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MAX6653AEE
Temperature Monitors and PWM Fan Controllers
General DescriptionThe MAX6653/MAX6663/MAX6664 are ACPI-compliant
local and remote-junction temperature sensors and fan
controllers. These devices measure their own die tem-
perature, as well as the temperature of a remote-PN
junction and control the speed of a DC cooling fan
based on the measured temperature. Remote tempera-
ture measurement accuracy is ±1°C from +60°C to
+100°C. Temperature measurement resolution is
0.125°C for both local and remote temperatures.
Internal watchdog set points are provided for both local
and remote temperatures. There are two comparison
set points for local temperatures and two for remote
temperatures. When a set point is crossed, the
MAX6653/MAX6663/MAX6664 assert either the INTorTHERMoutputs. These outputs can be used as inter-
rupts, clock throttle signals, or overtemperature shut-
down signals. Two pins on the MAX6653 control the
power-up values of the comparison set points, provid-
ing fail-safe protection even when the system is unable
to program the trip temperatures. The MAX6653 has
two additional shutdown outputs, SDRand SDL, that
are triggered when the remote or local temperatures
exceed the programmed shutdown set points. The INT
output for the MAX6653/MAX6663 and THERMoutputs
for the MAX6653/MAX6663/MAX6664 can also function
as inputs if either is pulled low to force the fan to full
speed, unless this function is masked by the user.
The MAX6653/MAX6663/MAX6664 are available in
16-pin QSOP packages and operate over the -40°C to
+125°C temperature range.
ApplicationsPersonal Computers
Servers
Workstations
Telecom Equipment
Networking Equipment
Test Equipment
Industrial Controls
FeaturesRemote-Junction Temperature Sensor Within
±1°C Accuracy (+60°C to +100°C)ACPI-Compatible Programmable Temperature
Alarms0.125°C Resolution Local and Remote-Junction
Temperature MeasurementProgrammable Temperature Offset for System
CalibrationSMBus 2-Wire Serial Interface with TimeoutAutomatic or Manual Fan-Speed ControlPWM Fan Control OutputFan-Speed Monitoring and WatchdogFan Fault and Failure IndicatorsCompatible with 2-Wire or 3-Wire Fans
(Tachometer Output)+3V to +5.5V Supply RangeAdditional Shutdown Set Point (MAX6653)Controlled PWM Rise/Fall Times
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
Pin Configurations19-2865; Rev 1; 12/03
Ordering Information
Typical Operating Circuits appear at end of data sheet.
Functional Diagram appears at end of data sheet.
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
ABSOLUTE MAXIMUM RATINGSStresses 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 Are Referenced to GND
TACH/AIN..............................................................-0.3V to +5.5V
VCC...........................................................................-0.3V to +6V
DXP, ADD, CRIT0, CRIT1........................-0.3V to + (VCC+ 0.3V)
DXN.......................................................................-0.3V to +0.8V
SMBDATA, SMBCLK, INT, THERM,
FAN_FAULT, SDL, SDR............................................-0.3V to +6V
SMBDATA, INT, THERM, FAN_FAULT,
PWM_OUT Current..............................................-1mA to +50mA
DXN Current.......................................................................±1mA
ESD Protection (all pins, Human Body Model)..................2000V
Continuous Power Dissipation (TA= +70°C)
16-Pin QSOP (derate 8.3 mW/°C above +70°C)..........667mW
Operating Temperature Range.........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +165°C
Lead Temperature (soldering, 10s).................................+300°C
ELECTRICAL CHARACTERISTICS
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
Note 2:Not production tested, guaranteed by design.
ELECTRICAL CHARACTERISTICS (continued)
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
Detailed DescriptionThe MAX6653/MAX6663/MAX6664 are local/remote
temperature monitors and fan controllers for micro-
processor-based systems. These devices communi-
cate with the system through a serial SMBus interface.
