TPS63030中文资料(15)

元器件交易网

SLVS696–OCTOBER2008

Withthechoseninductancevalue,thepeakcurrentfortheinductorinsteadystateoperationcanbecalculated.Equation4showshowtocalculatethepeakcurrentI1instepdownmodeoperationandEquation5showshowthepeakcurrentI2inboostmodeoperation.

VOUTVIN1*VOUT

I1+)

2 VIN1 f L

IOUT

VOUT IOUT

ǒǔ

(4)

VIN2 VOUT*VIN2

I2+)

2 VOUT f L0.8 VIN2

ǒǔ

(5)

Inbothequationsfistheminimumswitchingfrequency.VIN2istheminimuminputvoltage.Thecriticalcurrent

valueforselectingtherightinductoristhehighervalueofI1andI2.Italsoneedstobetakenintoaccountthatloadtransientsanderrorconditionsmaycausehigherinductorcurrents.Thisalsoneedstobetakenintoaccountwhenselectinganappropriateinductor.ThefollowinginductorseriesfromdifferentsuppliershavebeenusedwithTPS6303xconverters:

Table1.ListofInductors

VENDORCoilcraftMurataTajoYuden

INDUCTORSERIESLPS3015EPL3010LQH3NPNR3015

CAPACITORSELECTION

InputCapacitor

Atleasta4.7µFinputcapacitorisrecommendedtoimprovetransientbehavioroftheregulatorandEMIbehaviorofthetotalpowersupplycircuit.AceramiccapacitorplacedascloseaspossibletotheVINandPGNDpinsoftheICisrecommended.BypassCapacitor

Tomakesurethattheinternalcontrolcircuitsaresuppliedwithastablelownoisesupplyvoltage,ingaceramiccapacitorwithavalueof0.1µFisrecommended.Thevalueofthiscapacitorshouldnotbehigherthan0.22µF.OutputCapacitor

Fortheoutputcapacitor,itisrecommendedtousesmallceramiccapacitorsplacedascloseaspossibletotheVOUTandPGNDpinsoftheIC.If,foranyreason,theapplicationrequirestheuseoflargecapacitorswhichcannotbeplacedclosetotheIC,usingasmallerceramiccapacitorinparalleltothelargeoneisrecommended.ThissmallcapacitorshouldbeplacedascloseaspossibletotheVOUTandPGNDpinsoftheIC.Togetanestimateoftherecommendedminimumoutputcapacitance,Equation6canbeused.

mF

COUT+5 L

mH

(6)

rgercapacitorswillcauseloweroutputvoltagerippleaswellasloweroutputvoltagedropduringloadtransients.