MAX6643LBBAEE+T ,Automatic PWM Fan-Speed Controllers with Overtemperature OutputApplicationsNetworking EquipmentPIN- PKGPART TEMP RANGEPACKAGE CODEStorage EquipmentMAX6643LBFAEE - ..
MAX6643LBFAEE ,Automatic PWM Fan-Speed Controllers with Overtemperature OutputELECTRICAL CHARACTERISTICS(V = +3.0V to +5.5V, T = -40°C to +125°C, unless otherwise noted. Typical ..
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MAX6646MUA ,+145C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature AlarmsApplications0.1µ F200ΩGraphics ProcessorsVCC10kΩ EACHDesktop ComputersNotebook ComputersMAX6646DXP ..
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MAX6643LBBAEE+T-MAX6643LBFAEE-MAX6643LBFAEE+
Automatic PWM Fan-Speed Controllers with Overtemperature Output
General DescriptionThe MAX6643/MAX6644/MAX6645 monitor temperature
and automatically adjust fan speed to ensure optimum
cooling while minimizing acoustic noise from the fan.
Each device measures two temperature locations.
The MAX6643/MAX6644/MAX6645 generate a PWM
waveform that drives an external power transistor, which
in turn modulates the fan’s power supply. The
MAX6643/MAX6644/MAX6645 monitor temperature and
adjust the duty cycle of the PWM output waveform to con-
trol the fan’s speed according to the cooling needs of the
system. The MAX6643 monitors its own die temperature
and an optional external transistor’s temperature, while the
MAX6644 and MAX6645 each monitor the temperatures
of one or two external diode-connected transistors.
The MAX6643 and MAX6644 have nine selectable trip
temperatures (in 5°C increments). The MAX6645 is fac-
tory programmed and is not pin selectable.
All versions include an overtemperature output (OT).can be used for warning or system shutdown. The
MAX6643 also features a FULLSPD input that forces the
PWM duty cycle to 100%. The MAX6643/MAX6644/
MAX6645 also feature a FANFAILoutput that indicates
a failed fan. See the Selector Guidefor a complete list
of each device’s functions.
The MAX6643 and MAX6644 are available in a small
16-pin QSOP package and the MAX6645 is available in
a 10-pin µMAX®package. All versions operate from
3.0V to 5.5V supply voltages and consume 500µA (typ)
supply current.
ApplicationsNetworking Equipment
Storage Equipment
Servers
Desktop Computers
Workstations
FeaturesSimple, Automatic Fan-Speed ControlInternal and External Temperature SensingDetect Fan Failure Through Locked-Rotor Output,
Tachometer Output, or Fan-Supply Current
SensingMultiple, 1.6% Output Duty-Cycle Steps for Low
Audibility of Fan-Speed ChangesPin-Selectable or Factory-Selectable Low-
Temperature Fan ThresholdPin-Selectable or Factory-Selectable High-
Temperature Fan Threshold Spin-Up Time Ensures Fan StartFan-Start Delay Minimizes Power-Supply Load at
Power-Up32Hz PWM OutputControlled Duty-Cycle Rate-of-Change Ensures
Good Acoustic Performance2°C Temperature-Measurement AccuracyFULLSPD/FULLSPD Input Sets PWM to 100%
Pin-Selectable OTOutput Threshold16-Pin QSOP and 10-Pin µMAX Packages
MAX6643/MAX6644/MAX6645
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
Ordering Information19-3305; Rev 2; 3/07
EVALUATION KITAVAILABLE
Pin Configurations, Typical Operating Circuit, and Selector
Guide appear at end of data sheet.
PARTTEMP RANGEPIN-
PACKAGE
PKG
CODE
MAX6643LBFAEE-40°C to +125°C16 QSOPE16-1
MAX6643LBBAEE-40°C to +125°C16 QSOPE16-1
MAX6644LBAAEE-40°C to +125°C16 QSOPE16-1
MAX6645ABFAUB-40°C to +125°C10 µMAXU10-2
µMAX is a registered trademark of Maxim Integrated Products, Inc.
MAX6643/MAX6644/MAX6645
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VDD= +3.0V to +5.5V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at VDD= +3.3V, TA= +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.
