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BL4054/BL4054B Rev 1.4

Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited

5/2009

©2009 Belling All Rights Reserved

9

BL4054/BL4054B

800mA Standalone Linear Li-Ion Battery Charger

with Thermal Regulation in SOT23-5/TSOT23-5

Operation

The BL4054/BL4054B 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



BL4054/BL4054B

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

BL4054/BL4054B is capable of operating

from a USB power source.

Normal Charge Cycle

A charge cycle begins when the voltage at

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

BL4054/BL4054B

supplies

approximately 1/10 the programmed 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 programmed charge current is

supplied to the battery. If the battery voltage

is above 2.9V at power-on, BL4054B enters

the constant-current mode immediately,

while BL4054 will perform one more check.

If

the

battery

voltage

is

below

the

auto-recharge threshold, BL4054 enters the

constant current mode, otherwise it goes to

standby mode. This is the only difference

between the BL4054 and BL4054B. Refer

to Figure 1a and 1b for more details.

When the BAT pin approaches the final float

voltage (4.2V), the BL4054/BL4054B 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:

CHG

PROG

I

V

1000

R

=

PROG

CHG

R

V

1000

I

=

The charge current out of the BAT pin can

be determined at any time by monitoring the

PROG pin voltage using the following

equation:

1000

R

V

I

PROG

PROG

BAT

•

=

Charge Termination

A charge cycle is terminated when the

charge current falls to 1/10 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

(typically 1ms), charging is terminated. The

charge current is latched off and the

BL4054/BL4054B enters standby mode,

where the input supply current drops to

100

in trickle charging mode).

When charging, transient loads on the BAT