Preliminary Datasheet

LP28012

LP28012 – 00

Feb.-2014

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 6 of 10

Application Information

The LP28012 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 ±1%. The LP28012

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 LP28012 is capable

of operating from a USB power source.

Normal Charge Cycle

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

LP28012 supplies approximately 1/10 the ISET rammed charge

current to bring the battery voltage up to a safe level for full

current charging. (Note: The LP28012 does not include this

trickle charge feature).

When the BAT pin voltage rises above 2.9V, the charger enters

constant-current mode, where the ISET rammed charge current

is supplied to the battery. When the BAT pin approaches the

final float voltage (4.2V), the LP28012 enters constant-voltage

mode and the charge current begins to decrease. When the

charge current drops to 1/10 of the ISET rammed value, the

charge cycle ends.

ISET ramming Charge Current

The charge current is ISET rammed using a single resistor from

the ISET pin to ground. The battery charge current is 600 times

the current out of the ISET pin. The ISET ram resistor and the

charge current are calculated using the following equations:

RSET=1000V/ICHG，ICHG= 1000V/RSET

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= VSET x 500/RSET

Note: Vset 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 100mV

charging is terminated. The charge current is latched off and the

LP28012 enters standby mode, where the input supply current

drops to 200µA. (Note: C/10 termination is disabled in trickle

charging and thermal limiting modes).

When charging, transient loads on the BAT pin can cause the

ISET pin to fall below 200mV for short periods of time before the

DC charge current has dropped to 1/10th the ISET rammed

ensures that transient loads of this nature do not result in

premature charge cycle termination. Once the average charge

current drops below 1/10th the ISET rammed value, the

LP28012 terminates the charge cycle and ceases to provide

any current through the BAT pin. In this state, all loads on the

BAT pin must be supplied by the battery.

The LP28012 constantly monitors the BAT pin voltage in

standby mode. If this voltage drops below the 4.05V recharge

once again supplied to the battery. To manually restart a charge

cycle when in standby mode, the input voltage must be

removed and reapplied, or the charger must be shut down and

restarted using the ISET pin. Figure 1 shows the state diagram

of a typical charge cycle.

Charge Status Indicator (STAT)

The charge status output has three different states: strong

pull-down (~10mA), weak pull-down (~20µA) and high

impedance. The strong pull-down state indicates that the

LP28012 is in a charge cycle. Once the charge cycle has

terminated, the pin state is determined by under voltage lockout

UVLO conditions and the LP28012 is ready to charge. High

impedance indicates that the LP28012 is in under voltage

microprocessor can be used to distinguish between these three