• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 743 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Best decoupling for switch power in audio

Borge Strand-Bergesen
Intellectual 710 points
Other Parts Discussed in Thread: LM3224

I use the LM3224 to provide +-8V to a headphone amplifier circuit. In my circuit I see ringing around 108MHz. I suspect PCB trace stray inductance. In your experience, what is the best way to reduce unwanted ringing at frequencies much higher than regulator switching frequency and main inductor SRF?

Close to the amp I use large 470uF OS-CONs, but these let through quite a lot of the high-frequency switching noise of the regulator.

I have been reading up on Murata 3-termainal caps lately, see http://www.murata.com/~/media/webrenewal/support/library/catalog/products/emc/emifil/c39e.ashx?la=en-us

Are these a good fit next to an LM3224 and similar?

Thanks,

Børge

  • 0
    TI__Genius 13700 points
    Hello,

    At that frequency you are dealing with switch node ringing .

    I would recommend giving this App Note a read. It covers a number of methods for reducing the ringing on the switch node which will in turn reduce that high frequency noise across your circuit.
    www.ti.com/.../slva255.pdf


    Let me know if there are any questions.
  • 0 in reply to Ryan May
    Intellectual 710 points

    Thank you Ryan,


    I have downloaded the note and sent it to the printer.

    Actually, the 108MHz noise turned out to be the sum of the local FM transmitters! But there is still ringing to be eliminated in the circuit.

    Best regards,

    Borge

  • 0 in reply to Borge Strand-Bergesen
    TI__Genius 13700 points

    Hello Borge,

    That is great that you got the bottom of the 108MHz source.

    Let me know if there are any questions reading through the document I attached in the previous post.

    Also if you feel that this thread/question is closed click "Verify Answer".

  • 0 in reply to Ryan May
    Intellectual 710 points

    Hi,


    I have finally sorted out some state machine issues I had on the board and dug down into the power supply. The SLVA255 text is a good start. I'll have to get some new equipment that can do 200MHz, though.

    What I see in my LM3224 based boost converter is ringing when the switch closes. The paper focuses on ringing when the switch opens. I still gave the snubber a shot, and it definitely changes things. But there are oscillation nodes which the snubber doesn't touch which makes it hard to see what the snubber at the switch node can fix.

    Why does switch close caue ringing? I suspect a high parasitic L in the bond wires of the chip, and that an external transistor will help. In this design I'll have to kill high-frequency ringing, and I'm considering all sorts of redesigns, from using a controller to using reverse-geometry or other super-low-ESL decoupling.

    Thanks,

    Børge