Feature Integration Technology Inc.
Fintek
F75373
5.4.3
Fan speed control mechanism
There are 3 modes to control fan speed and they are manual, fan speed mode and temperature mode. For manual
mode, it generally acts as PWM fan speed control. As for speed mode and temperature mode, they are more
intelligent fan speed control and described as below:
5.4.3.1 Fan Speed mode
Fan speed mode is an intelligent method according to expected fan speed pre-setting by BIOS. In the beginning, fan speed
will operate at full speed and the F75373S will get the full speed count value. Then fan speed slows down to rotate
at about 72.5% (8/11) of full speed. After that, the fan speed will automatically rotate according to the expected fan
speed setting by BIOS. The register CR74h and CR75h are used for this mode.
5.4.3.2 Temperature mode
At this mode, F75373S provides the clever system to automatically control fan speed related to temperature of
GPU or the system. The F75373S can provide four temperature boundaries and five intervals, and each interval
has its related fan speed count. All these values should be set by BIOS first. Take figure 5-11 as example. When
temperature setting value is 45,55,65, and 75°C. There are five intervals and each interval is 10°C. The related
desired fan speed counts for each interval are 0500h, 0400h, 0300h, 0200h, 0100h. When the temperature is
within 55~65°C, the fan speed count 300h will be load into FAN EXPECT COUNTregisters(CR74h~CR75h,
CR84h~CR85h). Then, F75373S will adjust PWMOUT duty-cycle to make fan speed match the expected value. It
can be said that the fan will be turned on with a specific speed set by BIOS and automatically controlled with the
temperature varying. The F75373S will take charge of all the fan speed control and need no software support.
Desired Counts
0100h
75 Degree C
0200h
65 Degree C
0300h
55 Degree C
0400h
45 Degree C
0500h
Figure 5-11
9
V0.25P
FINTEK [ FEATURE INTEGRATION TECHNOLOGY INC. ]