VDDto GND..............................................................-0.3V to +6V
PWM_OUT, OT, and FANFAILto GND.....................-0.3V to +6V
FAN_IN1 and FAN_IN2 to GND...........................-0.3V to +13.2V
DXP_ to GND.........................................................-0.3V to +0.8V
FULLSPD, FULLSPD, TH_, TL_, TACHSET,
and OT_ to GND..................................-0.3V to +(VDD+ 0.3V)
FANFAIL, OTCurrent..........................................-1mA to +50mA
Continuous Power Dissipation (TA= +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)..........667mW
10-Pin µMAX (derate 5.6mW/°C above +70°C)...........444mW
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
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSOperating Supply Voltage RangeVDD+3.0+5.5V
TA = +20°C to +60°C±2
Remote Temperature Error
VDD = +3.3V,
+20°C ≤ TRJ ≤
+100°CTA = 0°C to +125°C±3°C
TA = +10°C to +70°C±2.5Local Temperature ErrorVCC = +3.3VTA = 0°C to +125°C±3.5°C
Temperature Error from Supply
Sensitivity±0.2°C/V
Power-On-Reset (POR) ThresholdVDD falling edge1.52.02.5V
POR Threshold Hysteresis90mV
Operating CurrentISDuring a conversion0.51mA
Average Operating CurrentDuty cycle = 50%, no load0.5mA
Remote-Diode Sourcing CurrentHigh level80100120µA
Conversion Time125ms
Spin-Up TimeMAX664_ _B_ _ _ _8s
Startup DelayMAX664_ _B_ _ _ _0.5s
Minimum Fan-Fail Tachometer
Frequency16Hz
PWM_OUT FrequencyFPWM_OUT32Hz
DIGITAL OUTPUTS (OT, FANFAIL, PWM_OUT)Output Low Voltage (OT)VOLISINK = 1mA0.4V
ISINK = 6mA0.5Output Low Voltage
(FANFAIL, PWM_OUT)VOLISINK = 1mA0.4V
Output-High Leakage CurrentIOHVOH = 3.3V1µA
MAX6643/MAX6644/MAX6645
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
OPERATING SUPPLY CURRENT
vs. SUPPLY VOLTAGEMAX6643 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (
PWMOUT FREQUENCY
vs. DIE TEMPERATURE
MAX6643 toc02
TEMPERATURE (°C)
PWMOUT FREQUENCY (Hz)
TRIP-THRESHOLD ERROR
vs. TRIP TEMPERATURE
MAX6643 toc04
TRIP TEMPERATURE (°C)
TRIP-THRESHOLD ERROR (6040
MAX664_L VERSIONS
PWMOUT FREQUENCY
vs. SUPPLY VOLTAGEMAX6643 toc03
SUPPLY VOLTAGE (V)
PWMOUT FREQUENCY (Hz)
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
ELECTRICAL CHARACTERISTICS (continued)(VDD= +3.0V to +5.5V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at VDD= +3.3V, TA= +25°C.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
DIGITAL INPUTS (FULLSPD, FULLSPD, TACHSET)VDD = 5.5V3.65Logic-Input HighVIHVDD = 3.0V2.2V
Logic-Input LowVILVDD = 3.0V0.8V
Input Leakage CurrentVIN = GND or VDD-1+1µA
Note 1:All parameters tested at TA= +25°C. Specifications over temperature are guaranteed by design.
MAX6643/MAX6644/MAX6645
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
Pin Description
PIN
MAX6643MAX6644MAX6645NAMEFUNCTION1, 151, 15—TH1, TH2
High-Temperature Threshold Inputs. Connect to VDD, GND, or
leave unconnected to select the upper fan-control trip
temperature (THIGH), in 5°C increments. See Table 1.
2, 32, 3—TL2, TL1
Low-Temperature Threshold Inputs. Connect to VDD, GND, or
leave unconnected to select the lower fan-control trip
temperature (TLOW), in 5°C increments. See Table 2.
441FANFAIL
Fan-Fail Alarm Output. FANFAIL is an active-low, open-drain
output. If the FAN_IN_ detects a fan failure, the FANFAIL output
asserts low.52TACHSET
FAN_IN_ Control Input. TACHSET controls what type of fan-fail
condition is being detected. Connect TACHSET to VDD, GND,
or leave floating to set locked rotor, current sense, or
tachometer configurations (see Table 3).——FULLSPDActive-High Logic Input. When pulled high, the fan runs at
100% duty cycle.
