in RPM.

N = Speed Range (Either 1, 2, 4, or 8)

The frequency of the oscillator can be adjusted to suit the expected running speed of the fan by varying N, the Speed Range. The oscillator frequency is set by Bits 7 and 6 of Fan Characteristics Registers 1, 2 (0x20, 0x21) as shown in Table XI. Figure 21 shows how the fan measurements relate to the PWM_OUT pulse trains.

Table XI. Oscillator Frequencies

Oscillator

Bit 7 Bit 6 N Frequency (kHz)

0 0 1 11.25 0 1 2 5.625 1 0 4 2.812 1 1 8 1.406

START OF

MONITORING

CYCLE

FAN MEASUREMENT PERIOD

Figure 21. Fan Speed Measurement

In situations where different output drive circuits are used for fan drive, it may be desirable to invert the PWM drive signal. Setting Bit 3 of Configuration Register 1 (0x00) to 1, inverts the PWM_OUT signal. This makes the PWM_OUT pin high for 100% duty cycle. Bit 3 of Configuration Register 1 should generally be set to 1, when using an n-MOS device to drive the fan. If using a p-MOS device, Bit 3 of Configuration Register 1 should be cleared to 0.

FAN FAULTS

The FAN_FAULT output (Pin 8) is an active-low, open-drain output used to signal fan failure to the system processor. Writing a Logic 1 to Bit 4 of Configuration Register 1 (0x00) enables the FAN_FAULT output pin. The FAN_FAULT output is enabled by default. The FAN_FAULT output asserts low only when five consecutive interrupts are generated by the ADM1031 device due to the fan running underspeed, or if the fan is completely stalled. Note that the Fan Tach High Limit must be exceeded by at least one before a FAN_FAULT can be generated. For example, if we are only interested in getting a FAN_FAULT if the fan stalls, then the fan speed value will be 0xFF for a failed fan. Therefore, we should make the Fan Tach High Limit = 0xFE to allow FAN_FAULT to be asserted after five consecutive fan tach failures.

Figure 22 shows the relationship between INT, FAN_FAULT, and the PWM drive channel. The PWM_OUT channel is driving a fan at some PWM duty cycle, say 50%, and the fan’s tach signal (or fan current for a 2-wire fan) is being monitored at the TACH/AIN pin. Tach pulses are being generated by the fan, during the high time of the PWM duty cycle train. The tach is pulled high during the off time of the PWM train because the fan is connected high-side to the n-MOS device.

Suppose the fan has twice previously failed its fan speed measurement. Looking at Figure 22, PWM_OUT is brought high for two seconds, to restart the fan if it has stalled. Sometime later a third tach failure occurs. This is evident by the tach signal being low during the high time of the PWM pulse, causing the Fan Speed Reading register to reach its maximum count of 255. Since the tach limit has been exceeded, an interrupt is generated on the INT pin. The Fan Fault bit (Bit 1) of Interrupt Status Register 1 (Register 0x02) will also be asserted. Once the processor has acknowledged the INT by reading the status register, the INT is cleared. PWM_OUT is then brought high for another two seconds to restart the fan. Subsequent fan failures cause INT to be reasserted and the PWM_OUT signal is brought high for two seconds (fan spin-up default) each time to restart the fan. Once the fifth tach failure occurs, the failure is deemed to be catastrophic and the FAN_FAULT pin is asserted low. PWM_OUT is brought high to attempt to restart the fan.

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ADM1031

The INT pin will continue to generate interrupts after the assertion of FAN_FAULT since tach measurement continues even after fan failure. Should the fan recover from its failure condition, the FAN_FAULT signal will be negated, and the fan will return to its normal operating speed.

