General Description
The MAX6660 is a remote temperature sensor and fanspeed regulator that provides a complete fan-control
solution. The remote temperature sensor is typically a
common-collector PNP, such as a substrate PNP of a
microprocessor, or a diode-connected transistor, typically a low-cost, easily mounted 2N3904 NPN type or
2N3906 PNP type.
The device also incorporates a closed-loop fan controller that regulates fan speed with tachometer feedback. The MAX6660 compares temperature data to a
fan threshold temperature and gain setting, both programmed over the SMBus™ by the user. The result is
automatic fan control that is proportional to the remotejunction temperature. The temperature feedback loop
can be broken at any time for system control over the
speed of the fan.
Fan speed is voltage controlled as opposed to PWM
controlled, greatly reducing acoustic noise and maximizing fan reliability. An on-chip power device drives
fans rated up to 250mA.
Temperature data is updated every 0.25s and is readable at any time over the SMBus interface. The
MAX6660 is accurate to 1°C (max) when the remote
junction is between +60°C to +100°C. Data is formatted
as a 10-bit + sign word with 0.125°C resolution.
The MAX6660 is specified for -40°C to +125°C and is
available in a 16-pin QSOP package.
Applications
PC
Notebooks
Telecom Systems
Industrial Control Systems
Servers
Workstations
Features
♦ Integrated Thermal Sensing and Fan-Regulation
Solution
♦ Programmable Fan Threshold Temperature
♦ Programmable Temperature Range for Full-Scale
Fan Speed
♦ Accurate Closed-Loop Fan-Speed Regulation
♦ On-Chip Power Device Drives Fans Rated
Up to 250mA
♦ Programmable Under/Overtemperature Alarms
♦ SMBus 2-Wire Serial Interface with Timeout
(Cannot “Lock Up” the SMBus)
♦ Supports SMBus Alert Response
♦ ACPI Compatible, Including OVERT System
Shutdown Function
♦ ±1°C (+60°C to +100°C) Thermal-Sensing Accuracy
♦ MAX6660EVKIT Available
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
________________________________________________________________ Maxim Integrated Products 1
19-2225; Rev 1; 5/06
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Pin Configuration appears at end of data sheet.
SMBus is a trademark of Intel Corp.
1µF
5kΩ
FAN
+12V
2200pF
PENTIUM
SMBCLK
SMBDATA
ALERT
OVERT
CLOCK
DATA
INTERUPT
TO µP
TO SYSTEM
SHUTDOWN
VFAN
ADD1ADD0
PGND
0.1µF
+3V TO +5.5V
50Ω
V
CC
STBY
TACH IN
FAN
DXP
DXN
AGND
10kΩ
EACH
MAX6660
Typical Operating Circuit
PART TEMP RANGE
PIN-
PKG
MAX6660AEE
16 QSOP
Ordering Information
PACKAGE
-40°C to +125°C
CODE
E16-5
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC= +3V to +5.5V, V
VFAN
= +12V, TA= -40°C to +125°C, unless otherwise specified. Typical values are at VCC= +3.3V and
T
A
= +25°C.) (Note 1)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
(All voltages referenced to GND.)
V
CC
, ADD0, ADD1, SMBDATA,
SMBCLK,
ALERT, OVERT ...................................-0.3V to +6V
V
FAN
, TACH IN, FAN .............................................-0.3V to +16V
DXP, GAIN..................................................-0.3V to (V
CC
+ 0.3V)
DXN.............................................................................-0.3V to 1V
SMBDATA, ALERT, OVERT Current ...................-1mA to +50mA
DXN Current ......................................................................±1mA
FAN Out Current ..............................................................500mA
ESD Protection (Human Body Model)................................2000V
Continuous Power Dissipation (T
A
= +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)..........667mW
Operating Temperature Range ........................ -40°C to +125°C
Junction Temperature .....................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER
CONDITIONS
UNITS
ADC AND POWER SUPPLY
VCC Supply Voltage V
CC
3.0 5.5 V
V
FAN
Supply Voltage V
VFAN
4.5 13.5 V
Operating Supply Current I
CC
Fan off
500 µA
Shutdown Supply Current I
SHDN
Shutdown 3 10 µA
°C
Temperature Resolution
11
Bits
TRJ = +60°C to +100°C -1 +1
TRJ = +25°C to +125°C -3 +3
Temperature Error (Note 2) T
E
T
A
= +85°C,
TRJ = -40°C to +125°C -5 +5
°C
Internal Reference Frequency
Accuracy
-25 %
Temperature Conversion Time
s
Conversion Rate Timing Error -25 +25 %
Undervoltage Lockout Threshold
V
UVLOVCC
falling
3.00 V
Undervoltage Lockout Threshold
Hysteresis
V
HYST
90 mV
Power-On-Reset (POR)
Threshold (V
CC
)
V
CC
rising 1.4
2.5 V
POR Threshold Hysteresis 90 mV
High level 80
120
Remote-Junction Source Current
I
RJ
Low level 8 10 12
µA
DXN Source Voltage V
DXN
V
SYM B O L
MIN TYP MAX
250
0.125
V
= +3.3V
CC
+25
2.50 2.80
0.25
2.0
100
0.7
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
_______________________________________________________________________________________ 3
Note 1: Junction Temperature = TA. This implies zero dissipation in pass transistor (no load, or fan turned off).
