PRODUCT DATASHEET
AAT2550178
SystemPowerTM
Total Power Solution for Portable Applications
charge control will enter into thermal regulation. When
the system thermal regulation becomes active, the pro-
grammed constant current charge amplitude will auto-
matically decrease to a safe level for the present operat-
ing conditions. If the ambient temperature drops to a
level sufficient to allow the device to come out of thermal
regulation, then the system will automatically resume
charging at the full programmed constant current level.
This intelligent thermal management system permits the
battery charger to operate and charge a battery cell
safely over a wide range of ambient conditions, while
maximizing the greatest possible charge current and
minimizing the battery charge time for a given set of
conditions.
Charging Operation
As shown in Figure 1, there are three basic phases for
the battery charge cycle:
1. Pre-conditioning / trickle charge
2. Constant current / fast charge
3. Constant voltage charge
Battery Preconditioning
Before the start of charging, the charger checks several
conditions in order to assure a safe charging environ-
ment. The input supply must be above the minimum
operating voltage, or under-voltage lockout threshold
(VUVLO), for the charging sequence to begin. Also, the
battery temperature, as reported by a thermistor con-
nected to the TS pin from the battery, must be within the
proper window for safe charging. When these conditions
have been met and a battery is connected to the BAT
pin, the charger checks the state of the battery. If the
battery voltage is below the preconditioning voltage
threshold (VMIN), then the charge control begins precon-
ditioning the battery. The preconditioning trickle charge
current is equal to the fast charge constant current
divided by 10. For example, if the programmed fast
charge current is 1A, then the preconditioning mode
(trickle charge) current will be 100mA. Battery precon-
ditioning is a safety precaution for deeply discharged
batteries and also helps to limit power dissipation in the
pass transistor when the voltage across the device is at
the greatest potential.
Status monitor output pins are provided to indicate the
battery charge state by directly driving two external
LEDs. A serial interface output is also available to report
any one of 12 distinct charge states to the host system
microcontroller / microprocessor. Battery temperature
and charge state are fully monitored for fault conditions.
In the event of an over-voltage or over-temperature
condition, the device will automatically shut down, pro-
tecting the charging device, control system, and the bat-
tery under charge. In addition to internal charge control-
ler thermal protection, the charger also offers a tem-
perature sense feedback function (TS pin) from the
battery to shut down the device in the event the battery
exceeds its own thermal limit during charging. All fault
events are reported to the user either by simple status
LEDs or via the DATA pin function.
Preconditioning
Trickle Charge
Phase
Constant Current
Charge Phase
Constant Voltage
Charge Phase
Charge Complete Voltage
Regulated Current
I = Max CC
Constant Current Mode
Voltage Threshold
Trickle Charge and
Termination Threshold
I = CC / 10
Figure 1: Typical Charge Profile.
w w w . a n a l o g i c t e c h . c o m
14
2550.2008.02.1.3
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
