Preliminary Datasheet

LP78092

LP78092 – 00 Version 1.0 Feb.-2014

www.lowpowersemi.com

Page 8 of 10

Application Information

The LP78092 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 LP78092

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 LP78092 is capable

of operating from a USB power source. For LDO part, like any

low-dropout regulator, the external capacitors used with the

LP78092 must be carefully selected for regulator stability and

performance. Using a capacitor whose value is > 2µF on the

LP78092 input and the amount of capacitance can be increased

without limit. The input capacitor must be located a distance of

not more than 0.5 inch from the input pin of the IC and returned

to a clean analog ground. There is a special attention which is

the input capacitance should not be less than output

capacitance. Any good quality ceramic or tantalum can be used

for this capacitor. The capacitor with larger value and lower

ESR (equivalent series resistance) provides better PSRR and

line-transient response. The output capacitor must meet both

requirements for minimum amount of capacitance and ESR in

all LDOs application. The LP78092 is designed specifically to

work with low ESR ceramic output capacitor in space-saving

and performance consideration. Using a ceramic capacitor

whose value is at least 1µF with ESR is > 25mΩ on the

LP78092 output ensures stability. The LP78092 still works well

with output capacitor of other types due to the wide stable ESR

range. Output capacitor of larger capacitance can reduce noise

and improve load transient response, stability, and PSRR. The

output capacitor should be located not more than 0.5 inch from

the VOUT pin of the LP78092 and returned to a clean analog

ground.

Normal Charge Cycle

A charge cycle begins when the voltage at the V

above the UVLO threshold level and a 1% SET ram resistor is

connected from the SET 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

LP78092 supplies approximately 1/10 the SET 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 SET rammed charge current

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

final float voltage (4.2V), the LP78092 enters constant-voltage

mode and the charge current begins to decrease. When the

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

charge cycle ends.

RSET ramming Charge Current

The charge current is SET rammed using a single resistor from

the SET pin to ground. The battery charge current is 500 times

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

charge current are calculated using the following equations:

LP78092:

RSET=1000V/ICHG，ICHG= 1000V/RSET

The charge current out of the BAT pin can be determined at any

time by monitoring the SET 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 SET rammed value after the final float voltage is

reached. This condition is detected by using an internal, filtered

comparator to monitor the SET pin. When the SET pin voltage

falls below 100mV for longer than t

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

LP78092 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

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

DC charge current has dropped to 1/10th the SET 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 SET rammed value, the

LP78092 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.