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LT3478/LT3478-1

34781f

APPLICATIO S I FOR ATIO

Inductor Selection

Several inductors that work well with the LT3478/LT3478-1

are listed in Table 1. However, there are many other manu-

facturers and inductors that can be used. Consult each

manufacturer for more detailed information and their entire

range of parts. Ferrite cores should be used to obtain the

best efﬁciency. Choose an inductor that can handle the

necessary peak current without saturating. Also ensure

that the inductor has a low DCR (copper-wire resistance)

to minimize I2R power losses. Values between 4.7µH and

22µH will sufﬁce for most applications.

Inductor manufacturers specify the maximum current

rating as the current where inductance falls by a given

percentage of its nominal value. An inductor can pass a

current greater than its rated value without damaging it.

Aggressive designs where board space is precious will

exceed the maximum current rating of the inductor to save

space. Consult each manufacturer to determine how the

maximum inductor current is measured and how much

more current the inductor can reliably conduct.

Capacitor Selection

Low ESR (equivalent series resistance) ceramic capaci-

tors should be used at the output to minimize the output

ripple voltage. Use only X5R or X7R dielectrics, as these

materials retain their capacitance over wider voltage and

temperature ranges than other dielectrics. A 4.7µF to

10µF output capacitor is sufﬁcient for most high output

current designs. Some suggested manufacturers are

listed in Table 2.

Diode Selection

Schottky diodes, with their low forward voltage drop and

fast switching speed, are ideal for LT3478/LT3478-1 ap-

plications. Table 3 lists several Schottky diodes that work

well. The diode’s average current rating must exceed the

application’s average output current. The diode’s maximum

reverse voltage must exceed the application’s output volt-

age. A 4.5A diode is sufﬁcient for most designs. For PWM

dimming applications, be aware of the reverse leakage

current of the diode. Lower leakage current will drain the

output capacitor less, allowing for higher dimming range.

The companies below offer Schottky diodes with high

voltage and current ratings.

Table 1. Suggested Inductors

MANUFACTURER PART NUMBER

IDC (A)

INDUCTANCE (µH)

MAX DCR (mΩ)L × W × H (mm)

MANUFACTURER

CDRH104R-100NC

CDRH103RNP-4R7NC-B

CDRH124R-100MC

CDRH104R-5R2NC

3.8

4.5

5.5

4.7

5.2

10.5 × 10.3 × 4.0

10.5 × 10.3 × 3.1

12.3 × 12.3 × 4.5

10.5 × 10.3 × 4.0

Sumida

www.sumida.com

FDV0630-4R7M

4.2

4.7

7.0 × 7.7 × 3.0

Toko

www.toko.com

UP4B-220

7.6

22 × 15 × 7.9

Cooper

www.cooperet.com

Table 2. Ceramic Capacitor Manufacturers

MANUFACTURER

PHONE NUMBER

WEB

Taiyo Yuden

(408) 573-4150

www.t-yuden.com

AVX

(803) 448-9411

www.avxcorp.com

Murata

(714) 852-2001

www.murata.com

Table 3. Suggested Diodes

MANUFACTURER PART NUMBER

MAX CURRENT (A)

MAX REVERSE VOLTAGE

WEB

UPS340

Microsemi

www.microsemi.com

B520C

B530C

B340A

B540C

PDS560

Diodes, Inc.

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