AAT2552
Total Power Solution for Portable Applications
peak switch current to force a constant output volt-
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
15mA up to a maximum of 500mA. Constant cur-
rent charging will continue until the battery voltage
reaches the voltage regulation point, VBAT. When
the battery voltage reaches VBAT, the battery charg-
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.
age for all load and line conditions. Internal loop
compensation terminates the transconductance
voltage error amplifier output. The error amplifier
reference is fixed at 0.6V.
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 VMIN, the charger begins bat-
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.
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 VRCH threshold; the
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.
Pre-conditioning continues until the battery voltage
reaches VMIN (see Figure 1). At this point, the
charger begins constant-current charging. The cur-
Preconditioning
Trickle Charge
Constant Current
Charge Phase
Constant Voltage
Charge Phase
Phase
Charge Complete Voltage
I = Max CC
Regulated Current
Constant Current Mode
Voltage Threshold
Trickle Charge and
Termination Threshold
I = CC / 10
Figure 1: Current vs. Voltage Profile During Charging Phases.
2552.2007.04.1.0
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