ADM1031 datasheet(22/32 Pages) AD

22 / 32 page

REV. 0

ADM1031

–22–

PWM_OUT

TACH/AIN

INT

FAN_FAULT

STATUS REG READ TO

CLEAR INTERRUPT

FULL SPEED

2 SECS

3RD TACH

FAILURE

4TH TACH

FAILURE

5TH TACH

FAILURE

CONTINUING

TACH FAILURE

Figure 22. Operation of

FAN_FAULT and Interrupt Pins

SDA

SCL

GND

VCC

ADM1031

INT (SMBALERT)

TACH1/AIN1

D1+

D1–/NTI

ADD

THERM

FAN_FAULT

PWM_OUT2

TACH2/AIN2

FAN_FAULT

TO SIGNAL

FAN FAILURE

CONDITION

CPU INTERRUPT

SDA

SCL

2N3904 OR PENTIUM III

CPU THERMAL DIODE

THERM

SIGNAL TO

THROTTLE

CPU CLOCK

3.3V

TACH

FAN1*

3-WIRE

FAN

PWM_OUT1

D2+

D2–

NDT3055L

(NMOS)

10k

TYP

3.3V

10k

TYP

3.3V

5V MAX

(DO NOT CONNECT

TO 12V)

10k

TYP

2.2k

3.3V

2.2k

3.3V

10k

TYP

3.3V

10k

TYP

10k

TYP

3.3V

FAN2

2-WIRE

FAN

NDT3055L

(N-MOS)

RSENSE

0.01 F

2N3904 OR PENTIUM III

CPU THERMAL DIODE

*IN ACTUAL APPLICATION, BOTH FANS MUST BE 2-WIRE OR 3-WIRE TYPE. A SINGLE BIT

CONTROLS WHETHER TACH1/AIN1 AND TACH2/AIN2 ARE ANALOG OR DIGITAL INPUTS.

Figure 23. Typical Application Circuit

The

INT pin will continue to generate interrupts after the asser-

tion of

FAN_FAULT since tach measurement continues even

after fan failure. Should the fan recover from its failure condi-

tion, the

FAN_FAULT signal will be negated, and the fan will

return to its normal operating speed.

Figure 23 shows a typical application circuit for the ADM1031.

Temperature monitoring can be based around a CPU diode or

discrete transistor measuring thermal hotspots. Either 2- or

3-wire fans may be monitored by the ADM1031, as shown.

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