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SC192

POWER MANAGEMENT

Inductor Selection

The inductor values listed in Table 1 will work for nearly

all combinations of output current and output voltages.

After selecting 4.7uH or 10uH for the inductor value two

additional inductor parameters should be considered. The

current rating of the inductor and the DC resistance.

The DC resistance has a great impact on efficiency due

to copper losses. However, small inductors tend to have

higher DC resistance. Therefore a compromise between

size and efficiency will need to be made.

The inductor current must be chosen to prevent the in-

ductor from saturation. The most conservative approach

would be to select an inductor with a saturation current

slightly above the maximum current capability of the

SC192 which is 1.56A peak current for ILIM = Vin or

780mA for ILIM = GND.

A more accurate design of the inductor would be to rate

the inductor for the maximum output current plus the

inductor ripple current that can be calculated as follows:

2

I

I

I

L

)

O(MAX

L(MAX)

Δ

+

=

OUT

IN

OUT

L

V

f

L

V

V

-

1

I

•

⎟

⎟

⎟

⎟

⎠

⎞

⎜

⎜

⎜

⎜

⎝

⎛

•

=

Δ

f = Switching frequency

L = Inductor Value

ΔI

I

V

V

C

I

I

Output Capacitor Selection

Because the SC192 has external compensation avail-

able, low ESR ceramic capacitors can be used. This elimi-

nates the need for bulky tantalum capacitors. Values for

the output capacitors in Table 1 will work for nearly all

combinations of output current and output voltages. The

equation for determining the size of the output capaci-

tor in terms of minimizing the ripple voltage is given as

follows:

⎟

⎠

⎞

⎜

⎝

⎛

+

•

•

•

Δ

=

Δ

ESR

f

C

8

1

I

V

OUT

L

O

Input Capacitor Selection

The input ripple current can be reduced with properly

selecting the input capacitor. Again, values for the input

capacitors in Table 1 will work for nearly all combina-

tions of input current and output voltages. The input ca-

pacitor should be rated for the maximum input ripple

current calculated as:

PSAVE, Cout = 4.7uF, Lout = 4.7uH

PWM, Cout = 4.7uF, Lout = 4.7uH

Applications Information Cont.