f75387 Feature Integration Technology Inc., f75387 Datasheet - Page 14

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

6.11. Fan Speed Monitoring and Control
Fan speed count
Inputs are provided by the signals from fans equipped with tachometer outputs. The level of these signals should
be set to TTL level, and maximum input voltage cannot be over 5V. If the input signals from the tachometer
outputs are over the 5V, the external trimming circuit should be added to reduce the voltage to obtain the input
specification. The normal circuit and trimming circuits are shown below:
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.
Fan speed control
FAN Out
+12V
GND
FAN Out
Fan with Tach Pull-Up to +12V, or Totern-Pole
+5V
GND
+12V
Fan with Tach Pull-Up to +5V, or Totern-Pole
Output and Register Attenuator
+5V
Output and Register Attenuator
Pull-up resister
4.7K Ohms
22K~30K
Pull-up resister
4.7K Ohms
1K~2.7K
Fan Input
Fan Input
10K
10K
FANIN1
F75387S
FANIN 1
F75387S
Count
RPM
12
=
=
1 ×
1 ×
5 .
Count
5 .
RPM
Connector
10
Connector
10
FAN
FAN
6
6
.
FAN Out
FAN Out
+12V
GND
+5V
GND
+12V
+5V
Totem-Pole Putput and Zener Clamp
Totem-Pole Putput and Zener Clamp
Fan with Tach Pull-Up to +12V, or
Fan with Tach Pull-Up to +5V, or
Pull-up resister < 1K
or totem-pole output
Pull-up resister < 1K
or totem-pole output
3.3V Zener
3.3V Zener
> 1K
> 1K
Fan Input
Fan Input
FANIN1
F75387S
FANIN 1
F75387S
July, 2007
F75387
0.27P