SC198A

12

Inductor Selection

The SC198A was designed for optimum performance

when using a 4.7μH inductor. The magnitude of the

inductor current ripple is dependent on the inductor value

and is determined by the equation

IN

OUT

osc

OUT

L

V

V

1

f

L

V

I

This equation demonstrates the relationship between

input voltage, output voltage, and inductor ripple current.

The inductor should also have a low DCR to minimize the

conduction losses and maximize efficiency. The minimum

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 equation

2

I

I

I

L

OUT(MAX)

L(Peak)

Final inductor selection will depend on various design

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

2 lists some manufacturers of practical inductor options.

Table 2 — Recommended Inductors

Manufacturer/

Part No.

Value

(μH)

DCR

(Ω)

Rate

Current

(A)

Tolerance

(+%)

Dimensions

LxWxH

(mm)

Coilcraft

LPO6610-472ML

4.7

0.20

1.1

±20

6.60 × 5.50 × 1.10

Coilcraft

1812PS-472KLB

4.7

0.11

2.10

±20

5.87 × 4.89 × 3.81

Coilcraft

D01608C-472ML

4.7

0.09

1.5

±20

6.60 × 4.50 × 13.0

Capacitor Selection

Input Capacitor

The source input current to a buck converter is non-con-

tinuous. To prevent large input voltage ripple a low ESR

ceramic capacitor is required. A minimum value of 4.7μF

should be used for sufficient input voltage filtering and a

22μF MLCC may be used for optimum input voltage

filtering.

Applications Information (continued)

Output Capacitor

Output voltage ripple is dominated by the filter capaci-

tance ESR as shown in the equation

V

OUT(P-P)

= DI

L

× ESR

COUT

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 unsuit-

able for this application.

When selecting capacitors for the application, first con-

sider the DC voltage characteristic of the capacitor. The

capacitance value at the DC operating voltage may be

considerably lower than the rated value. Table 3 lists rec-

ommended capacitor values which have been chosen to

minimize the impact of this limitation. A 10μF ceramic

capacitor is the minimum recommended value for the

output filter capacitor. It is important to ensure the capaci-

tor value does not drop below 9μF for the operating range

of the application.

Table 3 — Recommended Capacitors

Manufacturer/

Part No.

Value

(μF)

Rated

Voltage

(VDC)

Type

Case

Size

Murata

GRM21BR60J226ME39

22

6.3

X5R

0805

Murata

GRM188R60J106ME47

10

6.3

X5R

0603

Murata

GRM21BR60J106KE01B

10

6.3

X5R

0805