MPQ8904 abnormal output behaviour


I am using MPQ8904DD-AEC1-LF-Z in our project. I found it’s output behaviour is weird as the images shown.

MPQ8904’s output is worst with no loading and is better with larger load current but still has large ripple voltage. I am wondering what’s the root cause.


Hi lizhuoyang,
Thank you for utilizing MPS Technical Forum.

What is your input and output? and what is the output cap you are using?

Thank you,

Hi Nouman,

The input is 5V and output is 1.8V. The output cap is a 4.7uF ceramic cap.

Hi Lizhuoyang,
The circuit looks correct, not exactly sure then why output would have such ripple.

Can you please try the following -

  1. confirm how is EN pin powered or is it floating,
  2. Can you test without the 1nF cap?


Hi Nouman,

EN pin is not floating, powered by 5V voltage. The test result was without feedforward cap. Recently I haved tried 1nF to 15nF feedforward cap. I found the ripple is smaller with larger feedforward cap. Now I am using 15nF feedforward cap. The ripple is about 20mV p-p which is acceptble. But I am still confused why a LDO has such kind of ripple. Is it oscillating? MPQ8904 internal compensation is so bad?

Apologies on the late response,

That is correct, typically for LDOs the ripple must be much lower than 20mV. You may try a slightly higher capacitor on the output instead of 4.7uF.

I do not think the internal compensation would be an issue, you were able to lower the ripple via the 15nF cap.

Kind Regards,