W83791D Datasheet, PDF (27/46 Pages) Winbond – W83791D Winbond H/W Monitoring IC

W83791D
Preliminary
6.6.2 Monitor negative voltage:
The negative voltage should be connected to two series resistors and a positive voltage VREF (equal to 3.6V).
In the Figure 11, the voltage V3 and V4 are two negative voltages and are -12V and -5V respectively. The voltage
V3 is connected to two serial resistors as well as another positive terminal VREF. Therefore, the voltage node
N12VIN would be a positive voltage if the scale of the two serial resistors are carefully selected. It is recommended
from Winbond that the scale of the two serial resistors are R5=232K ohms and R6=56K ohm. The input voltage of
node -12VIN can be calculated by the following equation.
N1 2 VIN
=
(VREF
+
V₅
)
×
(
232KΩ
)
232KΩ + 56KΩ
+
V₅
where VREF is equal to 3.6V.
If the V₅ is equal to -12V then the voltage is equal to 0.567V and the converted hexdecimal data is set to 35h
by the 8-bit ADC with 16mV-LSB.This monitored value should be converted to the real negative voltage and the
express equation is shown as follows.
V₅
=
N12VIN − VREF
1−β
×β
Where β is 232K/(232K+56K). If the N2VIN is 0.567 then the V5 is approximately equal to -12V.
The other negative voltage input V6 (approximate -5V) can also be evaluated by the similar method and the
serial resistors can be R7=120K ohms and R8=56K ohms by the Winbond recommended. The expression equation
of V6 With -5V voltage is shown as follows.
V₆
=
N5VIN − VREF
1 −γ
×γ
Where the β is set to 120K/(120K+56K). If the monitored ADC value in the N5VIN channel is 0.8635,
VREF=3.6V and the parameter β is 0.6818, then the negative voltage of V6 can be evaluated -5V.
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Publication Release Date: Aug, 2001
Revision 0.41