DCDC外围器件选取计算

MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology外围器件选取MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology输入、输出电容INBSSWFBCOMPGNDENSSL1D1R1R2C2C3R3INPUTC1C5OUTPUTMPxxxxC6C4IntegratedMosfetvSWiL1iC2iC1iD1MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology•输入、输出电容PackageTypicalESL(nH)陶瓷电容06030.808051.012061.212101.0钽电容08051.612062.214112.324122.8电解电容SMT6.8Thru-hole10被忽略的参数！CapacitorTypeESRESL10uF/10VCeramic4mΩ1.25nH100uF/10VTantalum46mΩ3nH470uF/10VElectrolytic100mΩ15nH三大常用电容：1.陶瓷电容：高频特性好，贵，未来会便宜；2.钽电容：高频特性好，耐压差，稀有金属，非未来趋势；3.电解电容：高频特性差，耐压高，廉价；MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnologyESL0LC21f•CapacitorImpedancebelowf0:fC2j1ZC•CapacitorImpedanceabovef0:ESLCLf2jZ•CapacitorImpedanceatf0:ESRCRZ•ResonantFrequency:•输入、输出电容实际模型MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology陶瓷电容品质：NPOX7RX5RY5V低温启动问题！•陶瓷电容材质的影响MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology自举，自己抬升，为何要自己抬升电压？BS给谁供电？INBSSWFBCOMPGNDENSSL1D1R1R2C2C3R3INPUTC1C5OUTPUTMPxxxxC6C4IntegratedMosfet根据电容上电压不能突变原理，BS最高可以获得多少电压？BS什么时候给C5充电？C5何时放电？C5上电会不会耗尽？•陶瓷电容材质的影响MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology1.Core、DDR供电的DC-DC：输入和输出都为陶瓷2.其它部分IO口，系统电源：大电解（10倍于规格书中标称的陶瓷电容容量）+小陶瓷（104或者105即可）3.背光部分：钽电容或者电解（调光时候陶瓷会啸叫）•不同电路选取电容指南MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology•功率电感选择：1.电感量(有偏差，随着温度变化而变化)2.饱和电流，非标称的连续电流值，而是最大电流值！一般选取负载连续电流的120%-140%以上电感选取基本标准MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnologyvSWiL1iC2iC1iD1CurrentLimit是何物？2A的料为什么会有2.9ACurrentLimit？2A输出电流，选最大电流2A的电感够么？INBSSWFBCOMPGNDENSSL1D1R1R2C2C3R3INPUTC1C5OUTPUTMPxxxxC6C4IntegratedMosfet电感选取基本标准MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnologyFeedback反馈电阻只要比例够了就行了么？取决于芯片内部结构！+-VfbVrefVcompioio=(Vref-Vfb)gmVcomp=(Vref-Vfb)gmZcR1C1C2ZcVoR2R3反馈电阻为什么要按照规格书选取MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnologyINBSSWFBCOMPGNDENSSL1D1R1R2C2C3R3INPUTC1C5OUTPUTMPxxxxC6C4IntegratedMosfetCOMP补偿参数如何计算？COMP：COMPENSATION缩写，补偿为何要补偿？类似PID控制基本原理！+-VfbVrefVcompioio=(Vref-Vfb)gmVcomp=(Vref-Vfb)gmZcR1C1C2ZcVoR2R3MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnologyCOMPOV(s)EA(s)V(s)R3gm1sC1R1C1C2R2R3s(C1C2)1sR1C1C2Typically,C1C2R3gm1sC1R1EA(s)R2R3sC11sC2R1+-VfbVrefVcompioio=(Vref-Vfb)gmVcomp=(Vref-Vfb)gmZcR1C1C2ZcVoR2R3理论，但头晕！COMP补偿参数如何计算？MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology+-VfbVrefVcompioio=(Vref-Vfb)gmVcomp=(Vref-Vfb)gmZcR1C1C2ZcVoR2R3本质：Vo变化引起Vfb变化；---Vfb变化引起Io变化；-------Io变化引起Vcomp变化；所以，当R2、R3固定后，调节COMP会有啥疗效？COMP补偿参数如何计算？MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnologyINBSSWFBCOMPGNDENSSL1D1R1R2C2C3R3INPUTC1C5OUTPUTMPxxxxC6C4IntegratedMosfet又叫，续流二极管：续流，继续维持电感电流vSWiL1iC2iC1iD1压降一般情况下较大，损耗较高；后被MOS替代，以获得更高效率。肖特基二极管MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnologyPCBLAYOUT指南MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology•LAYOUT提示5秒钟判断电源部分LAYOUT好坏IC的输入电容的GND在哪？IC的输出电容的GND在哪？IC的GND在哪？（非同步IC，肖特基GND即可为IC的GND）它们离得远么？？？？？MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology每个环路都是一个干扰发射源尽可能缩小此两个环路！降压电路•LAYOUT提示MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology两个环路IN到SW集成了一颗MOSFETMOSFET开：红色环路MOSFET关：蓝色环路一、降压电路MOS开关电流流向•降压电路电流流向MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology升压电路MOS开关电流流向两个环路SW到GND集成了一颗MOSFETMOSFET开：红色环路MOSFET关：蓝色环路•升压电路电流流向MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology每个环路不仅是一个干扰发射源还成为了被干扰源！•LAYOUT提示原理图中的电路现实中PCB的电路，这么多电感，如何调板？LAYOUT不好MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology•LAYOUT提示1.SW引脚到电感的导线，尽可能粗而短；2.输入电容、输出电容尽可能离IC近些，LAYOUT优先保证功率环路，再考虑信号部分；3.如果外围电路有肖特基，肖特基的两端要和相邻器件最短链接，否则负向脉冲很大；MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology•EMI基本问题EMI从哪里来？dtdiMedtdvCiTimechangingcurrentinducesavoltageTimechangingvoltageinducesacurrentMPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology开关速度和开关频率不可混淆！•EMI问题追溯开关频率-EMI传导开关速度-EMI辐射MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology•EMI问题追溯开关频率-EMI传导开关频率越高，同样电感和电容，纹波越小；开关频率越高，同样纹波所用电感越小。开关速度-EMI辐射开关速度越快，IC转换效率越高；开关速度越慢，IC转换效率越低；MPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnology1.FB磁珠，单位100MHz欧姆？注意发热/方向•EMI问题后期解决方案2.辐射-共模电感3.降低开关速度-升压/降压ICMPSConfidential-InternalUseOnlyTheFutureofAnalogICTechnologyThankyou！