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EnglishDataSheet:SLUS872UC1842A-SP,UC1844A-SPZHCSDP1E–JANUARY2009–REVISEDFEBRUARY2019UC184xA-SPQMLV类类电电流流模模式式PWM控控制制器器1(1)仅UC1843A-SP(订货编号:5962-8670409VPA)提供低剂量率(LDR)改进型芯片.
要获取UC1842A-SP或UC1844A-SP的LDR改进型版本,请与厂家联系.
(2)抗辐射能力是基于初始器件认证(剂量率=10mrad(Si)/s)获得的典型值.
提供辐射批次验收测试-详细信息请联系厂家.
1特特性性1符合QMLV类(QMLV)标准,SMD5962-86704抗辐射能力:30kRad(Si)总电离剂量(TID)(1)(2)经过优化适用于离线和DC-DC转换器低启动电流(5kΩ)Figure17.
TimingResistancevsFrequency9.
2.
2.
2CurrentSensingandLimitingTheUC184xA-SPcurrentsenseinputisconfiguredasshowninFigure18.
Current-to-voltageconversionisdoneexternallywithground-referencedresistorRS.
Undernormaloperation,thepeakvoltageacrossRSiscontrolledbytheE/Aaccordingtothefollowingrelation:whereVC=Controlvoltage=E/Aoutputvoltage(2)RScanbeconnectedtothepowercircuitdirectlyorthroughacurrenttransformer,asFigure18shows.
Whileadirectconnectionissimpler,atransformercanreducepowerdissipationinRS,reduceerrorscausedbythebasecurrent,andprovidelevelshiftingtoeliminatetherestraintofground-referencedsensing.
TherelationbetweenVCandpeakcurrentinthepowerstageisgivenby:whereN=Currentsensetransformerturnsratio=1whentransformernotused.
(3)Forpurposesofsmall-signalanalysis,thecontrol-to-sensed-currentgainis:(4)Whensensingcurrentinserieswiththepowertransistor,asshowninFigure18,thecurrentwaveformoftenhasalargespikeatitsleadingedge.
Thisspikeisduetorectifierrecoveryand/orinter-windingcapacitanceinthepowertransformer.
Ifunattenuated,thistransientcanprematurelyterminatetheoutputpulse.
Asshown,asimpleRCfilterisusuallyadequatetosuppressthisspike.
TheRCtimeconstantshouldbeapproximatelyequaltothecurrentspikeduration(usuallyafewhundrednanoseconds).
TheinvertinginputtotheUC184xA-SPcurrent-sensecomparatorisinternallyclampedto1V(Figure18).
Currentlimitingoccursifthevoltageatpin3reachesthisthresholdvalue,thatis,thecurrentlimitisdefinedby:(5)20UC1842A-SP,UC1844A-SPZHCSDP1E–JANUARY2009–REVISEDFEBRUARY2019www.
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cnCopyright2009–2019,TexasInstrumentsIncorporatedFigure18.
Transformer-CoupledCurrentSensing9.
2.
2.
3ErrorAmplifierTheerroramplifier(E/A)configurationisshowninFigure19.
Thenon-invertinginputisnotbroughtouttoapin,butisinternallybiasedto5V±2%.
TheE/Aoutputisavailableatpin1forexternalcompensation,allowingtheusertocontroltheconverter'sclosed-loopfrequencyresponse.
Figure20showsanE/Acompensationcircuitsuitableforstabilizinganycurrent-modecontrolledtopologyexceptforflybackandboostconvertersoperatingwithinductorcurrent.
Thefeedbackcomponentsaddapoletothelooptransferfunctionatp=πRF.
RFandCFarechosensothatthispolecancelsthezerooftheoutputfiltercapacitorESRinthepowercircuit.
RIandRFfixthelow-frequencygain.
Theyarechosentoprovideasmuchgainaspossiblewhilestillallowingthepoleformedbytheoutputfiltercapacitorandloadtorollofftheloopgaintounity(0dB)at≈SWITCHING/4.
