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MAX6653AEE+-MAX6653AEE+T
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 INTor
THERMoutputs. 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 ControllersPWM_OUTSMBCLK
SMBDATA
INT
ADD
SDR
SDL
DXP
DXN
TOP VIEW
MAX6653
QSOPTACH/AIN
CRT0
VCC
CRT1
GND
THERM
FAN_FAULT
Pin Configurations19-2865; Rev 1; 12/03
Ordering Information
PARTTEMP RANGEPIN-PACKAGE
MAX6653AEE-40°C to +125°C16 QSOP
MAX6663AEE-40°C to +125°C16 QSOP
MAX6664AEE-40°C to +125°C16 QSOP
Typical Operating Circuits appear at end of data sheet.
Functional Diagram appears at end of data sheet.Pin Configurations continued 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(VCC= +3.0V to +5.5V, TA= 0°C to +125°C, unless otherwise noted. Typical values are at VCC= +3.3V,TA= +25°C.) (Note1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSOperating Supply Voltage RangeVCC3.05.5V
Standby CurrentSMBDAT = SMBCLK = 1, register 00h = 00h10µA
Operating CurrentISSMBDAT = SMBCLK = 10.51mA
Average Operating CurrentConversion rate = 4Hz (default)150300µAC C = + 3.3V , TA = 0° C to + 100° C ,60°C ≤ TR ≤ + 100° C ±1
VCC = +3.3V, 0° C ≤ TR ≤ +100° C±3External Temperature Error
VCC = +3.3V, -25° C ≤ TR ≤ +125° C±4C
VCC = +3.3V, 0° C ≤ TA ≤ +100° C±2Internal Temperature ErrorVCC = +3.3V, -40° C ≤ TA ≤ +125° C±4° C
0.125° CTemperature Resolution
(Internal and External)11Bits
Fan TACHOMETER Accuracy(Note 2)6%
Fan TACHOMETER Full-Scale
Count255
Divisor = 1, fan count = 1534400
Divisor = 2, fan count = 1532200
Divisor = 4, fan count = 1531100
TACHOMETER Nominal Input
RPM
Divisor = 8, fan count = 153550
RPM
Internal Clock Frequency254270286kHz
TACHOMETER Conversion Cycle
Time637ms
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
Note 1:Tested at +85oC. Values through the temperature range are guaranteed by design.
Note 2:Not production tested, guaranteed by design.
ELECTRICAL CHARACTERISTICS (continued)(VCC= +3.0V to +5.5V, TA= 0°C to +125°C, unless otherwise noted. Typical values are at VCC= +3.3V,TA= +25°C.) (Note1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSTemperature Conversion Time250ms
Conversion Rate Timing Error(Note 2)2525%
High level80100120Remote-Diode Sourcing CurrentLow level81012µA
DXN Source Voltage0.7V
TACHOMETER Input Hysteresis100mV
Output Low Voltage (Sink Current)VOL
SDL, SDR, THERM, FAN_FAULT, SMBDATA,
PWM_OUT, VCC = +3V, IOUT = 6mA,
INT, VCC = +3V, IOUT = 4mA
0.4V
Output High Leakage CurrentIOHINT, SDL, SDR, THERM, FAN_FAULT,
SMBDATA, PWM_OUT1µA
Logic Low Input VoltageVILSMBDATA, SMBCLK, INT, THERM, TACH/AIN0.8V
3.0V2.2Logic High Input VoltageVIHSMBDATA, SMBCLK, INT,
THERM, TACH/AIN5.5V2.6V
Input Leakage CurrentILEAKSMBDATA, SMBCLK, INT, THERM;
VIN = VCC or GND±1µA
Input CapacitanceCIN5pF
SMBus TIMINGSerial Clock FrequencyfSCLK(Note 2)10100kHz
Clock Low PeriodtLOW10% to 10% (Note 2)4µs
Clock High PeriodtHIGH90% to 90% (Note 2)4.7µs
Bus Free Time Between Stop and
Start ConditiontBUF(Note 2)4.7µs
SMBus Start Condition Setup
TimetSU:STA90% of SMBCLK to 90% of SMBDATA (Note 2)4.7µs
Start Condition Hold TimetHD:STO10% of SMBDATA to 10% of SMBCLK (Note 2)4µs
Stop Condition Setup TimetSU:STO90% of SMBCLK to 10% of SMBDATA (Note 2)4µs
Data Setup TimetSU:DAT10% of SMBDATA to 10% of SMBCLK (Note 2)250ns
Data Hold TimetHD:DAT10% of SMBCLK to 10% of SMBDATA (Note 2)300ns
SMBus Fall TimetF(Note 2)300ns
SMBus Rise TimetR(Note 2)1000ns
SMBus Timeout293745ms
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)
REMOTE TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATUREMAX6653 toc03
