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AAT3682

Li-Ion/Polymer Linear Battery Charger

Skyworks Solutions 

Preconditioning

(Trickle Charge)

Phase

Constant Current

Phase

Constant Voltage

Phase

Output Charge

Voltage (VCH)

Preconditioning

Voltage Threshold

(VMIN)

Regulation

Current

(ICHARGE(REG))

Trickle Charge

and Termination

Threshold

Figure 2: Typical Charge Profile.

When these conditions have been met and a battery is

connected to the BAT pin, the AAT3682 checks the state

of the battery. If the cell voltage is below VMIN, the

AAT3682 begins preconditioning the cell. This is per-

formed by charging the cell with 10% of the programmed

constant current amount. For example, if the programmed

charge current is 500mA, then the preconditioning mode

(trickle charge) current will be 50mA. Cell preconditioning

is a safety precaution for deeply discharged cells and,

furthermore, limits power dissipation in the pass transis-

tor when the voltage across the device is largest. The

AAT3682 features an optional T2X mode, which allows

faster trickle charging at approximately two times the

default rate. This mode is selected by connecting the T2X

pin to VSS. If an over-temperature fault is triggered, the

fast trickle charge will be latched off, and the AAT3682 will

continue at the default 10% charge current.

Constant Current Charging

The cell preconditioning continues until the voltage on

the BAT pin reaches VMIN. At this point, the AAT3682

begins constant current charging (fast charging). Current

level for this mode is programmed using a current sense

resistor RSENSE between the VCC and CSI pins. The CSI

pin monitors the voltage across RSENSE to provide feed-

back for the current control loop. The AAT3682 remains

in constant current charge mode until the battery reach-

es the voltage regulation point, VCH.

DATA SHEET

AAT3682

Li-Ion/Polymer Linear Battery Charger

Constant Voltage Charging

When the battery voltage reaches VCH during constant

current mode, the AAT3682 transitions to constant volt-

age mode. The regulation voltage is factory programmed

to 4.2V. In constant voltage operation, the AAT3682

monitors the cell voltage and terminates the charging

cycle when the voltage across RSENSE decreases to

approximately 10mV.

Charge Cycle Termination,

Recharge Sequence

After the charge cycle is complete, the AAT3682 shuts

off the pass device and automatically enters power-

saving sleep mode. Either of two possible conditions will

bring the IC out of sleep mode: the battery voltage at

the BAT pin drops below VRCH (recharge threshold volt-

age) or the AAT3682 is reset by cycling the input supply

through the power-on sequence. Falling below VRCH sig-

nals the IC that it is time to initiate a new charge cycle.

Sleep Mode

When the input supply is disconnected, the device auto-

matically enters power-saving sleep mode. Only con-

suming an ultra-low 2μA current, the AAT3682 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 AAT3682 input

voltage drops, the device will enter the sleep mode and

automatically resume charging once the input supply has

recovered from its fault condition. This makes the

AAT3682 well suited for USB battery charger applica-

tions.

Charge Inhibit

The AAT3682 charging cycle is fully automatic; however,

it is possible to stop the device from charging even when

all conditions are met for proper charging. Switching the

TS pin to either VIN or GND will force the AAT3682 to turn

off the pass device and wait for a voltage between the

low and high temperature voltage thresholds.

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com

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201884B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 25, 2012

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