PWM_OUT

TACH/AIN

INT

FAN_FAULT

FAN2

2-WIRE

FAN

NDT3055L

(N-MOS)

SENSE

2 SECS

3RD TACH

FAILURE

Figure 22. Operation of

5V MAX

(DO NOT CONNECT

TO 12V)

10kV

TYP

TACH

NDT3055L

(NMO S)

0.01mF

THERM

SIGNAL TO

THROTTLE

CPU CLOCK

FAN_FAULT

TO SIGNAL

FAN FAILURE

CONDITION

3.3V

10kV TYP

3.3V

10kV TYP

3.3V

10kV TYP

*IN ACTUAL APPLICATION, BOTH FANS MUST BE 2-WIRE OR 3-WIRE TYPE. A SINGLE BIT

CONTROLS WHETHER TACH1/ AIN1 AND TACH2 /AIN2 ARE ANALOG OR DIGITAL INPUTS.

FAN1* 3-WIRE FAN

3.3V

10kV TYP

2 SECS

PWM_OUT

TACH1/AIN

PWM_OUT2

TACH2/AIN2

GND

3.3V

THERM

FAN_FAULT

STATUS REG READ TO

CLEAR INTERRUPT

FAN_FAULT

Figure 23. Typical Application Circuit

Figure 23 shows a typical application circuit for the ADM1031. Temperature monitoring can be based around a CPU diode or discrete transistor measuring thermal hotspots. Either 2- or 3-wire fans may be monitored by the ADM1031, as shown.

FULL SPEED

CONTINUING

TACH FAILURE

4TH TACH

FAILURE

2 SECS

5TH TACH

FAILURE

and Interrupt Pins

3.3V

ADM1031

2.2kV

SCL

SDA

INT (SMBALERT)

ADD

D2+

D2–

D1+

D1–/NTI

2.2kV

3.3V

10kV TYP

SCL

SDA

CPU INTERRUPT

2N3904 OR PENTIUM III CPU THERMAL DIODE

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ADM1031

Table XII. Registers

Address A7–A0

Value Registers 0x08–0x1E See Table XIII. Device ID Register 0x3D This location contains the device identification number. Since this

device is the ADM1031, this register contains 0x31. This register is read only.

Company ID 0x3E This location contains the company identification number (0x41).

This register is read only.

THERM Behavior/Revision 0x3F This location contains the revision number of the device. The lower

four bits reflect device revisions [3:0]. Bit 7 of this register is the THERM-to-fan enable bit. See Table XXII.

Configuration Register 1 0x00 See Table XIV. Power-on value = 1001 0000. Configuration Register 2 0x01 See Table XV. Power-on value = 0111 1111. Status Register 1 0x02 See Table XVI. Power-on value = 0000 0000. Status Register 2 0x03 See Table XVII. Power-on value = 0000 0000. Manufacturer’s Test Register 0x07 This register is used by the manufacturer for test purposes only. This

Fan Characteristics Register 1 0x20 See Table XIX. Power-on value = 0101 1101. Fan Characteristics Register 2 0x21 See Table XX. Power-on value = 0101 1101. Fan Speed Configuration Register 0x22 See Table XXI. Power-on value = 0101 0101. Fan Filter Register 0x23 See Table XXII. Power-on value = 0101 0000. Local Temperature T

MIN/TRANGE

Remote 1 Temperature T Remote 2 Temperature T

MIN/TRANGE

0x24 See Table XXIII. Power-on value = 0100 0001. 0x25 See Table XXIV. Power-on value = 0110 0001. 0x26 See Table XXV. Power-on value = 0110 0001.

