F81867 Datasheet, PDF (43/315 Pages) Feature Integration Technology Inc. – 6 UARTs μSuper IO With 128 Bytes FIFO and Power Saving Functions

F81867
Fig 7-11 Linear mode fan control illustration
a. Once the temperature is lower than 40°C, the lowest fan speed keeps in 3,000 RPM (50% of full
speed).
b. Once the temperature is over 40°C,50°C and 60°C, the fan speed will vary from 3,000 to 4,800
RPM almost linearly with the temperature variation because the temp.-fan speed monitoring
flash interval is 1sec.
c. Once the temperature goes over 70°C, the fan speed will directly increase to full speed 6,000
RPM.
d. If the hysteresis is 5°C (default is 4°C), once the temperature becomes lower than 65°C (instead
of 70°C), the fan speed wull reduce from full speed and decrease linearly with the temperature.
PWMOUT Duty-cycle operating process
In both “Manual RPM” and “Temperature RPM” modes, the F81867 adjust PWMOUT duty-cycle
according to current fan count and expected fan count. It will operate as follows:
1. When expected count is 0xFFF, PWMOUT duty-cycle will be set to 0x00 to turn off fan.
2. When expected count is 0x000, PWMOUT duty-cycle will be set to 0xFF to turn on fan with full
speed.
3. If both (1) and (2) are not true,
When PWMOUT duty-cycle decrease to MIN_DUTY(≠ 00h), obviously the duty-cycle will
decrease to 00h next, the F81867 will keep duty-cycle at 00h for 1.6 seconds. After that,
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Dec, 2011
V0.12P