REMOTE-DIODE TEMPERATURE (°C)
TEMPERATURE ERROR (
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
MAX6653 toc04
DIE TEMPERATURE (°C)
LOCAL TEMPERATURE ERROR (
°C)
REMOTE TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
MAX6653 toc05
POWER-SUPPLY NOISE FREQUENCY (MHz)
REMOTE TEMPERATURE ERROR (
100mVP-P
250mVP-P
LOCAL TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
MAX6653 toc06
POWER-SUPPLY NOISE FREQUENCY (MHz)
REMOTE TEMPERATURE ERROR (
100mVP-P
250mVP-P
TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCYCOMMON-MODE NOISE FREQUENCY (MHz)
TEMPERATURE ERROR (
°C)
MAX6653 toc0740mVP-P
20mVP-P
TEMPERATURE ERROR
vs. DIFFERENTIAL-MODE NOISE FREQUENCY
MAX6653 toc08
DIFFERENTIAL-MODE NOISE FREQUENCY (MHz)
TEMPERATURE ERROR (30mVP-P
20mVP-P
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCEMAX6653 toc09
DXP-DXN CAPACITANCE (nF)
TEMPERATURE ERROR (10100
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6653 toc01
SUPPLY VOLTAGE (V)
STANDBY SUPPLY CURRENT (
AVERAGE OPERATING SUPPLY CURRENT
vs. CONVERSION RATE
MAX6653 toc02
CONVERSION RATE (Hz)
SUPPLY CURRENT (21
500
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
PIN
MAX6653
QSOP
MAX6663/
MAX6664
QSOP
NAMEFUNCTION1PWM_OUTDigital Output (Open Drain). Pulse-width modulated output to external power transistor.
Requires a pullup resistor (10kΩ typ).2TACH/AINDigital/Analog Input. Fan tachometer input. May be reprogrammed as an analog input to
measure speed of a 2-wire fan. See Figure 5.—CRIT0Input. Used in conjunction with CRIT1 to set THERM and SHUTDOWN default set points
(see Table 1).—CRIT1Input. Used in conjunction with CRIT0 to set THERM and SHUTDOWN default set points
(see Table 1).3, 4N.C.No Connection. Not internally connected.5GNDGroundVCCPower Supply. Bypass with a 0.01µF capacitor to GND.THERM
Digital I/O (Open Drain). An active-low thermal-overload output to indicate that the
overtemperature set point has been exceeded. 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 forced full-on. Requires a pullup resistor (10kΩ typ).FAN_FAULTDigital Output (Active Low, Open Drain). Signals a fan fault. Requires a pullup resistor
(10kΩ typ).DXNCombined Current Sink and A/D Negative Input. DXN is internally biased to a diode
voltage above ground.10DXP
Combined Current Source and A/D Positive Input for the Remote-Diode Channel. Do not
leave DXP floating; connect DXP to DXN if no remote diode is used. Place a 2200pF
capacitor between DXP and DXN for noise filtering.—SDLAn Active-Low Open-Drain Output. It indicates that local temperature is above the
shutdown set point. Normally used to directly deactivate the CPU power supply.—SDRAn Active-Low Open-Drain Output. It indicates that remote temperature is above the
shutdown set point. Normally used to directly deactivate the CPU power supply.11, 12N.C.Internal Connection. Leave floating or connect to GND.13ADDThree-State Logic Input. Sets the 2 lower bits of the device SMBus address (Table 2).
ADD is not an ordinary logic input pin; ADD should be connected to VCC, GND, or float.14INT
Digital Output (Open Drain). Can be programmed as an interrupt output for
temperature/fan speed interrupts. Requires a pullup resistor (10kΩ typ). For the
MAX6653/MAX6663, it can be used also as an input. If pulled low, fan speed is forced to
maximum unless masked.15SMBDATASMBus Serial-Data Input/Output (Open Drain). Requires a pullup resistor (10kΩ typ).16SMBCLKSMBus Serial-Clock Input. Requires a pullup resistor (10kΩ typ).12N.C.Internal Connection. Leave floating or connect to GND.
