W83782D Datasheet, PDF (21/73 Pages) Winbond – MONITORING IC

Preliminary W83782D
6.3.1 Monitor over 4.096V voltage:
The input voltage +12VIN can be expressed as 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 can be subject to less than 4.096V for the maximun
input range of the 8-bit ADC. Similarly, the node voltage of 5VSB (measure standby power VSB for
ATX power supply) also can be evaluated by using two series resistors R3 and R4 which real value
can be 5.1K ohms and 7.5K ohms so as to obtain the 5VSB is limited to less than 4.096V. The Pin 33
is connected to the power supply VCC with +5V. There are two functions in this pin with 5V. The first
function is to supply internal analog power in the W83782D and the second function is that this
voltage with 5V is connected to internal serial resistors to monitor the +5V voltage. The value of two
serial resistors are 34K ohms and 50K ohms so that input voltage to ADC is 2.98V which is less than
4.096V of ADC maximum input voltage. The express equation can represent as follows.
V_in
=
VCC
×
50KΩ
50KΩ + 34KΩ
≅
2.98V
where VCC is set to 5V.
6.3.2 Monitor negative voltage:
The negative voltage should be connected two series resistors and a positive voltage VREF (is equal
to 3.6V). In the Figure 11, the voltage V3 and V4 are two negative voltage which they are -12V and -
5V respectively. The voltage V3 is connected to two serial resistors then is connected to another
terminal VREF which is positive voltage. So as that the voltage node N12VIN can be obtain a
posedge voltage if the scales of the two serial resirtors are carefully selected. It is recommanded from
Winbond that the scale of two serial resistors are R5=232K ohms and R6=56K ohm. the The input
voltage of node -12VIN can be calculated by following equation.
N12VIN
=
(VREF
+
V₅
)×(
232KΩ
)
232KΩ + 56KΩ
+ V₅
where VREF is equal 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 votage and the express equation is shown as follows.
V₅
=
N12VIN − VREF
1−β
×β
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Publication Release Date: April 1999
Revision A1