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www.semtech.com

SC192

POWER MANAGEMENT

Applications Information

Selecting Components

When selecting components for the an SC192 application the main factors are typically performance, size and cost.

For higher performance the designer will select higher values of input and output capacitors to reduce ripple

current and voltage. However, for an application that can tolerate higher ripple, less expensive and smaller compo-

nents can be utilized. The schematics below show two possibilities. The first shows the use of 10μF capacitors on

the input and output with L1 = 10μH, while the second shows the use of smaller less expensive 4.7μF capacitors

and L1 = 4.7μH. The only circuit consideration for choosing one over the other is the compensation components C4

& R8. When these components are in place the values of R2 can be chosen for a given output voltage. The values

that should be used are indicated in Table 1 below. Using a different value for R1 is not advised since this will

change the loop characteristics and may cause the supply to become unstable. Any output voltage is achievable

using R1 of 442k and then selecting R2 to achieve the desired output voltage. The equation for VOUT is:

0.75

1

R2

R1

Vout

•

⎟

⎠

⎞

⎜

⎝

⎛

+

=

Because the SC192 has external compensation the use of small inexpensive ceramic capacitors can be used for

the output capacitor allowing the designer greater flexibility.

R2

L1

10uH

R8

12k

R1

442k

C3

0.1uF

C5

47pF

C1

4.7uF

C4

470pF

VIN

SC192

1

2

3

4

5

6

7

8

9

10

VIN

BP

GND

COMP

ADJ

ILIM

SY NC

EN

LX

PGND

VOUT

C4

470pF

VOUT

R8

6.19k

R2

C6

4.7uF

C1

10uF

R1

442k

C6

10uF

C3

0.1uF

L1

4.7uH

VIN

C5

47pF

SC192

1

2

3

4

5

6

7

8

9

10

VIN

BP

GND

COMP

ADJ

ILIM

SY NC

EN

LX

PGND