LP28021-04

Apr.-2017

www.lowpowersemi.com

Page 8 of 11

Preliminary Datasheet

LP28021

Application Information

The LP28021 is a single cell lithium-ion battery

charger using a constant-current/constant-voltage

algorithm. It can deliver up to 1000mA of charge

current (using a good thermal PCB layout) with a

final float voltage accuracy of ±1%. The LP28021

includes an internal P-channel power MOSFET and

thermal regulation circuitry. No blocking diode or

external current sense resistor is required; thus, the

basic charger circuit requires only two external

components. Furthermore, the LP28021 is capable

of operating from a USB power source.

Normal Charge Cycle

A charge cycle begins when the voltage at the VO

pin rises above the UVLO threshold level and a 1%

when a battery is connected to the charger output. If

the BAT pin is less than 2.8V, the charger enters

trickle charge mode. In this mode, the LP28021

supplies 30mA charge current to bring the battery

voltage up to a safe level for full current charging.

When the BAT pin voltage rises above 2.9V, the

charger enters constant-current mode, where the

battery. When the BAT pin approaches the final float

voltage, the LP28021 enters constant-voltage mode

and the charge current begins to decrease. The

charge cycle ends when the charge current drops to

Charge Termination

A charge cycle is terminated when the charge current falls to

1/10th the ISET rammed value after the final float voltage is

reached. This condition is detected by using an internal,

filtered comparator to monitor the ISET pin. When the ISET

pin voltage falls below 200mV for longer than tTERM(typically

1ms), charging is terminated. The charge current is latched off

and the LP28056S enters standby mode, where the input

supply current drops to 200µA. In this state, all loads on the

BAT pin must be supplied by the battery. (Note: C/10

termination is disabled in trickle charging and thermal limiting

modes).

ISET ramming Charge Current

resistor from the ISET pin to ground. The battery

charge current is 1000 times the current out of the

are calculated using the following equations:

The charge current out of the BAT pin can be

determined at any time by monitoring the IBAT pin

voltage using the following equation: