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SLVA390– February 2010 Calculating Efficiency - …

ApplicationReportSLVA390 February2010 CalculatingEfficiencySubmitDocumentation FeedbackCopyright 2010 ,TexasInstrumentsIncorporated2LR M S_LD CRP = IR 222 RMS_L OII= I +12 DRMS_LOI= largeportfolioofDC-DCconverterswhichoper ateovera , , quickandeasymethodtoobtainthepowersupply ' a DC-DCconverterare: Inductorconductionlosses MOSFET conductionlosses showsthecurrentthroughtheinductorin a givenby:(1)WhereRDCRis givenby:(2)Where I = ripplecurrentTypically I is about30% ,theinductorcurrentcanbecalculatedtobe:( 3)2 CalculatingEfficiencySLVA390 February2010 SubmitDocumentationFeedbackCopyright 2010 ,TexasInstrumentsIncorporated2 LODCRP = IR 2Q1 RMS_Q1 DSON1P = IR 22OQ1 ODSON1 INVIP =I +RV12 D 2Q2 RMS_Q2 DSON2P= IR , it :(4)3 PowerDissipatedintheMOSFETsFigure3 showsthecurrentthroughthehigh- thehigh-sideMOSFETis givenby:(5)WhereRDSON1is :(6)Figure4 showsthecurrentthroughthelow- thelow-sideMOSFETis givenby:(7)WhereRDSON2is :3 SLVA390 February2010 CalculatingEfficiencySubmitDocumentatio

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Transcription of SLVA390– February 2010 Calculating Efficiency - …

1 ApplicationReportSLVA390 February2010 CalculatingEfficiencySubmitDocumentation FeedbackCopyright 2010 ,TexasInstrumentsIncorporated2LR M S_LD CRP = IR 222 RMS_L OII= I +12 DRMS_LOI= largeportfolioofDC-DCconverterswhichoper ateovera , , quickandeasymethodtoobtainthepowersupply ' a DC-DCconverterare: Inductorconductionlosses MOSFET conductionlosses showsthecurrentthroughtheinductorin a givenby:(1)WhereRDCRis givenby:(2)Where I = ripplecurrentTypically I is about30% ,theinductorcurrentcanbecalculatedtobe:( 3)2 CalculatingEfficiencySLVA390 February2010 SubmitDocumentationFeedbackCopyright 2010 ,TexasInstrumentsIncorporated2 LODCRP = IR 2Q1 RMS_Q1 DSON1P = IR 22OQ1 ODSON1 INVIP =I +RV12 D 2Q2 RMS_Q2 DSON2P= IR , it :(4)3 PowerDissipatedintheMOSFETsFigure3 showsthecurrentthroughthehigh- thehigh-sideMOSFETis givenby:(5)WhereRDSON1is :(6)Figure4 showsthecurrentthroughthelow- thelow-sideMOSFETis givenby:(7)WhereRDSON2is.

2 3 SLVA390 February2010 CalculatingEfficiencySubmitDocumentation FeedbackCopyright 2010 ,TexasInstrumentsIncorporated22OQ2 ODSON2 INVIP = 1I +RV12 D- FETQ1Q2P = P + P()22 OFETODSON1 DSON2 DSON2 ININOOINVIP = I +R-R+ R12V(VV ) VWhere I =L f V D - D ()2 OFETODSON1 DSON2 DSON2 INVP = IRR+ RV - DLFETP = P + P+ Other_lossesOODP=P + PhDOO11 = VI= 5V 4A= -- hh()()2 OFET ODSON1 DSON2 DSON2IN2VP = IR-R+ RV5V= + ! = W -W PowerDissipatedin (8)Thetotalpowerdissipatedin bothMOSFET'sis givenby:(9)SubstitutingforPQ1andPQ2(10)W here:L = Inductance(H)f = Frequency(Hz)VIN= Inputvoltage(V)VO= Outputvoltage(V)Fortypicalbuckpowersuppl ydesigns,theinductor'sripplecurrent, I, is lessthan30%ofthetotaloutputcurrent,sothe contributionof I2/12totheis negligibleandcanbedroppedtoget:(11)Notet hatwhenRDSON1= RDSON2, thepowerdissipatedin theMOSFETsis , ,PDnowcanbecomputedas:(12)Theotherlosses includetheMOSFET switchinglosses, boththetotalpowersupplylossesandpowersup plyoutputpowerareknown,theoverallefficie ncyatanyoutputvoltagecanbecalculatedwith .

3 (13)EXAMPLET hefollowingexampleshowshowtocalculatea powersupply'sefficiencyatanyoutputvoltag eif thepowersupply'sefficiencyis usedwithVin= 12V andVo= at4 ,thedatasheetdoesprovideanefficiencygrap hwithVin= 12V andVo= 5 V at4 (14) (15)NotethatRDSON1andRDSON2areprovidedin February2010 SubmitDocumentationFeedbackCopyright 2010 ,TexasInstrumentsIncorporated22L ODCRP = I R = 4A = mW WDFETLO ther_losses = P PP = W--()()O(new)2 FET(new) ODSON1 DSON2 DSON2IN2VP= IRR+ + = mW12V - W -WW PD( ) = PL + PFET( ) + Other_losses = + + = ( ) V 4 A=== + V 4 A + W (16) (17) (18) (19) (20) showstheefficiencymeasuredatVo= 5 V 5 V,theefficiencywascalculatedatVo= 5 VVo= 5 VCalculatedIo(A) Efficiency (%)MeasuredEff iciency(%) Efficiency (%) secondexampleis wheretheTPS62750is usedwithVo= 2 2 V,butdoesprovideefficiencywithVo= showsmeasuredv/scalculatedefficiencyfort heTPS62750in (A) Efficiency (%)MeasuredEfficiency(%)Cal culatedEfficiency(%) February2010 CalculatingEfficiencySubmitDocumentation FeedbackCopyright 2010 , quickandeasymethodtocalculatetheefficien cyofa buckconverteratconditionsotherthanwhatis February2010 SubmitDocumentationFeedbackCopyright 2010 ,TexasInstrumentsIncorporatedIMPORTA NT NOTICET exas instruments Incorporated and its subsidiaries (TI)

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