MB3773 Datasheet, PDF (20/31 Pages) Fujitsu Component Limited. – Power Supply Monitor with Watch-Dog Timer

MB3773
EXAMPLE 8: Stopping Watch-dog Timer (Monitoring only supply voltage)
These are example application circuits in which the MB3773 monitors supply voltage alone without resetting the micropro-
cessor even if the latter, used in standby mode, stops sending the clock pulse to the MB3773.
• The watch-dog timer is inhibited by clamping the C_T terminal voltage to V_REF.
The supply voltage is constantly monitored even while the watch-dog timer is inhibited.
For this reason, a reset signal is output at the occurrence of either instantaneous disruption or a sudden drop to low voltage.
Note that in application examples (a) and (b), the hold signal is inactive when the watch-dog timer is inhibited at the time of
resetting.
If the hold signal is active when tie microprocessor is reset, the solution is to add a gate, as in examples (c) and (d).
(a) Using NPN transistor
V_CC(5 V)
MB3773
1
8
2
7
3
6
4
5
R₂=1 kΩ
R₁=1 MΩ
Logic circuit
RESET
RESET
CK
HALT
GND
C_T
(b) Using PNP transistor
V_CC (5 V)
C_T
MB3773
1
8
2
7
3
6
4
5
R₂=1 kΩ
R₁=51
Document Number: 002-08513 Rev. *A
Logic circuit
RESET
RESET
CK
HALT
GND
(Continued)
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