———FULLSPDActive-Low Logic Input. When pulled low, the fan runs at 100%
duty cycle.74GNDGround——DXP6, 83, 5DXP2, DXP1om b i ned C ur r ent S our ce and A/D P osi ti ve Inp ut for Rem otei od e. C onnect to anod e of r em ote d i od e- connected
tem p er atur e- sensi ng tr ansi stor . C onnect to G N D i f no r em otei od e i s used . P l ace a 2200p F cap aci tor b etw een D X P _ and N D for noi se fi l ter i ng .
996OTActive-Low, Open-Drain Overtemperature Output. When OT
threshold is exceeded, OT pulls low.
10, 1110, 117, 8FAN_IN2,
FAN_IN1
Fan- S ense Inp ut. FAN _IN _ can b e confi g ur ed to m oni tor ei ther a
fan’ s l og i c- l evel l ocked - r otor outp ut, tachom eter outp ut, or sense- esi stor w avefor m to d etect fan fai l ur e. The M AX 6643’ s FAN _IN _np ut can m oni tor onl y tachom eter si g nal s. The M AX 6644 and theAX 6645 can m oni tor any one of the thr ee si g nal typ es as
confi g ur ed usi ng the TAC H S E T i np ut.
Detailed DescriptionThe MAX6643/MAX6644/MAX6645 measure temperature
and automatically adjust fan speed to ensure optimum
cooling while minimizing acoustic noise from the fan.
The MAX6643/MAX6644/MAX6645 generate a PWM
waveform that drives an external power transistor,
which in turn modulates the fan’s power supply. The
MAX6643/MAX6644/MAX6645 monitor temperature and
adjust the duty cycle of the PWM output waveform to
control the fan’s speed according to the cooling needs
of the system. The MAX6643 monitors its own die tem-
perature and an optional external transistor’s tempera-
ture, while the MAX6644 and MAX6645 each monitor
the temperatures of one or two external diode-connect-
ed transistors.
Temperature SensorThe pn junction-based temperature sensor can mea-
sure temperatures up to two pn junctions. The
MAX6643 measures the temperature of an external
diode-connected transistor, as well as its internal tem-
perature. The MAX6644 and MAX6645 measure the
temperature of two external diode-connected transis-
tors. The temperature is measured at a rate of 1Hz.
If an external “diode” pin is shorted to ground or left
unconnected, the temperature is read as 0°C. Since the
larger of the two temperatures prevails, a faulty or
unconnected diode is not used for calculating fan
speed or determining overtemperature faults.
PWM OutputThe larger of the two measured temperatures is always
used for fan control. The temperature is compared to
three thresholds: the high-temperature threshold (THIGH),
the low-temperature threshold (TLOW), and the overtem-
perature threshold, OT. The OTcomparison is done once
per second, whereas the comparisons with fan-control
thresholds THIGHand TLOWare done once every 4s.
The duty-cycle variation of PWM_OUT from 0% to 100%
is divided into 64 steps. If the temperature measured
exceeds the threshold THIGH, the PWM_OUT duty cycle
is incremented by one step, i.e., approximately 1.5%
(100/64). Similarly, if the temperature measured is below
the threshold TLOW, the duty cycle is decremented by
one step (1.5%). Since the THIGHand TLOWcompar-
isons are done only once every 4s, the maximum rate of
change of duty cycle is 0.4% per second.
Tables 1 and 2 show the °C value assigned to the TH_
and TL_ input combinations.
MAX6643/MAX6644/MAX6645
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
Pin Description (continued)
PIN
MAX6643MAX6644MAX6645NAMEFUNCTION129PWM_OUT
PWM Output for Driving External Power Transistor. Connect to
the gate of an n-channel MOSFET or to the base of an npn.
PWM_OUT requires a pullup resistor. The pullup resistor can
be connected to a supply voltage as high as 5.5V, regardless
of the supply voltage.
13, 1413, 14—OT2, OT1
Overtemperature Threshold Inputs. Connect to VDD, GND, or
leave unconnected to select the upper-limit OT fault output trip
temperature, in 5°C increments. See Table 4.1610VDDPower-Supply Input. 3.3V nominal. Bypass VDD to GND with a
0.1µF capacitor.
TH2TH1THIGH (°C)
L SUFFIX
THIGH (°C)
H SUFFIX02040High-Z254513050
High-Z03555
High-ZHigh-Z4060
High-Z1456505070High-Z557516080
Table 1. Setting THIGH
(MAX6643 andMAX6644)High-Z = High impedance.
MAX6643/MAX6644/MAX6645There are two options for the behavior of the PWM out-
puts at power-up. Option 1 (minimum duty cycle = 0):
at power-up, the PWM duty cycle is zero. Option 2
(minimum duty cycle = the start duty cycle): at power-
up, there is a startup delay, after which the duty cycle
goes to 100% for the spin-up period. After the startup
delay and spin-up, the duty cycle drops to its minimum
value. The minimum duty cycle is in the 0% to 50%
range (see the Selector Guide).
To control fan speed based on temperature, THIGHis
set to the temperature beyond which the fan should spin
at 100%. TLOWis set to the temperature below which
the duty cycle can be reduced to its minimum value.
After power-up and spin-up (if applicable), the duty
cycle reduces to its minimum value (either 0% or the
start duty cycle). For option 1 (minimum duty cycle = 0),
if the measured temperature remains below THIGH, the
duty cycle remains at zero (see Figure 1). If the temper-
ature increases above THIGH, the duty cycle goes to
100% for the spin-up period, and then goes to the start
duty cycle (for example, 40%). If the measured temper-
ature remains above THIGHwhen temperature is next
measured (4s later), the duty cycle begins to increase,
incrementing by 1.5% every 4s until the fan is spinning
fast enough to reduce the temperature below THIGH.
For option 2 (minimum duty cycle = start duty cycle), if
the measured temperature remains below THIGH, the
duty cycle does not increase and the fan continues to
run at a slow speed. If the temperature increases
above THIGH, the duty cycle begins to increase, incre-
menting by 1.5% every 4s until the fan is spinning fast
enough to reduce the temperature below THIGH(see
Figure 2). In both cases, if only a small amount of extra
cooling is necessary to reduce the temperature below
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
Table 2. Setting TLOW
(MAX6643 andMAX6644)STARTUP
DUTY CYCLE
TEMPERATURE
TIME
TIME
THIGH
SPIN-UP
TLOW
Figure 1. Temperature-Controlled Duty-Cycle Change with
Minimum Duty Cycle 30%
STARTUP
MAX664_B HAS 30% PWM_OUT DUTY CYCLE DURING STARTUP.
DUTY CYCLE
TEMPERATURE
TIME
TIME
THIGH
TLOW
SPIN-UP
Figure 2. Temperature-Controlled Duty-Cycle Change with
TL2TL1TLOW (°C)
L SUFFIX15High-Z2025
High-Z030
High-ZHigh-Z35
High-Z14045High-Z5055
High-Z = High impedance.
THIGH, the duty cycle may increase just a few percent
above the minimum duty cycle. If the power dissipation or
ambient temperature increases to a high-enough value,
the duty cycle may eventually need to increase to 100%.
If the ambient temperature or the power dissipation
reduces to the point that the measured temperature is
less than TLOW, the duty cycle begins slowly decre-
menting until either the duty cycle reaches its minimum
value or the temperature rises above TLOW.
The small duty-cycle increments and slow rate-of-
change of duty cycle (1.5% maximum per 4s) reduce
the likelihood that the process of fan-speed control is
acoustically objectionable. The “dead band” between
TLOWand THIGHkeeps the fan speed constant when
the temperature is undergoing small changes, thus
making the fan-control process even less audible.
Fan-Fail SensingThe MAX6643/MAX6644/MAX6645 feature a FANFAIL
output. The FANFAILoutput is an active-low, open-
drain alarm. The MAX6643/MAX6644/MAX6645 detect
fan failure either by measuring the fan’s speed and rec-
ognizing when it is too low, or by detecting a locked-
rotor logic signal from the fan. Fan-failure detection is
enabled only when the duty cycle of the PWM drive sig-
nal is equal to 100%. This happens during the spin-up
period when the fan first turns on and whenever the
temperature is above THIGHlong enough that the duty
cycle reaches 100%.
Many fans have open-drain tachometer outputs that
produce periodic pulses (usually two pulses per revolu-
tion) as the fan spins. These tachometer pulses are
monitored by the FAN_IN_ inputs to detect fan failures.