Thistechniqueensuresconverterstabilitywhileprovidinggooddynamicresponse.
Figure19.
E/AConfiguration21UC1842A-SP,UC1844A-SPwww.
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cnZHCSDP1E–JANUARY2009–REVISEDFEBRUARY2019Copyright2009–2019,TexasInstrumentsIncorporatedFigure20.
CompensationTheE/Aoutputsources0.
5mAandsinks2mA.
AlowerlimitforRFisgivenby:(6)E/Ainputbiascurrent(2-Amax)flowsthroughRI,resultinginaDCerrorinoutputvoltage(VO)givenby:(7)Therefore,thedesignershouldkeepthevalueofRI,aslowaspossible.
Figure21showstheopen-loopfrequencyresponseoftheUC184xA-SPE/A.
ThegainrepresentsanupperlimitonthegainofthecompensatedE/A.
Phaselagincreasesrapidlyasfrequencyexceeds1MHzduetosecond-orderpolesatabout10MHzandabove.
Continuous-inductor-currentboostandflybackconverterseachhavearight-half-planezerointheirtransferfunction.
AnadditionalcompensationpoleisneededtorolloffloopgainatafrequencylessthanthatoftheRHPzero.
RPandCPinthecircuitofFigure14providethispole.
Figure21.
ErrorAmplifierOpen-LoopFrequencyResponse22UC1842A-SP,UC1844A-SPZHCSDP1E–JANUARY2009–REVISEDFEBRUARY2019www.
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cnCopyright2009–2019,TexasInstrumentsIncorporated9.
2.
3ApplicationCurvesFigure22.
OscillatorFrequencyvsTimingResistanceFigure23.
MaximumDutyCyclevsTimingResistorFigure24.
OscillationSchematic23UC1842A-SP,UC1844A-SPwww.
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cnZHCSDP1E–JANUARY2009–REVISEDFEBRUARY2019Copyright2009–2019,TexasInstrumentsIncorporated10PowerSupplyRecommendationsThedevicesaredesignedtooperatefromaninputvoltagesupplyrangebetween8Vand40V.
Thisinputsupplyshouldbewellregulated.
IftheinputsupplyislocatedmorethanafewinchesfromtheUC184xA-SPconverter,additionalbulkcapacitancemayberequiredinadditiontotheceramicbypasscapacitors.
Atantalumcapacitorwithavalueof47Fisatypicalchoice;however,thismayvarydependingupontheoutputpowerbeingdelivered.
Powersupplyspecifications:1.
Inputvoltage:95VACto130VAC(50Hz/60Hz)2.
Lineisolation:3750V3.
Switchingfrequency:40kHz4.
Efficiencyfullload:70%5.
Outputvoltage:a.
+5V,±5%;1-to4-Aload,ripplevoltage:50mVP-Pmaxb.
+12V,±3%;0.
1-to0.
3-Aload,ripplevoltage:100mVP-Pmaxc.
–12V,±3%;0.
1-to0.
3-Aload,ripplevoltage:100mVP-PmaxFigure25.
OfflineFlybackRegulator11Layout11.
1LayoutGuidelinesAlwaystrytousealow-EMIinductorwithaferrite-typeclosedcore.
SomeexampleswouldbetoroidandencasedEcoreinductors.
Opencorecanbeusediftheyhavelow-EMIcharacteristicsandarelocatedafartherawayfromthelow-powertracesandcomponents.
MakethepolesperpendiculartothePCBaswellifusinganopencore.
Stickcoresusuallyemitthemostunwantednoise.
11.
1.
1FeedbackTracesTrytorunthefeedbacktraceasfaraspossiblefromtheinductorandnoisypowertraces.
Thedesignershouldalsomakethefeedbacktraceasdirectaspossibleandsomewhatthick.
Thesetwoguidelinessometimesinvolveatrade-off,butkeepingthetraceawayfrominductorEMIandothernoisesourcesisthemorecriticalguideline.
RunthefeedbacktraceonthesideofthePCBoppositeoftheinductorwithagroundplaneseparatingthetwo.