The serial bus controller features a hard-wired address
pin for device selection, an input line for a serial clock,
and a serial line for reading and writing addresses and
data (see Functional Diagram).
The MAX6653/MAX6663/MAX6664 fan control section
can operate in three modes. In the automatic fan-control
mode, the fan’s power-supply voltage is automatically
adjusted based on temperature. The control algorithm
parameters are programmable to allow optimization to
the characteristics of the fan and the system. RPM select
mode forces the fan speed to a programmed tachome-
ter value. PWM duty cycle select mode allows user
selection of the PWM duty cycle. PWM rise and fall times
are limited to maximize fan reliability.
To ensure overall system reliability, the MAX6653/
MAX6663/MAX6664 feature an SMBus timeout so that
the MAX6653/MAX6663/MAX6664 can never “lock” the
SMBus. Furthermore, the availability of hard-wired
default values for critical temperature set points
ensures the MAX6653 controls critical temperature
events properly even if the SMBus is “locked” by some
other device on the bus.
SMBus Digital InterfaceFrom a software perspective, the MAX6653/MAX6663/
MAX6664 appear as a set of byte-wide registers. These
devices use a standard SMBus 2-wire/I2C-compatible
serial interface to access the internal registers. The
MAX6653/MAX6663/MAX6664 slave address can be
set to three different values by the input pin ADD
(Table 2) and, therefore, a maximum of three MAX6653/
MAX6663/MAX6664 devices can share the same bus.
The MAX6653/MAX6663/MAX6664 employ four stan-
dard SMBus protocols: Write Byte, Read Byte, Send
Byte, and Receive Byte (Figures 1, 2, and 3). The short-
er Receive Byte protocol allows quicker transfers, pro-
vided that the correct data register was previously
selected by a Read Byte instruction. Use caution with
the shorter protocols in multimaster systems, since a
second master could overwrite the command byte with-
out informing the first master.
Alert Response AddressThe MAX6653/MAX6663/MAX6664 respond to the
SMBus alert response address, an event which typical-
ly occurs after an SMBus host master detects an INT
interrupt signal going active (referred to as ALERTin
SMBus nomenclature). When the host master puts the
alert response address (0001 1001) on the bus, all
devices with an active INToutput respond by putting
their own address onto the bus. The alert response can
activate several different slave devices simultaneously,
similar to the I2C general call. If more than one slave
attempts to respond, bus arbitration rules apply, and
the device with the lowest address code wins. The
master then services the devices from the lowest
address up.
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
The MAX6663 resets its INToutput and some of the
status bits in the status register after responding to an
alert response address; however, if the error condition
that caused the interrupt is still present, INTis reassert-
ed on the next monitoring cycle. INTis maskable to
allow full control of ALERT conditions.
Temperature MeasurementThe MAX6653/MAX6663/MAX6664 contain on-chip tem-
perature sensors to sense their own die (local) tempera-
tures. These devices can also measure remote
temperatures such as the die temperature of CPUs or
other ICs having on-chip temperature-sensing diodes, or
discrete diode-connected transistors as shown in the
Typical Operating Circuits. For best accuracy, the dis-
crete diode-connected transistor should be a small-signal
device with its collector and base connected together.
The on-chip ADC converts the sensed temperature and
outputs the temperature data in the format shown in
Tables 3 and 4. The temperature measurement resolution
is 0.125°C for both local and remote temperatures. The
temperature accuracy is within ±1°C for remote tempera-
ture measurements from +60°C to +100°C.
The Local Temperature Offset (0Dh) and Remote
Temperature Offset (0Eh) registers allow the measured
temperature to be increased or decreased by a fixed
value to compensate for errors due to variations in diode
resistance and ideality factor (see the Remote Diode
Considerationssection). The reported temperature is the
measured temperature plus the correction value. Both the
measured temperature and the reported value are limited
by the sensor’s temperature range. For example, if a
remote thermal diode is being measured and its tempera-
ture is 135°C, the measured temperature is the maximum
value of 127.875°C. If the remote offset value is set to -
10°C, the reported value is 117.875°C, not 125°C.
