MAX6316–MAX6322
5-Pin μP Supervisory Circuits with
Watchdog and Manual Reset
Maxim Integrated | 10www.maximintegrated.com
Applications Information
Watchdog Input Current
The WDI input is internally driven through a buffer and
series resistor from the watchdog counter. For minimum
watchdog input current (minimum overall power con-
sumption), leave WDI low for the majority of the watch-
dog timeout period. When high, WDI can draw as much
as 160µA. Pulsing WDI high at a low duty cycle will
reduce the effect of the large input current. When WDI
is left unconnected, the watchdog timer is serviced
within the watchdog timeout period by a low-high-low
pulse from the counter chain.
Negative-Going VCC Transients
These supervisors are immune to short-duration, nega-
tive-going V
CC
transients (glitches), which usually do
not require the entire system to shut down. Typically,
200ns large-amplitude pulses (from ground to V
CC
) on
the supply will not cause a reset. Lower amplitude puls-
es result in greater immunity. Typically, a V
CC
transient
that goes 100mV under the reset threshold and lasts
less than 4µs will not trigger a reset. An optional 0.1µF
bypass capacitor mounted close to V
CC
provides addi-
tional transient immunity.
Ensuring Valid Reset Outputs
Down to V
CC
= 0V
The MAX6316_/MAX6317H/MAX6318_H/MAX6319_H/
MAX6321HP/MAX6322HP are guaranteed to operate
properly down to V
CC
= 1V. In applications that require
valid reset levels down to V
CC
= 0V, a pulldown resistor
to active-low outputs (push/pull and bidirectional only,
Figure 8) and a pullup resistor to active-high outputs
(push/pull only, Figure 9) will ensure that the reset line
is valid while the reset output can no longer sink or
source current. This scheme does not work with the
open-drain outputs of the MAX6320/MAX6321/MAX6322.
The resistor value used is not critical, but it must be
large enough not to load the reset output when V
CC
is
above the reset threshold. For most applications,
100kΩ is adequate.
Watchdog Software Considerations
(MAX6316/MAX6317/MAX6318/
MAX6320/MAX6321)
One way to help the watchdog timer monitor software
execution more closely is to set and reset the watchdog
input at different points in the program, rather than
pulsing the watchdog input high-low-high or low-high-
low. This technique avoids a stuck loop, in which the
watchdog timer would continue to be reset inside the
loop, keeping the watchdog from timing out.
OUTPUTS OF THE MAX6321/MAX6322.
