AAT2552
Total Power Solution for Portable Applications
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 1% toler-
ance metal film resistor is recommended for the set
resistor function. Fast charge constant current lev-
els from 30mA to 500mA may be set by selecting
the appropriate resistor value from Table 1.
Application Information
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 control circuit will automatically
reset and resume charging functions with the appro-
priate charging mode based on the battery charge
state and measured cell voltage from the BAT pin.
Normal
Set Resistor
ICHARGE (mA)
Value R1 (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
Separate ENA and ENB inputs are provided to
independently enable and disable the LDO and
step-down converter, respectively. This allows
sequencing of the LDO and step-down outputs dur-
ing startup.
The LDO is enabled when the ENA pin is pulled
high. The control and feedback circuits have been
optimized for high-speed, monotonic turn-on char-
acteristics.
The step-down converter is enabled when the ENB
pin is pulled high. Soft start increases the inductor
current limit point in discrete steps when the input
voltage or ENB input is applied. It limits the current
surge seen at the input and eliminates output voltage
overshoot. When pulled low, the ENB input forces the
AAT2552 into a low-power, non-switching state. The
step-down converter input current during shutdown is
less than 1µA.
Table 1: RSET Values.
1000
100
10
1
Adapter or USB Power Input
1
10
100
1000
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.
RSET (kΩ)
Figure 2: Constant Charging Current
vs. Set Resistor Values.
Charge Status Output
The AAT2552 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.
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
2552.2007.04.1.0
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