MB3773
EXAMPLE 8 : Stopping Watch-dog Timer (Monitering only supply voltage)
These are example application circuts in which the MB3773 monitors supply voltage alone without resetting
the microcomputer 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 Cr pin voltage to VREF .
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 instataneous 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 microcomputer is reset, the solution is to add a gate, as in examples c and d.
a Using NPN transistor
VCC(5V)
MB3773
Logic circuit
1
2
3
4
8
7
6
5
RESET
RESET
CK
HALT
GND
R2=1k
R1=1M
CT
b Using PNP transistor
VCC (5V)
MB3773
Logic circuit
RESET
RESET
CK
1
2
3
4
8
7
6
5
HALT
GND
R2=1k
R1=51k
CT
(Continued)
16
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