24UC1842A-SP,UC1844A-SPZHCSDP1E–JANUARY2009–REVISEDFEBRUARY2019www.
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cn版权2009–2019,TexasInstrumentsIncorporatedLayoutGuidelines(continued)11.
1.
2Input/OutputCapacitorsWhenusingalow-valueceramicinputfiltercapacitor,locateitascloseaspossibletotheVINpinoftheIC.
ThiseliminatesasmuchtraceinductanceeffectsaspossibleandgivestheinternalICrailacleanervoltagesupply.
Somedesignsrequiretheuseofafeed-forwardcapacitorconnectedfromtheoutputtothefeedbackpinaswell,usuallyforstabilityreasons.
Inthiscase,itshouldalsobepositionedascloseaspossibletotheIC.
Usingsurfacemountcapacitorsalsoreducesleadlengthandlessensthechanceofnoisecouplingintotheeffectiveantennacreatedbythrough-holecomponents.
11.
1.
3CompensationComponentsExternalcompensationcomponentsforstabilityshouldalsobeplacedclosetotheIC.
TIrecommendstoalsousesurfacemountcomponentsforthesamereasonsdiscussedforthefiltercapacitors.
Theseshouldnotbelocatedveryclosetotheinductoreither.
11.
1.
4TracesandGroundPlanesMakeallofthepower(high-current)tracesasshort,direct,andthickaspossible.
ItisgoodpracticeonastandardPCBtomakethetracesanabsoluteminimumof15mils(0.
381mm)perampere.
Theinductor,outputcapacitors,andoutputdiodeshouldbeascloseaspossibletoeachother.
ThishelpsreducetheEMIradiatedbythepowertracesduetothehigh-switchingcurrentsthroughthem.
Thisalsoreducesleadinductanceandresistance,whichinturnreducesnoisespikes,ringing,andresistivelossesthatproducevoltageerrors.
ThegroundsoftheIC,inputcapacitors,outputcapacitors,andoutputdiode(ifapplicable)shouldbeconnectedclosetogetherdirectlytoagroundplane.
ItwouldalsobeagoodideatohaveagroundplaneonbothsidesofthePCB.
ThisreducesnoisebyreducinggroundlooperrorsandabsorbingmoreoftheEMIradiatedbytheinductor.
Formulti-layerboardswithmorethantwolayers,agroundplanecanbeusedtoseparatethepowerplane(wherethepowertracesandcomponentsare)andthesignalplane(wherethefeedbackandcompensationandcomponentsare)forimprovedperformance.
Onmulti-layerboards,viasarerequiredtoconnecttracesanddifferentplanes.
Itisagoodpracticetouseonestandardviaper200mAofcurrentifthetraceneedstoconductasignificantamountofcurrentfromoneplanetotheother.
Arrangethecomponentssothattheswitchingcurrentloopscurlinthesamedirection.
Duetothewayswitchingregulatorsoperate,therearetwopowerstates:onestatewhentheswitchisonandonewhentheswitchisoff.
Duringeachstatethereisacurrentloopmadebythepowercomponentsthatarecurrentlyconducting.
Placethepowercomponentssothatduringeachofthetwostatesthecurrentloopisconductinginthesamedirection.
Thispreventsmagneticfieldreversalcausedbythetracesbetweenthetwohalf-cyclesandreducesradiatedEMI.
11.
2LayoutExampleHighpeakcurrentsassociatedwithcapacitiveloadsnecessitatecarefulgroundingtechniques.
Timingandbypasscapacitorsshouldbeconnectedclosetopin5inasinglepointground.
Thetransistorand5kpotentiometerareusedtosampletheoscillatorwaveformandapplyanadjustableramptopin3.
Figure26.
Open-LoopLaboratoryTestFixture25UC1842A-SP,UC1844A-SPwww.
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cnZHCSDP1E–JANUARY2009–REVISEDFEBRUARY2019版权2009–2019,TexasInstrumentsIncorporated12器器件件和和文文档档支支持持12.
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