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LTC3455

3455f

Switching Regulator Inductor Selection

Many different sizes and shapes of inductors are available

from numerous manufacturers. Choosing the right induc-

tor from such a large selection of devices can be over-

whelming, but following a few basic guidelines will make

the selection process much simpler. To maximize effi-

ciency, choose an inductor with a low DC resistance. Keep

in mind that most inductors that are very thin or have a very

small volume typically have much higher core and DCR

losses, and will not give the best efficiency.

Choose an inductor with a DC current rating at least 1.5

times larger than the maximum load current to ensure that

the inductor does not saturate during normal operation.

Table 1 shows several inductors that work well with the

LTC3455. These inductors offer a good compromise in

current rating, DCR and physical size. Consult each manu-

facturer for detailed information on their entire selection of

inductors.

APPLICATIO S I FOR ATIO

Table 1. Recommended Inductors

Max

Inductor

IDC

DCR

Height

Type

(

µH)

(A)

(

Ω)

(mm)

Manufacturer

DB318C

4.7

0.86

0.1

1.8

Toko

0.58

0.18

1.8

(847)297-0070

www.toko.com

CLS4D09

4.7

0.75

0.19

Sumida

0.5

0.37

(847)956-0666

www.sumida.com

CDRH3D16

4.7

0.9

0.11

1.8

Sumida

0.55

0.21

1.8

SD12

4.7

1.29

0.12

1.2

Cooper

0.82

0.28

1.2

(561)752-5000

www.cooperet.com

ELT5KT

4.7

0.2

1.2

Panasonic

0.68

0.36

1.2

(408)945-5660

www.panasonic.com

Switching Regulator Output Capacitor Selection

Low ESR (equivalent series resistance) ceramic capaci-

tors should be used at both switching regulator outputs.

Only X5R or X7R ceramic capacitors should be used

because they retain their capacitance over wider voltage

and temperature ranges than other ceramic types. A 10

µF

output capacitor is sufficient for most applications. Table

2 shows a list of several ceramic capacitor manufacturers.

Consult each manufacturer for detailed information on

their entire selection of ceramic capacitors. Many manu-

facturers now offer very thin (<1mm tall) ceramic capaci-

tors ideal for use in height-restricted designs.

VBAT Pin Capacitor Selection

For the VBAT pin, a 4.7µF to 10µF ceramic capacitor is the

best choice. Only X5R or X7R ceramic capacitors should

be used.

VMAX Pin Capacitor Selection

For the VMAX pin, a 10µF ceramic capacitor is the best

choice. Only X5R or X7R ceramic capacitors should be

used. Do not use less than 10

µF on this pin. For some

designs it may be desirable to use a larger capacitor

connected to VMAX to act as a reservoir when the LTC3455

is USB powered. Up to 50

µF of ceramic capacitance may

be connected to the VMAX pin without difficulty. More than

µF requires using a capacitor with some ESR (like a

Tantalum or OS-CON) or adding some resistance in series

with some of the ceramic capacitance. This is necessary

to ensure loop stability in the battery charger loop when

under USB power.

Table 2. Recommended Ceramic Capacitor Manufacturers

Taiyo Yuden

(408) 573-4150

www.t-yuden.com

AVX

(803) 448-9411

www.avxcorp.com

Murata

(714) 852-2001

www.murata.com

TDK

(888) 835-6646

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