Rev 2, Feb-04-2016

- 10 -

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Copyright © 2016 Active-Semi, Inc.

ACT2804

ACT2804 is a complete battery charging and

discharging

power

management

solution

for

applications of dull-cell lithium-based backup

battery pack or power bank.

With the advanced bidirectional architecture, a

synchronous boost/buck converter is connected

from VOUT to switching node (SW). The converter

could be configured as either boost to charge

battery or buck to discharge battery.

Modes of Operation

ACT2804 has 3 operation modes: charge mode,

discharge mode, and high-impedance (HZ) mode.

High Impedance (HZ) Mode

HZ mode is the default mode. In HZ mode, all the

switches are turned off , only PB circuit alive and

the IC draws less than 10uA current from VBAT.

Discharge Mode

In discharge mode, Buck converter operates in CV/

CC regulation. VOUT1 current limit is set at 1.25A

and VOUT2 current limit is set at 2.65A.

Charge Mode

ACT2804 is configured in charge mode (boost

mode) when VIN is valid. In this mode, a battery is

charged with trickle, preconditioning, fast charge,

top-off and end of charge (EOC). The typical

charge management is shown in Figure 1.

Precondition Charge

When operating in precondition state, the cell is

charged at a reduced current at 15% of the

programmed

maximum

fast

charge

constant

threshold voltage the state machine jumps to the

fast charge state.

Fast Charge

If

battery

voltage

is

above

preconditioning

threshold, boost converter charges battery with

constant current. In fast charge state, the ACT2804

charges at the current set by the external resistor

connected at the ICST pin. During a normal charge

reaches the charge termination voltage, at which

point the ACT2804 charges in top off state.

Top Off

Device transitions from Fast Charge (CC) to Top

Off (CV), and moves to EOC (End of Charge) state

End of Charge

In Top Off mode, when charges current decreases

to 10% of set fast charge current, the boost

converter goes into end of charge mode and keep

monitoring the battery voltage.

Recharge

In EOC, device would re-charge batteries when

Battery Removal

If the battery is removed, boost converter regulates

at the programmed regulation voltage.

Cell Balance

Cell Balance is activated in both Fast Charge and

Top Off modes. Each battery is connected with a

parallel bleeding switch.

Push Button

PB is always watched in HZ mode and discharge

mode. If the push but on PB is pressed for >40mS

in HZ mode, the LED (s) will turn on for 5 seconds.

In the mean time, discharge mode is enabled.

FUNCTIONAL DESCRIPTION

FAST CHARGEB CURRENT

PRECONDITION CHARGE CURRENT

A

B

C

D

STATE

B

RECHARGE

Current

Voltage

END-OF-CHARGE CURRENT

A: PRECONDITION STATE

B: FAST-CHARGE STATE

C: TOP-OFF STATE

D: END-OF-CHARGE STATE

Figure 1. Typical Li+ Charge Profile and ACT2804 Charge States