THMC50_08 Datasheet, PDF (12/34 Pages) Texas Instruments – REMOTE/LOCAL TEMPERATURE MONITOR AND FAN CONTROLLER WITH SMBus INTERFACE

THMC50
REMOTE/LOCAL TEMPERATURE MONITOR AND
FAN CONTROLLER WITH SMBus INTERFACE
SLIS090 – JULY 1999
PRINCIPLES OF OPERATION
interrupt status register/interrupt status register mirror
The THMC50 contains a pair of interrupt status registers. These registers reflect the state of all of the possible
error conditions that the THMC50 monitors. When an error occurs during the conversion cycle, the
corresponding bit is set in the interrupt status register and the interrupt status register mirror. Once set, the bit
in the interrupt status register is cleared upon reading that register. Reading the interrupt status register does
not clear the mirror register, and vice versa. If the error condition persists after being cleared, the bit is again
set in both the interrupt status register and the mirror register.
analog output - FAN_SPD
The THMC50 has a single analog output, FAN_SPD/NTEST_IN, from an unsigned 8-bit DAC which produces
0 V to 2.5 V. This register is set to 0x00 on RST, which results in the minimal fan speed possible.
Note that if RST is asserted low, it is still possible for the FAN_SPD analog output to go to full scale (0xFF) if
THERM is asserted.
The FAN_SPD output must be amplified with external circuitry in order to achieve an output voltage range of
0 V to 12 V and an output current of at least 250 mA in order to drive a cooling fan. Figure 6 through Figure 11
illustrate external circuits that can be used to drive a fan.
FAN_SPD/NTEST_IN
+12 V
Q1
+
2N2219A
_
LM324
+12 V
R1
36 kΩ
R2
10 kΩ
Figure 6. External Fan Drive Circuit Using 1/4 LM324 and NPN Emitter-Follower, Single Supply
FAN_SPD/NTEST_IN
+12 V
R3
–
1 kΩ
+ _LM324
R4
1 kΩ
+12 V
Q1
BD136
2SA968
R1
39 kΩ
R2
10 kΩ
Figure 7. External Fan Drive Circuit Using 1/4 LM324 and PNP Transistor, Single Supply
12
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