MAX6715A–MAX6729A/MAX6797A
Dual/Triple, Ultra-Low-Voltage, SOT23 µP
Supervisory Circuits
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magnitude indicated (reset threshold overdrive). The
graph shows the maximum pulse width that a negative-
going V
CC
transient may typically have without causing
a reset pulse to be issued. As the amplitude of the tran-
sient increases (i.e., goes farther below the reset
threshold), the maximum allowable pulse width
decreases. A 0.1µF bypass capacitor mounted close to
the V
CC
pin provides additional transient immunity.
Watchdog Software Considerations
Setting and resetting the watchdog input at different
points in the program, rather than “pulsing” the watch-
dog input high-low-high or low-high-low, helps the
watchdog timer to closely monitor software execution.
This technique avoids a “stuck” loop where the watch-
dog timer continues to be reset within the loop, keeping
the watchdog from timing out. Figure 6 shows an exam-
ple flow diagram where the I/O driving the watchdog
input is set high at the beginning of the program, set low
at the beginning of every subroutine or loop, then set
high again when the program returns to the beginning. If
the program should “hang” in any subroutine, the I/O is
continually set low and the watchdog timer is allowed to
time out, causing a reset or interrupt to be issued.
