Feature Integration Technology Inc.
Fintek
F75373
+5V
+5V
Pull-up resister
4.7K Ohms
Pull-up resister < 1K
or totem-pole output
+5V
FAN Out
GND
1K~2.7K
+5V
FAN Out
GND
Fan Input
10K
> 1K
FANIN1
Fan Input
FANIN1
3.3V Zener
F75373S
F75373S
FAN
Connector
.Figure 5-8 Fan with Tach Pull-Up to +5V, or
Totem-Pole Putput and Zener Clamp
Figure 5-7. Fan with Tach Pull-Up to +5V, or Totern-Pole
Output and Register Attenuator
Determine the fan counter according to:
1.5×106
Count =
RPM
In other words, the fan speed counter has been read from register, the fan speed can be evaluated by the following equation. As
for fan, it would be best to use 2 pulses tachmeter output per round.
1.5×106
RPM =
Count
5.4.2
Fan speed control
The F75373S provides 2 fan PWM speed control. The duty cycle of PWM can be programmed by a 8-bit register which are
defined in the CR76h and CR86h. 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.
Programmed8 - bit Register Value
Duty_cycle(%) =
×100%
255
+5V
+12V
R1
R1
R2
R2
PNP Transistor
PNP Transistor
D
G
D
G
PWM Clock Input
NMOS
PWM Clock Input
NMOS
S
+
-
S
+
-
C
C
FAN
FAN
Figure 5-9
Figure 5-10
8
V0.25P
FINTEK [ FEATURE INTEGRATION TECHNOLOGY INC. ]
