LP28056S datasheet(6/8 Pages) POWER

6 / 8 page

LP28056S-02

May.-2013

Email: marketing@lowpowersemi.com

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Page 6 of 8

Preliminary Datasheet

LP28056S

Application Information

The LP28056S is a single cell lithium-ion battery

charger using a constant-current/constant-voltage

algorithm. It can deliver up to 1200mA of charge

current (using a good thermal PCB layout) with a

final float voltage accuracy of 4.2V. The LP28056S

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 com-

ponents. Furthermore, the LP28056S is capable of

operating from a USB power source.

Normal Charge Cycle

A charge cycle begins when the voltage at the VIN

pin rises above the UVLO threshold level and a 1%

ISET ram resistor is connected from the ISET pin to

ground or when a battery is connected to the charger

output. If the BAT pin is less than 2.9V, the charger

enters trickle charge mode. In this mode, the

LP28056S supplies approximately 1/10 the RISET

rammed 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

RISET rammed charge current is supplied to the

battery. When the BAT pin approaches the final float

voltage, the LP28056S enters constant-voltage

mode and the charge current begins to decrease.

The charge cycle ends when the charge current

drops to 1/10 of the RISET rammed value.

ISET ramming Charge Current

The charge current is RISET rammed using a single

resistor from the ISET pin to ground. The battery

charge current is 500 times the current out of the

ISET pin. The ISET ram resistor and the charge

current are calculated using the following equations:

RISET=1000V/ICHG, IBAT=1000V/RISET

The charge current out of the BAT pin can be

determined at any time by monitoring the ISET pin

voltage using the following equation:

IBAT=VISET×500/RISET

Note: VISET is 2Volts.

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).

Automatic Recharge

The LP28056S constantly monitors the BAT pin

voltage in standby mode. If this voltage drops below

the 4.05V recharge threshold (VRECHRG), another

charge cycle begins and current is once again

supplied to the battery. To manually restart a charge

cycle when in standby mode, the input voltage must

be removed and reapplied.

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