The temperature conversion rate is programmable using
bits [4:2] of the fan filter register (23h) as shown in Table 5.
The DXN input is biased at 0.65V above ground by an
internal diode to set up the analog-to-digital inputs for a
differential measurement. The worst-case DXP-DXN dif-
ferential input voltage range is from 0.25V to 0.95V.
Excess resistance in series with the remote diode caus-
es about 0.5°C error per ohm. Likewise, a 200µV offset
voltage forced on DXP-DXN causes about 1°C error.
High-frequency EMI is best filtered at DXP and DXN with
an external 2200pF capacitor. This value can be
increased to about 3300pF, including cable capacitance.
Capacitance higher than 3300pF introduces errors due to
the rise time of the switched current source.
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan ControllersINTis an open-drain digital output that reports the sta-
tus of temperature interrupt limits and fan out-of-limit
conditions. Set bit 1 of configuration register 1 (00h) to
1 to enable INToutput or reset this bit to zero to disable
the INToutput function. Status register 1 contains sta-
tus information for the conditions that cause INTto
assert. Reading status register 1 resets INT, but INTis
reasserted if the fault condition still exists. Connect a
10kΩpullup resistor between INTand VCC.
SDLand SDRare open-drain digital outputs on the
MAX6653 that can be used to shut the system down
based on the local (die) temperature of the MAX6653 or
the temperature of the remote sensor, respectively. The
trip thresholds for SDLand SDRare normally set above
the THERMand INTlimits. Their power-up values are
set by the CRIT1 and CRIT0 pins, as shown in Table 1.
Fan-Speed ControlThe MAX6653/MAX6663/MAX6664 fan-control section
can operate in one of three modes depending on the set-
ting of bit 7 to bit 5 of configuration register 1 (00h).
Regardless of the mode of operation, the PWM output fre-
quency is programmable, and the fan speed is measured
with the result stored in the fan-speed register (08h).
PWM Output FrequencyThe PWM output frequency is programmed by bit 5, bit
4, and bit 3 of the fan characteristics register (20h),
regardless of the mode of operation. See Table 7.
Fan-Control ModeThe mode of fan-speed control operation is set by bit 7,
bit 6, and bit 5 in configuration register 1 (00h), as
shown in Table 8.
PWM Duty-Cycle Fan-Control ModeBits [3:0] of the fan-speed configuration register set the
PWM duty cycle. See Table 9 for more details.
RPM Select Fan-Control ModeIn RPM select mode, the MAX6653/MAX6663/MAX6664
adjust their PWM output duty cycle to match a selected
fan speed measured by a tachometer count value. Before
selecting this mode by setting bits [7:5] of configuration
register 1 (00h) to 0x1, the desired tachometer count
value should be written to the fan tachometer high-limit
register (10h). In this mode, the MAX6653/MAX6663/
MAX6664 are not able to detect underspeed fan faults
because the fan tachometer high-limit register (10h) func-
tions as the target tachometer count.
The MAX6653/MAX6663/MAX6664 detect fan stall
faults by comparing the fan-speed reading to the full-
scale constant of 254 (FEh). Therefore, the
MAX6653/MAX6663/MAX6664 signal a fan fault when
the fan-speed reading is 255 (FFh). Note that the RPM
mode cannot be used for speeds below 10% of the
fan’s maximum speed. It is important to verify that a fan
works properly at lower RPM values if a low-RPM oper-
ation in this mode is desired.
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
Automatic Fan-Control ModeAutomatic fan-speed control is selected by setting bits
[7:5] of configuration register 1 (00h) to 100 (to control
speed based on the remote temperature) or 101 (to
control speed based on both remote and local temper-
ature). Program a threshold, or starting temperature
TMIN, and the desired temperature range, TRANGE, into
the local temp TMIN/TRANGEregister (24h) for local
temperature and into the remote temp TMIN/TRANGE
register (25h) for remote temperature (Tables 10 and
11). If the fan control responds to both local and remote
temperatures, the higher PWM duty cycle has priority.
