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MAX1669EEE
Fan Controller and Remote Temperature Sensor with SMBus Serial Interface
General DescriptionThe MAX1669 fan controller includes a precise digital
thermometer that reports the temperature of a remote
sensor. The remote sensor is a diode-connected transis-
tor—typically a low-cost, easily mounted 2N3906 PNP
type—replacing conventional thermistors or thermocou-
ples. Remote accuracy is ±3°C for transistors from multi-
ple manufacturers, with no calibration needed. The
MAX1669 has an independent fan controller with a low-
current logic output requiring external power compo-
nents to interface to a DC brushless fan. The fan
controller has two modes of operation: a low-frequency
(20Hz to 160Hz) PWM mode intended for driving the fan
motor, or a high-impedance DAC output that generates
a variable DC control voltage. In PWM mode, the FAN
frequency can be synchronized to an external clock.
Other key features include general-purpose inputs/out-
puts (GPIOs) for fan presence detection and a thermo-
stat output intended as a fan override signal in case the
host system loses the ability to communicate. The inter-
nal ADC has a wide input voltage range and gives
overrange readings when too large an input voltage is
applied. Other error-checking includes temperature
out-of-range indication and diode open/short faults.
The MAX1669 is available in a space-saving 16-pin
QSOP package that allows it to fit adjacent to the
SLOT1 connector.
ApplicationsPentium®CPU Cooling
Desktop Computers
Notebook Computers
Servers
Workstations
FeaturesMeasures Remote CPU TemperatureNo Calibration Required20Hz to 160Hz PWM Output for FanPWM Frequency Sync Input (260kHz)Flexible Fan Interface: Linear or PWMSMBus 2-Wire Serial InterfaceProgrammable Under/Overtemperature AlarmsALERT
Latched Interrupt OutputOVERT
Thermostat OutputTwo GPIO PinsWrite-Once Configuration ProtectionSupports SMBus Alert Response±3°C Temperature Accuracy (-40°C to +125°C,
remote)3µA Standby Supply Current+3V to +5.5V Supply RangeSmall 16-Pin QSOP Package
MAX1669
Fan Controller and Remote Temperature Sensor
with SMBus Serial Interface19-1574; Rev 0; 1/00
Pentium is a registered trademark of Intel Corp.
Pin Configuration
Ordering Information
Typical Operating Circuit appears at end of data sheet.
MAX1669
Fan Controller and Remote Temperature Sensor
with SMBus Serial Interface
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC= +3.3V, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
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.
VCCto AGND...........................................................-0.3V to +6V
DXP, ADD_ to AGND.................................-0.3V to (VCC+ 0.3V)
DXN to AGND.......................................................-0.3V to +0.8V
SMBCLK, SMBDATA, ALERT, SYNC,
I/O1, I/O2, OVERT, FAN to AGND......................-0.3V to +6V
FAN to PGND............................................-0.3V to (VCC+ 0.3V)
PGND to AGND....................................................-0.3V to +0.3V
PWM Current....................................................-50mA to +50mA
SMBDATA Current.............................................-1mA to +50mA
I/O1, I/O2 Current...............................................-1mA to +25mA
DXN Current......................................................................±1mA
ESD Protection (all pins, Human Body Model).................2000V
Continuous Power Dissipation (TA= +70°C)
16-Pin QSOP (derate 8.30mW/°C above +70°C).......667mW
Operating Temperature Range (extended)......-55°C to +125°C
Junction Temperature.....................................................+150°C
Storage Temperature Range............................-65°C to +150°C
Lead Temperature (soldering, 10s)................................+300°C
MAX1669
Fan Controller and Remote Temperature Sensor
with SMBus Serial Interface
ELECTRICAL CHARACTERISTICS (continued)(VCC= +3.3V, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
Note 1:Guaranteed but not 100% tested.
