LTC3428

7

3428f

COMPONENT SELECTION

Inductor Selection

The high frequency operation of the LTC3428 allows for

the use of small surface mount inductors. The inductor

ripple current is typically set to between 20% and 40% of

the maximum inductor current. For a given set of condi-

tions, the inductance is given as follows:

L

VV

V

RV

LH

IN MIN

OUT

IN MIN

OUT

≥

>

()

()

•(

–

)

•

,2µ

where:

R = Allowable inductor current ripple (Amps P-P)

For high efficiency, the inductor should have a high

frequency core material, such as ferrite, to reduce core

losses. The inductor should have a low ESR (equivalent

to handle the peak inductor current without saturating.

Use of a toroid, pot core, or shielded bobbin inductor will

minimize radiated noise. See Table 1 for a list of inductor

manufacturers. Some example inductor part types are:

Coilcraft 1608 and 3316 series, Murata LQH55D series,

APPLICATIO S I FOR ATIO

Sumida CDRH4D22C/LD or CDRH5D28 series, Toko

FDV0630 or D62CB series.

Table 1. Inductor Vendor Information

Supplier

Phone

Fax

Website

Coilcraft

(847) 639-6400 (847) 639-1469

www.coilcraft.com

Murata

USA:

USA:

www.murata.com

(814) 238-1431 (814) 238-0490

Sumida

USA:

USA:

www.sumida.com

(847) 956-6666 (847) 956-0702

Japan:

Japan:

81-3-3607-5111 81-3-3607-5144

TDK

(847) 803-6100 (847) 803-6296

www.component.tdk.com

Toko

(847) 299-0070 (847) 699-7864

www.toko.com

Wurth

(201)785-8800

(201)785-8810

www.we-online.com

Output Capacitor Selection

The minimum value of the capacitor is set to reduce the

output ripple voltage due to charging and discharging the

capacitor each cycle. The steady state ripple due to this

charging is given by:

V

IV

V

CV

f

RIPPLE C

PEAK

OUT

IN MIN

OUT

OUT

()

()

•

•(

–

)

••

=

1

2

The equivalent series resistance (ESR) of the output

capacitor will contribute another term to output voltage

ripple. Ripple voltage due to capacitor ESR is:

VI

R

RIPPLE ESR

PEAK

ESR C

()

( )

•

=

where:

The ESL (Equivalent Series Inductance) is another

capacitor characteristic that needs to be minimized. ESL

will be minimized by using small surface mount ceramic

Input Capacitor Selection

circuitry, it is recommended to place at least a 4.7µF, low

the IC as possible. See Table 2 for a list of capacitor

manufacturers.

Figure 2. Output Ripple Current Comparison

Between Single Phase and Two Phase Boost

Converters with a 2A Load and 50% Duty Cycle

TIME (µs)

0

1.6

3428 F02

0.4

0.2

0.6

1.0

1.4

1.8

0.8

1.2

2.0

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

1 PHASE

CONVERTER

2 PHASE

CONVERTER