[{"insert":"#测试技巧分享#\n"},{"attributes":{"color":"#000000"},"insert":"大家好，我是工程师看海。"},{"insert":"\n"},{"attributes":{"color":"#000000"},"insert":"前一阵朋友和我说当初用某型号LDO时，发现输出异常，仔细阅读datasheet后，更换输出电容解决。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"color":"#000000"},"insert":"LDO的输出电容对性能至关重要，除了会提高电源抑制比PSRR抑制噪声外，对环路稳定性也至关重要，电容除了容值参数外还有ESR(Equivalent Series Resistance)等效串联电阻参数，二者在选型设计时都要仔细考虑。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"color":"#000000"},"insert":"我们以PMOS LDO为例来仿真下ESR对LDO输出的影响，LDO输出电压为3.2V，输出电容为2.2uF，ESR是R4我们选取为0.1Ω，负载为50Ω（负载电流为3.2/50=70mA），当开关S1闭合时，负载为R6和R5的并联，此时负载电流大约是700mA，我们仿真的方法就是改变ESR电阻R4，切换负载电流，观察输出电压的变化。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"color":"#000000"},"insert":" "},{"insert":{"image":"https://community-1252773949.cos.ap-guangzhou.myqcloud.com/article/2033/2f43277c4d3ba147.png"}},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"color":"#000000"},"insert":"下图是R4 ESR取0.1Ω时的输出结果，黑色曲线是从70mA到700mA反复切换负载电流的电流波形，红色是输出电压波形，可以看到电流变化时，输出电压只有微小的波动，整体还是稳定在3.2V。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"color":"#000000"},"insert":" "},{"insert":{"image":"https://community-1252773949.cos.ap-guangzhou.myqcloud.com/article/2033/a6da6df8f52bc673.png"}},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"color":"#000000"},"insert":"下图是把ESR改为0.001Ω后的结果，刚开始输出是稳定的，一切换负载电流时，输出就异常。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"color":"#000000"},"insert":" "},{"insert":{"image":"https://community-1252773949.cos.ap-guangzhou.myqcloud.com/article/2033/f74d0b887d72e66f.png"}},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"color":"#000000"},"insert":"下图是把ESR改为100Ω后的结果，刚开始输出是稳定的，切换负载电流时，输出也容易出现异常。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"color":"#000000"},"insert":" "},{"insert":{"image":"https://community-1252773949.cos.ap-guangzhou.myqcloud.com/article/2033/1e5c2c03e1484036.png"}},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"color":"#000000"},"insert":"总之，LDO的输出电容对于维持稳压器的稳定性至关重要，并且必须满足最小电容和等效串联电阻 (ESR) 的要求。输出电容的增加会影响环路稳定性和瞬态响应， 电容的容值和ESR，太大或太小都不行 ，都容易引起环路震荡。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"color":"#000000","bold":true},"insert":"感谢点赞、分享、在看，让知识变得更简单"},{"attributes":{"align":"right"},"insert":"\n"}]
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发表于 2022-11-10 10:30
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