Table XIII. Value Registers

Address Read/Write Description

0x06 Read/Only Extended Temperature Resolution (see Table XVIII). 0x08 Read/Write Fan 1 Speed—this register contains the value of the Fan 1 tach measurement. 0x09 Read/Write Fan 2 Speed—this register contains the value of the Fan 2 tach measurement. 0x0A Read/Only Local Temperature Value—this register contains the 8 MSBs of the local temperature measurement. 0x0B Read/Only Remote 1 Temperature Value—this register contains the 8 MSBs of the Remote 1 temperature reading. 0x0C Read/Only Remote 2 Temperature Value—this register contains the 8 MSBs of the Remote 2 temperature reading. 0x0D Read/Write Local Temperature Offset—See Table XXVII. (Power-On Default = 00h.) 0x0E Read/Write Remote 1 Temperature Offset—See Table XXVIII. (Power-On Default = 00h.) 0x0F Read/Write Remote 2 Temperature Offset—See Table XXIX. (Power-On Default = 00h.) 0x10 Read/Write Fan 1 Tach High Limit—this register contains the limit for the Fan 1 tach measurement. Since the

tach circuit counts between pulses, a slow fan will result in a large measured value, so exceeding the limit is the way to detect a slow or stalled fan. (Power-On Default = FFh.)

0x11 Read/Write Fan 2 Tach High Limit—this register contains the limit for the Fan 2 tach measurement. Since the

tach circuit counts between pulses, a slow fan will result in a large measured value, so exceeding the

limit is the way to detect a slow or stalled fan. (Power-On Default = FFh.) 0x14 Read/Write Local Temperature High Limit (Power-On Default 60°C). 0x15 Read/Write Local Temperature Low Limit (Power-On Default 0°C). 0x16 Read/Write Local Temperature Therm Limit (Power-On Default 70°C). 0x18 Read/Write Remote 1 Temperature High Limit (Power-On Default 80°C). 0x19 Read/Write Remote 1 Temperature Low Limit (Power-On Default 0°C). 0x1A Read/Write Remote 1 Temperature Therm Limit (Power-On Default 100°C). 0x1C Read/Write Remote 2 Temperature High Limit (Power-On Default 80°C). 0x1D Read/Write Remote 2 Temperature Low Limit (Power-On Default 0°C). 0x1E Read/Write Remote 2 Temperature Therm Limit (Power-On Default 100°C).

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ADM1031

Table XIV. Register 0x00 Configuration Register 1 Power-On Default 90h

Bit Name R/W Description

0 MONITOR Read/Write Setting this bit to a “1” enables monitoring of temperature and enables measurement of

the fan tach signals. (Power-Up Default = 0.)

1 INT Enable Read/Write Setting this bit to a “1” enables the INT output.

1 = Enabled 0 = Disabled (Power-Up Default = 0.)

2 TACH/AIN Read/Write Clearing this bit to “0” selects digital fan speed measurement via the TACH pins. Setting

this bit to “1” configures the TACH pins as analog inputs that can measure the speed of 2-wire fans via a sense resistor. (Power-Up Default = 0.)

3 PWM Invert Read/Write Setting this bit to “1” inverts the PWM signal on the output pins. (Power-Up Default = 0.) 4Fan Fault Enable Read/Write Logic 1 enables FAN_FAULT pin; Logic 0 disables FAN_FAULT output. (Power-Up

Default = 1.)

6–5 PWM Mode Read/Write These two bits control the behavior of the fans in Auto Fan Speed Control Mode.

00 = Remote Temp 1 controls Fan 1; Remote Temp 2 controls Fan 2. 01 = Remote Temp 1 controls Fan 1 and Fan 2. 10 = Remote Temp 2 controls Fan 1 and Fan 2. 11 = Max of Local Temp and Remote Temp 1 and 2 drives Fans 1 and 2.

These two bits have the following effect in Software Control Mode.

00 = Program PWM duty cycles for Fans 1 and 2. 11 = Program RPM Speeds for Fans 1 and 2.

7Auto/SW Ctrl Read/Write Logic 1 selects Automatic Fan Speed Control; Logic 0 selects SW control. (Power-Up

Default = 1) When under software control, PWM duty cycle or RPM values may be programmed for each fan.

