PRODUCT DATASHEET
AAT2557
TM
SystemPower
500mA Battery Charger and 300mA LDO Regulator for Portable Systems
Application Information
Event Description
Status
No battery charging activity
Battery charging via adapter or USB port
Charging completed
OFF
ON
OFF
Soft Start / Enable
The EN_BAT pin is internally pulled down. When pulled
to a logic high level, the battery charger is enabled.
When left open or pulled to a logic low level, the battery
charger is shut down and forced into the sleep state.
Charging will be halted regardless of the battery voltage
or charging state. When it is re-enabled, the charge con-
trol circuit will automatically reset and resume charging
functions with the appropriate charging mode based on
the battery charge state and measured cell voltage from
the BAT pin.
Table 1: LED Status Indicator.
Constant Charge
Current ICH_CC (mA)
Set Resistor Value
(kΩ)
500
400
300
250
200
150
100
50
40
30
20
15
3.24
4.12
5.36
6.49
8.06
10.7
16.2
31.6
38.3
53.6
78.7
105
The LDO is enabled when the EN_LDO pin is pulled high.
The control and feedback circuits have been optimized
for high-speed, monotonic turn-on characteristics.
Adapter or USB Power Input
Constant current charge levels up to 500mA may be
programmed by the user when powered from a sufficient
input power source. The battery charger will operate
from the adapter input over a 4.0V to 6.5V range.
Table 2: RSET Values.
1000
100
10
Programming Charge Current
The fast charge constant current charge level is user
programmable with a set resistor placed between the
ISET pin and ground. The accuracy of the fast charge, as
well as the preconditioning trickle charge current, is
dominated by the tolerance of the set resistor used. For
this reason, a 1% tolerance metal film resistor is recom-
mended for the set resistor function. Fast charge con-
stant current levels from 15mA to 500mA may be set by
selecting the appropriate resistor value from Table 2.
1
1
10
100
1000
RSET (kΩ)
Figure 2: Constant Charging Current
vs. Set Resistor Values.
Charge Status Output
The LED should be biased with as little current as neces-
sary to create reasonable illumination; therefore, a bal-
last resistor should be placed between the LED cathode
and the STAT pin. LED current consumption will add to
the overall thermal power budget for the device pack-
age, hence it is good to keep the LED drive current to a
minimum. 2mA should be sufficient to drive most low-
cost green or red LEDs. It is not recommended to exceed
8mA for driving an individual status LED.
The AAT2557 provides battery charge status via a status
pin. This pin is internally connected to an N-channel
open drain MOSFET, which can be used to drive an exter-
nal LED. The status pin can indicate several conditions,
as shown in Table 1.
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