AAT2557
500mA Battery Charger and 300mA
LDO Regulator for Portable Systems
Application Information
Normal
Set Resistor
ICHARGE (mA)
Value R1 (kΩ)
Soft Start / Enable
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 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 control
circuit will automatically reset and resume charg-
ing functions with the appropriate charging mode
based on the battery charge state and measured
cell voltage from the BAT pin.
The LDO is enabled when the ENLDO pin is pulled
high. The control and feedback circuits have been
optimized for high-speed, monotonic turn-on char-
acteristics.
Table 1: RSET Values.
1000
100
10
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. The constant current fast charge cur-
rent for the adapter input is set by the RSET resistor
connected between ISET and ground. Refer to
Table 1 for recommended RSET values for a desired
constant current charge level.
1
1
10
100
1000
RSET (kΩ)
Figure 2: Constant Charging Current
vs. Set Resistor Values.
Programming Charge Current
The fast charge constant current charge level is
user programmed with a set resistor placed
between the ISET pin and ground. The accuracy of
the fast charge, as well as the preconditioning trick-
le charge current, is dominated by the tolerance of
the set resistor used. For this reason, a 1ꢀ toler-
ance metal film resistor is recommended for the set
resistor function. Fast charge constant current lev-
els from 15mA to 500mA may be set by selecting
the appropriate resistor value from Table 1.
Charge Status Output
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 external LED. The status pin can indicate
several conditions, as shown in Table 2.
16
2557.2007.06.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
