f75387 Feature Integration Technology Inc., f75387 Datasheet - Page 15

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

The F75387 provides 2 fan speed control methods:
Linear Fan Control
The range of DC output is 0~3.3V, controlled by 8-bit register (CR75 for FAN1 and CR85 for FAN2). 1 LSB is
about 0.013V. The output DC voltage is amplified by external OP circuit, thus to reach maximum FAN
OPERATION VOLTAGE, 12V. The output voltage will be given as followed:
And the suggested application circuit for linear fac control would be:
PWM duty Fan Control
The duty cycle of PWM can be programmed by a 8-bit register which are defined in the CR75h and CR85h.
The default duty cycle is set to 100%, that is, the default 8-bit registers is set to FFh. The expression of duty
can be represented as follows.
Fan speed control mechanism
PWM Clock Input
DC OUTPUT VOLTAGE
G
3.9K
D
S
Output_vol
R1
NMOS
R
Duty_cycle
+12V
R2
3
2
12V
+
-
tage
(%)
LM358
(V)
+
-
DC FAN Control with OP
1
=
R 10K
PNP Transistor
=
C
Programmed
3
3 .
PMOS
×
FAN
Programmed
C
47u
13
1. LINEAR FAN CONTROL
JP1
CON3
- 8
3
2
1
255
bit
1N4148
PWM Clock Input
- 8
Register
D1
255
bit
Register
C
0.1u
Value
R
4.7K
G
R 27K
Value
R
10K
×
D
S
R1
NMOS
100
FANIN MONITOR
%
2. PWM DUTY CYCLE
+5V
R2
+
-
PNP Transistor
C
July, 2007
FAN
F75387
0.27P