MAX691ACWE+ Maxim Integrated Products, MAX691ACWE+ Datasheet - Page 15

• Manufacturer Part Number: MAX691ACWE+
• Description: IC MPU SUPERVISOR CIRCUIT 16SOIC
• Manufacturer: Maxim Integrated Products
• Type: Battery Backup Circuitr

Specifications of MAX691ACWE+

• Number Of Voltages Monitored: 1
• Output: Push-Pull, Push-Pull
• Reset: Active High/Active Low
• Reset Timeout: 140 ms Minimum
• Voltage - Threshold: 4.65V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.300", 7.5mm Width)
• Monitored Voltage: 0 V to 5.5 V
• Undervoltage Threshold: 4.5 V
• Overvoltage Threshold: 4.75 V
• Manual Reset: No
• Watchdog: Yes
• Battery Backup Switching: Yes
• Power-up Reset Delay (typ): 280 ms
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 0 V
• Supply Current (typ): 100 uA
• Maximum Power Dissipation: 762 mW
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 70 C
• Chip Enable Signals: Yes
• Minimum Operating Temperature: 0 C
• Output Type: Active High or Active Low or Open Drain
• Power Fail Detection: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The V
the battery switchover comparator and should not
exceed 0.03V/µs. A standard rule of thumb for filter
capacitance on most regulators is on the order of 100µF
per amp of current. When the power supply is shut off or
the main battery is disconnected, the associated initial
V
The V
nentially, which more than satisfies the maximum fall-time
requirement.
A way to help the watchdog timer keep a closer watch
on software execution 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
where the watchdog timer continues to be reset within
the loop, keeping the watchdog from timing out. Figure
14 shows an example flow diagram where the I/O dri-
ving the watchdog input is set high at the beginning of
the program, set low at the beginning of every subrou-
tine or loop, then set high again when the program
returns to the beginning. If the program should “hang”
in any subroutine, the I/O is continually set low and the
watchdog timer is allowed to time out, causing a reset
or interrupt to be issued.
CC
fall rate is just the inverse or 1A/100µF = 0.01V/µs.
CC
CC
fall rate decreases with time as V
fall time is limited by the propagation delay of
Watchdog Software Considerations
______________________________________________________________________________________
Maximum V
Microprocessor Supervisory Circuits
CC
CC
Fall Time
falls expo-
Figure 14. Watchdog Flow Diagram
OR PROGRAM LOOP
SUBROUTINE
SET WDI
RETURN
START
LOW
HIGH
END
WDI
SET
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