MAX6316 Datasheet, PDF (10/16 Pages) Maxim Integrated Products – 5-Pin μP Supervisory Circuits with Watchdog and Manual Reset

5-Pin µP Supervisory Circuits with
Watchdog and Manual Reset
V_CC
t_RST
RESET
t_RP
WDI
t_WD
t_RP
MAX6316/MAX6317
MAX6318/MAX6320
MAX6321
V_CC
MAX6316
MAX6318
MAX6319
V_CC
GND
RESET
100k
Figure 7. Watchdog Timing Relationship
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 V_CC 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 = 0
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 = 0, a pull-down resistor
to active-low outputs (push/pull and bidirectional only,
Figure 8) and a pull-up 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
Figure 8. Ensuring RESET Valid to V_CC = 0 on Active-Low
Push/Pull and Bidirectional Outputs
MAX6317
MAX6318
V_CC
MAX6319
MAX6321*
100k
MAX6322* V_CC
GND
RESET
*THIS SCHEMATIC DOES NOT WORK ON THE OPEN-DRAIN
OUTPUTS OF THE MAX6321/MAX6322.
Figure 9. Ensuring RESET Valid to V_CC = 0 on Active-High
Push/Pull Outputs
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.
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