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LMR16030: LMR16030 Can not pass the AT&T certification

vincent wei
Prodigy 110 points
Part Number: LMR16030

Dears,

My customer to do the AT&T certification but they reported that we are failing with a strong component at 106.8 MHz.

Could you please check if you see this and what could be done to fix it? Thanks!

  • 0
    TI__Mastermind 25590 points
    Vincent,

    I suspect the switch node is ringing at this frequency. Please probe and confirm.

    If this is not the case please probe VIN with AC coupling and zoom in on the y-axis to see any ringing. Is this ringing at 106.8MHz?

    I suspect this is caused by some resonance due to the layout and/or component selection. Please check my suggestions above and share the layout so we can find a solution.

    Thanks,

    -Sam
  • 0
    TI__Mastermind 35210 points
    Hi Vincent,

    1 . Is this a radiated or conducted EMI sweep?
    2. Is the test being done in an isolated chamber or Faraday cage of some sort? This could be especially important if the testing being done is a radiated sweep. It looks like spectral component of interest falls in the USA FM band (88M-108M), where some other countries it might be over-the-air TV broadcast (VHF) band.
    3. Is the testing being done with only the LMR16030 powered on/switching?
  • 0 in reply to Samuel Jaffe
    Prodigy 110 points

    Dear Sam,

    The issue is still nor fixed.

    Attached is the SCH and PCB layout， Please give some suggestion,thanks!

    8357.Layout.pdf5621.Sch.pdf

    Vincent Wei

  • 0 in reply to vincent wei
    TI__Mastermind 35210 points
    Hi Vincent,

    To better answer your question can you answer Sam and my questions in the above posts?
    We would like to see a switch node waveform highlighting the frequency of oscillation (and amplitude) of the switch node ringing, if present.

    Could we get an EMI sweep with only the DC/DC converter powered on and an external resistive load applied to the converter's output? It looks like there are many clocking sources onboard, with a few whose lower-order harmonics that might fall in this frequency band?
  • 0 in reply to Marshall_Beck
    TI__Expert 6245 points
    Hello Vincent,

    It has been a while since Marshall’s response which contained a good hypothesis as the where this circuit’s noise is coming from. If you have further questions, please send me an email at robert.blattner@TI.com

    Regards, Robert