f75377 Feature Integration Technology Inc., f75377 Datasheet - Page 17

• Manufacturer Part Number: f75377
• Description: Monitor With Automatic Speed Control
• Manufacturer: Feature Integration Technology Inc.

Fan speed control mechanism
There are some modes to control fan speed and they are 1.Stage auto mode, 2. Linear auto mode. More
detail, please refer the description of registers.
Stage auto mode
At this mode, the F75377 provides automatic fan speed control related to temperature variation of
CPU/GPU or the system. The F75377 can provide two temperature boundaries and three intervals, and
each interval has its related fan speed PWM duty. All these values should be set by BIOS first. Take
figure as example. When temperature boundaries are set as 45 and 75°C and there are three intervals.
The related desired fan speed for each interval are 40%, 80% and 100% (fixed). When the temperature is
within 45~75’C, the fan speed will follow 80% PWM duty and that define in registers. 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 F75377 will take charge of all the fan speed control and need no software
support.
Below is a sample for Stage auto mode: Set temperature as 60°C, 40°C and Duty as 100%, 70%, 50%
PWM Clock Input
Temperature
75 Degree C
45 Degree C
Temperature
Fan Speed
G
D
S
R1
NMOS
+12V
R2
+
-
PNP Transistor
C
FAN
17
PWM Clock Input
100%
PWM Duty
80%
40%
G
D
S
R1
NMOS
+5V
R2
+
-
PNP Transistor
C
FAN
F75377
March.
V0.12P
, 2008