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EXAMPLE 4: Monitoring Two Supply Voltages (with hysteresis, reset output and NMI)
V
(12 V)
CC2
V
(5 V)
CC1
C
T
Example : Comp. 1, Comp. 2
: MB4204, MB47393
Notes : The 5 V supply voltage is monitored by the MB3773.
The 12 V supply voltage is monitored by the external circuit. Its output is connected to the NMI
terminal and, when voltage drops, Comp. 2 interrupts the logic circuit.
Use V
(
5 V) to power the comparators (Comp. 1 and Comp. 2) in the external circuit shown
CC1
above.
The detection voltage of the V
a hysteresis width of approximately 0.2 V.
V
detection voltage and hysteresis width can be found using the following formulas:
CC2
Detection voltage
Hysteresis width
MB3773
1
8
2
7
3
6
4
5
1.2 k
R
1
4.7 k
5.1 k
R
R
5
2
(
12 V) supply voltage is approximately 9.2 V/9.4 V and has
CC2
R
(R
// R
3
4
V
2H
R
// R
4
5
R
R
3
5
V
2L
R
5
V
V
V
HYS
2H
2L
30 k
R
3
180 k
10 k
R
R
4
6
+
+
_
_
Comp. 1
Comp. 2
)
5
V
REF
(Approximately 9.4 V in the above illustration)
V
REF
(Approximately 9.2 V in the above illustration)
MB3773
Logic circuit
RESET
RESET
CK
NMI or port
GND
15
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