Table XV. Register 0x01 Configuration 2 Power-On Default = 7FH

Bit Name R/W Description

0 PWM 1 En Read/Write Enables Fan 1 PWM output when this bit is a “1.” 1 PWM 2 En Read/Write Enables Fan 2 PWM output when this bit is a “1.” 2 TACH 1 En Read/Write Enables Tach 1 input when set to “1.” 3 TACH 2 En Read/Write Enables Tach 2 input when set to “1.” 4Loc Temp En Read/Write Enables Interrupts on Local Temperature Channel when set to “1.” 5Remote 1 Temp En Read/Write Enables Interrupts on Remote 1 Channel when set to “1.” Default is normally

enabled, except when a diode fault is detected on power-up.

6Remote 2 Temp En Read/Write Enables Interrupts on Remote 2 Channel when set to “1.” Default is normally

enabled, except when a diode fault is detected on power-up.

7SW Reset Read/Write When set to “1,” resets the device. Self-clears. Power-Up Default = 0.

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ADM1031

Table XVI. Register 0x02 Status Register 1 Power-On Default = 00H

Bit Name R/W Description

0Alarm 1 Speed Read Only This bit is set to “1” when fan is running at alarm speed. Once read, this bit

will not reassert on next monitoring cycle, even if the fan is still running at

alarm speed. 1Fan 1 Fault Read Only This bit is set to “1” if Fan 1 becomes stuck or is running under speed. 2Remote 1 High Read Only “1” indicates Remote 1 high temperature limit has been exceeded. If the

temperature is still outside the Remote 1 Temp High Limit, this bit will reas-

sert on next monitoring cycle. 3Remote 1 Low Read Only “1” indicates Remote 1 low temperature limit exceeded (below). If the tem-

perature is still outside the Remote 1 Temp Low Limit, this bit will reassert

on next monitoring cycle. 4Remote 1 Therm Read Only “1” indicates Remote 1 temperature Therm limit has been exceeded. This bit

is cleared on a read of Status Register 1. 5Remote Diode 1 Error Read Only This bit is set to “1” if a short or open is detected on the Remote 1 tempera-

ture channel. This test is only done on power-up, and if set to 1 cannot be

cleared by reading the Status Register 1. 6Local Temp High Read Only “1” indicates Local Temp High Limit has been exceeded. If the temperature

is still outside the Local Temp High Limit, this bit will reassert on next

monitoring cycle. 7Local Temp Low Read Only “1” indicates Local Temp Low Limit has been exceeded (below). If the tem-

perature is still outside the Local Temp Low Limit, this bit will reassert on

next monitoring cycle.

Table XVII. Register 0x03 Status Register 2 Power-Up Default = 00H

Bit Name R/W Description

0Alarm 2 Speed Read Only This bit is set to “1” when Fan 2 is running at alarm speed. Once read, this

bit will not reassert on next monitoring cycle, even if the fan is still running at

alarm speed. 1Fan 2 Fault Read Only This bit is set to “1” if Fan 2 becomes stuck or is running under speed. 2Remote 2 High Read Only “1” indicates Remote 2 high temperature limit has been exceeded. If the

temperature is still outside the Remote 2 Temp High Limit, this bit will reas-

sert on the next monitoring cycle. 3Remote 2 Low Read Only “1” indicates Remote 2 low temperature limit exceeded (below). If the tem-

perature is still outside the Remote 2 Temp Low Limit, this bit will reassert

on the next monitoring cycle. 4Remote 2 Therm Read Only “1” indicates Remote 2 temperature Therm limit has been exceeded. This bit

is cleared on reading Status Register 2. 5Remote Diode 2 Error Read Only This bit is set to “1” if a short or open is detected on the Remote 2 tempera-

ture channel. This test is only done on power-up, and if set to 1 cannot be

cleared by reading Status Register 2. 6Local Therm Read Only “1” indicates Local temperature Therm limit has been exceeded. This bit

clears on a read of Status Register 2. 7 THERM Read Only Set to “1” when THERM is pulled low as an input. This bit clears on a read

of Status Register 2.

