MB3773 Datasheet, PDF (15/29 Pages) Fujitsu Component Limited. – Power Supply Monitor with Watch-Dog Timer

MB3773
EXAMPLE 4: Monitoring Two Supply Voltages (with hysteresis, reset output and NMI)
VCC2(12 V)
VCC1 (5 V)
MB3773
Logic circuit
1
8
RESET
2
7
RESET
CT
3
6
4
5
30 kΩ
R3
180 kΩ
R4
10 kΩ
R6
CK
NMI or port
GND
+
+
_
1.2 kΩ
R1
Comp. 1
_
Comp. 2
5.1 kΩ
R2
4.7 kΩ
R5
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 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
V2H =
R3 + (R4 // R5)
R4 // R5
× VREF
(Approximately 9.4 V in the above illustration)
R3 + R5
V2L =
R5
× VREF
(Approximately 9.2 V in the above illustration)
→ Hysteresis width VHYS = V2H − V2L
15