Note 2: T
RJ
, Remote Temperature accuracy is guaranteed by design, not production tested.
Note 3: Guaranteed by design. Not production tested.
Note 4: The MAX6660 includes an SMBus timeout, which resets the interface whenever SMBCLK or SMBDATA has been low for
greater than 25ms. This feature can be disabled by setting bit 2 of the Fan Gain register at 16h/1Bh to a 1. When the timeout
is disabled, the minimum clock frequency is DC.
Note 5: Note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of
SMBCLK’s falling edge.
ELECTRICAL CHARACTERISTICS (continued)
(VCC= +3V to +5.5V, V
VFAN
= +12V, TA= -40°C to +125°C, unless otherwise specified. Typical values are at VCC= +3.3V and
T
A
= +25°C.) (Note 1)
PARAMETER
CONDITIONS
UNITS
Tach Input Transition Level V
VFAN
= 12V
V
Tach Input Hysteresis V
FAN
= 12V
mV
Current-Sense Tach Threshold 20 mA
Current-Sense Tach Hysteresis 0.3 mA
Fan Output Current
mA
Fan Output Current Limit (Note 3)
410 mA
Fan Output On-Resistance R
ONF
250mA load 4 Ω
SMBus INTERFACE: SMBDATA, ALERT, STBY, OVERT
Logic Input Low Voltage V
IL
VCC = +3.0V to +5.5V 0.8 V
VCC = +3.0V 2.2
Logic Input High Voltage V
IH
VCC = +5.5V 2.6
V
Input Leakage Current I_leak VIN = GND or V
CC
-2 +2 µA
Output Low Sink Current I
OL
VOL = 0.4V 6 mA
Input Capacitance C
in
5pF
Output High Leakage Current VOH = 5.5V 1 µA
Serial Clock Frequency f
SCL
(Note 4) 0 100
kHz
Bus Free Time Between Stop
and Start Conditions
t
BUF
4.7 µs
Start Condition Setup Time 4.7 µs
Repeat Start Condition Setup
Time
90% to 90% 50 µs
Start Condition Hold Time
10% of SMBDATA to 90% of SMBCLK 4 µs
Stop Condition Setup Time
90% of SMBCLK to 10% of SMBDATA 4 µs
Clock Low Time t
LOW
10% to 10% 4.7 µs
Clock High Time t
HIGH
90% to 90% 4 µs
Data Setup Time
90% of SMBDATA to 10% of SMBCLK
ns
Data Hold Time
(Note 5) 0 µs
Receive SMBCLK/SMBDATA
Rise Time
t
R
1µs
Receive SMBCLK/SMBDATA
Fall Time
t
F
300 ns
SMBus Timeout
SMBDATA and SMBCLK time low for reset
of serial interface
25 40 ms
SYM B O L
t
SU:STA
t
HD:STA
t
SU:STO
t
SU:DAT
t
HD:DAT
t
TIMEOUT
MIN TYP MAX
10.5
190
250
320
250
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
4 _______________________________________________________________________________________
110100
TEMPERATURE ERROR
vs. PC BOARD RESISTANCE
MAX6660 toc01
LEAKAGE RESISTANCE (MΩ)
TEMPERATURE ERROR (°C)
20
-30
-25
-20
-15
-10
-5
0
15
10
5
PATH = DXP TO GND
PATH = DXP TO VCC (+5V)
-5
-2
-3
-4
-1
0
1
2
3
4
5
-50 0 50 100 150
MAX6660 toc02
TEMPERATURE (°C)
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
110010k 1M10 1k 100k 10M 100M
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
MAX6660 toc03
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
20
-30
-25
-20
-15
-10
-5
0
15
10
5
VIN = 100mVp-p
VIN = SQUARE WAVE APPLIED TO V
CC
WITH NO 0.1µF VCC CAPACITOR
VIN = 250mVp-p
4.0
-1.5
-1.0
MAX6660 toc04
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
-0.5
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
110 100M1M 10M100 1k 10k 100k
TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
VIN = 50mVp-p
VIN = SQUARE WAVE
AC-COUPLED TO DXN
VIN = 100mVp-p
VIN = 25mVp-p
-8
-6
-7
-4
-5
-3
-2
0
-1
1
0102030405060708090100
MAX6660 toc05
DXP-DXN CAPACITANCE (nF)
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
0
1
3
2
4
5
MAX6660 toc06
SUPPLY VOLTAGE (V)
STANDBY SUPPLY CURRENT (µA)
3.0 4.0 4.53.5 5.0 5.5
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
3.0 3.9 4.23.3 3.6 4.5 4.8 5.1 5.4
MAX6660 toc07
SUPPLY VOLTAGE (V)
AVERAGE SUPPLY CURRENT (µA)
100
200
300
400
AVERAGE SUPPLY CURRENT
vs. SUPPLY VOLTAGE
Typical Operating Characteristics
(VCC= +3.3V, TA= +25°C, unless otherwise noted.)
