W83782D Datasheet, PDF (23/73 Pages) Winbond – MONITORING IC

Preliminary W83782D
Bipolar Transistor
Temperature Sensor
C
B _2N3904
E
OR
Pentium II
CPU
D+
Therminal
Diode
D-
R=30K, 1%
VREF
PIITDx
C=3300pF
R=30K, 1%
W83782D
PIITDx
C=3300pF
Figure 12.
6.4 FAN Speed Count and FAN Speed Control
6.4.1 Fan speed count
Inputs are provides for signals from fans equipped with tachometer outputs. The level of these signals
should be set to TTL level, and maximum input voltage can not be over +5.5V. If the input signals
from the tachometer outputs are over the VCC, the external trimming circuit should be added to
reduce the voltage to obtain the input specification. The normal circuit and trimming circuits are
shown as Figure 13.
Determine the fan counter according to:
Count = ^{1.35 × 106}
RPM × Divisor
In other words, the fan speed counter has been read from register CR28 or CR29 or CR2A, the fan
speed can be evaluated by the following equation.
R P M = ^{1.35 × 10 6}
Count × Divisor
- 17 -
Publication Release Date: April 1999
Revision A1