LP78073A-01

Jun.-2015

www.lowpowersemi.com

Page 8 of 10

Preliminary Datasheet

LP78073A

Application Information

The LP78073A 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

LP78073A 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 LP78073A is capable of operating from a USB power

source.

For boost function, LP78073Awill stay in PSM(Pulse Skipping

Modulation) mode when there is a light load. This could

reduce unnecessary dissipation to promote efficiency. When

the load grow to a certain level the boost circuit would turn to

PWM mode gradually.

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 LP78073A supplies approximately 1/10 the ISET 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 ISET rammed

charge current is supplied to the battery. When the BAT pin

approaches the final float voltage (4.2V), the LP78073A

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 500

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

and the charge current are calculated using the following

equations:

LP78073A:

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

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 value. The 1ms filter time (t

comparator 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 LP78073A 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 LP78073A constantly monitors the BAT pin voltage in

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

threshold (V

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, or the charger must be shut down

and restarted using the ISET pin.

Charge Status Indicator (STAT)

The charge status output has two different states: strong

pull-down (~10mA) and high impedance. The strong

pull-down state indicates that the LP78073A is in a charge

cycle. Once the charge cycle has terminated, the pin state is

determined by under voltage lockout conditions. High

impedance indicates that the LP78073A is in under voltage

lockout mode: either VIN is less than 100mV above the BAT

pin voltage or insufficient voltage is applied to the VIN pin.