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 2006 Semtech Corp.

www.semtech.com

SC196A

PRELIMINARY

POWER MANAGEMENT

Applications Information (Cont.)

Table 2 — Recommended Capacitors

Note: Where PSAVE operation is required, 22µF must be used for C

Manufacturer/Part #

Value

(μF)

Rated

Voltage

(VDC)

Temperature

Characteristic

Case Size

Murata

GRM21BR60J226ME39L

22

6.3

X5R

0805

Murata

GRM188R60J106

MKE19

10

6.3

X5R

0603

TDK

C2012X5R0J106K

10

6.3

X5R

0603

Inductor Selection

The SC196A is designed for use with a 4.7μH inductor.

The magnitude of the inductor current ripple is dependent

on the inductor value and can be determined by the

following equation:

This equation demonstrates the relationship between

input voltage, output voltage, and inductor ripple current.

The inductor should have a low DCR to minimize the

conduction losses and maximize efficiency. As a minimum

requirement, the DC current rating of the inductor

should be equal to the maximum load current plus half

of the inductor current ripple, as shown by the following

equation:

Final inductor selection will depend on various design

considerations, such as efficiency, EMI, size and cost.

Table  lists the manufacturers of practical inductor

options.

C

The source input current to a buck converter is non-

continuous. To prevent large input voltage ripple, a low

ESR ceramic capacitor is required. A minimum value of

10μF should be used for sufficient input voltage filtering,

and a 22μF should be used for improved input voltage

filtering.

C

The internal compensation is designed to work with a

certain output filter corner frequency, which is defined by

the equation:

This single pole filter is designed to operate with a

minimum output capacitor value of 10μF. Larger output

capacitor values will improve transient performance.

If PSAVE operation is required, the minimum capacitor

value is 22µF.

Output voltage ripple is a combination of the voltage ripple

from the charge - discharge cycle of the output capacitor

and the voltage created by the inductor ripple current

passing through the output capacitor ESR. Selecting an

output capacitor with a low ESR will reduce the output

voltage ripple component, as can be seen in the following

equation:

Capacitors with X7R or X5R ceramic dielectric are

strongly recommended for their low ESR and superior

temperature and voltage characteristics. Y5V capacitors

should not be used as their temperature coefficients

make them unsuitable for this application. Table 2 lists

the manufacturers of recommended capacitor options.

Table 1 — Recommended Inductors

Manufacturer/Part #

Value

(μH)

DCR

(Ω)

Rated

Current

(A)

Tolerance

(%)

Dimensions

LxWxH

(mm)

BI Technologies

HM66404R1

4.1

0.057

1.95

20

5.7 × 5.7 ×2.0

Coilcraft

D01608C-472ML

4.7

0.09

1.5

20

6.6 × 4.5 × 3.0

TDK

VLCF4020T- 4R7N1R2

4.7

0.098

1.24

30

4.0 × 4.0 × 2.0

Taiyo Yuden

LMNP04SB4R7N

4.7

0.050

1.2

30

5.0 × 5.0 × 2.0

TOKO

D52LC

4.7

0.087

1.14

20

5.0 × 5.0 × 2.0

Sumida

CDRH3D16

4.7

0.050

1.2

30

3.8 × 3.8 × 1.8

Coilcraft

LPS3015

4.7

0.2

1.1

20

3.0 × 3.0 × 1.5

Note: recommended Inductors do not necessarily guarantee rated perfor-

mance of the part.