When the temperature exceeds TMIN, the fan is
enabled at a minimum duty cycle programmed in bits
[3:0] of the fan-speed configuration register (22h). The
duty cycle increases in proportion to the temperature
difference and reaches 100% at a temperature equal to
(TMIN+ TRANGE). A hysteresis of 5°C is built into the
TMINset point to prevent the fan from starting and stop-
ping when the temperature is at the set point.
Spin-UpTo ensure proper fan startup, the MAX6653/MAX6663/
MAX6664 can be set to drive the fan to 100% duty
cycle for a short period on startup, and then revert to
the correct duty cycle. The spin-up time is programmed
by bits [2:0] in the fan characteristics register (20h).
The spin-up feature can be disabled by setting bit 7 of
the fan-filter register (23h) to 1; POR value is zero.
Table 12 shows programming of the spin-up time.
Fan-Filter ModeWhen the MAX6653/MAX6663/MAX6664 are used for
automatic fan-speed control, the fan-filter mode helps
minimize the audible effects of varying fan speeds. The
fan-filter mode limits the rate at which fan speed can
change. Each time a new temperature measurement is
made, the fan-filter mode allows the PWM duty cycle to
increment by a selectable amount. The duty cycle can
change by 1/240, 2/240, 4/240, or 8/240 (0.416%,
0.833%, 1.667%, or 3.333%) of the PWM period after
each temperature-monitoring cycle. This prevents sud-
den changes in fan speed, even when temperature
changes suddenly.
The filter mode is set by bit 0 of the fan-filter register
(23h). To enable the fan-filter mode, write a 1 to this bit.
Bits [6:5] of the same register control the size of the
PWM steps.
Note that the rate of change depends on both the value
selected by the fan-filter bits and on the temperature
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllersmeasurement rate, which is controlled by bits [4:2] of
the fan-filter register (23h). Table 5 shows the effect of
the temperature measurement rate control bits. As an
example, assume that the temperature measurement
rate is 2Hz, or 0.5s per monitoring cycle, and the fan-fil-
ter rate is 0.416% per monitoring cycle. For the fan drive
to change from 50% to 100% requires 50% / 0.416% =
120 temperature monitoring cycles. Thus, for a tempera-
ture-monitoring cycle of 0.5s, the time required for the
drive to change from 50% to 100% is 60s.
Fan-Speed MeasurementThe fan speed is measured by using the relatively slow
tachometer signal from the fan to gate an 11.25kHz
clock frequency into a fan-speed counter. The mea-
surement is initialized on the starting edge of a PWM
output if fan-speed measurement is enabled by setting
bit 2 of configuration register 2 (01h) to 1. Counting
begins on the leading edge of the second tachometer
pulse and lasts for two tachometer periods or until the
counter overranges (255). The measurement repeats
unless monitoring is disabled by resetting bit 2 in the
configuration register 2 (01h). The measured result is
stored in the fan-speed reading register (08h).
The fan-speed count is given by:
The fan-speed count is given by:
where RPM = fan speed in RPM.
N determines the speed range and is programmed by
bits [7:6] in the fan characteristics register (20h) as
shown in Table 14. When the speed falls below the value
in the speed range column, a fan failure is detected.
The TACH/AIN input can be either a digital signal (from
the fan’s tachometer output) or an analog signal,
depending on the setting of bit 2 of the configuration
register 1 (00h). The default setting is zero, which sets
up TACH/AIN as a digital input. For the analog input
(Figure 4), the detected voltage threshold is typically at
250mV, which is appropriate for sensing the voltage of
a sense resistor connected to the ground lead of a 2-
wire fan. The AIN input only responds to pulse widths
greater than 10µs.
