MAX6439–MAX6442
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 1.5kΩ pullup resistor to V
CC
and can be left
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
is internally debounced for the t
DEB
timeout period) to
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
oscillating (chattering) when V
BATT
is near the low-bat-
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
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