LTC3401 datasheet(9/16 Pages) LINER

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LTC3401

3401fa

APPLICATIO S I FOR ATIO

Burst Mode operation is user controlled by driving the

MODE/SYNC pin high to enable and low to disable. It is

recommended that Burst Mode operation be entered after

the part has started up.

COMPONENT SELECTION

Inductor Selection

The high frequency operation of the LTC3401 allows the

use of small surface mount inductors. The minimum

inductance value is proportional to the operating fre-

quency and is limited by the following constraints:

H and L

f Ripple V

IN MIN

OUT MAX

IN MIN

OUT MAX

>µ

()

(

)

()

•–

••

where

f = Operating Frequency (Hz)

Ripple = Allowable Inductor Current Ripple (A)

VIN(MIN) = Minimum Input Voltage (V)

VOUT(MAX) = Maximum Output Voltage (V)

The inductor current ripple is typically set to 20% to 40%

of the maximum inductor current.

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

quency core material, such as ferrite, to reduce core

losses. The inductor should have low ESR (equivalent

series resistance) to reduce the I2R losses and must be

able to handle the peak inductor current at full load without

saturating. Molded chokes or chip inductors usually do

not have enough core to support the peak inductor cur-

rents in the 1A to 2A region. To minimize radiated noise,

use a toroid, pot core or shielded bobbin inductor. See

Table 1 for a list of component suppliers.

VOUT

3401 F01

MODE

VIN

GND

SHDN

VOUT

PGOOD

Figure 1. Recommended Component Placement. Traces

Carrying High Current Are Direct. Trace Area FB and VC Pins

Are Kept Low. Lead Length to Battery Should be Kept Short

Output Capacitor Selection

The output voltage ripple has several components. The

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

to charge into the capacitor each cycle. The max ripple due

to charge is given by:

BULK

OUT

•

••

where

IP = Peak Inductor Current

The ESR can be a significant factor for ripple in most power

converters. The ripple due to capacitor ESR is simply given

by:

VRCESR = IP • RESR V

where

RESR = Capacitor Series Resistance

Low ESR capacitors should be used to minimize output

voltage ripple. For surface mount applications, AVX TPS

series tantalum capacitors, Sanyo POSCAP, or Taiyo-

Yuden ceramic capacitors are recommended. For through-

hole applications Sanyo OS-CON capacitors offer low ESR

in a small package size. See Table 2 for a list of component

suppliers.

Table 1. Inductor Vendor Information

SUPPLIER

PHONE

FAX

WEBSITE

Coilcraft

(847) 639-6400

(847) 639-1469

www.coilcraft.com

Coiltronics

(516) 241-7876

(516) 241-9339

www.coiltronics.com

Murata

(814) 237-1431

(814) 238-0490

www.murata.com

(800) 831-9172

Sumida

USA: (847) 956-0666

(847) 956-0702

www.japanlink.com

Japan: 81-3-3607-5111 81-3-3607-5144

sumida

Table 2. Capacitor Vendor Information

SUPPLIER

PHONE

FAX

WEBSITE

AVX

(803) 448-9411

(803) 448-1943

www.avxcorp.com

Sanyo

(619) 661-6322

(619) 661-1055

www.sanyovideo.com

Taiyo Yuden

(408) 573-4150

(408) 573-4159

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