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
_______________________________________________________________________________________ 5
PIN NAME FUNCTION
1 VFAN Fan Drive Power-Supply Input. 4.5V to 13.5V.
2VCCSupply Voltage Input. +3V to +5.5V. Bypass VCC to ground with a 0.1µF capacitor.
3 DXP Input: Remote-Junction Anode. Place a 2200pF capacitor between DXP and DXN for noise filtering.
4 DXN Input: Remote-Junction Cathode. DXN is internally biased to a diode voltage above ground.
5 FAN Open-Drain Output to Fan Low Side. Connect a minimum 1µF capacitor between FAN and VFAN.
6 ADD1 SMBus Address Select Pin. ADD0 and ADD1 are sampled upon power-up.
7 PGND Power Ground
8 AGND Analog Ground
9 OVERT Overtemperature Shutdown Output. Active-low output (programmable for active high if desired). Open drain.
10 ADD0 SMBus Slave Address Select Pin. ADD0 and ADD1 are sampled upon power-up.
11 ALERT SMBus Alert (Interrupt) Output. Open-drain, active-low output.
12
SMBus Serial Data Input/Output. Open drain.
13 GAIN Gain Control. Connect an external resistor from GAIN to VCC to reduce the gain of the current-sense mode.
14 SMBCLK SMBus Clock Line from Controller. This line tolerates inputs up to VCC even if MAX6660 is not powered.
15 STBY
Hardware Standby Input. Drive STBY low to reduce supply current. Temperature and comparison
data are retained in standby mode.
16 TACH IN Fan Tachometer Input. Tolerates voltages up to VFAN.
Detailed Description
The MAX6660 is a remote temperature sensor and fan
controller with an SMBus interface. The MAX6660 converts the temperature of a remote-junction temperature
sensor to a 10-bit + sign digital word. The remote temperature sensor can be a diode-connected transistor,
such as a 2N3906, or the type normally found on the
substrate of many processors’ ICs. The temperature
information is provided to the fan-speed regulator and
is read over the SMBus interface. The temperature
data, through the SMBus, can be read as a 10-bit +
sign two’s complement word with a 0.125°C resolution
(LSB) and is updated every 0.25s.
The MAX6660 incorporates a closed-loop fan controller
that regulates fan speed with tachometer feedback. The
temperature information is compared to a threshold and
range setting, which enables the MAX6660 to automatically set fan speed proportional to temperature. Full control of these modes is available, including being able to
open either the thermal control loop or the fan control
loop. Figure 1 shows a simplified block diagram.
ADC
The ADC is an averaging type that integrates over a
60ms period with excellent noise rejection. A bias cur-
rent is steered through the remote diode, where the forward voltage is measured, and the temperature is computed. The DXN pin is the cathode of the remote diode
and is biased at 0.65V above ground by an internal
diode to set up the ADC inputs for a differential measurement. The worst-case DXP-DXN differential input
voltage range is 0.25V to 0.95V. Excess resistance in
series with the remote diode causes about +1/2°C error
per ohm. Likewise, 200mV of offset voltage forced on
DXP-DXN causes approximately 1°C error.
A/D Conversion Sequence
A conversion sequence is initiated every 250ms in the
free-running autoconvert mode (bit 6 = 0 in the
Configuration register) or immediately by writing a OneShot command. The result of the new measurement is
available after the end of conversion. The results of the
previous conversion sequence are still available when
the ADC is converting.
Remote-Diode Selection
Temperature accuracy depends on having a goodquality, diode-connected small-signal transistor.
