ACT8712 datasheet(35/36 Pages) ACTIVE-SEMI

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SINGLE-CELL Li+ BATTERY CHARGER (CHGR)

Rev0, 25-Feb-08

ACT8712

Innovative Products. Active Solutions.

- 35 -

www.active-semi.com

ActivePMU

TM is a trademark of Active-Semi.

2CTM is a trademark of Philips Electronics.

Reverse Leakage Current

The ACT8712 includes internal circuitry that elimi-

nates the need for series blocking diodes, reducing

solution size and cost as well as dropout voltage

relative to conventional battery chargers. When the

input supply is removed, when VVIN goes below its

under-voltage-lockout (UVLO) voltage, or when VVIN

drops below VBAT, the ACT8712 automatically goes

into SUSPEND mode and reconfigures its power

switch to minimize current drain from the battery.

Charger State Machine

PRECONDITION State

A new charging cycle begins in the PRECONDI-

TION state. In this state, the cell is charged at a

reduced current of either 45mA or 10% of the se-

lected maximum fast-charge current, whichever is

greater. During a normal charge cycle, charging

continues at this rate until VBAT reaches the Precon-

dition Threshold Voltage, at which point the state

machine jumps to the FAST-CHARGE state. If VBAT

does not reach the Precondition Threshold Voltage

before the Precondition Charge Timeout period ex-

pires, then a damaged cell is detected and the state

machine jumps to the TIMEOUT-FAULT state.

FAST-CHARGE State

In the FAST-CHARGE state the charger operates in

Constant-Current (CC) mode and charges the cell

at the programmed charge current. During a normal

charge cycle, constant-current charging continues

until VBAT reaches the charge termination voltage, at

which point the state machine jumps to the TOP-

OFF state.

TOP-OFF State

In the TOP-OFF state the cell is charged in Con-

stant-Voltage (CV) mode with the charge current

limited by the internal chemistry of the cell, decreas-

ing as the cell charges. A normal charging cycle

continues until the charge current decreases to be-

low the End-Of-Charge (EOC) threshold. In order to

improve immunity to conditions that can result in

false-EOC detection, the charging continues until

the EOC condition persists for 4 consecutive min-

utes. Once this condition is met, the charge cycle is

terminated and the state machine jumps to the

SLEEP state.

SLEEP State

In the SLEEP state the ACT8712 presents a high-

impedance to the battery, allowing the cell to “relax”

and minimizing battery leakage current. The

ACT8712 continues to monitor the cell voltage,

however, so that it can reinitiate a charging cycle as

necessary to ensure that the cell remains fully

charged.

Charge Restart

After a charge cycle successfully terminates, the

ACT8712 jumps to its SLEEP state to minimize bat-

tery drain, but continues to actively monitor the cell

voltage. A new charging cycle begins when the cell

voltage has dropped by 200mV (typ), keeping the

cell fully charged. This charge restart process mini-

mizes cycle-life degradation of the cell by allowing it

to “relax” between charges, while ensuring that the

cell remains fully-charged while connected to a

power source.

SUSPEND State

When in the SUSPEND state, the charger is dis-

abled and the charger presents a high-impedance

to the battery, but the charge-control circuitry re-

mains functional. When exiting the SUSPEND

state, the charge timer is reset and the state ma-

chine jumps to the PRECONDITION state.

TIMEOUT-FAULT State

When a TIMEOUT-FAULT occurs, charging is sus-

pended, CHGR/TIMOFLT[ ] is set to [1], and the

charger presents a high-impedance to the battery.

To maximize safety, there is no direct path to re-

sume charging from the TIMEOUT-FAULT state. A

new charging cycle may only be initiated if the state

machine first jumps to the SUSPEND state then

each of the conditions necessary to enter the PRE-

CONDITION state are satisfied.

ACT8712 Datasheet(PDF) 35 Page - Active-Semi, Inc

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