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LTC3586/LTC3586-1

3586fb

load current. 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. If output short circuit is a possible condition,

the inductor should be rated to handle the maximum peak

current speciﬁed for the buck converters.

Differentcorematerialsandshapeswillchangethesize/cur-

rent and price/current relationship of an inductor. Toroid

or shielded pot cores in ferrite or Permalloy materials are

small and don’t radiate much energy, but generally cost

more than powdered iron core inductors with similar

electrical characteristics. 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.

The choice of which style inductor to use often depends

more on the price vs size, performance and any radiated

EMI requirements than on what the LTC3586/LTC3586-1

require to operate.

The inductor value also has an effect on Burst Mode

operations. Lower inductor values will cause the Burst

Mode switching frequencies to increase.

Table 5 shows several inductors that work well with the

LTC3586/LTC3586-1’sbuckregulators.Theseinductorsof-

feragoodcompromiseincurrentrating,DCRandphysical

size. Consult each manufacturer for detailed information

on their entire selection of inductors.

Buck Regulator Input/Output Capacitor Selection

Low ESR (equivalent series resistance) MLCC capacitors

should be used at both buck regulator outputs as well as at

eachbuckregulatorinputsupply(VIN1andVIN2).OnlyX5R

or X7R ceramic capacitors should be used because they

retaintheircapacitanceoverwidervoltageandtemperature

ranges than other ceramic types. A 10µF output capaci-

tor is sufﬁcient for most applications. For good transient

response and stability the output capacitor should retain

at least 4µF of capacitance over operating temperature

and bias voltage. Each buck regulator input supply should

be bypassed with a 1µF capacitor. Consult with capacitor

manufacturers for detailed information on their selection

and speciﬁcations of ceramic capacitors. Many manufac-

turers now offer very thin (<1mm tall) ceramic capacitors

ideal for use in height-restricted designs. Table 6 shows a

list of several ceramic capacitor manufacturers.

applicaTions inForMaTion

Table 5. Recommended Inductors for Buck Regulators

INDUCTOR

TYPE

(µH)

MAX

IDC

(A)

MAX

DCR

(Ω)

SIZE IN mm

× W × H) MANUFACTURER

DE2818C

4.7 1.25 0.072* 3.0 × 2.8 × 1.8 Toko

www.toko.com

DE2812C

4.7 1.15 0.13* 3.0 × 2.8 × 1.2

CDRH3D16 4.7

0.9

0.11

× 4 × 1.8

Sumida

www.sumida.com

SD3118

4.7

1.3 0.162 3.1 × 3.1 × 1.8 Cooper

www.cooperet.com

SD3112

4.7

0.8 0.246 3.1 × 3.1 × 1.2

LPS3015

4.7

1.1

0.2

3.0

× 3.0 × 1.5 Coilcraft

www.coilcraft.com

*Typical DCR

Table 6. Recommended Ceramic Capacitor Manufacturers

AVX

www/avxcorp.com

Murata

www.murata.com

Taiyo Yuden

www.t-yuden.com

Vishay Siliconix

www.vishay.com

TDK

www.tdk.com

BUCK-BOOST REGULATOR APPLICATIONS SECTION

Buck-Boost Regulator Inductor Selection

Inductor selection criteria for the buck-boost are similar

to those given for the buck switching regulator. The buck-

boost converter is designed to work with inductors in the

rangeof1µHto5µH.Formostapplicationsa2.2µHinductor

will sufﬁce. Choose an inductor with a DC current rating

at least 2 times larger than the maximum load current to

ensure that the inductor does not saturate during normal

operation. If output short circuit is a possible condition,

the inductor should be rated to handle the maximum peak

current speciﬁed for the buck-boost converter.

Table 7 shows several inductors that work well with the

LTC3586/LTC3586-1’sbuck-boostregulator.Theseinduc-

tors offer a good compromise in current rating, DCR and

physical size. Consult each manufacturer for detailed

information on their entire selection of inductors.

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