LM27762负电源出现尖峰

LM27762做电源，输入+5.5V,输出正负5V，供3个运放使用，输入电流大概为35mA。观察到负电源输出噪声过大导致输出噪声非常高。负电源输出噪声大概为40mV的锯齿波。输出电容为4.7uF钽电容，开关电容为100nF的陶瓷电容。尝试过将开关电容换成1uF，将输出电容换成10uF，均没有明显改善。电路图如下：

前级的输入噪声如下，

Hi

    将输出电容换成低ESR的陶瓷电容如4.7uF，这个电路中不建议用钽电容，因为其ESR偏大。（所有电容都建议是低ESR陶瓷电容）

    你的电流不大，chargepump电容可以适当小点，可以0.47uF，或者更小一点。

    所有芯片连接的电容都尽量靠近其对应pin脚。 如果这样仍然noise偏大，确认一下是否是GND的布局不好。作为LDO输出，本身纹波是很小的, 注意选择较为干净（低noise）的GND Plane.

手册第14页有描述

The LM27762 requires 5 external capacitors for proper operation. Surface-mount multi-layer ceramic capacitors
are recommended. These capacitors are small, inexpensive, and have very low ESR (≤ 15 mΩ typical). Tantalum
capacitors, OS-CON capacitors, and aluminum electrolytic capacitors generally are not recommended for use
with the LM27762 due to their high ESR compared to ceramic capacitors.

For most applications, ceramic capacitors with an X7R or X5R temperature characteristic are preferable for use
with the LM27762. These capacitors have tight capacitance tolerances (as good as ±10%) and hold their value
over temperature (X7R: ±15% over –55°C to +125°C; X5R ±15% over –55°C to +85°C).