the PMOS is switched on continuously, the output voltage

tracks the input voltage minus the voltage drop across

the PMOS power device and inductor according to the

following relationship:

V

where

V

V

I

R

R

Inductor Selection

TheSC196isdesignedforusewitha4.7μHinductor.Where

V

The magnitude of the inductor current ripple depends on

the inductor value and can be determined by the following

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 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:

2

I

I

I

L

L(PK)

UT(MAX)

O

Final inductor selection will depend on various design con-

siderations such as efficiency, EMI, size and cost. Table 2

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 input voltage filtering, while a

22μF capacitor is recommended for improved input

voltage filtering.

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

C

The internal compensation is designed to work with a

certain output filter corner frequency defined by the

equation:

OUT

C

C

L

2

1

f

This filter has a single pole and 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 inductor current charging and discharging

the output capacitor and the voltage created from the

inductor current ripple 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:

ΔV

Capacitors with X7R or X5R ceramic dielectric are strongly

recommended for their low ESR and superior temperature

Note: recommended Inductors do not necessarily guarantee rated perfor-

mance of the part.

Applications Information (Cont.)

9

© 2007 Semtech Corp.

www.semtech.com

SC196

PRELIMINARY

POWER MANAGEMENT