How to decouple Ground and Earth on Colibri Evaluation board

Hi,

We are using Colibri Evaluation board version 3.2 in our project and we found that the Earth and Ground is common on the board.

We want to decouple the Earth and Ground. Is there any way to achieve this on the evaluation board ?

Regards
Bipin

Hi @bipin7301

Thanks for writing to the Toradex Community!

What exactly do you mean with Earth Connection?
We don’t have any Earth connection on the Colibri Evalulation Board.

What is your application?

Best regards,
Jaski

Shield of all the peripheral connectors viz.VGA port, USB slave(X27) etc. are connected to ground of the main power supply. As per our understanding shield should be isolated from Ground and connected to main Earth.

We have designed a custom board that extends the colibri evaluation board IO’s for our application and we need to connect the cable shields to power supply earth. As Shield/earth and ground is common on evaluation board so we are not able to isolate the ground with earth.

In our application we have a up to 3 meter long cables carrying LVDS signals running through the machine harness and to make it immune from EMI we planned to connect the cable shields to mains earth.

As of now when we connect any peripheral like a monitor etc. to the Toradex Colibri eval (base board) the mains earth and the digital ground become common, effectively connecting the cable shields to the digital ground. Which we don’t see as the best way to go forward. We would also like to hear from you about any recommendations regarding improving the noise immunity of signals running on the board and in the cables.

Hi @bipin7301

The Colibri Evaluation Board is not a good example, how the shield and ground should be connected. However, the shield has nothing to do with earth. Earth is the wire you have in the domestic power outlets.

What I recommend is keeping all grounds on the carrier board (regular, analog, power, etc) connected together. I recommend not splitting any grounds on the carrier board since this causes normally more problems than it solves. This does not mean that you should route the signals without care. Keep the analog signals together and try not to cross the return path of high-speed signals.

The shield pins of the different connectors should be kept on an individual net, separated from the regular ground. Instead of using ferrite beads as on the evaluation, I recommend using a combination of a parallel 1M resistor and 1nF (2kV) capacitor for stitching the shield to the regular ground. Add this combination close to each connector. We will update to this approach in the next revision of the Colibri Evaluation Board. We have already updated it on the Ixora V1.2 schematics.