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Original question:

TPA3126D2: high frequency pitch

TPA3126D2: best layout practice

steve de coen
Prodigy 140 points

Part Number: TPA3126D2

Hi, 

I have several options to route my PCB, and wonder what you would do..

1) leave the board as it is now, preamp is protected by GND PLANE SPLIT , high switching currents will flow at the bottom from amplifier to GND connection (the 4x4 pin headers under preamp)

2) make 1 large GND plane at the bottom and reroute the VCC line connections at the right edge op the toplayer , next to the right upper mounting hole and under the speaker connectors.

in this case GND split is removed, then i wonder if high frequency currents will not pass under preamp circuit and cause problems ....

3) or any better proposal then  1 or 2 ?

thank you

  • 0
    TI__Mastermind 24835 points
    Hi Steve,
    Are you using single-ended or differential input for the AMP? We usually recommend user to make one GND plane and not split it. A seperated GND design could degrades the class-d amp EMI performance.
    Best regards,
    Shawn Zheng
  • 0
    Guru 140200 points
    Hi Steve,

    as Shawn allready mentioned, splitting the ground plane is no good idea. The disadvantages outweigh the advantages. Splitting the ground planes is no longer done today. Today we use a solid ground plane and strictly separate the analog input section from the output section as shown in figure 37 and 38 of datasheet. The proximity effect makes that the HF ground return currents are only flowing directly under the HF currents in the output section of ground plane. And the proximity effect works the better the more solid the ground plane is.

    Kai
  • 0 in reply to Shawn Zheng
    Prodigy 140 points

    thank you !.

    i use single ended input

    I followed both your advice, and attached the layout .

    Placed many 0.25mm  hole diameter via's.

    try to kept preamp part seperated from the rest.

    the sync line is a high frequency line i expect,  i routed him in the middle of the toplayer, the only part it need to pass under input lines is at the input lines of the subwoofer amp, though i pass with 90° angle and on the other layer.

    Does this layout makes sense, or did i overlooked something else?

    appreciate the advice :)

  • 0 in reply to steve de coen
    TI__Mastermind 24835 points
    Hi Steve,
    One thing you need to take care of is that please make sure to use the front-end GND for INN for single-ended input mode.
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Prodigy 140 points

    Hi Shawn,

    I’m not sure What u mean with front-end GND for INN, as I now use 1 big GND plane, I dont have a seperate front end gnd anymore...

  • 0 in reply to Shawn Zheng
    Prodigy 140 points

    I guess you mean to use a seperate analog GND net for the input signal,  analog pre-amp part and negative INN connections , and use the digital (plane) GND for the power GND (PAD) GND)
    Right?

  • 0 in reply to steve de coen
    TI__Mastermind 24835 points
    Hi Steve,
    I appologize for the confusion. INP signal is from DAC/Codec or buffer in your SCH, right? The front-end GND means the GND around there, and INN nees to be connected to front-end GND to avoid any imbalance between the near GND and the front-end GND, which could help the pop noise performance.
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Prodigy 140 points

    Hi ,

    no appology needed, just want to make sure this board is perfect.

    This board does not contain the DAC, it just have an single ended analog in.

    The DAC is on another board, this board is low current, isolated high speed lines and have massive GND too, i do not expect much influence from there.

    i have made some changes to the schematic, so now the analog input GND is seperated from the massive GND on the board..

    Both GND's come together on the other board. The 4 mounting holes on this board are on (digital) GND too, and connect to the GND of the other board.

    If you think this perform better then using only 1 GND, i will rout it this way.

     

  • 0 in reply to steve de coen
    TI__Mastermind 24835 points
    Steven,
    I'm worrying about the pop performance. Single-ended input mode is used here - INN is connected to the GND by 1uF capacitor while the INP is actually from the DAC on the other board through a long trace(including buffer), which causes imbalance between INN and INP. During power-up, the imbalance could cause the pop click noise. The best way to minize the pop noise is to use differential input mode. If single-ended mode has to be used, please make the circuit/trace between DAC/Codec output and AMP input as simple/short as possible - only 1uF DC block caps is good.
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Prodigy 140 points

    Hi Shawn,

    A plop is not a big issue because the amplifier Will be on all the time . Plops happen only ar power on or off.

    Only 1 thing I worry about which is whistling noices or high frequency pitch sound trough the 2 speakers.

    That issue I had in my first design (slightly), But now I use better gnd connection by using the 4 mounting holes as gnd too.

    I want to go back to my question , is iT better to use only 1 gnd in amplifier schematic (AMP + pre AMP on same gnd ) or use a seperate analog gnd like the schematic I provided?

    Thank you .

    Steve

  • 0 in reply to steve de coen
    TI__Mastermind 24835 points
    Hi Steve,
    Thank you for the explanation. You are right that bad GNDing could introduce whistling noise. According to my personal experience, most of the application use signle GND for both pre-amp and AMP. PLease also make sure the GNDing between DAC board and AMP board is good.
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Prodigy 140 points
    Great support!
    Thanks Shawn,
    I Will use TI more often.