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MAX6439 Datasheet(PDF) 10 Page - Maxim Integrated Products

Part No. MAX6439
Description  Low-Power, Single-/Dual-Level Battery Monitors with Hysteresis and Integrated uP Reset
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Maker  MAXIM [Maxim Integrated Products]
Homepage  http://www.maxim-ic.com
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MAX6439 Datasheet(HTML) 10 Page - Maxim Integrated Products

 
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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
Ω pullup resistor to VCC 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 tDEB 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 VBATT 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
10
______________________________________________________________________________________
VBATT
LBO
tLBOP
VHTH
VLTH
VHYST
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
VBATT
VCC
CURRENT-
LIMITED
AC WALL
ADAPTER
IN
OUT
SHDN
DC/DC CONVERTER
Figure 6. Li+ Charger Application (Using MAX1879)
DC/DC
SHDN
MR
VBATT
RESET
MAX6441
MAX6442
NMI
RESET
µP
VCC
GND
GND
VCC
Li+
3.6V
LBOL
LBOH
OUT
IN
Figure 7. DC-to-DC Converter Application


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