• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 597 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

LM3424: Problem with ringing on SW signal and input voltage supply

Mario Jimenez
Prodigy 200 points
Part Number: LM3424

Hello,

I'm using the LM3424 as buck-boost to drive 8 LED's at 1.5A. I had thermal issues causating current derating over time, I remade the design and their performance is a lot better.

Now the problem is that I'm getting a lot of ringing on the SW signal and input voltage supply, I'm attaching scope shots.

Input voltage supply:

SW node waveform:

And a shot with zoom on the peak.

How can I reduce this ringing? I was thinking about adding a common mode choke right on the input to resonate at that frequency, but also, I'm not sure if I need to adjust some passives related to the control loop compensation.

I'm worried that this ringing gonna be a trouble with EMC radiation when we send it to certificate.

I'm adding schematics for reference.

Thanks!

  • 0
    TI__Mastermind 25500 points

    Hello Mario,

    The high frequency ringing you are seeing is normal. It's caused by a variety of parasitics, but the parasitics in the FET and diode play the most part. Often times the magnitude is not high enough to make you fail EMC, especially since EMC is usually current noise not voltage noise related, it depends on the spec you are trying to pass.

    In any case a common mode filter on the input and/or output can help to pass EMC if the noise it too much.

    But you can search ti.com or google for other way to reduce the noise if you like, this is a common and widely discussed issue. But some of the more common I have seen:

    1. A ferrite bead in series with the diode and/or the FET (high resistance at high frequency).

    2. Adding some gate resistance to slow the turn on/off of the FET.

    3. Placing an RC snubber across the FET and/or the diode.

    Any one of those (or combination of) can greatly reduce high frequency ringing on the switch edges.

    Regards,

    Clint