MB3773
15
EXAMPLE 4: Monitoring Two Supply Voltages (with hysteresis, reset output and NMI)
VCC1 (5 V)
1
2
3
4
8
7
6
5
MB3773
RESET
RESET
CK
GND
Comp. 2
Example : Comp. 1, Comp. 2
: MB4204, MB47393
NMI or port
R6
+
_
+
_
VCC2(12 V)
180 kΩ
R4
30 kΩ
R3
5.1 kΩ
R2
1.2 kΩ
R1
4.7 kΩ
R5
Comp. 1
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 VCC1 ( = 5 V) to power the comparators (Comp. 1 and Comp. 2) in the external circuit shown
above.
• The detection voltage of the VCC2 ( = 12 V) supply voltage is approximately 9.2 V/9.4 V and has
a hysteresis width of approximately 0.2 V.
VCC2 detection voltage and hysteresis width can be found using the following formulas:
→ Detection voltage
→ Hysteresis width VHYS = V2H − V2L
R3 + (R4 // R5)
R4 // R5 × VREF
V2L = R3 + R5
R5 × VREF
(Approximately 9.4 V in the above illustration)
(Approximately 9.2 V in the above illustration)
CT
Logic circuit
V2H =
10 kΩ