Manual Reset

Many microprocessor-based products require manual

reset capability, allowing the operator, a test technician,

or external logic circuitry to initiate a reset while the

monitored supplies remain above their reset thresholds.

These devices have a dedicated active-low MR pin.

When MR is pulled low, RESET asserts a one-shot low

pulse for the MR reset timeout period. The MR input has

an internal 1.5k

unconnected if not used. MR can be driven with CMOS-

logic levels, open-drain/open-collector outputs, or a

momentary push-button switch to GND (the MR function

create a manual reset function. If MR is driven from long

cables, or if the device is used in a noisy environment,

connect a 0.1µF capacitor from MR to GND to provide

additional noise immunity (see Figure 4).

Hysteresis

Hysteresis increases the comparator’s noise margin by

increasing the upper threshold or decreasing the lower

threshold. The hysteresis prevents the output from

tery threshold. This is especially important for applica-

tions where the load on the battery creates significant

fluctuations in battery voltages (see Figure 5).

Applications Information

Li+ Battery Charger Application

The MAX6441/MAX6442 dual-output battery monitors

can be used in conjunction with a battery charger to

provide a system with additional information about the

battery charge state. Many battery chargers, such as

the MAX1879, provide the user with a CHG output,

which tells the system when the battery is charged. The

MAX6441/MAX6442 dual-output battery monitors pro-

vide three outputs, which can be used to relay the bat-

tery condition to the system. This information is useful in

determining which system resources can be powered by

the battery at the current charge state (see Figure 6).

Low-Power, Single-/Dual-Level Battery Monitors

with Hysteresis and Integrated µP Reset

10

______________________________________________________________________________________

LBO

HTH = BATTERY VOLTAGE GOOD, ENABLE OPERATION.

LTH = BATTERY VOLTAGE LOW, SUSPEND/DISABLE OPERATION.

Figure 5. Hysteresis

BATT

GND

1-CELL

Li+

BATTERY

THERM

ADJ

GATE

PULSE-WIDTH

SELECT INPUT

CHG

LED

THERMISTOR

IN

MAX1879

MAX6441

MAX6442

TSEL

GND

LBOL

LBOLH

RESET

LBOH

CURRENT-

LIMITED

AC WALL

ADAPTER

IN

OUT

SHDN

DC/DC CONVERTER

Figure 6. Li+ Charger Application (Using MAX1879)

DC/DC

SHDN

MR

RESET

MAX6441

MAX6442

NMI

RESET

µP

GND

GND

Li+

3.6V

LBOL

LBOH

OUT

IN

Figure 7. DC-to-DC Converter Application