MAX793SCSE+C48 Maxim Integrated, MAX793SCSE+C48 Datasheet - Page 18

• Manufacturer Part Number: MAX793SCSE+C48
• Description: Supervisory Circuits 3.0V/3.3V Adjustable Microprocessor Supervisory Circuits
• Manufacturer: Maxim Integrated
• Series: MAX793, MAX793R, MAX793S, MAX793T, MAX794, MAX795, MAX795R, MAX795S, MAX795Tr

Specifications of MAX793SCSE+C48

• Number Of Voltages Monitored: 1
• Monitored Voltage: 3 V, 3.3 V
• Output Type: Active High, Active Low, Open Drain
• Manual Reset: Resettable
• Watchdog: Watchdog
• Battery Backup Switching: Backup
• Supply Voltage - Max: 5.5 V
• Chip Enable Signals: Yes
• Maximum Power Dissipation: 842 mW
• Power Fail Detection: Yes
• Supply Current (typ): 62 uA
• Supply Voltage - Min: 1 V

Figure 18 shows maximum transient duration vs. reset-
comparator overdrive, for which reset pulses are not
generated. The graph was produced using negative-
going V
the reset threshold by the magnitude indicated (reset
comparator overdrive). The graph shows the maximum
pulse width a negative-going V
have without causing a reset pulse to be issued. As
the amplitude of the transient increases (i.e., goes far-
ther below the reset threshold), the maximum allowable
pulse width decreases. Typically, a V
goes 40mV below the reset threshold and lasts for 10µs
or less does not cause a reset pulse to be issued.
A 0.1µF bypass capacitor mounted close to the V
pin provides additional transient immunity.
3.0V/3.3V Adjustable Microprocessor
Supervisory Circuits
Figure 18. Maximum Transient Duration without Causing a
Reset Pulse vs. Reset Comparator Overdrive
18
______________________________________________________________________________________
CC
100
pulses, starting at 3.3V and ending below
90
80
70
50
30
20
10
60
40
0
10 20
RESET COMPARATOR OVERDRIVE, V
30
40
50
CC
60 70
transient can typically
RST
CC
80
- V
CC
transient that
90
(mV)
100
CC
There is a way to help the watchdog timer monitor soft-
ware execution more closely, which involves setting
and resetting 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 within the loop, keeping the watchdog from
timing out. Figure 19 shows an example of a flow dia-
gram 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 problem
would quickly be corrected, since the I/O is continually
set low and the watchdog timer is allowed to time out,
causing a reset or interrupt to be issued.
Figure 19. Watchdog Flow Diagram
Watchdog Software Considerations
Program Loop
SET WDI LOW
Subroutine or
PROGRAM
SET WDI
RETURN
START
CODE
HIGH