f75387 Feature Integration Technology Inc., f75387 Datasheet - Page 16

• Manufacturer Part Number: f75387
• Description: ?1o C Accuracy H/w Monitor Ic With Automatic Fan Speed Control
• Manufacturer: Feature Integration Technology Inc.

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 software fan speed control. As for speed mode and temperature mode, they are more
intelligent fan speed control and described as below:
1. Speed mode
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 F75387 will get the full speed count value. 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.
2. Temperature mode
At this mode, the F75387 provides automatic fan speed control related to temperature variation of CPU/GPU or the
system. The F75387 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 6-2 as example. When temperature boundaries
are set as 45, 55, 65, and 75°C and there are five intervals (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, the
F75387 will adjust PWMOUT duty-cycle to meet 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 variation. The F75387 will take
charge of all the fan speed control and need no software support.
PWMOUT
In both “SPEED” and “TEMPERATURE” modes, the F75387 adjust PWMOUT duty-cycle according to current fan
count and expected fan count. It will operate as follows:
(1). When expected count is FFFFh, PWMOUT duty-cycle will be set to 00h to turn off fan.
(2). When expected count is 0000h, PWMOUT duty-cycle will be set to FFh to turn on fan with full speed.
(3). If both (1) and (2) are not true,
Duty-cycle operating process
75 Degree C
65 Degree C
55 Degree C
45 Degree C
14
Figure 6-2
Desired Counts
0100h
0200h
0300h
0400h
0500h
July, 2007
F75387
0.27P