Pin Description
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.
THERM SET POINT (°C)
SHUTDOWN SET POINT (°C)CRIT1CRIT0REMOTELOCALREMOTELOCALGNDOpen855511080
GNDGND906011585
GNDVCC956512090
OpenOpen1007012595
OpenGND1057512595
OpenVCC1108012595
VCCOpen1158512595
VCCGND1209012595
VCCVCC1259512595
Table 1. MAX6653 Power-Up Set-Point Decoding
Table 2. MAX6653/MAX6663/MAX6664
Slave Address Decoding
ADD PINADDRESSGND0101 100
No connect0101 110
VCC0101 101
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan ControllersFigure 1. SMBus Protocols
Write Byte Format
Read Byte Format
Send Byte FormatReceive Byte FormatSlave Address: equiva-
lent to chip-select line of
a 3-wire interface
Command Byte: selects which
register you are writing to
Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
Slave Address: equiva-
lent to chip-select line
Command Byte: selects
which register you are
reading from
Slave Address: repeated
due to change in data-
flow direction
Data Byte: reads from
the register set by the
command byte
Data Byte: writes data to the
register commanded by the
last read byte or write byte
transmission
Data Byte: reads data from
the register commanded
by the last read byte or
write byte transmission;
also used for SMBus alert
response return addressS = Start condition
P = Stop condition
Shaded = Slave transmission
/ / / = Not acknowledged
ACK7 bits
ADDRESSACK8 bits
DATAACKP8 bits
COMMANDWR
ACK7 bits
ADDRESSACKSACK8 bits
DATA7 bits
ADDRESSRD8 bits
SCOMMAND/ / / WR
ACK7 bits
ADDRESS8 bits
COMMANDACKPSWRACK7 bits
ADDRESSRD8 bits
DATAPS/ / / Figure 2. SMBus Write Timing Diagram
SMBCLKCDEFGHIJK
SMBDATA
tSU:STAtHD:STA
tLOWtHIGH
tSU:DATtHD:DATtSU:STOtBUF
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW M
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION, DATA EXECUTED BY SLAVE
M = NEW START CONDITION
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 ControllersFigure 3. SMBus Read Timing Diagram
SMBCLKCDEFGHIJK
SMBDATA
tSU:STAtHD:STA
tLOWtHIGH
tSU:DATtHD:DATtSU:STOtBUFM
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLEAR PULSE
L = STOP CONDITION, EXECUTED BY SLAVE
M = NEW START CONDITION
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
Table 3. Temperature Data High Byte Format
TEMP (°C)DIGITAL
OUTPUT (°C)
DIGITAL OUTPUT
(BINARY)130.00+1270111 1111
127.00+1270111 1111
126.00+1260111 1110
25.25+250001 1001
0.5000000 0000
0.0000000 0000—1111 1111
-125—1000 0011
-128—1000 0000
Diode fault
(short or open)—1000 0000
MAX6653/MAX6663/MAX6664emperature Monitors and
PWM Fan Controllers
Temperature Comparison
and Interrupt SystemAt the end of each conversion cycle, the converted
temperature data are compared to various set-point
thresholds to control the INT, THERM, SDL, and SDR
outputs. All temperature threshold limits are stored in
the threshold limit registers (Table 6) and can be
changed through the SMBus digital interface.
THERMis an active-low thermal-overload output indicat-
ing that the THERM overtemperature set point is exceed-
ed. With the THERMthreshold set to an appropriate value,
the THERMoutput can be used to control clock throttling.
When this pin is pulled low by an external signal, a status
bit (bit 7, status register 2) is set, and the fan speed is
unconditionally forced to full-on speed. The only way to
reset the status bit is to read status register 2. Connect a
10kΩpullup resistor between THERMand VCC.
Table 4. Temperature Data Low Byte Format Structure: LLLXXRRR*
Table 5. Temperature Conversion Rate Setting (Fan Filter Register (23h)—POR = 111)
FRACTIONAL TEMPERATURE (°C)DIGITAL OUTPUT (LOCAL)DIGITAL OUTPUT (REMOTE)0.000000X XXXXXXX XX 000
0.125001X XXXXXXX XX 001
0.25010X XXXXXXX XX 010
0.375011X XXXXXXX XX 011
0.5100X XXXXXXX XX 100
0.625101X XXXXXXX XX 101
0.75110X XXXXXXX XX 110
0.875111X XXXXXXX XX 111
BIT 4BIT 3BIT2CONVERSION RATE (Hz)CONVERSION TIME (s)000.062516010.1258100.254110.52
10011*Where: LLL = local fractional temperature bits, XX = don’t care, RRR = remote fractional temperature bits.
