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I just designed a simple class D amp pcb in which the ground plane is in a star configuration with the IC as center as suggested by the datasheet (cuts in signal areas vs big cap areas, etc..). VCC plane is on the other side. It is as "clean" as I can do it. On the remainder of the board (borders mostly) I have blank pcb space (the pcb has to be this size). I was not sure if it would be a good idea to put a ground plane around all that as I think it would disrupt the star scheme, so I left a floating plane on both sides of the PCB. Would this be detrimental in any way? Is there a better option?

Floating plane is highlighted.

enter image description here enter image description here

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  • \$\begingroup\$ Floating planes have no way to discharge anything that happens to build up. \$\endgroup\$ – Ignacio Vazquez-Abrams Mar 4 '15 at 0:58
  • \$\begingroup\$ You could make the filler ground a separate ray(s) of the star connection. (That is, if I understand your layout correctly. A screenshot of the layout could help here.) \$\endgroup\$ – Nick Alexeev Mar 4 '15 at 1:16
  • \$\begingroup\$ Screenshots added. Floating plane is highlighted, red "star" = ground, blue square plane is vcc. \$\endgroup\$ – Wesley Lee Mar 4 '15 at 1:23
  • \$\begingroup\$ If I were to tie this plane with ground, where does it make more sense to do so? Close to the input connector? \$\endgroup\$ – Wesley Lee Mar 4 '15 at 3:13
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  1. You can simply extend your ground regions out towards the edge of the board.

  2. If you are not designing for extremely low cost at extremely high volume, you can simply leave those areas blank (no copper). Most board shops won't charge noticeably extra for large etched areas in prototype quantities.

  3. You can use copper thieving to fill those areas. This is numerous small disconnected copper areas. It is good for manufacturability because it ensures copper is balanced between the different layers and reduces the rate that etchant is depleted when etching the boards, but at the same time it is not likely to affect your circuit because relatively the copper regions are relatively small with relatively large gaps between them and active areas of the circuit (so there's little capacitance to couple signals).

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  • \$\begingroup\$ I tried using the thieving method in Eagle, but apparently it doesnt have an automated method of doing it. So I hatched the floating plane and added a solder jumper between them and ground. This way I can leave them floating or tie them to ground to see if it makes any difference.. \$\endgroup\$ – Wesley Lee Mar 4 '15 at 7:02

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