Table XVIII. Register 0x06 Extended Temperature Resolution Power-On Default = 00H

Bit Name R/W Description

<2:0> Remote Temp 1 Read Only Holds extended temperature resolution bits for Remote 1 channel. <5:3> Remote Temp 2 Read Only Holds extended temperature resolution bits for Remote 2 channel. <7:6> Local Temp Read Only Holds extended temperature resolution bits for Local Temperature channel.

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ADM1031

Table XIX. Register 0x20 Fan Characteristics Register 1 Power-On Default = 5DH

Bit Name R/W Description

<2:0> Fan 1 Spin-up Read/Write These bits contain the Fan Spin-up time to allow Fan 1 to overcome its own

inertia. 000 = 200 ms 001 = 400 ms 010 = 600 ms 011 = 800 ms 100 = 1 sec 101 = 2 secs (Default) 110 = 4 secs 111 = 8 secs

<5:3> PWM 1 Frequency Read/Write These bits allow programmability of the nominal PWM 1 output frequency

driving Fan 1. (Default = 31 Hz.) 000 = 11.7 Hz 001 = 15.6 Hz 010 = 23.4 Hz 011 = 31.25 Hz (Default) 100 = 37.5 Hz 101 = 46.9 Hz 110 = 62.5 Hz 111 = 93.5 Hz

<7:6> Speed Range, N Read/Write Speed Range

00 = 1 01 = 2 10 = 4 11 = 8

Table XX. Register 0x21 Fan Characteristics Register 2 Power-On Default = 5DH

Bit Name R/W Description

<2:0> Fan 2 Spin-up Read/Write These bits contain the Fan Spin-up time to allow Fan 2 to overcome its own

inertia. 000 = 200 ms 001 = 400 ms 010 = 600 ms 011 = 800 ms 100 = 1 sec 101 = 2 secs (Default) 110 = 4 secs 111 = 8 secs

<5:3> PWM 2 Frequency Read/Write These bits allow programmability of the nominal PWM 2 output frequency

driving Fan 2. (Default = 31 Hz.) 000 = 11.7 Hz 001 = 15.6 Hz 010 = 23.4 Hz 011 = 31.25 Hz (Default) 100 = 37.5 Hz 101 = 46.9 Hz 110 = 62.5 Hz 111 = 93.5 Hz

<7:6> Speed Range, N Read/Write Speed Range

00 = 1 01 = 2 10 = 4 11 = 8

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Table XXI. Register 0x22 Fan Speed Config Register Power-On Default = 55H

Bit Name R/W Description

<3:0> Normal/Min Spd 1 Read/Write This nibble contains the normal speed value for Fan 1. When in Automatic

Fan Speed Control Mode, this nibble contains the minimum speed at which

Fan 1 will run. Default is 0x05 for 33% PWM duty cycle. <7:4> Normal/Min Spd 2 Read/Write This nibble contains the normal speed value for Fan 2. When in Automatic

Fan Speed Control Mode, this nibble contains the minimum speed at which

Fan 2 will run. Default is 0x05 for 33% PWM duty cycle.

Table XXII. Register 0x23 Fan Filter Register Power-On Default = 50H

Bit Name R/W Description

<7> Spin-Up Disable Read/Write When set to 1, disables fan spin-up. <6:5> Ramp Rate Read/Write These bits set the ramp rate.

00 = 1

01 = 2

10 = 4 (Default)

11 = 8 <4:2> ADC Sample Rate Read/Write These bits set the sampling rate for the ADC.

000 = 87.5 Hz

001 = 175 Hz

010 = 350 Hz

011 = 700 Hz

100 = 1.4 kHz (Default)

101 = 2.8 kHz

110 = 5.6 kHz

111 = 11.2 kHz <1> Fan 2 Filter En Read/Write This bit enables fan filtering for Fan 2. <0> Fan1 Filter En Read/Write This bit enables fan filtering for Fan 1.

