USB Port or AC Adapter
Lithium-Ion/Polymer Battery Charger
Functional Block Diagram
Reverse Blocking
AAT3681
ADP
BAT
Current
Compare
CV/
Precharge
ISET
Constant
Current
Charge
Control
UVLO
STAT
Charge
Status
Over-
Temperature
Protection
EN
GND
Functional Description
The AAT3681 is a high performance battery charg-
er designed to charge single cell lithium-ion/poly-
mer batteries with up to 300mA of current from an
external power source. It is a stand-alone charging
solution, with just one external component required
for complete functionality. The AAT3681 precisely
regulates battery charge voltage and current for
4.2V lithium-ion/polymer battery cells.
The adapter/USB charge input constant current
level can be programmed up to 300mA for rapid
charging applications. The AAT3681 is rated for
operation from -40°C to +85°C. In the event of oper-
ating ambient temperatures exceeding the power
dissipation abilities of the device package for a given
constant current charge level, the charge control will
enter into thermal limit.
A status monitor output pin is provided to indicate
the battery charge state by directly driving one
external LED.
Device junction temperature and charge state are
fully monitored for fault conditions. In the event of
an over-voltage or over-temperature failure, the
device will automatically shut down, protecting the
charging device, control system, and the battery
under charge.
Charging Operation
The AAT3681 has four basic modes for the battery
charge cycle: pre-conditioning/trickle charge; con-
stant current/fast charge; constant voltage; and
end of charge (see Figure 1). (AAT3681-1 does not
have trickle charge.)
8
3681.2007.01.1.2
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