Note 2:TRis the junction temperature of the remote diode. The temperature error specification is optimized to and guaranteed for a
diode-connected 2N3906 transistor with ideality factor = 1.013. Variations in the ideality factor “m” of the actual transistor
used will increase the temperature error by *. See the Temperature Error vs. Remote Diode Temperature graph in the
Typical Operating Characteristicsfor typical temperature errors using several random 2N3906s. See Remote Diode
Selectionfor remote diode forward-voltage requirements.
Note 3:The SMBus logic block is a static design that works with clock frequencies down to DC. While slow operation is possible, it
violates the 10kHz minimum clock frequency and SMBus specifications, and may monopolize the bus.
Note 4: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.
Note 5:Specifications to -40°C are guaranteed by design and not production tested.
MAX1669
Fan Controller and Remote Temperature Sensor
with SMBus Serial Interface
ELECTRICAL CHARACTERISTICS(VCC= +3.3V, TA
= -40°C to +85°C, unless otherwise noted.) (Note 5)
MAX1669
Fan Controller and Remote Temperature Sensor
with SMBus Serial Interface
TEMPERATURE ERROR
vs. LEAKAGE RESISTANCEMAX1669-01
LEAKAGE RESISTANCE (MΩ)
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR
vs. REMOTE DIODE TEMPERATURE
MAX1669-02
TEMPERATURE (°C)
TEMPERATURE ERROR (10K100K1M10M100M
TEMPERATURE ERROR vs.
POWER-SUPPLY NOISE FREQUENCY MAX1669-03
PSNF (Hz)
TEMPERATURE ERROR (
TEMPERATURE ERROR
vs. DXP - DXN CAPACITANCE
MAX1669-05
DXP-DXN CAPACITANCE (nF)
TEMPERATURE ERROR (
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX1669-06
SUPPLY VOLTAGE (V)
STANDBY SUPPLY CURRENT (
RESPONSE TO THERMAL SHOCK
MAX1669-07
TIME (sec)
TEMPERATURE (
°C)0
PWM FREQUENCY vs. CODE (F3F2F1F0)
MAX1669-08
CODE (F3F2F1F0)
PWM FREQUENCY (Hz)
Typical Operating Characteristics(Temperature error = measured - actual, TA= +25°C, unless otherwise noted.)
MAX1669
Fan Controller and Remote Temperature Sensor
with SMBus Serial Interface
Typical Operating Characteristics (continued)(Temperature error = measured - actual, TA= +25°C, unless otherwise noted.)
Pin Description
MAX1669
Fan Controller and Remote Temperature Sensor
with SMBus Serial Interface
_______________Detailed DescriptionThe MAX1669 temperature sensor is designed to work
with an external microcontroller (µC) or other intelligent
devices in computer fan-control applications. The µC is
typically a power-management or keyboard controller,
generating SMBus serial commands by “bit-banging’’
general-purpose input/output (GPIO) pins or through a
dedicated SMBus interface block.
Essentially an 8-bit serial analog-to-digital converter
(ADC) with a sophisticated front end, the temperature
measurement channel contains a switched-current
source, a multiplexer, and an integrating ADC.
Temperature data from the ADC is loaded into a data
register, where it is automatically compared with data
previously stored in over/undertemperature alarm regis-
ters and the critical register (Figure 1).
Figure 1. MAX1669 Temperature Sensor Functional Diagram
MAX1669
Fan Controller and Remote Temperature Sensor
with SMBus Serial InterfaceThe PWM or DAC fan control circuitry is completely
independent from the temperature measurement, and
software closes the temperature-control feedback loop
(Figure 2).
ADC and MultiplexerThe ADC is an averaging type that integrates over a
62ms period (typ), with excellent noise rejection. The
multiplexer automatically steers bias currents through
the remote diode, measures the forward voltage, and
calculates the temperature.
The DXN input is biased at 0.7V above ground by an
internal diode to set up the analog-to-digital (A/D)
inputs for a differential measurement. The worst-case
DXP-DXN differential input voltage range is 0.21V to
0.95V. Diode voltages that are outside the ADC input
range cause overrange indications rather than non-
monotonic readings. Overrange readings will return
+127°C. Excess resistance in series with the remote
diode causes approximately +1/2°C error/Ω. Likewise,
200µV of offset voltage forced on DXP-DXN causes
approximately +1°C error.
