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AAT3697

2A Lithium-Ion/Polymer Battery Charger

Advanced Analogic Technologies 

BatteryManagerTM

PRODUCT DATASHEET

AAT3697

2A Lithium-Ion/Polymer Battery Charger

Charge Complete Voltage

Regulated Current

Preconditioning

Trickle Charge

Phase

Constant Current

Charge Phase

I = Max CC

Constant Voltage

Charge Phase

Constant Current Mode

Voltage Threshold

Trickle Charge and I = CC / 10

Termination Threshold

Figure 1: Current vs. Voltage Profile During Charging Phases.

Charging Operation

The AAT3697 has four basic modes for the battery

charge cycle: pre-conditioning/trickle charge; constant

current/fast charge; constant voltage; and end of charge

(see Figure 1).

Battery Preconditioning

Before the start of charging, the AAT3697 checks sev-

eral conditions in order to assure a safe charging envi-

ronment. The input supply must be above the minimum

operating voltage, or under-voltage lockout threshold

(VUVLO), for the charging sequence to begin. Also, the cell

temperature, as reported by a thermistor connected 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

AAT3697 checks the state of the battery. If the cell volt-

age is below the preconditioning voltage threshold (VMIN),

the charge control begins preconditioning the cell.

The battery preconditioning trickle charge current is equal

to the fast charge constant current divided by 10. For

example, if the programmed fast charge current is 1.5A,

then the preconditioning mode (trickle charge) current

will be 150mA. Cell preconditioning is a safety precaution

for deeply discharged battery cells and also aids in limit-

ing power dissipation in the pass transistor when the volt-

age across the device is at the greatest potential.

Fast Charge / Constant Current Charging

Battery cell preconditioning continues until the voltage

on the BAT pin exceeds the preconditioning voltage

threshold (VMIN). At this point, the AAT3697 begins the

constant current fast charging phase. The fast charge

constant current (ICH) amplitude is programmed by the

user via the RSET resistor. The AAT3697 remains in the

constant current charge mode until the battery reaches

the voltage regulation point, VBAT_EOC.

Constant Voltage Charging

The system transitions to a constant voltage charging

mode when the battery voltage reaches the output

charge regulation threshold (VBAT_EOC) during the con-

stant current fast charge phase. The regulation voltage

level is factory programmed to 4.2V (±1%). Charge cur-

rent in the constant voltage mode drops as the battery

cell under charge reaches its maximum capacity.

End of Charge Cycle Termination

and Recharge Sequence

When the charge current drops to 7.5% of the pro-

grammed fast charge current level in the constant volt-

age mode, the device terminates charging and goes into

a sleep state. The charger will remain in a sleep state

until the battery voltage decreases to a level below the

battery recharge voltage threshold (VRCH).

When the input supply is disconnected, the charger will

automatically transition into a power-saving sleep mode.

Only consuming an ultra-low 0.3µA in sleep mode, the

AAT3697 minimizes battery drain when it is not charging.

This feature is particularly useful in applications where

the input supply level may fall below the battery charge

or under-voltage lockout level. In such cases where the

AAT3697 input voltage drops, the device will enter sleep

mode and automatically resume charging once the input

supply has recovered from the fault condition.

3697.2008.02.1.3

www.analogictech.com

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