Preliminary Datasheet

LP78090

LP78090 – 00

Version 1.0

Feb.-2014

www.lowpowersemi.com

Page 8 of 10

Application Information

The LP78090 is a linear switching charger IC with smart power

path management integrated for powering the system and

charging a single cell lithium-ion battery simultaneously. It can

deliver up to 1000mA of charge current (using a good thermal

PCB layout) with a final float voltage accuracy of ±1%. The

LP78090 includes an internal P-channel power MOSFET and

thermal regulation circuitry. No blocking diode or external

current sense resistor is required; thus, the basic application

circuit requires only four external components. Furthermore, the

LP78090 is capable of operating from a USB power source，

500mA for USB 2.0 and 850mA for USB3.0 with resistor change

on ISET pin.

It has precious average input current limit and average current

limit form battery to system, to make maximum use of the

allowable input power. And LP78090 would give priority to

ensuring the system load approximately up to 2.4A, which

contains 1.2A form VIN and 1.2A form battery. LP78090 will

reduce charging current or even power from battery to satisfy

the system load when its demand is over the input current limit.

In low system load situation, the remaining current is supply for

charger programmed by an external resistor connected from

ISET pin to GND. The device would reduce the charge current

when the die temperature exceeds 120℃.

Two 130mΩ MOSFET integrated work as an ideal diode to

connecting the battery and VIN to the system load, and one of

this two MOSFET will turn on allowing the battery to power up

the system when the input is removed with circuit in page 3.

SYS Pin Voltage Switch

The voltage on the SYS pin is set by the SC voltage, VIN

voltage and battery voltage. VIN<4.3V condition, voltage power

for system always keeps with battery voltage. 4.3V < VIN

condition, voltage power for system always keeps with VIN

voltage

Current Limit

The current limit regulate in two directions: from VIN to system

and from battery to system, each one is limited to 1.2A. When

the system load needs the current above 1.2A, LP78090 would

divert part of charge current to system. And the device would

power system from VIN and battery when the system current is

more than charge current plus 1.2A.

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

LP78090 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 LP78090 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:

LP78090:

RSET=1200V/ICHG，ICHG= 1200V/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 600/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

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

LP78090 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.