W83627THF_06 Datasheet, PDF (33/142 Pages) Winbond – Winbond LPC I/O

W83627THF/W83627THG
Bipolar Transistor
Temperature Sensor
C
B
2N3904
E
R=30K,1%
R=30K,1%
VREF
C=3300pF
VTIN
W83627THF
OR
Pentium II/III
CPU
D+
Therminal
Diode
D-
C=3300pF
CPUTIN
AGND
Figure 5-3
5.4 FAN Speed Count and FAN Speed Control
5.4.1 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’t be over VCC. 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
5-4 ~ 5-7.
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.
RPM = ^{1.35 × 106}
Count × Divisor
The default divisor is 2 and defined at CR47.bit7~4, CR4B.bit7~6, and Bank0 CR5D.bit5~7 which are
three bits for divisor. That provides very low speed fan counter such as power supply fan. The
followed table is an example for the relation of divisor, RPM, and count
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