Accuracy has been experimentally verified for all
devices listed in Table 1. The MAX6660 can also direct-
Pin Description
SMBDATA
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
6 ________________________________________________________________________________________
N
FAN
FAN
TACH IN
VFAN
FAN-SPEED
REGULATOR
MUXDXP
DXN
T
HIGH
T
LOW
CONFIGURATION
FAN COUNT DIVISOR
(FC)
FAN SPEED LIMIT
(FS)
FAN GAIN (FG)
T
FAN
(FT)
FAN CONVERSION
RATE (FCR)
MODE (M)
FAN LIMIT (FL)
FAN-SPEED CONTROL
(FSC)
STATUS
T
HYST
COMPARAT0R
T
MAX
THERMAL OPEN/
CLOSED LOOP
FAN OPEN/
CLOSED LOOP
FAN
CONTROL
CIRCUIT
REMOTE DATA
TEMPERATURE
REGISTERS
SMBCLK
SMBDATA
ADD0
ADD1
ADC
CENTRAL
LOGIC
SMBus
INTERFACE
ADDRESS
DECODER
OVERT
ALERT
Figure 1. MAX6660 Block Diagram
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
_______________________________________________________________________________________ 7
ly measure the die temperature of CPUs and other ICs
that have on-board temperature-sensing diodes.
The transistor must be a small-signal type with a relatively high forward voltage. Otherwise, the A/D input
range could be violated. The forward voltage must be
greater than 0.25V at 10µA. Check to ensure this is true
at the highest expected temperature. The forward voltage must be less than 0.95V at 100µA. Check to ensure
that this is true at the lowest expected temperature.
Large power transistors, power diodes, or small-signal
diodes must not be used. Also, ensure that the base
resistance is less than 100Ω. Tight specifications for
forward current gain (50 < β <150, for example) indicate that the manufacturer has good process controls
and that the devices have consistent VBE characteristics. Bits 5–2 of the Mode register can be used to
adjust the ADC gain to achieve accurate temperature
measurements with diodes not included in the recommended list or to individually calibrate the MAX6660 for
use in specific control systems.
Thermal Mass and Self-Heating
When measuring the temperature of a CPU or other IC
with an on-chip sense junction, thermal mass has virtually no effect; the measured temperature of the junction
tracks the actual temperature within a conversion cycle.
When measuring temperature with discrete remote sensors, smaller packages (e.g., a SOT23) yield the best
thermal response times. Take care to account for thermal gradients between the heat source and the sensor,
and ensure that stray air currents across the sensor
package do not interfere with measurement accuracy.
Self-heating does not significantly affect measurement
accuracy. Remote-sensor self-heating due to the diode
current source is negligible.
ADC Noise Filtering
The ADC is an integrating type with inherently good noise
rejection, especially of low-frequency signals such as
60Hz/120Hz power-supply hum. Micropower operation
places constraints on high-frequency noise rejection;
therefore, careful PC board layout and proper external
noise filtering are required for high-accuracy remote measurements in electrically noisy environments.
High-frequency EMI is best filtered at DXP and DXN
with an external 2200pF capacitor. This value can be
increased to about 3300pF (max), including cable
capacitance. Capacitance higher than 3300pF introduces errors due to rise time of the switched current
source. Nearly all noise sources tested cause the ADC
measurements to be higher than the actual temperature, typically by +1°C to +10°C, depending on the frequency and amplitude.
PC Board Layout
Follow these guidelines to reduce the measurement
error of the temperature sensors:
1) Place the MAX6660 as close as is practical to the
remote diode. In noisy environments, such as a
computer motherboard, this distance can be 4in to
8in (typ). This length can be increased if the worst
noise sources are avoided. Noise sources include
CRTs, clock generators, memory buses, and
ISA/PCI buses.
2) Do not route the DXP-DXN lines next to the deflec-
tion coils of a CRT. Also, do not route the traces
across fast digital signals, which can easily introduce +30°C error, even with good filtering.
3) Route the DXP and DXN traces in parallel and in
close proximity to each other, away from any higher voltage traces, such as +12VDC. Leakage currents from PC board contamination must be dealt
with carefully since a 20MΩ leakage path from
DXP to ground causes about +1°C error. If highvoltage traces are unavoidable, connect guard
traces to GND on either side of the DXP-DXN
traces (Figure 2).
4) Route through as few vias and crossunders as pos-
sible to minimize copper/solder thermocouple
effects.
5) When introducing a thermocouple, make sure that
both the DXP and the DXN paths have matching
thermocouples. A copper-solder thermocouple
exhibits 3µV/°C, and it takes about 200µV of voltage
error at DXP-DXN to cause a +1°C measurement
error. Adding a few thermocouples causes a negligible error.
6) Use wide traces. Narrow traces are more inductive
and tend to pick up radiated noise. The 10mil widths
and spacings that are recommended in Figure 2 are
not absolutely necessary, as they offer only a minor
MANUFACTURER MODEL NO.
Central Semiconductor (USA) 2N3904, 2N3906
Fairchild Semiconductor (USA) 2N3904, 2N3906
Rohm Semiconductor (Japan) SST3904
Samsung (Korea) KST3904-TF
Siemens (Germany) SMBT3904
Zetex (England) FMMT3904CT-ND
Table 1. Remote-Sensor Transistor
Note: Transistors must be diode connected (base shorted to
collector).
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