MAX819MESA Maxim Integrated, MAX819MESA Datasheet - Page 15

• Manufacturer Part Number: MAX819MESA
• Description: Supervisory Circuits
• Manufacturer: Maxim Integrated
• Series: MAX817, MAX817L, MAX817M, MAX818, MAX818L, MAX818M, MAX819, MAX819L, MAX819Mr

Specifications of MAX819MESA

• Number Of Voltages Monitored: 1
• Monitored Voltage: 4.4 V
• Undervoltage Threshold: 4.25 V
• Overvoltage Threshold: 4.5 V
• Output Type: Active Low, Open Drain
• Manual Reset: Resettable
• Watchdog: No Watchdog
• Battery Backup Switching: Backup
• Power-up Reset Delay (typ): 280 ms
• Supply Voltage - Max: 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: SOIC-8 Narrow
• Chip Enable Signals: No
• Maximum Power Dissipation: 471 mW
• Minimum Operating Temperature: - 40 C
• Power Fail Detection: No
• Supply Current (typ): 11 uA
• Supply Voltage - Min: 0 V

To help the watchdog timer monitor software execution
more closely, 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 contin-
ue to be reset within the loop, keeping the watchdog from
timing out. Figure 15 shows an example of a 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 problem would quickly be
corrected, since the I/O is continually set low and the
watchdog timer is allowed to time out, triggering a reset or
an interrupt. As described in the Watchdog Input Current
section, this scheme results in higher average WDI input
current than does the method of leaving WDI low for the
majority of the timeout period and periodically pulsing it
low-high-low.
__________Typical Operating Circuit
*CE IN AND CE OUT APPLY TO MAX818 ONLY.
**WDI APPLIES TO MAX817/MAX818 ONLY.
+5V
0.1 F
Watchdog Software Considerations
0.1 F
BATT
CE IN*
MAX817
MAX818
MAX819
GND
V
+5V Microprocessor Supervisory Circuits
CC
CE OUT*
______________________________________________________________________________________
RESET
WDI**
OUT
0.1 F
CMOS
RAM
(MAX817/MAX818)
ADDRESS
DECODE
RESET
I/O
A0–A15
CLOCK
REAL-
TIME
P
Figure 15. Watchdog Flow Diagram
____Pin Configurations (continued)
TOP VIEW
CE IN
GND
GND
OUT
OUT
V
V
PFI
CC
CC
OR PROGRAM LOOP,
1
2
3
4
1
2
3
4
SUBROUTINE
SET WDI
DIP/SO/ MAX
DIP/SO/ MAX
RETURN
START
HIGH
LOW
WDI
END
SET
MAX818
MAX819
8
7
6
5
8
7
6
5
BATT
RESET
WDI
CE OUT
BATT
RESET
MR
PFO
15