Table XXIII. Register 0x24 Local Temp T

Bit Name R/W Description

<7:3> Local Temp T

MIN

Read/Write Contains the minimum temperature value for Automatic Fan Speed Control

based on Local Temperature Readings. T

values only in 4°C increments. Default is 32°C.

00000 = 0°C

00001 = 4°C

00010 = 8°C

00011 = 12°C

01000 = 32°C (Default)

11110 = 120°C

11111 = 124°C <2:0> Local Temp T

RANGE

Read/Write This nibble contains the temperature range value for Automatic Fan Speed

Control based on the Local Temp Readings.

000 = 5°C

001 = 10°C (Default)

010 = 20°C

011 = 40°C

100 = 80°C

MIN/TRANGE

Power-On Default = 41H

can be programmed to positive

MIN

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ADM1031

Table XXIV. Register 0x25 Remote 1 Temp T

Bit Name R/W Description

<7:3> Remote 1 Temp T

MIN

Read/Write Contains the minimum temperature value for Automatic Fan Speed Control

based on Remote 1 Temperature Readings. T positive values only in 4°C increments. Default is 48°C. 00000 = 0°C 00001 = 4°C 00010 = 8°C 00011 = 12°C | | 01100 = 48°C (Default) | | | 11110 = 120°C 11111 = 124°C

<2:0> Remote 1 Temp T

RANGE

Read/Write This nibble contains the temperature range value for Automatic Fan Speed

Control based on the Remote 1 Temp Readings. 000 = 5°C 001 = 10°C (Default) 010 = 20°C 011 = 40°C 100 = 80°C

MIN/TRANGE

Power-On Default = 61H

can be programmed to

MIN

Table XXV. Register 0x26 Remote 2 Temp T

Bit Name R/W Description

<7:3> Remote 2 Temp T

MIN

Read/Write Contains the minimum temperature value for Automatic Fan Speed Control

based on Remote 2 Temperature Readings. T positive values only in 4°C increments. Default is 48°C. 00000 = 0°C 00001 = 4°C 00010 = 8°C 00011 = 12°C | | 01100 = 48°C (Default) | | 11110 = 120°C 11111 = 124°C

<2:0> Remote 2 Temp T

RANGE

Read/Write This nibble contains the temperature range value for Automatic Fan Speed

Control based on the Remote 2 Temp Readings. 000 = 5°C 001 = 10°C (Default) 010 = 20°C 011 = 40°C 100 = 80°C

Table XXVI. Register 0x3F Therm Behavior/Revision Power-On Default = 80H

MIN/TRANGE

Power-On Default = 61H

can be programmed to

MIN

Bit Name R/W Description

<7> Therm-to-Fan En Read/Write Setting this bit to 1, enables the fan to run full-speed when THERM is

asserted low. This allows the system to be run in performance mode. Clearing this bit to 0 disables the fan from running full-speed whenever THERM is asserted low. This allows the system to run in silent mode. (Power-On Default = 1).

<3:0> Revision Read Only This nibble contains the revision number for the ADM1031.

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Table XXVII. Register 0x0D Local Temp Offset Power-On Default = 00H

Bit Name R/W Description

<7> Sign Read/Write When this bit is 0, the local offset will be added to the Local Temp Reading.

When this bit is set to 1, the local offset will be subtracted from the Local Temp Reading.

<3:0> Local Offset Read/Write These four bits are used to add an offset to the Local Temperature Reading.

These bits allow an offset value of up to ±15°C to be added to or subtracted from the temperature reading.

