Backup-Battery Switchover

In a brownout or power failure, it may be necessary to

preserve the contents of the RAM. With a backup bat-

tery installed at BATT, the MAX6361/MAX6363/

MAX6364 automatically switch the RAM to backup

output that goes high when in battery-backup mode.

These devices require two conditions before switching

to battery-backup mode:

of the inputs and outputs in battery-backup mode.

The device will not power up if the only voltage

source is on BATT. OUT will only power up from

Manual Reset Input (MAX6361 only)

Many µP-based products require manual reset capabili-

ty, allowing the operator, a test technician, or external

logic circuitry to initiate a reset. For the MAX6361, a logic

low on MR asserts reset. Reset remains asserted while

returns high. MR has an internal 20k

Ω pull-up resistor.

This input can be driven with TTL/CMOS logic levels or

with open-drain/collector outputs. Connect a normally

open momentary switch from MR to GND to create a

manual reset function; external debounce circuitry is not

required. If MR is driven from long cables or the device

is used in a noisy environment, connect a 0.1µF capaci-

tor from MR to GND to provide additional noise immunity.

Reset In (MAX6364 only)

RESET IN is compared to an internal 1.235V reference.

If the voltage at RESET IN is less than 1.235V, reset is

asserted. The RESET IN comparator may be used as

an undervoltage detector to signal a failing power sup-

ply. It can also be used as a secondary power-supply

reset monitor.

Reset Output

A µP’s reset input starts the µP in a known state. The

MAX6361/MAX6363/MAX6364 µP supervisory circuits

assert a reset to prevent code-execution errors during

power-up, power-down, and brownout conditions.

RESET is guaranteed to be a logic low or high depend-

ing on the device chosen (see Ordering Information).

above the reset threshold. RESET or RESET also

asserts when MR is low (MAX6361) and when RESET

IN is less than 1.235V (MAX6364).

Applications Information

Operation Without a Backup

Power Source

The MAX6361/MAX6363/MAX6364 were designed for

battery-backed applications. If a backup battery is not

Replacing the Backup Battery

If BATT is decoupled with a 0.1µF capacitor to ground,

remains valid without danger of triggering a reset pulse.

The device does not enter battery-backup mode when

These supervisors are relatively immune to short-dura-

desirable.

The Typical Operating Characteristics section shows a

graph of Maximum Transient Duration vs. Reset

Threshold Overdrive for which reset is not asserted.

threshold by the magnitude indicated (reset threshold

overdrive). The graph shows the maximum pulse width

SOT23, Low-Power µP Supervisory Circuits

with Battery Backup

6

_______________________________________________________________________________________

PIN

STATUS

Disconnected from OUT

OUT

Connected to BATT

BATT

Connected to OUT. Current drawn from

RESET/RESET

Asserted

BATT ON

High state

MR, RESET IN

Inputs ignored

Table 2. Input and Output Status in

Battery-Backup Mode

SUFFIX

46

4.50

4.63

44

4.25

4.38

31

3.00

3.08

4.75

4.50

3.15

23

2.25

29

2.85

2.93

2.32

26

2.55

2.63

2.38

3.00

2.70

RESET THRESHOLD RANGES (V)

Table 1. Reset Threshold Ranges

MIN

MAX

TYP