W83792AD/AG/D/G
7.6.2 Monitor negative voltage:
The negative voltage should be connected to two series resistors and a positive voltage VREF (equal
to 2.048V). 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=10K ohm. The input voltage of node -12VIN can be calculated
by the following equation.
232KΩ
232KΩ +10KΩ
N12VIN = (VREF + V5 )× (
) +V5
where VREF is equal to 2.048V.
If the V5 is equal to -12V then the voltage is equal to 1.467V and the converted hexdecimal data is set
to 60h by the 8-bit ADC with 8mV-LSB.This monitored value should be converted to the real negative
voltage and the express equation is shown as follows.
N12VIN −VREF × β
V5 =
1− β
Where β is 232K/(232K+10K). If the N2VIN is 1.467 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=10K ohms by the Winbond recommended. The
expression equation of V6 With -5V voltage is shown as follows.
N5VIN −VREF ×γ
V6 =
1−γ
Where the γ is set to 120K/(120K+10K). If the monitored ADC value in the N5VIN channel is 1.505,
VREF=2.048V and the parameter γ is 0.923, then the negative voltage of V6 can be evaluated -5V.
Publication Release Date: April 26, 2006
- 19 -
Revision 0.9
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