W83781D Datasheet, PDF (18/53 Pages) Winbond – MONITORING IC

W83781D
PRELIMINARY
The input voltage can be expressed as following equation.
V_IN
=
V_s
×
R₂
R₁ + R₂
The value of R₁ and R₂ can be selected to 28K Ohms and 10K Ohms, respectively, when the input
voltage is 12V. The Pin 33 is connected to +5V power supply to provide analog power, and this
voltage is connected to internal resistors to monitor the +5V voltage.
The negative voltage should be connected an op amps to invert and reduce the -5V and -12V
voltage. The input voltage can be calculated by following equation.
V_S
=
−V_IN
× ( ^RF
R _IN
)
The Winbond recommended value is R_IN=90.9K Ohms and R_F=60.4K Ohms for -5V voltage input,
R_IN=210K Ohms and R_F=60.4K Ohms for -12V voltage input.
The temperature sensors are connected by a 10K Ohms, then connect to VREF (Pin 37). The sensors
should choose 10K Ohms at 25øC and B-value is 3435 for default R-T table. If the B-value is not
3435, the R-T table should be re-program to generate a correct temperature.
7.3 FAN Inputs and FAN Control
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 following.
Determine the fan counter according to:
Count = ^{1.35 × 106}
RPM × Divisor
The default divisor is 2 and defined at CR47.bit7~4 and CR4B.bit7~6. The followed table is an
example for the relation of divisor, PRM, and count.
Divisor
Nominal
PRM
Time per
Revolution
Counts
70% RPM Time for 70%
1
8800
6.82 ms
153
6160
9.74 ms
2
4400
13.64 ms
153
3080
19.48 ms
3
2200
27.27 ms
153
1540
38.96 ms
4
1100
54.54 ms
153
770
77.92 ms
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Publication Release Date : Nov. 1997
Revision 0.60