ACT8740 datasheet(39/40 Pages) ACTIVE-SEMI

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SINGLE-CELL Li+ BATTERY CHARGER (CHGR)

ACT8740

Rev PrB, 25-Feb-08

Innovative Products. Active Solutions.

- 39 -

www.active-semi.com

ActivePMU

TM is a trademark of Active-Semi.

2CTM is a trademark of Philips Electronics.

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 ACT8740 presents a high-

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

and minimizing battery leakage current. The

ACT8740 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

ACT8740 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.

FUNCTIONAL DESCRIPTION CONT’D

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