ACT2801_16 datasheet(11/25 Pages) ACTIVE-SEMI

11 / 25 page

Rev 8, 01-Nov-16

Innovative PowerTM

- 11 -

www.active-semi.com

ACT2801/ACT2801B

Figure 2:

ACT2801B System Operation Flow Chart

FUNCTIONAL DESCRIPTION

Latch-Off

ACT2801/ACT2801B has latch off function. If

discharging stops due to battery cut-off, and latch

off will be triggered, it would prevent battery from

discharging again, latch-off is released when input

power is recycled.

Input Current Limit

When the input current reaches the programmed

value, switch Q1 goes into linear mode and output

voltage starts to drop. When output voltage drops to

4.25V, hiccup mode is triggered and switch Q1

turns off and restart in 2 seconds.

Switching Battery Charger

ACT2801/ACT2801B is configured in charge mode

(buck mode) when VIN is valid. In this mode, a

battery is charged with preconditioning, fast charge,

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

management is shown in Figure 3 and Figure 4.

CC/CV Regulation Loop

There are CC/CV regulation loops built in ACT2801/

ACT2801B, which regulates either current or

voltage as necessary to ensure fast and safe

charging of the battery. In a normal charge cycle,

this loop regulates the current to the value set by

the external resistor at the ICST pin. Charging

continues at this current until the battery cell voltage

reaches the termination voltage. At this point the

CV loop takes over, and charge current is allowed

to decrease as necessary to maintain charging at

the termination voltage.

Precondition Charge

A new charging cycle begins with the precondition

state, and operation continues in this state until VBAT

exceeds the precondition threshold voltage. When

operating in precondition state, the cell is charged

at a reduced current, 10% of the programmed

maximum fast charge constant current. Once VBAT

reaches the precondition threshold voltage the state

machine jumps to the fast charge state.

Fast Charge

battery

voltage

above

preconditioning

threshold, buck converter charges battery with

constant current. In fast charge state, the ACT2801/

ACT2801B charges at the current set by the

external resistor connected at the ICST pin. During

a normal charge cycle fast charge continues in CC

mode until VBAT reaches the charge termination

voltage, at which point the ACT2801/ACT2801B

charges in top off state.

Top Off

With the battery voltage approaches the EOC

voltage set by the BTV pin. Charge current

decreases as charging continues. In the top off

state, the cell is charged in constant voltage (CV)

mode. During a normal charging cycle charging

proceeds until the charge current decreases below

the end of charge (EOC) threshold, defined as 13%

of fast charge current. When this happens, the state

machine terminates the charge cycle and jumps to

the EOC state.

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