NAMEADDRESSR/WMAX6653 POR VALUEMAX6663/MAX6664 POR STATEDESCRIPTIONLTH14hR/WSet by CRIT0 and CRIT10011 1100Local temp high limit
LTL15hR/WSet by CRIT0 and CRIT10000 0000Local temp low limit
LTHER16hR/WSet by CRIT0 and CRIT10100 0110Local temp THERM limit
RTH18hR/WSet by CRIT0 and CRIT10101 0000Remote temp high limit
RTL19hR/WSet by CRIT0 and CRIT10000 0000Remote temp low limit
RTHER1AhR/WSet by CRIT0 and CRIT10110 0100Remote temp THERM limit
LTSD1BhR/WSet by CRIT0 and CRIT1N/ALocal temp shutdown limit
(MAX6653 only)
RTSD1ChR/WSet by CRIT0 and CRIT1N/ARemote temp shutdown limit
(MAX6653 only)
Table 6. Threshold Limit Registers
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.
Bits [7:5]MODE OF OPERATIONDESCRIPTION0x0PWM duty-cycle modeDirectly program the PWM duty cycle by writing to bits [3:0] of the fan-speed
configuration register (22h).
0x1RPM select mode
Program the desired fan speed by writing to the fan tachometer high-limit register
(10h). This value should be written after selecting the RPM mode. The
MAX6653/MAX6663/MAX6664 then adjust the PWM duty cycle to cause the fan to
spin at the programmed speed.
100Automatic modePWM duty cycle is automatically controlled by the remote temperature.
111Automatic modePWM duty cycle is automatically controlled by both the remote and the local
temperatures. See the Automatic Fan-Control Mode section.
Table 8. Setting the Fan-Speed Control Mode (Default = 100)
FAN CHARACTERISTICS REGISTER
(20H) POR = 011
BIT 5BIT 4BIT 3
PWM
FREQUENCY
(Hz)0011.70115.61023.4
1131.250037.50146.91062.51193.5
Table 7. Setting PWM Output Frequency
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
BITS [3:0] OF FAN-SPEED
CONFIGURATION REGISTER (22h)
BIT 3BIT 2BIT 1BIT 0
% DUTY
CYCLE (%)000017101411200027
0133104011470053016010671173008001871093111100
Table 9. Setting PWM Duty Cycle
Table 10. TRANGEFan-Control Temperature
Range Bits [2:0] TMIN/TRANGERegisters
(24h and 25h)—POR = 001
BIT 2BIT 1BIT 0TEMPERATURE
RANGE (°C)00110
Table 11.TMINFan-Control Start
Temperature; Bits [7:3] TMIN/TRANGE
Registers (24h—POR = 01000 and
25h—POR = 01100
BIT 7BIT 6BIT5BIT 4BIT3
MSB = +64°CLSB = +4°C
Min threshold = 0°C
Max threshold = +127°C
LSB/step size = +4°C
POR = +48°C or 01100b
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.
CountRPMN=×
675000,
Table 12. Spin-Up Time; Bits [2:0] Fan
Characteristics Register (20h)—POR = 101
BIT 2BIT 1BIT 0SPIN-UP
TIME (s)000.2010.4100.6110.801
120418
Table 13. Fan Filter Ramp Rate; Bits [6:5]
Fan Filter Register (23h)—POR = 10;
BIT 6BIT 5RAMP RATE
(x100% / 240)
RAMP RATE
(% DUTY CYCLE)010.416120.833
041.667183.333
FAN CHARACTERISTICS REGISTER (20h) POR = 01
BIT 7BIT 6NSPEED RANGE (FAIL SPEED)
(RPM)012647
1213240466218331
Table 14. N Factor for Speed-Range Adjustment (Assuming Two Tachometer Pulses
per Revolution)Figure 4. Simplified Tachometer Analog Input Structure
100Ω
VREF 10.1μF
TACH
INPUT
VREF 2CLK
MAX6653
MAX6663
MAX6664
