去掉LDO的输入电容，LDO的输出纹波反而减小了，这是怎么回事呢？

一个LDO，前级加30uf电容，后级30uf电容，后面加载100ma。输入10v，输出5v。这个时候LDO前级纹波在500mv左右，后级纹波300mv左右。把LDO前级的30uf电容拿掉后，LDO前级和后级电压的纹波都很小了，10mv以内，满足设计要求。

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踢哀（TI）文檔

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帮你顶

从手册上看：The input capacitor (CIN) compensates for line fluctuation. Using a resistor of approximately 1 Ω in
series with CIN dampens the oscillation of input capacitance.
The device is designed to operate from an input voltage supply range between 4 V and 40 V. This input supply
must be well regulated. If the input supply is located more than a few inches from the device, TI recommends
adding an electrolytic capacitor with a value of 47 μF and a ceramic bypass at the input.
你前面的电容是贴片的陶瓷电容么?要不试下47uf电解电容?看到上面需要ESR接近1ohm的。

顶！d=====(￣▽￣*)b

后面的滤波电容按手册上面的就行，之前一个LDO电路，手册上面写的是2.2UF，我放了一个10UF，一个0.1UF，在上电的时候就有很大的纹波，

虽说一般是严格按照手册上来，不过这么挑电容，也不是什么好芯片。

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我顶，不错学习了