MB3773 Datasheet, PDF (16/31 Pages) Fujitsu Component Limited. – Power Supply Monitor with Watch-Dog Timer

MB3773
EXAMPLE 4: Monitoring Two Supply Voltages (with hysteresis, reset output and NMI)
V_CC2(12
V_CC1 (5
MB3773
Logic circuit
1
8
RESET
2
7
RESET
C_T
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 V_CC1 (  5 V) to power the comparators (Comp. 1 and Comp. 2) in the external circuit shown above.
• The detection voltage of the V_CC2 (  12 V) supply voltage is approximately 9.2 V/9.4 V and has a hysteresis width
of approximately 0.2 V.
V_CC2 detection voltage and hysteresis width can be found using the following formulas:
→ Detection voltage
V_2H

R₃  (R₄ // R₅)
R₄ // R₅
× V_{REF (Approximately 9.4 V in the above illustration)}
V_2L 
R₃  R₅
R₅
× V_REF
(Approximately 9.2 V in the above illustration)
→ Hysteresis width V_HYS  V_2H  V_2L
Document Number: 002-08513 Rev. *A
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