12

I

VV

VV

RC

T

R

BAT

S

BAT

S

BAT

CC

A

JA

CC

=

°

⎛

⎝⎜

⎞

⎠⎟

()

()

()

120

2

θ

charge current to be:

While this application delivers more energy to the battery

and reduces charge time in thermal mode, it may actually

0

1000

800

600

400

200

0

0.5

1.0

1.25

0.25

0.75

1.5

1.75

CONSTANT

CURRENT

THERMAL

MODE

DROPOUT

enough to put the KB4540 into dropout. Figure 4 shows

large.

to keep component size small and avoid dropout. Remem-

ber to choose a resistor with adequate power handling

capability.

Many types of capacitors can be used for input bypassing,

however, caution must be exercised when using multi-

layer ceramic capacitors. Because of the self-resonant and

high Q characteristics of some types of ceramic capaci-

tors, high voltage transients can be generated under some

start-up conditions, such as connecting the charger input

to a live power source. Adding a 1.5

Ω resistor in series

with an X5R ceramic capacitor will minimize start-up

voltage transients. For more information, refer to Applica-

tion Note 88.

Charge Current Soft-Start

The KB4540 includes a soft-start circuit to minimize the

inrush current at the start of a charge cycle. When a charge

cycle is initiated, the charge current ramps from zero to the

full-scale current over a period of approximately 100

µs.

This has the effect of minimizing the transient current load

on the power supply during start-up.

will not generate enough heat to require thermal regulation.

Figure 3. A Circuit to Maximize Thermal Mode Charge Current

Li-Ion

CELL

KB4540

1

µF

BAT

PROG

GND

KB4540

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APPLICATIONS INFORMATION