AAT2557 AnalogicTech, AAT2557 Datasheet - Page 14

• Manufacturer Part Number: AAT2557
• Description: 500mA Battery Charger and 300mA LDO Regulator for Portable Systems
• Manufacturer: AnalogicTech

Battery Charging Operation
Battery charging commences only after checking
several conditions in order to maintain a safe charg-
ing environment. The input supply (ADP) must be
above the minimum 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 condition of the battery and
determines which charging mode to apply. If the bat-
tery voltage is below V
tery pre-conditioning by charging at 10% of the pro-
grammed constant current; e.g., if the programmed
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 pass MOSFET when the input-output voltage
differential is at its highest.
Pre-conditioning continues until the battery voltage
reaches V
charger begins constant-current charging. The cur-
rent level for this mode is programmed using a sin-
gle resistor from the ISET pin to ground.
Programmed current can be set from a minimum
14
MIN
Charge Complete Voltage
Constant Current Mode
Termination Threshold
(see Figure 1). At this point, the
Regulated Current
Trickle Charge and
Voltage Threshold
Figure 1: Current vs. Voltage Profile During Charging Phases.
MIN
, the charger begins bat-
I = CC / 10
Preconditioning
Trickle Charge
Phase
I = Max CC
Constant Current
Charge Phase
LDO Regulator for Portable Systems
500mA Battery Charger and 300mA
15mA up to a maximum of 500mA. Constant cur-
rent charging will continue until the battery voltage
reaches the voltage regulation point, V
the battery voltage reaches V
er begins constant voltage mode. The regulation
voltage is factory programmed to a nominal 4.2V
(±0.5%) and will continue charging until the charg-
ing current has reduced to 10% of the programmed
current.
After the charge cycle is complete, the pass device
turns off and the device automatically goes into a
power-saving sleep mode. During this time, the
series pass device will block current in both direc-
tions, preventing the battery from discharging
through the IC.
The battery charger will remain in sleep mode,
even if the charger source is disconnected, until
one of the following events occurs: the battery ter-
minal voltage drops below the V
charger EN pin is recycled; or the charging source
is reconnected. In all cases, the charger will mon-
itor all parameters and resume charging in the
most appropriate mode.
Constant Voltage
Charge Phase
BAT
, the battery charg-
RCH
AAT2557
threshold; the
2557.2007.06.1.0
BAT
. When