PRODUCT DATASHEET
AAT2552178
SystemPowerTM
Total Power Solution for Portable Applications
stant current levels from 30mA to 500mA may be set by
selecting the appropriate resistor value from Table 1.
Application Information
Soft Start / Enable
Normal ICHARGE (mA) Set Resistor Value R1 (kΩ)
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.
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 indepen-
dently enable and disable the LDO and step-down con-
verter, respectively. This allows sequencing of the LDO
and step-down outputs during startup.
Table 1: RSET Values.
1000
100
10
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 characteristics.
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 con-
verter input current during shutdown is less than 1μA.
1
1
10
100
1000
RSET (kΩ)
Figure 2: Constant Charging Current
vs. Set Resistor Values.
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 7.5V range. The
constant current fast charge current for the adapter
input is set by the RSET resistor connected between ISET
and ground. Refer to Table 1 for recommended RSET val-
ues for a desired constant current charge level.
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 exter-
nal LED. The status pin can indicate several conditions,
as shown in Table 2.
Event Description
Status
Programming Charge Current
No battery charging activity
Battery charging via adapter or USB port
Charging completed
OFF
ON
OFF
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 trickle charge current, is domi-
nated 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-
Table 2: LED Status Indicator.
The LED should be biased with as little current as neces-
sary to create reasonable illumination; therefore, a bal-
w w w . a n a l o g i c t e c h . c o m
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2552.2008.02.1.2
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