AMC6821-Q1 Datasheet, PDF (23/54 Pages) Texas Instruments – INTELLIGENT TEMPERATURE MONITOR AND PWM FAN CONTROLLER

AMC6821-Q1
www.ti.com ...................................................................................................................................................................................................... SBAS475 – JUNE 2009
When the THERM limit is exceeded, the corresponding status flag bit (R-THERM or L-THERM of Status Register
1 or Status Register 2) is set to '1', and the THERM interrupt through the SMBALERT pin is generated if it is
enabled (THERMOVIE of bit Configuration Register 1 is set to '1'). This interrupt forces the SMBALERT pin low.
Note that the THERM pin is always forced to low when R-THERM = 1 or L-THERM = 1, no matter what the
status of THERMOVIE is. Reading the status registers clears the flag bit (R-THERM and L-THERM). Clearing the
flag bit makes the SMBALERT pin go back to high, but does not negate the THERM pin. It remains low until the
temperature falls 5＝C below the exceeded THERM limit. After this bit is cleared, the active flag bit (R-THERM
for remote temperature or L-THERM for local temperature) and the THERM interrupt are not re-armed until the
temperature falls 5°C below the exceeded THERM limit. This procedure is shown in Figure 23.
THERM Limit
5°
Temperature
THERM
INT via SMBALERT
INT via SMBALERT
Status Register Read
Figure 23. Operation of the THERM Interrupt and the THERM Pin
When working as an output, the status of the THERM pin affects the RPM fan. If the THERM-FAN-EN bit is set
('1'), the fan goes to full-speed (that is, the duty cycle is 100%) when the THERM pin goes low. However, when
THERM-FAN-EN = 0, the status of the THERM pin does not affect the fan speed.
THERM Pin As An Input
When this pin works as input, it is the input of the external hardware control signal; the THERM-IN bit of Status
Register 2 reflects the input. When the THERM pin is pulled low as an input, THERM-IN is set ('1') and the fan is
driven at full speed (that is, the duty cycle is 100%), no matter what THERM-FAN-EN is. The THERM-FAN-EN
bit has no effect when the THERM pin works as an input.
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