Preliminary Datasheet

LP78073

LP78073 – 00 Version 1.0

Feb.-2014

www.lowpowersemi.com

Page 7 of 9

Application Information

The LP78073 is a single cell lithium-ion battery charger using a

constant-current/constant-voltage algorithm. It can deliver up to

700mA of charge current (using a good thermal PCB layout)

with a final float voltage accuracy of ±1%. The LP78073

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 LP78073 is capable

of operating from a USB power source.

Normal Charge Cycle

A charge cycle begins when. If the BAT pin is less than 2.9V,

the charger enters trickle charge mode. In this mode, the

LP78073 supplies approximately 70mA 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 charge current is 700mA.

When the BAT pin approaches the final float voltage (4.2V), the

LP78073 enters constant-voltage mode and the charge current

begins to decrease. When the charge current drops to 1/10 of

the 700mA, the charge cycle ends.

Charge Status Indicator (CHARGEB)

The charge status output has two different states: strong

pull-down and high impedance. The strong pull-down state

indicates that the LP78073 is in a charge cycle. Once the

charge cycle has terminated, the pin state is determined by

under voltage lockout conditions. A weak pull-down indicates

that the battery is not connecting to chip. High impedance

indicates that the charge cycle is terminated.

Automatic Recharge

Once the charge cycle is terminated, the LP78073 continuously

monitors the voltage on the BAT pin using a comparator with a

2ms filter time (t

battery voltage falls below 4.1V (which corresponds to

approximately 80% to 90% battery capacity). This ensures that

the battery is kept at or near a fully charged condition and

eliminates the need for periodic charge cycle initiations.

Boost Output voltage Setting

Set the output voltage by selecting the resistive voltage divider

ratio. The voltage divider drops the output voltage to the 1.0V

feedback voltage. Use a 100K resistor for R2 of the voltage

divider. Determine the high-side resistor R1 by the equation:

Vout=(R1/R2+1) x VFB

Vout=(R1/R2+1) x 1.0V

Table:

Vout

R1

R2

C3

3.3V

100K

230K

22pF

5V

100K

400K

22pF

Power Dissipation

The conditions that cause the LP78073 battery charger to

reduce charge current through thermal feedback can be

approximated by considering the total power dissipated in

the IC. For high charge currents, the LP78073 power

dissipation is approximately:

Where PD is the total power dissipated within the IC, ADP is

particular load.

It is not necessary to perform worst-case power dissipation

scenarios because the LP78073 will automatically reduce

the charge current to maintain the die temperature at

approximately 125°C.