ACT2823 datasheet(12/25 Pages) ACTIVE-SEMI

12 / 25 page

ACT2823

REV 1, 01-DEC-2016

Innovative PowerTM

ActiveSwitcherTM

is a trademark of Active-Semi.

GENERAL INFORMATION

ACT2823 is a complete battery charging and

discharging

power

management

solution

for

applications of duel-cell, lithium-based backup battery

pack or power bank. With a USB input, the ACT2823

charges a dual cell Li-Ion battery and provides power to

the output. When USB power is removed, it powers the

output from the battery. The ACT2823 contains a fully

integrated,

advanced,

bidirectional,

synchronous

boost/buck converter. The converter automatically

configures itself as a boost or a buck, depending on the

system level conditions. No microprocessor or user

intervention is needed to switch between operating

modes.

ACT2823 operates in three modes: charge mode,

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

operates in charge mode when an input voltage is

present. It operates in discharge mode when the input

source is not present. It also contains a High Impedance

(HZ) Mode to minimize standby power when input

power is not present and a load is not connected.

The ACT2823 automatically prioritizes power to the load.

If the input voltage drops due to a weak input source,

the charger reduces charging current to ensure the load

can continue to operate.

FEATURES

Charger

The ACT2823 charger contains a boost converter that

charges a dual Li-Ion battery from a USB input. If a

battery is connected, charging is accomplished with a

fully integrated boost converter and consists of five

phases: trickle charge, preconditioning, fast charge, top

off, and end of charge. It contains full, built in charging

protection, including over-charge protection, over

discharge protection, thermal regulation, and automatic

power path priority to the load.

Trickle Charge

When the battery is over-discharged, it must be charged

with a very small current to prevent battery damage.

The ACT2823 provides this protection by charging the

battery with 40mA directly from VIN when the battery

voltage is lower than 96% of VIN. When the battery

voltage increases to greater than 96% of VIN, the

charger transitions to Precondition Charge mode. Note

that Q1 is turned off and VOUT is not present in Trickle

Charge mode.

Precondition Charge

When the battery voltage is below the precondition

threshold, typically 5.6V, the charger operates in

Precondition mode. In this mode, it charges the battery

with a constant current that is set to 15% of the

programmed fast charge current. This prevents damage

to a heavily discharged battery. When the battery

voltage increases above the precondition threshold, the

charger transitions to Fast Charge mode. The battery

voltage is measured between the BATP and BATN pins.

Fast Charge

When the battery voltage is above precondition

threshold, the charger operates in Fast Charge mode.

Fast Charge mode charges the battery with a constant

current set to the programmed fast charge current. The

fast charge current is set by the resistor on the ICST pin.

The charger stays in Fast Charge mode until the battery

voltage reaches the End-of-Charge Voltage, typically

8.4V or 8.7V.

Figure 3 shows a block diagram with current sensing.

ACT2823

VIN

Input

VOUT

RCS

Cin

Cout1

Battery1

Output

Iin

BAT

Battery2

ICST

RICST

BATP

BATN

Figure 3: Battery Current Monitoring

The following equation calculates the fast charge

current, Ic.

)

(

200

)

(

ICST



Where RCS is the current sense resistor in mΩand

RICSTis the fast charge current setting resistor in kΩ. As

an example, setting RCS=25mΩ and RICST=8kΩ results

in a 1A fast charge current. Always design for a current

sense resistor voltage between 20mV-75mV in fast

charge mode.

During discharge mode, the IC inverts the inputs to the

battery current sense amp and the voltage on ICST can

be used to measure the discharge current. The

following equation calculates the discharge current.

)

(

ICST

DISCHARGE





Where VICST is the voltage on the ICST pin in volts, RICST

is the fast charge current setting resistor in kΩ, and

IDISCHARGE is the battery discharge current in amps. As

an example, measuring VICST=0.4V with RICST=8kΩ

indicates 1A discharge current.

ACT2823 Datasheet(PDF) 12 Page - Active-Semi, Inc

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