W83791G Datasheet, PDF (26/99 Pages) Winbond – Winbond H/W Monitoring IC

W83791D/G
6.6.1 Monitor over 4.096V voltage:
The input voltage +12VIN can be expressed as the following equation.
12VIN
= V₁
×
R₂
R₁ + R₂
The value of R1 and R2 can be selected to 28K Ohms and 10K Ohms, respectively, when the input
voltage V1 is 12V. The node voltage of +12VIN should be subject to under 4.096V for the maximum
input range of the 8-bit ADC. The pin 13 and pin 29 are discretely connected to the power supply +5V
and 5VSB. There are two functions in these pins with 5V. The first function is to supply internal analog
power in the W83791D/G and the second one is that these voltages are all connected to internal serial
resistors to monitor the +5V and 5VSB voltage.
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.
N12VIN
=
(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 γ is set to 120K/ (120K+56K). If the monitored ADC value in the N5VIN channel is 0.8635,
VREF=3.6V and the parameter γ is 0.6818, then the negative voltage of V6 can be evaluated -5V.
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Publication Release Date: April 14, 2006
Revision 1.1