LTC3443 datasheet(11/16 Pages) LINER

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LTC3443

sn3443 3443fs

COMPONENT SELECTION

APPLICATIO S I FOR ATIO

For high efficiency, choose an inductor with a high fre-

quency core material, such as ferrite, 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. Molded

chokes or chip inductors usually do not have enough core

to support the peak inductor currents in the 1A to 2A

region. To minimize radiated noise, use a toroid, pot core

or shielded bobbin inductor. See Table 1 for suggested

components and Table 2 for a list of component suppliers.

Table 1. Inductor Vendor Information

SUPPLIER

PHONE

FAX

WEB SITE

Coilcraft

(847) 639-6400

(847) 639-1469

www.coilcraft.com

Coiltronics

(561) 241-7876

(561) 241-9339

www.coiltronics.com

Murata

USA:

www.murata.com

(814) 237-1431

(814) 238-0490

(800) 831-9172

Sumida

USA:

www.japanlink.com/

(847) 956-0666

(847) 956-0702

sumida

Japan:

81(3) 3607-5111 81(3) 3607-5144

Output Capacitor Selection

The bulk value of the capacitor is set to reduce the ripple

due to charge into the capacitor each cycle. The steady

state ripple due to charge is given by:

•–

•

••

•–

•

••

•

()

(

)

()

Ripple Boost

Ripple Buck

OUT MAX

OUT

IN MIN

OUT

OUT MAX

IN MAX

OUT

IN MAX

OUT

()

100

where COUT = output filter capacitor, F

The output capacitance is usually many times larger in

order to handle the transient response of the converter.

For a rule of thumb, the ratio of the operating frequency to

the unity-gain bandwidth of the converter is the amount

the output capacitance will have to increase from the

VIN

PVIN

VOUT

MODE

SHDN/SS

GND

PGND

SW1

SW2

PGND

VIN

VOUT

GND

MULTIPLE VIAS

3443 F06

Figure 6. Recommended Component Placement. Traces Carrying

High Current are Direct. Trace Area at FB and VC Pins are Kept

Low. Lead Length to Battery Should be Kept Short. VOUT and VIN

Ceramic Capacitors Close to the IC Pins

Inductor Selection

The high frequency operation of the LTC3443 allows the

use of small surface mount inductors. The inductor cur-

rent ripple is typically set to 20% to 40% of the maximum

inductor current. For a given ripple the inductance terms

are given as follows:

f I

Ripple V

f I

Ripple V

IN MIN

OUT

IN MIN

OUT MAX

OUT

IN MAX

OUT

OUT MAX

IN MAX

()

•–

•

•• %

•

•–

•

•• %

•

100

where f = operating frequency, Hz

%Ripple = allowable inductor current ripple, %

VIN(MIN) = minimum input voltage, V

VIN(MAX) = maximum input voltage, V

VOUT = output voltage, V

IOUT(MAX) = maximum output load current

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