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LTC3444

3444fb

Inductor Selection

The high frequency operation of the LTC3444 allows the

use of small surface mount inductors. The internal loop

compensation is designed to work with a 2.2

μH inductor

(1.5

μH for VIN < 3.1V). The 2.2μH inductor was selected to

optimize the transient response to the control input. The

use of a 2.2

μH inductor pushes out the right half plane

(RHP) zero frequency and allows the loop crossover to

occur at frequencies higher than the output L-C double

pole.

For external compensation the inductor selection is based

on the desired inductor ripple current. The inductor ripple

current is typically set to 20% to 40% of the average

inductor current. Increased inductance results in lower

ripple current, however, higher inductance pulls in the

RHP zero frequency and limits the maximum crossover

frequency possible. Refer to Closing the Feedback Loop

for more information on the RHP zero. For a given ripple

the inductance terms are given as follows:

BOOST

IN MIN

OUT

IN MIN

OUT MAX

•

••

()

(–

)

ΔΔIV

OUT

•

BUCK

OUT

IN MAX

OUT

OUT MAX

IN MAX

•

••

•

(–

)

()

where f = operating frequency, Hz

ΔIL = inductor ripple current, A

VIN(MIN) = minimum input voltage, V

VIN(MAX) = maximum input voltage, V

VOUT = output voltage, V

IOUT(MAX) = maximum output load current

In most cases, the boost configuration will be used to

determine the minimum inductance allowed for a given

ripple current.

For high efficiency, choose a ferrite inductor with a high

frequency core material to reduce core loses. The inductor

should have low ESR (equivalent series resistance) to

reduce the I2R losses, and must be able to handle the peak

inductor current without saturating. To minimize radiated

noise, use a shielded inductor. See Table 2 for a suggested

list of inductor suppliers.

Table 2. Inductor Vendor Information

SUPPLIER

PHONE

FAX

WEB SITE

Coilcraft

(847) 639-6400

(847) 639-1469

www.coilcraft.com

CoEv Magnetics

(800) 227-7040

(650) 361-2508

www.circuitprotection.com/magnetics.asp

COOPER Bussmann

(636) 394-2877

1-800-544-2570

www.coooperET.com

Murata

(814) 237-1431

(814) 238-0490

www.murata.com

(800) 831-9172

Sumida

USA: (847) 956-0666

USA: (847) 956-0702

www.sumida.com

Japan: 81(3) 3607-5111

Japan: 81(3) 3607-5144

TDK

(847) 803-6100

(847) 803-6296

www.component.tdk.com

TOKO

(847) 297-0070

(847) 699-7864

www.tokoam.com

OPERATIO

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