优化带前馈电容的内置补偿-DC-DC转换器的瞬态响应

优化带前馈电容的内置补偿DC-DC转换器的瞬态响应BrianButterfieldPMP–便携式电源摘要本应用报告阐述了如何选择内置补偿dc-dc电源的前馈电容值(Cff)以实现最优化的瞬态响应。应用报告的论述顺序提供了指向性，通过增加转换器的带宽，同时保持足够的相位裕量以实现瞬态响应的优化。本文档旨在辅助所有希望优化其内置补偿dc-dc转换器运转时的瞬态响应的电源设计人员。简介内置补偿dc-dc转换器尽可能的减少了设计人员必须选取的外部元件数量，从而节省了设计及调试流程的耗时。此类简化也从根本上制约了设计人员对转换器的瞬态响应进行优化的能力。尽管如此，对于某些内置补偿转换器而言，在反馈网络中采用前馈电容仍然是推荐的优化方式。本文仅提供一般性的指南以辅助选1优化带前馈电容的内置补偿DC-DC转换器的瞬态响应目录1简介12带或不带前馈电容的反馈网络23结论114参考文献11图表目录1两个偏置电阻所组成的、用于设定输出电压的反馈网络22标准反馈分压器的传递函数23带附加前馈电容的反馈网络34带前馈电容的标准反馈分压器传递函数35不带前馈电容的内置补偿转换器46Tip&&Barrel测量方法57无前馈电容时电压瞬变对负载瞬变的响应58阶跃响应vs环路相位裕量69不带前馈电容的TPS61081电路的环路增益及相位曲线图610带82pF前馈电容时电压瞬变对负载瞬变的响应811带82pF前馈电容时TPS61081电路的环路增益及相位曲线图812带1000pF前馈电容时电压瞬变对0至100%负载瞬变的响应913带1000pF前馈电容时TPS61081电路的环路增益及相位曲线图914带33pF前馈电容时电压瞬变对负载瞬变的响应1015带33pF前馈电容时TPS61081电路的环路增益及相位曲线图10优化带前馈电容的内置补偿DC-DC转换器的瞬态响应带或不带前馈电容的反馈网络取电容值，以改善瞬态响应。通过测量运作状态下的dc-dc转换器的瞬态或环路特性，可选定前馈电容值，从而极大的改善转换器带宽，同时仍保持足够的相位裕量。此外，若能对前馈电容有更深的理解，设计人员便能做更进一步的优化——获取更大的带宽或更大的相位裕量以满足其特定的性能需求。�k�R2180�k�VFBVOUTDC�gain�=�20log�[R2/(R1xR2)]FeedbackNetworkWithandWithouttheFeedforwardCapacitortransientresponse.Withmeasuredtransientorloopcharacteristicsofaworkingdc-dcconverter,afeedforwardcapacitorvaluecanbechosensuchthattheconverterbandwidthissignificantlyimprovedwhilestillmaintainingadequatephasemargin.Furthermore,withabetterunderstandingofthefeedforwardcapacitor,thedesignercangoonestepfurthertooptimizeeitherhigherbandwidthorgreaterphasemargintomeetspecificperformancerequirements.Withoutafeedforwardcapacitor,thefeedbacknetworkofaninternallycompensateddc-dcconverterconsistsoftwofeedbackresistorsusedtosettheoutputvoltageoftheconverter,asshowninFigure1.Figure2showsthecorrespondinggainandphaseplot.Figure1.FeedbackNetworkConsistingofTwoBiasResistorsUsedtoSetOutputVoltageFigure2.StandardFeedbackDividerTransferFunctionFigure3showstheadditionofthefeedforwardcapacitor,C1(Cff),inthefeedbacknetworkandFigure4showsthecorrespondinggainandphaseplot.Withtheadditionofthefeedforwardcapacitornetwork,theconvertercanmoreeffectivelyrespondtohigh-frequencydisturbancesontheoutputvoltagerail.ThebodeplotsinFigure2andFigure4showthattheresponsesofeachfeedbacknetworkareidenticalatlowerfrequencies.Atmid-to-higherfrequencies,disturbancesontheoutputrailareattenuatedlessastheimpendencepaththroughC1decreasesandeffectivelyprovidesaboostingainandphase.Inaworkingpowersupply,theincreasedgainandphasecorrelatestotheconverterrespondingfastertotransientloadsbecausethevoltagedeviation,sensedatthefeedbacknode,isattenuatedlessathigherfrequencies.Theconverterreactsbyadjustingthedutycycletomorequicklycorrecttheoutputvoltagedeviation.2OptimizingTransientResponseofInternallyCompensateddc-dcConvertersWithFeedforwardCapacitorSLVA289–January2008SubmitDocumentationFeedback�k�R2180�k�VFBVOUTDC�gain�=�20log�[R2/(R1xR2)]FeedbackNetworkWithandWithouttheFeedforwardCapacitortransientresponse.Withmeasuredtransientorloopcharacteristicsofaworkingdc-dcconverter,afeedforwardcapacitorvaluecanbechosensuchthattheconverterbandwidthissignificantlyimprovedwhilestillmaintainingadequatephasemargin.Furthermore,withabetterunderstandingofthefeedforwardcapacitor,thedesignercangoonestepfurthertooptimizeeitherhigherbandwidthorgreaterphasemargintomeetspecificperformancerequirements.Withoutafeedforwardcapacitor,thefeedbacknetworkofaninternallycompensateddc-dcconverterconsistsoftwofeedbackresistorsusedtosettheoutputvoltageoftheconverter,asshowninFigure1.Figure2showsthecorrespondinggainandphaseplot.Figure1.FeedbackNetworkConsistingofTwoBiasResistorsUsedtoSetOutputVoltageFigure2.StandardFeedbackDividerTransferFunctionFigure3showstheadditionofthefeedforwardcapacitor,C1(Cff),inthefeedbacknetworkandFigure4showsthecorrespondinggainandphaseplot.Withtheadditionofthefeedforwardcapacitornetwork,theconvertercanmoreeffectivelyrespondtohigh-frequencydisturbancesontheoutputvoltagerail.ThebodeplotsinFigure2andFigure4showthattheresponsesofeachfeedbacknetworkareidenticalatlowerfrequencies.Atmid-to-higherfrequencies,disturbancesontheoutputrailareattenuatedlessastheimpendencepaththroughC1decreasesandeffectivelyprovidesaboostingainandphase.Inaworkingpowersupply,theincreasedgainandphasecorrelatestotheconverterrespondingfastertotransientloadsbecausethevoltagedeviation,sensedatthefeedbacknode,isattenuatedlessathigherfrequencies.Theconverterreactsbyadjustingthedutycycletomorequicklycorrecttheoutputvoltagedeviation.2OptimizingTransientResponseofInternallyCompensateddc-dcConvertersWithFeedforwardCapacitorSLVA289–January2008SubmitDocumentationFeedback带或不带前馈电容的反馈网络无前馈电容时，内置补偿dc-dc转换器的反馈网络由两个反馈电阻构成，用于设定转换器的输出电压，如图1所示。图2展示了相应的增益及相位图。2图.由两个偏置电阻组成的、用于设定输出电压的反馈网络图.标准反馈分压器的传递函数图3展示了反馈网络及其附加的反馈电容C1(Cff)，图4则展示了响应的增益及相位图。在网络中添加前馈电容后，转换器的输出电源轨可以更高效的响应高频扰动。图2及图4所示的粗体曲线所指明了两类反馈网络在低频区域具有一致的响应。在中高频区域，C1通路的阻抗降低造成了输出电源轨上扰动被衰减至较低，并有效地提供了更高的增益及相位。对于处于运作状态下的电源而言，增益及相位的增加将促使转换器对瞬变负载产生更快的响应，因为反馈节点上所感应到的电压变化在更高的频率域被衰减至较低。转换器进而产生响应，调节责任周期以便更快的修正输出电压的偏差。优化带前馈电容的内置补