ACT8810 datasheet(51/54 Pages) ACTIVE-SEMI

51 / 54 page

ActivePath

TM CHARGER

ACT8810

Rev 9, 15-Nov-12

Innovative Power

- 51 -

www.active-semi.com

ActivePMU

TM and ActivePathTM are trademarks of Active-Semi.

2CTM is a trademark of NXP.

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 FAST-CHARGE 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

In FAST-CHARGE state, the ACT8810 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 ACT8810 jumps to the TOP-OFF

state. If VBAT does not reach VTERM before the total

time out period expires then state-machine will jump

to the END-OF-CHARGE (EOC) state and will re-

initiate a new charge cycle after 2-4ms “relax”.

TOP-OFF State

In the TOP-OFF state, the cell charges in constant

voltage (CV) mode. In CV mode operation, the

charger regulates its output voltage to the 4.20V

(typ) charge termination voltage, and the charge

current is naturally reduced as the cell approaches

full charge. Charging continues until the charge

current

drops

END-OF-CHARGE

current

threshold, at which point the state machine jumps to

the END-OF-CHARGE (EOC) state. If the state-

machine does not jump out of the TOP-OFF state

before the Total-Charge Timeout period expires, the

state machine jumps to the EOC state and will re-

initiate a new charge cycle if VBAT falls below

termination

voltage

170mv

(typ).

For

information about the charge safety timers, see the

Charging Safety Times section.

END-OF-CHARGE State

In the End-of-Charge (EOC) state, the ACT8810

presents a high-impedance to the battery, allowing

the cell to “relax” and minimizes battery leakage

current. The ACT8810 continues to monitor the cell

voltage, so that it can re-initiate charging cycles

when VBAT drops to 170mV (typ) below the Charge

Termination Voltage.

SUSPEND State

In the SUSPEND state, ACT8810 disables the

charger but keeps other circuiting functional. Upon

exiting the SUSPEND State, the charge timer is

reset

and

the

state

machine

jumps

PRECONDITION state.

CHG_IN Bypass Capacitor Selection

CHG_IN is the power input for the ACT8810 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

resulting

from

the

current

limit

slew

rate

(100mA/µS) limitations of the USB bus, the

CHG_IN bypass capacitance value must to be

between 4.7µF and 10µF for the ACT8810.

Ceramic

capacitors

are

often

preferred

for

bypassing applications due to their small size and

good surge current ratings, but care must be taken

in applications that can encounter hot plug

conditions as their very low ESR, in combination

with the inductance of the cable, can create a high-

Q filter that induces excessive ringing at the

CHG_IN pin. This ringing can couple to the output

and be mistaken as loop instability, or the ringing

may be large enough to damage the input itself.

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