MAX792MEPE Maxim Integrated, MAX792MEPE Datasheet - Page 12
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MAX792MEPE
Manufacturer Part Number
MAX792MEPE
Description
Supervisory Circuits
Manufacturer
Maxim Integrated
Series
MAX792, MAX792L, MAX792M, MAX792R, MAX792S, MAX792T, MAX820, MAX820L, MAX820M, MAX820R, MAX820S, MAX820Tr
Datasheet
1.MAX19586ETNTD.pdf
(16 pages)
Specifications of MAX792MEPE
Number Of Voltages Monitored
1
Monitored Voltage
2.75 V to 5.5 V
Undervoltage Threshold
4.25 V
Overvoltage Threshold
4.5 V
Output Type
Active High, Active Low, Push-Pull
Manual Reset
Resettable
Watchdog
Watchdog
Battery Backup Switching
No Backup
Power-up Reset Delay (typ)
280 ms
Supply Voltage - Max
5.5 V
Maximum Operating Temperature
+ 85 C
Mounting Style
Through Hole
Package / Case
PDIP N
Chip Enable Signals
Yes
Maximum Power Dissipation
842 mW
Minimum Operating Temperature
- 40 C
Power Fail Detection
Yes
Supply Current (typ)
150 uA
Supply Voltage - Min
2.75 V
default is 1.6s. Select alternative timeout periods by
connecting an external capacitor from SWT to GND
(see Selecting an Alternative Watchdog Timeout sec-
tion). When V
dog function is disabled.
WDO remains high if there is a transition or pulse at WDI
during the watchdog timeout period. The watchdog
function is disabled and WDO is a logic high when V
is below the reset threshold. If a system reset is desired
on every watchdog fault, simply diode-OR connect WDO
to MR (Figure 8). When a watchdog fault occurs in this
mode, WDO goes low, pulling MR low and causing a
reset pulse to be issued. As soon as reset is asserted,
the watchdog timer clears and WDO goes high. With
WDO connected to MR, a continuous high or low on WDI
will cause 200ms reset pulses to be issued every
1.6sec (SWT connected to V
asserted, if no transition occurs at WDI during the
watchdog timeout period, WDO goes low 70ns after the
falling edge of WDPO and remains low until the next tran-
sition at WDI (Figure 7). A single additional flip-flop can
force the system into a hardware shutdown if there are
two successive watchdog faults (Figure 8). When the
MAX792/MAX820 are operated from a 5V supply, WDO
has a 2 x TTL output characteristic.
As described in the preceding section, WDPO can be
used as the clock input to an external D flip-flop. Upon
the absence of a watchdog edge or pulse at WDI at the
end of a watchdog timeout period, WDPO will pulse low
for 1.7ms. The falling edge of WDPO precedes WDO by
70ns. Since WDO is high when WDPO goes low, the flip-
flop’s Q output remains high after WDO goes low (Figure
8). If the watchdog timer is not reset by a transition at
Microprocessor and Nonvolatile
Memory Supervisory Circuits
Figure 7. WDI, WDO, and WDPO Timing Diagram
12
WDPO
WDO
WDI
V
CC
______________________________________________________________________________________
= 5V
CC
is below the reset threshold, the watch-
70ns
1.6s
Watchdog-Pulse Output
CC
). When reset is not
Watchdog Output
MIN 100ns (V
MIN 300ns (V
CC
CC
= 5V)
= 3V)
CC
WDI, WDO remains low and the next WDPO following a
second watchdog timeout period clocks a logic low to
the Q output, pulling MR low and causing the
MAX792/MAX820 latch in reset. If the watchdog timer is
reset by a transition at WDI, WDO will go high and the
flip-flop’s Q output will remain high. Thus a system
shutdown is only caused by two successive watchdog
faults.
The SWT input controls the watchdog timeout period.
Connecting SWT to V
watchdog timeout period. Select an alternative watch-
dog timeout period by connecting a capacitor between
SWT and GND. Do not leave SWT floating and do not
connect it to ground. The following formula determines
the watchdog timeout period:
Watchdog Timeout Period =
where k = 27 for V
This applies for capacitor values in excess of 4.7nF. If
the watchdog function is unused, connect SWT to V
Figure 8. Two consecutive watchdog faults latch the system in
reset.
REACTIVATE
V
Selecting an Alternative Watchdog Timeout Period
CC
+5V
k x (capacitor value in nF)ms
9
4.7k
0.1µF
MR
CC
MAX792
MAX820
= 3V, and k = 16.2 for V
GND
V
* FOR SYSTEM RESET ON EVERY
CC
CC
WATCHDOG FAULT, OMIT THE
FLIP-FLOP, AND DIODE–OR
CONNECT WDO TO MR.
12
3
RESET
WDPO
WDO
WDI
selects the internal 1.6sec
15
1
11
16
*
D
CLOCK
CLEAR
0.1µF
V
CC
Q
Q
CC
RESET
I/O
µP POWER
CONSECUTIVE
WATCHDOG
INDICATION
= 5V.
V
FAULT
TWO
CC
CC
.