SOT23, Low-Power µP Supervisory Circuits

with Battery Backup and Chip-Enable Gating

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11

watchdog is set low in the beginning of the program,

set high at the beginning of every subroutine or loop,

and set low again when the program returns to the

beginning. If the program should hang in any subrou-

tine, the problem would be quickly corrected.

Replacing the Backup Battery

be removed without danger of triggering a reset pulse.

The device does not enter battery-backup mode when

Negative-Going VCC Transients

These supervisors are relatively immune to short-dura-

desirable.

The Typical Operating Characteristics section has a

Maximum Transient Duration vs. Reset Threshold

Overdrive graph for which reset is not asserted. The

the magnitude indicated (reset threshold overdrive).

The graph shows the maximum pulse width that a neg-

triggering a reset pulse. As the amplitude of the tran-

sient increases (i.e., goes further below the reset

threshold), the maximum allowable pulse width

below the reset threshold and lasts for 30µs will not trig-

ger a reset pulse.

pin provides additional transient immunity.

BATT

BATT ON

OUT

CMOS RAM

0.1

µF

GND

RESET

CE IN

CE

RESET

CE OUT

MAX6367

A0–A15

µP

+2.4V TO +5.5V

ADDRESS

DECODE

Figure 3. MAX6367 BATT ON Driving an External Pass

Transistor

Figure 4. Watchdog Flow Diagram

START

SET

WDI

LOW

RETURN

END

SUBROUTINE

OR PROGRAM LOOP

SET WDI

HIGH