f75377 Feature Integration Technology Inc., f75377 Datasheet - Page 16

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

Fan speed control
to obtain the input specification. The normal circuit and trimming circuits are shown as follows:
Determine the fan counter according to:
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 tachometer output per round.
The F75377 provides PWM DUTY fan speed control method. The duty cycle of PWM can be
programmed by a 8-bit register. 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.
Count
RPM
Duty_cycle
=
=
FAN Out
FAN Out
1 ×
1 ×
Fan with Tach Pull-Up to +12V, or Totern-Pole
+5V
GND
5 .
Count
Fan with Tach Pull-Up to +5V, or Totern-Pole
5 .
+12V
GND
RPM
10
+5V
10
+12V
(%)
6
6
Output and Register Attenuator
Output and Register Attenuator
=
Programmed
Pull-up resister
4.7K Ohms
1K~2.7K
Pull-up resister
4.7K Ohms
22K~30K
Fan Input
10K
Fan Input
8bit
10K
255
FANIN1
Register
F75377
FANIN 1
F75377
16
Value
Connector
×
Connector
FAN
100
FAN
FAN Out
FAN Out
+5V
GND
%
+12V
GND
+5V
Totem-Pole Putput and Zener Clamp
+12V
Totem-Pole Putput and Zener Clamp
Fan with Tach Pull-Up to +5V, or
Fan with Tach Pull-Up to +12V, or
Pull-up resister < 1K
or totem-pole output
3.3V Zener
Pull-up resister < 1K
or totem-pole output
> 1K
3.3V Zener
> 1K
Fan Input
Fan Input
FANIN1
F75377
F75377
FANIN 1
F75377
March.
V0.12P
, 2008