If a 2-wire fan with no tachometer output is used, the
fan’s speed can be monitored by using an external
sense resistor at the source of the driving FET (see
Figure 3). In this manner, the variation in the current
flowing through the fan develops a periodic voltage
waveform across the sense resistor. This periodic
waveform is then highpass filtered and AC-coupled to
the FAN_IN_ input. Any variations in the waveform that
have an amplitude of more than ±150mV are converted
to digital pulses. The frequency of these digital pulses
is directly related to the speed of the rotation of the fan
and can be used to detect fan failure.
Note that the value of the sense resistor must be
matched to the characteristics of the fan’s current
waveform. Choose a resistor that produces voltage
variations of at least ±200mV to ensure that the fan’s
operation can be reliably detected. Note that while
most fans have current waveforms that can be used
with this detection method, there may be some that do
not produce reliable tachometer signals. If a 2-wire fan
is to be used with fault detection, be sure that the fan is
compatible with this technique.
To detect fan failure, the analog sense-conditioned
pulses or the tachometer pulses are deglitched and
counted for 2s while the duty cycle is 100% (either dur-
ing spin-up or when the duty cycle rises to 100% due to
measured temperature). If more than 32 pulses are
counted (corresponding to 480rpm for a fan that pro-
duces two pulses per revolution), the fan is assumed to
be functioning normally. If fewer than 32 pulses are
received, the FANFAILoutput is enabled and the PWM
duty cycle to the FET transistor is either shut down in
case of a single-fan (MAX6643) configuration or contin-
ues normal operation in case of a dual-fan configuration
(MAX6644/MAX6645).
Some fans have a locked-rotor logic output instead of a
tachometer output. If a locked-rotor signal is to be used
to detect fan failure, that signal is monitored for 2s while
the duty cycle is 100%. If a locked-rotor signal remains
active (low) for more than 2s, the fan is assumed to
have failed.
The MAX6643/MAX6644/MAX6645 have two channels
for monitoring fan-failure signals, FAN_IN1 and
FAN_IN2. For the MAX6643, the FAN_IN_ channels
monitor a tachometer. The MAX6643’s fault sensing can
also be turned off by floating the TACHSET input.
For the MAX6644 and MAX6645, the FAN_IN1 and
FAN_IN2 channels can be configured to monitor either
a logic-level tachometer signal, the voltage waveform
on a current-sense resistor, or a locked-rotor logic sig-
nal. The TACHSET input selects which type of signal is
to be monitored (see Table 3). To disable fan-fault
sensing, TACHSET should be unconnected and
FAN_IN1 and FAN_IN2 should be connected to VDD.
OutputThe MAX6643/MAX6644/MAX6645 include an over-
temperature output that can be used as an alarm or a
system-shutdown signal. Whenever the measured tem-
perature exceeds the value selected using the OT pro-
gramming inputs OT1 and OT2 (see Table 4), OTis
asserted. OTdeasserts only after the temperature
drops below the threshold.
FULLSPD InputThe MAX6643 features a FULLSPD input. Pulling FULL-
SPD high forces PWM_OUT to 100% duty cycle. The
FULLSPD input allows a microcontroller to force the fan
to full speed when necessary. By connecting FANFAIL
to an inverter, the MAX6643 can force other fans to
100% in multifan systems, or for an over-temperature
MAX6643/MAX6644/MAX6645
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
MAX6643/MAX6644/MAX6645Applications InformationFigures 3–6 show various configurations.
Remote-Diode ConsiderationsWhen using an external thermal diode, temperature
accuracy depends upon having a good-quality, diode-
connected, small-signal transistor. Accuracy has been
experimentally verified for a variety of discrete small-
signal transistors, some of which are listed in Table 5.
The MAX6643/MAX6644/MAX6645 can also directly
measure the die temperature of CPUs and other ICs
with on-board temperature-sensing diodes.
The transistor must be a small-signal type with a rela-
tively high forward voltage. This ensures that the input
voltage is within the ADC input voltage range. The for-
ward voltage must be greater than 0.25V at 10µA at the
highest expected temperature. The forward voltage
must be less than 0.95V at 100µA at the lowest expect-
ed temperature. The base resistance has to be less
than 100Ω. Tight specification of forward-current gain
(+50 to +150, for example) indicates that the manufac-
turer has good process control and that the devices
have consistent characteristics.
