AAT2556 Datasheet, PDF (15/27 Pages) Advanced Analogic Technologies – Battery Charger and Step-Down Converter for Portable Applications

DATA SHEET
AAT2556
Battery Charger and Step-Down Converter for Portable Applications
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 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.
The step-down converter features a soft start that limits
the inrush current and eliminates output voltage over-
shoot during startup. The circuit is designed to increase
the inductor current limit in discrete steps when the
input voltage or enable input is applied. Typical start up
time is 100μs.
Pulling EN_BUCK to logic low forces the converter in a
low power, non-switching state, and it consumes less
than 1μA of quiescent current. Connecting it to logic high
enables the converter and resumes normal operation.
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 current for the adapter
input is set by the R_SET resistor connected between ISET
and ground. Refer to Table 1 for recommended R_SET val-
ues for a desired constant current charge level.
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 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-
stant current levels from 15mA to 500mA may be set by
selecting the appropriate resistor value from Table 1.
Normal
I_CHARGE (mA)
500
400
300
250
200
150
100
50
40
30
20
15
Set Resistor
Value R2 (k)
3.24
4.12
5.36
6.49
8.06
10.7
16.2
31.6
38.3
53.6
78.7
105
Table 1: R_SET Values.
1000
100
10
1
1
10
100
1000
R_SET (kΩ)
Figure 2: Constant Charging Current
vs. Set Resistor Values.
Charge Status Output
The AAT2556 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
No battery charging activity
Battery charging via adapter or USB port
Charging completed
Status
OFF
ON
OFF
Table 2: LED Status Indicator.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202177B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
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