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Analog & Power Ground Connections

alvjorge

Hi,

in the new board I'm working now, I have to different DC converters, one step-down (buck) and one step-up (boost), also other analog components, moreover some digital components.

PCB is a 4-layer one distributed as:

  • L1: Power traces & some signal traces.
  • L2: GND.
  • L3: Signal traces.
  • L4: GND, and one power trace surrounding the PCB (to avoid split the GND plane as much as possible).

From manufacturers the best option is to split the ground planes for analog and power, joining them at one single point.

So, at Captue (schematics) I have used two different symbols in order to differentiate both ground planes.

The issue comes when at PCB Editor, I try to place the different ground shapes. There is only one GND signal, not two (GND & GND_SIGNAL).

Could anyone show the best way to place both planes at PCB Editor?

The option I was thinking about is to split ground planes on L1 as shown at picture below:

3D Bottom Layer (Green L1 Etch)

It would be suitable enough? Or does power planes need to be re-dimension to include all power traces length?

KR!

  • Use a 0R resistor to connect the two GND together.

    That will be the single point where they join.

  • Hi , it is a good trick, I supposed you are suggesting to work with static ground planes, with same signal assigned but connected to different pads. Otherwise, Planes will be merged due to smooth function. But I would rather to have two different ground planes (GND & GND_SIGNAL), and then join them.

  • 1. Why not use a net short (no zero resistor required)?  Create a symbol in Capture and then create a symbol in Allegro for the net short.  I usually use a via for the Footprint.

    2. Use the split ground feature.  Add anti etch lines to split the planes.

  • Hi ,

    let me ask some simple doubts:

     1. You use a via for the footprint, so you connect splitted planes through a via footprint. Then you are connecting both planes with ground planes below at this point. Is this right? Or maybe you have modify the padstack for this via footprint?

     2. Split ground feature. Do you mean isolation/cavity? Place an entire ground plane, and the with this feature (manual isolation/cavity), draw the anti etch line to split the planes.

    KR!

  • Attaching two images from a current design.

    First is the Capture Symbol - two pis with the net shorts defined.

    Second is a picture from the layout - What is shown is the top layer - Red, Ground layer - Green and anti etch (all layers) Pink.

    In the case my foot print is two pins (via's) with etch connecting them.

    Please let me know if you need more details.

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