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LTC3535

3535fa

APPLICATIONS INFORMATION

COMPONENT SELECTION

Inductor Selection

The LTC3535 can utilize small surface mount chip induc-

tors due to their fast 1MHz switching frequency. Inductor

values between 3.3µH and 6.8µH are suitable for most

applications.Largervaluesofinductancewillallowslightly

greater output current capability (and lower the Burst

Mode threshold) by reducing the inductor ripple current.

Increasing the inductance above 10µH will increase com-

ponent size while providing little improvement in output

current capability.

The minimum inductance value is given by:

RippleV

IN MIN

OUT MAXINMIN

OUT

()

(

•–

•

MAX)

where:

Ripple = Allowable inductor current ripple (amps peak-

peak)

VIN(MIN) = Minimum input voltage

VOUT(MAX) = Maximum output voltage

The inductor current ripple is typically set for 20% to

40% of the maximum inductor current. High frequency

ferritecoreinductormaterialsreducefrequencydependent

power losses compared to cheaper powdered iron types,

improving efficiency. The inductor should have low ESR

(seriesresistanceofthewindings)toreducetheI2Rpower

losses, and must be able to support the peak inductor

current without saturating. Molded chokes and some chip

inductorsusuallydonothaveenoughcoreareatosupport

the peak inductor current of 750mA seen on the LTC3535.

To minimize radiated noise, use a shielded inductor. See

Table 1 for suggested components and suppliers.

Table 1. Recommended Inductors

VENDOR

PART/STYLE

Coilcraft

(847) 639-6400

www.coilcraft.com

LPO4815

LPS4012, LPS4018

MSS5131

MSS4020

MOS6020

ME3220

DS1605, DO1608

Coiltronics

www.cooperet.com

SD10, SD12, SD14, SD18, SD20,

SD52, SD3114, SD3118

FDK

(408) 432-8331

www.fdk.com

MIP3226D4R7M, MIP3226D3R3M

MIPF2520D4R7

MIPWT3226D3R0

Murata

(714) 852-2001

www.murata.com

LQH43C

LQH32C (-53 series)

301015

Sumida

(847) 956-0666

www.sumida.com

CDRH5D18

CDRH2D14

CDRH3D16

CDRH3D11

CR43

CMD4D06-4R7MC

CMD4D06-3R3MC

Taiyo-Yuden

www.t-yuden.com

NP03SB

NR3015T

NR3012T

TDK

(847) 803-6100

www.component.tdk.com

VLP

VLF, VLCF

Toko

(408) 432-8282

www.tokoam.com

D412C

D518LC

D52LC

D62LCB

Wurth

(201) 785-8800

www.we-online.com

WE-TPC type S, M

Output and Input Capacitor Selection

Low ESR (equivalent series resistance) capacitors should

be used to minimize the output voltage ripple. Multilayer

ceramic capacitors are an excellent choice as they have

extremely low ESR and are available in small footprints. A

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