SP7661ERLSLASHTR datasheet(10/20 Pages) SIPEX

10 / 20 page

Mar -07 Rev N

SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator

APPLICATIONS INFORMATION

andprovidelowcorelossatthehigh

switchingfrequency.Lowcostpowdered-

ironcoreshaveagradualsaturationchar-

acteristicbutcanintroduceconsiderable

ACcoreloss,especiallywhentheinduc-

torvalueisrelativelylowandtheripple

currentishigh.Ferritematerials,although

moreexpensive,haveanabruptsatura-

tioncharacteristicwiththeinductance

droppingsharplywhenthepeakdesign

currentisexceeded.Nevertheless,they

arepreferredathighswitchingfrequen-

ciesbecausetheypresentverylowcore

losswhilethedesignerisonlyrequired

to preventsaturation.Ingeneral,ferrite

ormolypermalloymaterialsareabetter

choiceforallbutthemostcostsensitive

applications.

Optimizing Efficiency

Thepowerdissipatedintheinductorisequal

tothesumofthecoreandcopperlosses.

To minimize copper losses, the winding

resistanceneedstobeminimized,butthis

usuallycomesattheexpenseofalarger

inductor.Corelosseshaveamoresignificant

contributionatlowoutputcurrentwherethe

copperlossesareataminimum,andcan

typicallybeneglectedathigheroutputcur-

rents where the copper losses dominate.

Core loss information is usually available

fromthemagneticsvendor.Properinduc-

torselectioncanaffecttheresultingpower

supplyefficiencybymorethan15%!

Thecopperlossintheinductorcanbecal-

culatedusingthefollowingequation:

PL(Cu) = I

L(rMS)

• rwiNDiNg

whereIL(rMS)istheRMSinductorcurrent

thatcanbecalculatedasfollows:

IL(rMS) = IOut(MAx) •

√+ (. IPP )2

IOut(MAx)

Inductor Selection

Therearemanyfactorstoconsiderinse-

lectingtheinductorincludingcorematerial,

inductancevs.frequency,currenthandling

capability,efficiency,sizeandEMI.Inatypi-

calSP7661circuit,theinductorischosen

primarilyforvalue,saturationcurrentandDC

resistance.Increasingtheinductorvaluewill

decreaseoutputvoltageripple,butdegrade

transientresponse.Lowinductorvaluespro-

videthesmallestsize,butcauselargeripple

currents,poorefficiencyandrequiremore

outputcapacitancetosmoothoutthelarger

ripple current. The inductor must be able

tohandlethepeakcurrentattheswitching

frequencywithoutsaturating,andthecopper

resistanceinthewindingshouldbekeptas

lowaspossibletominimizeresistivepower

loss.Agoodcompromisebetweensize,loss

andcostistosettheinductorripplecurrent

tobewithin20%to40%ofthemaximum

outputcurrent.

Theswitchingfrequencyandtheinductor

operatingpointdeterminetheinductorvalue

asfollows:

VOut•(ViN(MAx) - VOut)

ViN(MAx) • ƒs•Kr • IOut(MAx)

where:

ƒs=switchingfrequency

Kr=ratiooftheACinductorripplecurrent

tothemaximumoutputcurrent

Thepeak-to-peakinductorripplecurrentis:

IPP

VOut•(ViN(MAx) - VOut)

ViN(MAx) • ƒs•L

Oncetherequiredinductorvalueisselected,

theproperselectionofcorematerialisbased

onpeakinductorcurrentandefficiencyre-

quirements.Thecoremustbelargeenough

nottosaturateatthepeakinductorcurrent

IPeAk = IOut(MAx) +

IPP

SP7661ERL/TR Fiches technique(PDF) 10 Page - Sipex Corporation

SP7661ERL/TR Fiches technique(HTML) 10 Page - Sipex Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Fiches technique Télécharger

Lien URL