ACT8828 datasheet(47/49 Pages) ACTIVE-SEMI

47 / 49 page

ActivePath

TM CHARGER

ACT8828

Rev 3, 24-Sep-09

Active-Semi

Innovative Power

- 47 -

www.active-semi.com

ActivePMU

TM and ActivePathTM are trademarks of Active-Semi.

2CTM is a trademark of Philips Electronics.

FUNCTIONAL DESCRIPTION CONT’D

Charger State-Machine

PRECONDITION State

new

charging

cycle

begins

with

the

PRECONDITION state, and operation continues in

this state until VBAT exceeds the Precondition

Threshold Voltage of 2.85V (typ). When operating

in PRECONDITION state, the cell is charged at a

reduced current, 12% of the programmed maximum

fast-charge constant current, ISET. Once VBAT

reaches the Precondition Threshold Voltage the

state machine jumps to the NORMAL state. If VBAT

does not reach the Precondition Threshold Voltage

before the Precondition Timeout period tPRECONDITION

expires, then a damaged cell is detected and the

state machine jumps to the TIMEOUT-FAULT State.

For the Precondition Timeout period, see the

Charging Safety Timers section

for more information.

FAST CHARGE State

Normal state is made up of two operating modes,

fast charge Constant-Current (CC) and Constant-

Voltage (CV). In CC mode, the ACT8828 charges at

the current programmed by RISET (see the Current

Limits

and Charge Current Programming section for

more information). During a normal charge cycle

fast-charge continues in CC mode until VBAT

reaches the charge termination voltage (VTERM), at

which point the ACT8828 charges in CV mode.

Charging continues in CV mode until the charge

current drops to 10% (ACIN = 1) or 5% (ACIN = 0)

of the programmed maximum charge current, at

which point the state machine jumps to the TOP-

OFF state. If VBAT does not proceed out of the

NORMAL state before the Normal Timeout period

(TNORMAL) expires, then a damaged cell is detected

and the state machine jumps to the TIMEOUT-

FAULT State. See the Charging Safety Times

section for more information.

TOP-OFF State

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

constant-voltage

(CV) mode.

Charge

current

decreases as charging continues. During a normal

charging cycle charging proceeds until the charge

current decreases below the End-Of-Charge (EOC)

threshold, defined as 10% of ISET (ACIN = 1) or

5% of ISET (ACIN = 0) . When this happens, the

state machine terminates the charge cycle and

jumps to the SLEEP state.

End of Charge State

In the End-of-Charge (EOC) state, the ACT8828

presents a high-impedance to the battery, allowing

the cell to “relax” and minimizes battery leakage

current. The ACT8828 continues to monitor the cell

voltage, however, so that it can re-initiate charging

cycles as necessary to ensure that the cell remains

fully charged.

SUSPEND State

The ACT8828 features an user-selectable suspend-

charge mode, which disables the charger but keeps

other circuiting functional. The charger can be put

into suspend mode by driving EN to logic low. Upon

exiting the SUSPEND State, the charge timer is

reset

and

the

state

machine

jumps

PRECONDITION state.

SLEEP State

In SLEEP mode the ACT8828 presents a high-

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

and minimizes battery leakage current. The

ACT8828 continues to monitor the cell voltage,

however, so that it can re-initiate charging as

necessary to ensure that the cell remains fully

charged. Under normal operation, the state

machine initiates a new charging cycle by jumping

to the FAST-CHARGE state when VBAT drops below

the Charge Termination Threshold.

CHG_IN Bypass Capacitor Selection

CHG_IN is the power input for the ACT8828 battery

charger. The battery charger is automatically

enabled whenever a valid voltage is present on

CHG_IN.

most

applications,

CHG_IN

connected to either a wall adapter or USB port.

Under normal operation, the input of the charger will

often be “hot-plugged” directly to a powered USB or

wall adapter cable, and supply voltage ringing and

overshoot may appear at the CHG_IN pin.

In most applications a high quality capacitor

connected from CHG_IN to GA, placed as close as

possible to the IC, is sufficient to absorb the energy.

Wall-adapter powered applications provide flexibility

input

capacitor

selection,

but

the

USB

specification

presents

limitations

input

capacitance selection. In order to meet both the

USB 2.0 and USB OTG (On The Go) specifications

while avoiding USB supply under-voltage conditions

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