W83783S Datasheet, PDF (17/57 Pages) Winbond – MONITORING IC

W83783S
Preliminary
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
Where β is 232K/(232K+56K). If the N2VIN is 0.567 then the V5 is approximately equal to -12V.
The another negative voltage input V6 (approximate -5V) also can be evaluated by the similar
method and the serial resistors can be selected with R7=120K ohms and R8=56K ohms by the
Winbond recommended. The expression equation of V6 With -5V voltage is shown as follows.
V₆
=
N 5VIN − 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 evalated to be -
5V.
- 12 -
Publication Release Date: April 1999
Revision 0.55