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Class D Switching Power Amplifiers and Power D/A conversion

My tpa3118 board - comments/critiques?
My tpa3118 board - comments/critiques?
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Old 13th June 2016, 03:12 PM   #1
matt_garman is offline matt_garman  United States
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My tpa3118 board - comments/critiques?
Default My tpa3118 board - comments/critiques?

Update Aug 26, 2016: See post #61 on page 7 for Eagle files, BOM, and Gerbers, as well as pics of the final board.

Original post:

I am working on a tpa3118d2 PCB. This is literally the first PCB I've ever designed. It's not yet fully complete, but I'd like to think I'm done with the major design, and getting to the fine-tuning phase. So I was hoping to solicit some comments, critiques, tips, etc.

My main goal here was to familiarize myself with the PCB design and manufacturing process.

The schematic is an almost verbatim copy of DUG's DUG-1 PBTL board. DUG was nice enough to let me copy his design. It's not as fancy as the GMARSH Wiener boards, and that's not what I'm going for. I really like the DUG-1 boards, and basically want those with a few small tweaks:
  • Use of Coilcraft VER2923 inductors to save some board space
  • Room for through-hole input capacitors (actually I'll probably tweak the design a bit so you can use either SMD or leaded)
  • Room for multiple OS-CON caps
  • Room for leaded caps in part of the output filter

I haven't created the ground plane yet, only the signal and power lines are routed.

I know there is an error on the output side, it seems Eagle is omitting a net.

Thanks for any feedback!
Attached Images
File Type: png tpa3118_board_20160610.png (57.6 KB, 838 views)
File Type: png tpa3118_schematic_20160610.png (38.3 KB, 821 views)

Last edited by matt_garman; 26th August 2016 at 10:44 PM. Reason: Link to post summary post #61
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Old 13th June 2016, 07:30 PM   #2
doctormord is offline doctormord  Germany
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Only C7 and C8 are in the HF path of power decoupling, the other 4 aren't. Output stage isassymetric, wouldn't do that.
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Old 13th June 2016, 09:26 PM   #3
matt_garman is offline matt_garman  United States
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My tpa3118 board - comments/critiques?
Quote:
Originally Posted by doctormord View Post
Only C7 and C8 are in the HF path of power decoupling, the other 4 aren't. Output stage isassymetric, wouldn't do that.
Thank you, doctormord.

Would you be willing to elaborate a bit?

Specifically, with regards to "only C7 and C8 are in the HF path of power decoupling", why aren't the others in the path? What have I done wrong or failed to do?

With regards to the asymmetric output stage: do you mean in terms of the circuit (schematic) or the PCB design? I believe the circuit should be symmetric. Though it is obvious the routing wires aren't symmetric. I can understand why the circuit should be the same, but is that also necessary for the PCB layout?

I had (at least) one known problem with the output wiring, I now believe it's fixed in the attached picture. I shuffled stuff around a bit too for a more compact and hopefully better overall layout.

Thanks again!
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Old 13th June 2016, 09:33 PM   #4
Nisbeth is offline Nisbeth  Denmark
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My tpa3118 board - comments/critiques?
I think you should add the ground plane and see what that looks like - for me at least it saves confusion over which air wires still need to be routed.

/U.
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Old 13th June 2016, 09:47 PM   #5
matt_garman is offline matt_garman  United States
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My tpa3118 board - comments/critiques?
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Originally Posted by Nisbeth View Post
I think you should add the ground plane and see what that looks like - for me at least it saves confusion over which air wires still need to be routed.
Agreed. The real reason I didn't post the ground plane is that it turns the whole board background blue, and makes everything else even harder to read. I'm doing this with the free version of Eagle, so if there's a smart way to have the ground plane filled and still keep things somewhat readable, I'm all ears!
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Old 13th June 2016, 09:53 PM   #6
Nisbeth is offline Nisbeth  Denmark
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My tpa3118 board - comments/critiques?
If your plane is in a separate layer you can just hide the layer. Otherwise clicking on the polygon with the "ripup" tool removes the polygon fill (until you hit the "ratsnest" command again).

/U.
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Old 13th June 2016, 10:09 PM   #7
matt_garman is offline matt_garman  United States
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My tpa3118 board - comments/critiques?
Here we go. Somehow the Eagle background was set to white, which kinda sucks. Changing the background to black makes things more readable, even with the ground plane.
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Old 13th June 2016, 10:16 PM   #8
Nisbeth is offline Nisbeth  Denmark
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My tpa3118 board - comments/critiques?
Much better Suggest you hide layer 27 as well (top side component values) to reduce the clutter

/U.
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Old 13th June 2016, 10:40 PM   #9
matt_garman is offline matt_garman  United States
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My tpa3118 board - comments/critiques?
Quote:
Originally Posted by Nisbeth View Post
Suggest you hide layer 27 as well (top side component values) to reduce the clutter
Done! Definitely much less cluttered.
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Old 13th June 2016, 11:29 PM   #10
doctormord is offline doctormord  Germany
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Default My tpa3118 board - comments/critiques?

The higher the frequency the more narrow the current will follow the path with least impedance. If you look at your latest board design and think of the current "flowing" from your input terminals to the amp pins, you'll notice that C26/27 are not in the current path - they're on a stub. So they won't help to decouple.

For the output stage, you want to have them symmetrical because of all the parasitically influences to your filter. (inductance, capacitance) As there's switching HF, unsymmetrical layout increases the chance for increased EMI, distortion, etc. Beside this, keep all high current and HF traces/areas short and tight.

Beside this, your TPA3118 is missing thermal vias under the package for heat transfer and low impedance ground connection. Actually the PVCC stubs blocks the ground route when just filled on top.

Every (power/signal) trace has n return path, even if you don't see them because all is "ground" potential.

Last edited by doctormord; 13th June 2016 at 11:31 PM.
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