A/D Conversion SequenceWhen the device is taken out of standby mode, the
result of the measurement is available one conversion
time later (78ms max). If the ADC is busy, the results of
the previous conversion are always available. Toggling
the standby mode on and off is a good way to initiate a
new conversion since this action resets the rate timer.
Low-Power Standby ModeSupply-current drain during the 62ms conversion peri-
od is 500µA. Between conversions, the instantaneous
supply current is 18µA. In standby mode, supply cur-
rent drops to 3µA and the fan output is disabled.
SMBus Digital InterfaceFrom a software perspective, the MAX1669 appears as
a set of byte-wide registers that contain temperature
data, alarm threshold values, or control bits. A standard
SMBus 2-wire serial interface is used to read tempera-
ture data and write control bits and alarm threshold
data.
The MAX1669 employs four standard SMBus protocols:
write byte, read byte, send byte, and receive byte
(Figure 3). The two shorter protocols (receive and
send) allow quicker transfers, provided that the correct
data register was previously selected by a write or read
byte instruction. Use caution with the shorter protocols
in multimaster systems since a second master could
overwrite the command byte without informing the first
master.
The temperature data format is 7 bits plus sign in two’s
complement form for each channel, with the LSB repre-
senting +1°C (Table 1), MSB transmitted first.
Measurements are offset by +1/2°C to minimize internal
rounding errors; for example, +99.5°C to +100.4°C is
reported as +100°C.
Alarm Threshold RegistersThree registers store alarm threshold data, with high-
temperature (THIGH) and low-temperature (TLOW) reg-
isters that activate the ALERToutput, and a critical
overtemperature register (TCRIT) that activates theOVERToutput. If a measured temperature equals or
exceeds the THIGHor TLOWthreshold value, an ALERT
interrupt is asserted. Do not set the TCRITregister to
values outside of the temperatures in Table 1.
The power-on-reset (POR) state of the THIGHregister is
full scale (0111 1111b or +127°C). The POR state of the
TLOWregister is 1100 1001b or -55°C. The POR state of
the TCRITregister is 0110 0100b or +100°C.
OVERT Thermostat OutputThe OVERToutput is a self-clearing interrupt output
that is activated when the temperature equals or
exceeds TCRIT. OVERTnormally goes low when active,
but this polarity can be changed through the configura-
tion register. The latch is cleared when the temperature
reading is equal to or less than TCRITminus 5°C, which
provides for 5°C of hysteresis.
The ALERTand OVERTcomparisons are made after
each conversion, and at the end of a write command to
their respective temperature limit registers. For exam-
ple, if the limit is changed while the device is in standby
MAX1669
Fan Controller and Remote Temperature Sensor
with SMBus Serial Interfacemode, the ALERTand OVERToutputs respond correct-
ly according to the last valid A/D result.
Note that the ALERToutput does not respond to TCRIT
(OVERT) comparisons.
The OVERTlatch can implement an override control to
the FAN output, which forces the fan to VCC whenever
the TCRIT threshold is crossed. This override switch is
the backup fan control loop, and is enabled through the
FAN ON bit in the configuration register (bit 2). Note
that changing the duty to 100% in this way doesn’t
affect the contents of the DUTY register, and the FAN
output reverts to the preprogrammed duty factor (or
DAC voltage) when the OVERTlatch is reset.
Diode Fault AlarmA continuity fault detector at DXP detects whether the
remote diode has an open-circuit condition, short-cir-
cuit to GND, or short-circuit DXP-to-DXN condition. At
the beginning of each conversion, the diode fault is
checked and the status byte updated. This fault detec-
tor is a simple voltage detector; DXP rising above VCC-
1V or falling below DXN + 40mV constitutes a fault con-
dition. Also, if the ADC has an extremely low differential
input voltage, the diode is assumed to be shorted and
a fault occurs. Note that the diode fault isn’t checked
until a conversion is initiated, so immediately after
power-on reset the status byte indicates no fault is pre-
sent even if the diode path is broken. Any diode fault
will return a +127°C fault reading and cause ALERTto
go low.
