PRODUCT DATASHEET
AAT2557
TM
SystemPower
500mA Battery Charger and 300mA LDO Regulator for Portable Systems
the ISET pin to ground. Programmed current can be set
Battery Charging Operation
from a minimum 15mA up to a maximum of 500mA.
Constant current charging will continue until the battery
voltage reaches the voltage regulation point, VBAT and
the battery charger begins constant voltage mode. The
regulation voltage is factory programmed to a nominal
4.2V and will continue charging until the charging cur-
rent has reduced to 10% of the programmed current.
Battery charging commences only after checking several
conditions in order to maintain a safe charging environ-
ment. The input supply (ADP) must be above the mini-
mum operating voltage (UVLO) and the enable pin must
be high (internally pulled down). When the battery is
connected to the BAT pin, the charger checks the condi-
tion of the battery and determines which charging mode
to apply. If the battery voltage is below VMIN, the charger
begins battery pre-conditioning by charging at 10% of
the programmed constant current; e.g., if the pro-
grammed current is 150mA, then the pre-conditioning
current (trickle charge) is 15mA. Pre-conditioning is
purely a safety precaution for a deeply discharged cell
and will also reduce the power dissipation in the internal
series MOSFET pass device when the input-output volt-
age differential is at its highest.
After the charge cycle is complete, the pass device turns
off and the device automatically goes into a power-sav-
ing sleep mode. During this time, the series pass device
will block current in both directions, preventing the bat-
tery from discharging through the IC.
The battery charger will remain in sleep mode, even if
the charger source is disconnected, until one of the fol-
lowing events occurs: the battery terminal voltage drops
below the VRCH threshold; the charger EN pin is recycled;
or the charging source is reconnected. In all cases, the
charger will monitor all parameters and resume charging
in the most appropriate mode.
Pre-conditioning continues until the battery voltage
reaches VMIN (see Figure 1). At this point, the charger
begins constant-current charging. The current level for
this mode is programmed using a single resistor from
Battery
UVLO
Trickle
Charge
Constant Current
Charge Phase (CC)
Constant Voltage Charge
Phase (CV)
Constant Current
Charge Phase
Constant Voltage Charge
Phase
Recharge Phase
ICH_CC
ICH_CC
Termination
Phase
Termination
Phase
VCO(REG)
VRCH
VMIN
ICH_TERM
when
ICH_TERM
when
VBAT
=
VBAT
=
VCO( REG)
VCO(REG)
VUVLO
ICH_TKL
Figure 1: Current vs. Voltage Profile During Charging Phases.
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2557.2009.07.1.2
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