F71805 Datasheet, PDF (16/94 Pages) Feature Integration Technology Inc. – Super H/W Monitor + LPC IO

F71805
+5V
+5V
FAN Out
GND
Pull-up resister
4.7K Ohms
1K~2.7K
Fan Input
FANIN1
10K
F71805
Fan with Tach Pull-Up to +5V, or Totern-Pole
Output and Register Attenuator
+5V
+5V
FAN Out
GND
FAN
Connector
Pull-up resister < 1K
or totem-pole output
> 1K
Fan Input
FANIN1
3.3V Zener
F71805
Fan with Tach Pull-Up to +5V, or
Totem-Pole Putput and Zener Clamp
Determine the fan counter according to:
Count = ^{1.5 ×106}
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.
RPM = ^{1.5 ×106}
Count
6.2.4 Fan speed control
The F71805 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:
Output_voltage (V) = 3.3× ^{Programmed 8 - bit Register Value}
255
And the suggested application circuit for linear fac control would be:
14
Dec., 2006
V0.25P