Table XXVIII. Register 0x0E Remote 1 Temp Offset Power-On Default = 00H

Bit Name R/W Description

<7> Sign Read/Write When this bit is 0, the remote offset will be added to the Remote 1 Temp

Reading. When this bit is set to 1, the remote offset will be subtracted from

the Remote 1 Temp Reading. <6.4> Unused Read/Write Unused. Read back 0. <3:0> Remote 1 Offset Read/Write These four bits are used to add an offset to the Remote 1 Temperature

Reading. These bits allow an offset value of up to ±15°C to be added to or

subtracted from the temperature reading, depending on the sign bit.

Table XXIX. Register 0x0F Remote 2 Temp Offset Power-On Default = 00H

Bit Name R/W Description

<7> Sign Read/Write When this bit is 0, the remote offset will be added to the Remote 2 Temp

Reading. When this bit is set to 1, the remote offset will be subtracted from

the Remote 2 Temp Reading. <6.4> Unused Read/Write Unused. Read back 0. <3:0> Remote 2 Offset Read/Write These four bits are used to add an offset to the Remote 2 Temperature Reading.

These bits allow an offset value of up to ±15°C to be added to or subtracted

from the temperature reading, depending on the sign bit.

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ADM1031

OUTLINE DIMENSIONS

16-Lead Shrink Small Outline Package [QSOP]

(RQ-16)

Dimensions shown in inches

0.193 BSC

0.065

0.049

0.010

0.004 COPLANARITY

0.004

0.012

0.008

0.154 BSC

0.236

0.069

0.053

SEATING PLANE

BSC

PIN 1

0.025 BSC

COMPLIANT TO JEDEC STANDARDS MO-137AB

0.010

0.006

8ⴗ 0ⴗ

0.050

0.016

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ADM1031

Revision History

Location Page

4/03—Data Sheet changed from REV. 0 to REV. A.

Added ESD Caution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

REV. A

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C02402–0–4/03(A)

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Datasheet ADM1031 Datasheet (Analog Devices)

Specifications and Main Features

Frequently Asked Questions

User Manual

PRODUCT DESCRIPTION

FUNCTIONAL BLOCK DIAGRAM

ABSOLUTE MAXIMUM RATINGS*

THERMAL CHARACTERISTICS

ORDERING GUIDE

PIN FUNCTION DESCRIPTIONS

PIN CONFIGURATION

GENERAL DESCRIPTION

INTERNAL REGISTERS OF THE ADM1031

Configuration Register

Address Pointer Register

Status Registers

Value and Limit Registers

Fan Speed Config Register

Offset Registers

Fan Characteristics Registers

THERM Limit Registers

SERIAL BUS INTERFACE

ALERT RESPONSE ADDRESS

External Temperature Measurement

LAYOUT CONSIDERATIONS

ADDRESSING THE DEVICE

THE ADM1031 INTERRUPT SYSTEM

USING THERM AS AN INPUT

STATUS REGISTERS

MODES OF OPERATION

AUTOMATIC FAN SPEED CONTROL

HOW DOES THE CONTROL LOOP WORK?

FAN SPIN-UP

PROGRAMMING THE AUTOMATIC FAN SPEED CONTROL LOOP

OTHER CONTROL LOOP PARAMETERS

Register 0x20, 0x21 Fan Characteristics Registers 1, 2

Register 0x22 Fan Speed Configuration Register

FILTERED CONTROL MODE

Effect of Ramp Rate on Filtered Mode

Effect of ADC Sample Rate on Filtered Mode

RELEVANT REGISTERS FOR FILTERED AUTOMATIC FAN SPEED CONTROL MODE

Register 0x23 Fan Filter Register

PROGRAMMING THE FILTERED AUTOMATIC FAN SPEED CONTROL LOOP

PWM DUTY CYCLE SELECT MODE

RPM FEEDBACK MODE

Programming RPM Values in RPM Feedback Mode

Programming RPM Values

RPM Feedback Mode Limitations

FAN SPEED MEASUREMENT EQUATIONS

FAN DRIVE USING PWM CONTROL

FAN SPEED MEASUREMENT

FAN FAULTS

OUTLINE DIMENSIONS