Effect of Ideality FactorThe accuracy of the remote temperature measurements
depends on the ideality factor (n) of the remote diode
(actually a transistor). The MAX6643/MAX6644/MAX6645
are optimized for n = 1.01, which is typical of many dis-
crete 2N3904 and 2N3906 transistors. It is also near the
ideality factors of many widely available CPUs, GPUs, and
FPGAs. However, any time a sense transistor with a differ-
ent ideality factor is used, the output data is different.
Fortunately, the difference is predictable. Assume a
remote-diode sensor designed for a nominal ideality fac-
tor nNOMINALis used to measure the temperature of a
diode with a different ideality factor, n1. The measured
temperature TMcan be corrected using:
where temperature is measured in Kelvin.
As mentioned above, the nominal ideality factor of the
MAX6643/MAX6644/MAX6645 is 1.01. As an example,
assume the MAX6643/MAX6644/MAX6645 are config-
ured with a CPU that has an ideality factor of 1.008. If
the diode has no series resistance, the measured data
is related to the real temperature as follows:
For a real temperature of +60°C (333.15K), the mea-
sured temperature is 59.33°C (332.49K), which is an
error of -0.66°C.nT1.01
1.008TACTUALMNOMINALMM=⎛⎜⎞⎟=⎛⎜⎞⎟=() .100198nMACTUAL1
NOMINAL=⎛⎜⎞⎟
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
MANUFACTURERMODEL NO.Central Semiconductor (USA)CMPT3906
Rohm Semiconductor (USA)SST3906
Samsung (Korea)KST3906-TF
Siemens (Germany)SMBT3906
Table 5. Remote-Sensor Transistor
Manufacturers
OT2OT1TOVERT (°C)
L SUFFIX60High-Z6570
High-Z075
High-ZHigh-Z80
High-Z18590High-Z951100
Table 4. Setting the Overtemperature
Thresholds (TOVERT)(MAX6643 and MAX6644)
Table 3. Configuring the FAN_IN_ Inputs with TACHSET
VDDGNDUNCONNECTEDTACHSETFAN_IN1FAN_IN2FAN_IN1FAN_IN2FAN_IN1FAN_IN2MAX6643TachometerTachometerDo not connect
to GND
Do not connect
to GND
Disables fan-
failure detection
Disables fan-
failure detection
MAX6644TachometerTachometerCurrent senseCurrent senseLocked rotorLocked rotor
MAX6645TachometerTachometerCurrent senseCurrent senseLocked rotorLocked rotor
High-Z = high impedance
MAX6643/MAX6644/MAX6645
Automatic PWM Fan-Speed Controllers with
Overtemperature OutputMAX6644
TH1
TL2
TL1
FANFAIL
TACHSET
DXP2
GND
DXP1
VDD
TH2
OT1
OT2
PWM_OUT
FAN_IN1
FAN_IN2
4.7kΩ4.7kΩ
+VFAN (5V OR 12V)VDD (+3.0V TO +5.5V)+VFAN (5V OR 12V)
2.0Ω2.0Ω
4.7kΩ
TO FANFAIL
ALARM
0.1μF
0.1μF
CURRENT-SENSE
MODE
CURRENT-SENSE
MODE
TO OVERTEMPERATURE
ALARM
MAX6645FANFAIL
TACHSET
DXP2
GND
DXP1
VDD
PWM_OUT
FAN_IN1
FAN_IN2
4.7kΩ4.7kΩ
+VFAN (5V OR 12V)VDD (+3.0V TO +5.5V)+VFAN (5V OR 12V)
4.7kΩ
TO FANFAIL
ALARM
TACHOMETER MODE
TACHOMETER MODE
TO OVERTEMPERATURE
ALARM
Figure 3. MAX6644 Using Two External Transistors to Measure Remote Temperatures and Control Two 2-Wire Fans. The fan’s power-
supply current is monitored to detect failure of either fan. Connect pin 10 to pin 11 if only one fan is used.
Figure 4. MAX6645 Using Two External Transistors to Measure Remote Temperatures and Control Two 2-Wire Cooling Fans. The
fan’s power-supply current is monitored to detect failure of either fan. Connect FAN_IN1 to FAN_IN2 if only one fan is used.