Table 1. Data Format (Two’s Complement)
MAX1669
Fan Controller and Remote Temperature Sensor
with SMBus Serial Interface
ALERTInterruptsThe ALERTinterrupt output signal is latched and can
only be cleared by reading the Alert Response
address. Interrupts are generated in response to THIGH
and TLOWcomparisons, when there is a fault with the
remote diode, or when a high-to-low or low-to-high tran-
sition at I/O1 or I/O2 is detected.
The interrupt does not halt automatic conversions; new
temperature data continues to be available over the
SMBus interface after ALERTis asserted. The interrupt
output is open-drain so that devices can share a com-
mon interrupt line. The interface responds to the SMBus
Alert Response address, an interrupt pointer return-
address feature (see the AlertResponse Addresssec-
tion).
The ALERTinterrupt latch is set when the temperature
exceeds an ALARM threshold. ALERTwill not be set
again until the threshold is reprogrammed. This pre-
vents the ALERTlatch from being set again during the
interval between reading the Alert Response address
and updating the offending alarm threshold. Note that
this behavior is identical to the MAX1618 but is slightly
different from the MAX1617, which continues to inter-
rupt until the temperature no longer exceeds the alarm
threshold. Note also that if some new alarm condition
occurs, such as crossing the other alarm threshold or
having a GPIO transition, a new interrupt is generated.
ALERT Response AddressThe SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices that
lack the complex, expensive logic needed to be a bus
master. Upon receiving an ALERTinterrupt signal, the
host master can broadcast a receive byte transmission
to the Alert Response slave address (0001100b). Then
any slave device that generated an interrupt attempts
to identify itself by putting its own address on the bus
(Table 2).
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 arbitra-
tion rules apply, and the device with the lower address
code wins. The losing device does not generate an
acknowledge and continues to hold the ALERTline low
until serviced. Successful reading of the alert response
address clears the interrupt latch.
Command Byte FunctionsThe 8-bit command byte register (Table 3) is the master
index that points to the MAX1669’s other registers. The
register’s POR state is 00000001b, so a receive byte
transmission (a protocol that lacks the command byte)
that occurs immediately after POR returns the current
remote temperature data.
One-Shot ConversionThe one-shot command immediately forces a new con-
version cycle to begin. In software standby mode
(STBY bit = 1), a new conversion starts, after which the
device returns to standby mode. If a conversion is in
progress when a one-shot command is received, the
command is ignored. If a one-shot command is
received in autoconvert mode (STBY bit = 0) between
conversions, a new conversion begins, the conversion
rate timer is reset, and the next automatic conversion
takes place after a full period.
Configuration Byte FunctionsThe configuration byte register (Table 4) is used to
mask (disable) interrupts, set the OVERToutput polari-
ty, and put the device in software standby mode. Bit 1
of the configuration byte in Table 4 is for factory use
only and must be set to 1 (value at POR). This register’s
contents can be read back over the serial interface.
FAN PWM Frequency and
Duty Factor ControlThe fan speed is controlled by the average voltage
applied to the fan. The average voltage is equal to the
product of the motor power-supply voltage and the
duty factor. The duty factor is equal to zero upon start-
up and it is software controlled. The FAN output fre-
quency is controlled by the PWM frequency register
unless this register’s code is set to 1111b (Table 5). A
PWM frequency code of 1111b puts the FAN output in
DAC mode. For all other codes, the FAN frequency is in
the 20Hz to 160Hz range as shown in Table 5. For the
possible synchronized frequencies, also see Table 5.
The FAN output duty factor is controlled by the FAN
duty factor register unless the PWM frequency code is
Table 2. Read Format for the Alert
Response Address (0001100b)
