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Layout: Isolated Ground

Renae Martinez
Prodigy 20 points

I was reading App Note SLAA322B on how to layout the crystal for the MSP430.  Section 3 recommends either an isolated ground island and/or a ground guard ring.  I wanted to add an isolated ground island underneath my crystal.  It is unclear from the descriptions/figures if the isolated ground island is connected to the board ground.  Is the island connected to the board ground by a via?

  • 0
    Intellectual 410 points
    Connected by a via. You can see the via on the top-right of the area on all the figures, right next to a chip pin.
  • 0
    Guru 227245 points

    if it is an isolated ground island, then it requires of course a connection to teh ground. Else it would be an isolated copper island. :)

    The  important thing here is that this ground copper is conencted to the ground signal only at one point. Just having a general ground plane is not okay. If you have a ground plane already, you can make a trench around the crystal area with a connection to the rest of the ground plane only at one side. Else other (external) currents may cross this area and influence the crystal.

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