LP4062 datasheet(8/13 Pages) POWER

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Preliminary

Datasheet

LP4062

LP4062 –00

Ver. 1.0 Datasheet

Nov.-2007

Page 8 of 13

Applications Information

Operation

The LP4062 is a single cell lithium-ion battery charger

using a constant-current/constant-voltage algorithm. It

can deliver up to 600mA of charge current (using a

good thermal PCB layout) with a final float voltage

accuracy of ± 1%. The LP4062 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 LP4062 is capable of operating from a USB power

source.

Normal Charge Cycle

A charge cycle begins when the voltage at the VCC pin

rises above the UVLO threshold level and a 1%

program resistor is connected from the PROG 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 LP4062

supplies approximately 1/10 the programmed charge

current to bring the battery voltage up to a safe level

for full current charging. (Note: The LP4062X does not

include this trickle charge feature).

When the BAT pin voltage rises above 2.9V, the

charger enters constant-current mode, where the

programmed charge current is supplied to the battery.

When the BAT pin approaches the final float voltage

(4.2V), the LP4062 enters constant-voltage mode and

the charge current begins to decrease. When the charge

current drops to 1/10 of the programmed value, the

charge cycle ends.

Programming Charge Current

The charge current is programmed using a single

resistor from the PROG pin to ground. The battery

charge current is 880 times the current out of the

PROG pin. The program resistor and the charge current

are calculated using the following equations:

RSET=880/ISET

The charge current out of the BAT pin can be

determined at any time by monitoring the PROG pin

voltage using the following equation:

ISET = 880/ RSET

Charge Termination

A charge cycle is terminated when the charge current

falls to 1/10th the programmed value after the final

float voltage is reached. This condition is detected by

using an internal, filtered comparator to monitor the

PROG pin. When the PROG pin voltage falls below

100mV for longer than tTERM (typically 1ms),

charging is terminated. The charge current is latched

off and the LP4062 enters standby mode, where the

input supply current drops to 200µA. When charging,

transient loads on the BAT pin can cause the PROG

pin to fall below 100mV for short periods of time

before the DC charge current has dropped to 1/10th the

programmed value. The 1ms filter time (TTERM) on

the termination 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 programmed value, the LP4062

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

LP4062 constantly monitors the BAT pin voltage in

standby mode. If this voltage drops below the 4.05V

recharge threshold (VRECHRG), another charge cycle

begins and current 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 PROG pin. Figure 7 shows the state diagram of a

typical charge cycle.

Charge Status Indicator(CHRG)

The charge status output has three different states:

strong pull-down(~10mA), weak pull-down (~12µA)

and high impedance. The strong pull-down state

indicates that the LP4062 is in a charge cycle. Once the

charge cycle has terminated , the pin state is

determined by undervoltage lockout conditions. A

weak pull-down indicates that VCC meets the UVLO

conditions and the LP4062 is ready to charge. High

impedance indicates that the LP4062 is in undervoltage

lockout mode: either VCC is less than 100mV above

the BAT pin voltage or insufficient voltage is applied

to the VCC pin. A microprocessor can be used to

distinguish between these three states –this method is

discussed in the Applications Information section.

Charge Termination

internal

thermal

feedback

loop

reduces

the

programmed charge current if the die temperature

attempts

rise

above

preset

value

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