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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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TS51221 датащи(PDF) 14 Page - Semtech Corporation |
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TS51221 датащи(HTML) 14 Page - Semtech Corporation |
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14 / 18 page  TS51221 Final Datasheet Rev 1.1 April 6, 2015 www.semtech.com 14 of 18 Semtech External Component Selection The1MHzinternalswitchingfrequencyoftheTS51221 facilitateslowcostLCfiltercombinations.Additionally,the fixedoutputversionsenableaminimumexternalcomponent counttoprovideacompleteregulationsolutionwithonly4 externalcomponents:aninputbypasscapacitor,aninductor, anoutputcapacitor,andthebootstrapcapacitor.Theinternal compensationisoptimizedfora44uFoutputcapacitoranda 4.7uHinductor. Forbestperformance,alowESRceramiccapacitorshouldbe usedforCBYPASS.IfCBYPASSisnotalowESRceramiccapacitor,a 0.1uFceramiccapacitorshouldbeaddedinparalleltoCBYPASS. Theminimumallowablevaluefortheoutputcapacitoris 33uF.Tokeeptheoutputripplelow,alowESR(lessthan 35mOhm)ceramicisrecommended.Multiplecapacitorscan beparalleledtoreducetheESR. Theinductorrangeis4.7uH+/-20%.Foroptimalover-current protection,theinductorshouldbeabletohandleuptothe regulatorcurrentlimitwithoutsaturation.Otherwise,an inductorwithasaturationcurrentratinghigherthanthe maximumIOUTloadrequirementplustheinductorcurrent rippleshouldbeused. Forhighcurrentmodes,theoptionalSchottkydiodewill improvetheoverallefficiencyandreducetheheat.Itisup totheusertodeterminethecost/benefitofaddingthis additionalcomponentintheuser’sapplication.Thediodeis typicallynotneeded. FortheadjustableoutputversionoftheTS51221,theoutput voltagecanbeadjustedbysizingRTOPandRBOTfeedback resistors.Theequationfortheoutputvoltageis Fortheadjustableversion,theratioofVCC/VOUTcannot exceed16. RPUPisonlyrequiredwhenthePowerGoodsignal(PG)is utilized. Thermal Information TS51221isdesignedforamaximumoperatingjunction temperatureTJof125°C.Themaximumoutputpoweris limitedbythepowerlossesthatcanbedissipatedover thethermalresistancegivenbythepackageandthePCB structures.ThePCBmustprovideheatsinkingtokeepthe TS51221cool.TheexposedmetalonthebottomoftheQFN packagemustbesolderedtoagroundplane.Thisground shouldbetiedtoothercopperlayersbelowwiththermalvias. Addingmorecoppertothetopandthebottomlayersand tyingthiscoppertotheinternalplaneswithviascanreduce thermalresistancefurther.Forahi-KJEDECboardand13.5 squareinchof1ozCu,thethermalresistancefromjunction toambientcanbereducedtoΘJA=38°C/W.Thepower dissipationofotherpowercomponents(catchdiode,inductor) causeadditionalcopperheatingandcanfurtherincreasewhat theTS51221seesasambienttemperature. 0.9 1 TOP BOT R Vout R = ⋅+ |
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