power supply Isolation issue

[myatham]

Hi Friends,
I really facing big issue with the isolation issue in our circuitry. We isolated the microcontroller power supply from other noisy power supply completely. There is no direct connection between these grounds at all. But, I observed 400mV noise at the microcontroller pin even though it is not powered. I am assuming that this is because of capacitive coupling of PCB planes as we routed one ground in one layer and another ground in another layer exact below. There are so many confusions are running in my mind. Please help me to solve this issue.

• What are the minimal guidelines to isolate two different supplies.
• What should be isolation distance between two grounds
• Can we run one ground in one layer and the other ground in another layer.
• Can vias of one ground pass throgh the other ground with anti pad. How much isolation we need to provide here?

 

[cks3976]

Hi Friends,
We isolated the microcontroller power supply from other noisy power supply completely. There is no direct connection between these grounds at all.

Have you isolated the Power islands, or Grounds ? if you have isolated Grounds...then that's wrong....it will lead to errors in the circuit. You should never have isolated Ground planes. This will definitely lead to such problems...