Lithium-Ion/Polymer Linear Battery Charger
system. This is done to prevent the charger from
erroneously turning on and off once a battery
charge cycle is complete.
For example, the AAT3682 has a typical V
RCH
threshold of 4.1V. A battery under charge is above
4.1V, but is still in the constant voltage mode
because it has not yet reached 4.2V to complete
the charge cycle. If the battery is removed and
then placed back on the charger, the charge cycle
will not resume until the battery voltage drops
below the V
RCH
threshold. In another case, a bat-
tery under charge is in the constant current mode
and the cell voltage is 3.7V when the input supply
is inadvertently removed and then restored. The
battery is below the V
RCH
threshold and the charge
cycle will immediately resume where it left off.
each output period is one second long; thus one
status word will take four seconds to display
through an LED. The five modes include:
1. Sleep/Charge Complete: The IC goes into
Sleep mode when no battery is present -OR-
when the charge cycle is complete.
2. Fault: When an over-current (OC) condition is
detected by the current sense and control cir-
cuit -OR- when an over-voltage (OV) condition
is detected at the BAT pin -OR- when a battery
over-temperature fault is detected on the
TEMP pin.
3. Battery Conditioning: When the charge system
is in 1X or 2X trickle charge mode.
4. Constant Current (CC) Mode: When the sys-
tem is in constant current charge mode.
5. Constant Voltage (CV) Mode: When the sys-
tem is in constant voltage charge mode.
An additional feature of the LED status display is for
a Battery Not Detected state. When the AAT3682
senses there is no battery connected to the BAT
pin, the STAT output will turn the LED on and off at
a rate dependent on the size of the output capacitor
being used. The LED cycles on for two periods then
remains off for two periods. See Figure 3 below.
AAT3682
LED Display Charge Status Output
The AAT3682 provides a battery charge status out-
put via the STAT pin. STAT is an open-drain serial
data output capable of displaying five distinct status
functions with one LED connected between the
STAT pin and VP. There are four periods which
determine a status word. Under default conditions,
Charge Status
Sleep / Charge Complete
Temp., OC, OV Fault
Battery Conditioning
Constant Current Mode
Constant Voltage Mode
Output Status
off / off / off / off
on / on / off / off
on / on / on / on
on / on / on / off
on / off / off / off
LED Display
on/off
ON
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
on/off
on/off
on/off
Figure 3: LED Display Output.
3682.2006.12.1.3
11
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
