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1、Proprietary Information1Resonant Half Bridge LLC Controller enhance slim Digital TV design 蒋怀刚 德州仪器技术应用工程师Owen Jiang Oct 31 2008Proprietary Information2AgendaIntroduction to LLC resonant converterStep by step design methodOther design issues for LLC resonant converterTI 8 pin LLC controller introduc
2、tion Application example 300W slim digital TV power solution Proprietary Information3Design Challenges for DC/DCHigher power densityHigher efficiency,smaller heat sinkHigher switching frequency,smaller magneticsLess energy storage capacitors,smaller sizeHoldup time requirementLarge energy storage ca
3、pacitorHigher costLarge sizeProprietary Information4Holdup Time RequirementVmintV400V48V20mSHoldup time Large capacitor required to provide energy during holdup time Wide operation range DC/DC can reduce holdup cap requirement4X220uF2X330uF2X220uF50%Proprietary Information5 Low Efficiency at normal
4、condition due to wide operation rangePWM Converter with Wide Operation RangeOptimized Asym.HB for 400V onlyAsym.HB designed for 300V to 400VLLC designed for 300V to 400V LLC resonant converter can achieve higher efficiencyProprietary Information6LLC Resonant Converter with Wide Operation RangeAt 400
5、V input,switching frequency is resonant frequencyDuring holdup time,switching frequency is reducedTransformer turns-ratioResonant frequencyProprietary Information7Operation PrinciplesAt Resonant FrequencyAt resonant frequency,maximum efficiency is expectedProprietary Information8Operation PrincipleB
6、elow Resonant Frequencyt0t1 t2 t3Vg_Q1Vg_Q2VpirimisWhen switching frequency is below resonant frequency,magnetizing inductor begins to participate in resonant and increase voltage gainSecondary diode becomes discontinuousProprietary Information9Operation PrincipleAbove Resonant FrequencyWhen switchi
7、ng frequency is above resonant frequency,circuit behaves as SRCSecondary current becomes CCM,reverse recovery loss increasesProprietary Information10Benefits of LLC Resonant ConverterZVS can be achieved by utilizing transformer magnetizing inductorCapacitor filter,less voltage stress on rectifiersSm
8、aller switching loss due to small turn off currentVariable switching frequency control,not sensitive to load changeWide operation range without reducing normal operation efficiencyProprietary Information11Design Goals for LLC Resonant Converter Minimize RMS current under normal operation condition E
9、nsure ZVS operationInductor RatioQuality factor Ensure desired operation rangeProprietary Information12Impacts of Circuit Parameters Larger Ln,Lm bigger,RMS current smaller,efficiency higher Proprietary Information13Choice of LmCriteria 1:Primary RMS Current at Normal OperationPrimary side RMS curre
10、nt is determined by magnetizing inductor Larger Lm the betterProprietary Information14Choice of LmCriteria 2:Secondary RMS Current Secondary side current is the difference between resonant tank current and magnetizing current Larger Lm the betterPrimary side currentProprietary Information15Choice of
11、 LmCriteria 3:Zero Voltage SwitchingILm(max)Turn off current should be able to discharge junction caps during dead-timeVinCrCeqCeqILm(max)Proprietary Information16Trade-off Design of Dead TimeSmaller turn off currentSmaller magnetizing currentIncrease RMS current due to duty cycle lossSmaller duty c
12、ycle lossLarger magnetizing currentLarger turn off lossProprietary Information17Trade-off Design of Dead TimeConduction lossSwitching lossTotal loss 100nS shows the trade-off between the switching loss and conduction lossProprietary Information18Achievable Peak Gain for Different Ln and Q For each L
13、n and Q combination,the maximum gain can be achieved is determinedLn=5Q=0.05Q=14X220uF2X220uF Only certain Ln and Q region can meet gain requirement Colored surface represent the maximum gain for different Ln and Q combinationsProprietary Information19Peak Gains for Different Designs To keep Lm cons
14、tant and achieve low conduction loss and switching loss at normal operation,product of Ln and Q is expected to be constant Reduce Lm can help achieve higher peak gainConstant LmLm decreasesProprietary Information20Start Up Current Consideration“A Novel Precise Design Method for LLC Series Resonant C
15、onverter”,Teng liu,etc.,INTELEC 06 Larger Q value gives smaller start up current with less frequency rangeProprietary Information21Design Flow Chart for LLC Resonant ConverterConverter SpecificationPrimary switching DeviceMagnetizing inductorPeak gain enough?YesChoose cross section of required gain
16、and constant LmNoReduce LmResonant inductorResonant capacitorProprietary Information22Other Design IssuesAsymmetrical LLC48%and 52%49%and 51%50%and 50%Asymmetrical duty cycle makes resonant tank current unbalancedLoad current will be concentrated in one diode and increase conduction loss and switchi
17、ng lossController should provide well matched PWM signalProprietary Information23Other Design IssuesOver Current Protection At over load condition,in order to maintain gain,loop will run into ZCS region so leads to damage,one of solution is to:switching frequency needs to be increased to maintain ou
18、tput currentTo shutdown MOSFET for protection Proprietary Information24LLC SummaryDue to low switching loss,LLC resonant converter is able to operate high switching frequency,while maintain high efficiencyLLC resonant converter design needs to find a suitable magnetizing inductor to ensure smaller c
19、onduction loss and switching lossLLC resonant converter is able to achieve wide operation together with high efficiencyBy choosing a suitable Ln value,desired voltage gain can be achieved to reduce holdup time capacitor requirementProprietary Information25UCC25600 Key Features 8 pin SOIC package sim
20、plifies circuit design Adjustable dead time allows optimal design for different applications Simple frequency control with minimum and maximum frequency limiting 3%min.frequency limiting reduces design margin Programmable soft start time with simple ON/OFF control Zero power shut down for light load
21、 regulation Two level over current protection with latch off Over temperature protection Gate driver capable directly drive half bridge with transformerProprietary Information26UCC25600 LLC controller Application CircuitProgrammable dead timeFrequency control with minimum/maximum frequency limitingP
22、rogrammable soft start with on/off controlTwo level over current protection,auto-recovery and latch upMatching output with 50ns toleranceProprietary Information27Slim 300W DTV designProprietary Information28Interleave transition mode PFC UCC28061Proprietary Information29Performance and BOM cost Prop
23、rietary Information30SummaryTI 8 Pin Resonant Half Bridge Controller provides simple and reliable solution for resonant half bridge converter,including3%accurate switching frequencyProgrammable max.&min.switching frequencyProgrammable dead timeSoft start with easy ON/OFF controlOver current protectionVCC UVLO and over voltage protectionIntegrated gate driverProvides system cost reduction through less external component and easy layoutProprietary Information31Thank you