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The KB4540 is a single cell lithium-ion battery charger

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

can deliver up to 800mA of charge current (using a good

thermal PCB layout) with a final float voltage accuracy of

±1%. The KB4540 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 com-

ponents. Furthermore, the KB4540 is capable of operat-

ing from a USB power source.

Normal Charge Cycle

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 KB4540 supplies approximately 1/10

the programmed charge current to bring the battery volt-

age up to a safe level for full current charging. (Note: The

KB4540X 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 KB4540

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 1000 times the current out of the PROG pin. The

program resistor and the charge current are calculated

using the following equations:

R

V

I

I

V

R

PROG

CHG

CHG

PROG

==

1000

1000

,

The charge current out of the BAT pin can be determined

at any time by monitoring the PROG pin voltage using the

following equation:

I

V

R

CHG

PROG

PROG

=

1000

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

current is latched off and the KB4540 enters standby

mode, where the input supply current drops to 200

µA.

(Note: C/10 termination is disabled in trickle charging and

thermal limiting modes).

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

termination comparator ensures that transient loads of

this nature do not result in premature charge cycle termi-

nation. Once the

average charge current drops below

1/10th the programmed value, the KB4540 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 KB4540 constantly monitors the BAT pin voltage in

standby mode. If this voltage drops below the 4.05V

gins 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 1 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 (~20

µA) and high

impedance. The strong pull-down state indicates that the

KB4540 is in a charge cycle. Once the charge cycle has

terminated, the pin state is determined by undervoltage

Note 1: Any external sources that hold the PROG pin above 100mV will prevent the KB4540

from terminating a charge cycle.

KB4540

Kingbor Technology Co.,Ltd

TEL:(86)0755-26508846 FAX:(86)0755-26509052

OPERATION

(V

=1V)

PROG