AAT2556
Battery Charger and Step-Down
Converter for Portable Applications
Functional Block Diagram
Reverse Blocking
BAT
ADP
-
+
Constant
Current
Charge
Control
ISET
VREF
Over-
Temperature
Protection
STAT
UVLO
T
EN_BA
VIN
FB
DH
DL
-
+
LX
Logic
VREF
Input
EN_BUCK
GND
state are fully monitored for fault conditions. In the
event of an over-voltage or over-temperature fail-
ure, the device will automatically shut down, pro-
tecting the charging device, control system, and
the battery under charge. Other features include
an integrated reverse blocking diode and sense
resistor.
Functional Description
The AAT2556 is a high performance power system
comprised of a 500mA lithium-ion/polymer battery
charger and a 250mA step-down converter.
The battery charger is designed for single-cell
lithium-ion/polymer batteries using a constant cur-
rent and constant voltage algorithm. The battery
charger operates from the adapter/USB input volt-
age range from 4V to 6.5V. The adapter/USB
charging current level can be programmed up to
500mA for rapid charging applications. A status
monitor output pin is provided to indicate the bat-
tery charge state by directly driving one external
LED. Internal device temperature and charging
The step-down converter operates with an input volt-
age of 2.7V to 5.5V. The switching frequency is
1.5MHz, minimizing the size of the inductor. Under
light load conditions, the device enters power-saving
mode; the switching frequency is reduced, and the
converter consumes 30µA of current, making it ideal
for battery-operated applications. The output volt-
age is programmable from VIN to as low as 0.6V.
12
2556.2006.09.1.2
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
