F71872
+12V
+12V
Pull-up resister
4.7K Ohms
Pull-up resister < 1K
or totem-pole output
+12V
FAN Out
GND
22K~30K
+12V
FAN Out
GND
Fan Input
10K
> 1K
FANIN 1
Fan Input
FANIN 1
3.3V Zener
F71872
F71872
FAN
Connector
Fan with Tach Pull-Up to +12V, or
Fan with Tach Pull-Up to +12V, or Totern-Pole
Output and Register Attenuator
Totem-Pole Putput and Zener Clamp
+5V
+5V
Pull-up resister
4.7K Ohms
Pull-up resister < 1K
or totem-pole output
+5V
1K~2.7K
Fan Input
+5V
> 1K
FAN Out
GND
FANIN1
Fan Input
FAN Out
GND
FANIN1
10K
3.3V Zener
F71872
F71872
FAN
Connector
Fan with Tach Pull-Up to
Fan with Tach Pull-Up to +5V, or Totern-Pole
Output and Register Attenuator
+5V, or
Totem-Pole Putput and
Zener 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
6.4.4 Fan speed control
The F71872 provides 2 fan speed control methods: 1. Linear FAN Control 2. PWM Duty Cycle
Linear Fan Control
The range of DC output is 0~3.3V, controlled by 8-bit register (CR6Bh for FAN1, CR7Bh for FAN2 and
CR8Bh for FAN3). 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:
19
July, 2007
V0.28P
FINTEK [ FEATURE INTEGRATION TECHNOLOGY INC. ]
