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I've got some questions regarding my stack-up and power layer, which is layer 3 on my PCB.

But before I ask my question I will describe my PCB. Most components are SMD parts (capacitors etc.).

Top layer is used to route almost all signals which is required for SMD components. Top and bottom layer is not filled with ground polygon, because I already got 2nd layer which is my reference plane. OFC top layer uses some polygons and vias to connect SMD parts to 2nd layer, but I'm not using via stitching and free space is not filled with ground.

Bottom layer is pretty empty, I can place some parts there (but I could use top layer as well), if there will be some traces it will be power traces or non critical signals like enable, sense etc.

My question is if I've got whole power supply how to use power inner layer? Should I split it to VCC and VEE only (I've got bipolar power supply), or should I split it even further?

My power supply look like this :

Full bridge rectifier -> CRC -> LC - LDO -> LOAD. I also got some comparators a front of LDO to control startup and UV/OV state.

As you might see from picture below this is not so advanced circuit. Almost whole top layer is empty (for now) and whole bottom is free for routing. So I'm little confused how to use 3rd layer which will be usefull for connecting other parts which will be included on same PCB later (aprox. 10 opamps and some other analog muxes etc.).

I've got few ideas described below :

  • I will use TOP plane to route power directly do LDO input then whole third layer will be used as VCC and/or VEE plane,
  • whole third layer will be used for power routing (including LDO input and output) and TOP layer will be used when it's required to connect SMD parts,
  • third layer will be used as a ground plane and whole power will be routed using top and bottom plane.

enter image description here

I think my picture is rather easy to understand :) BTW I'm not using bottom and top for ground because I don't to make many cutouts and splits, after that I will still need to place many vias to connect planes together to avoid making antennas.

If you got some question feel free to ask :) Have a nice day.

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  • \$\begingroup\$ Decisions on stack-up are usually made by analysing a schematic of the circuit. \$\endgroup\$ – Andy aka May 17 '18 at 9:30
  • \$\begingroup\$ Indeed, but this whole thing looks like some sort of rather weird low speed thing (Probably for audio, where fashion dictates CRC and such like), not sure I see much point in 4 layers for something like this, each channel only has a handful of passives and maybe a few active devices, with nothing producing fast edges. I would do this on two layers and use the savings to add two more layers to some downstream board where the edge rates make it matter. \$\endgroup\$ – Dan Mills May 17 '18 at 14:46
  • \$\begingroup\$ Yep. It's a power supply for audio device without any fancy stuff like an MCU or hi speed amplifiers. But 4 layer PCB is not that expensive (few USD more than standard 2 layer). As you might see above it's whole power supply with LDO (positive and negative) with some passive filter (CRC and LC) to improve PSRR a little. \$\endgroup\$ – mikolaj612 May 18 '18 at 11:11

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