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TPS23756 Noise

Joe Rule
Intellectual 330 points
Other Parts Discussed in Thread: TPS23756

Hello,

     I've recently used the TPS23756 in my PoE design, utilizing the TPS23756 EVM circuit design (5V output).  I've noticed quite a lot of emission noise in the ~60MHz range.  When probing the TPS23756 EVM, I find similar noise in a similar spectrum.  Can you help me understand the possible source of this noise so that I many address in the layout?

Thanks,
Joe

  • 0
    TI__Mastermind 41790 points
    Hi Joe,

    Increasing the isolation caps to 4700pf and try adding a common mode choke after the ferrite bead filters will help. You can try modifying it on the EVM to verify its performance.
  • 0 in reply to Darwin Fernandez
    Intellectual 330 points

    Darwin,

         Thanks for the response.  Which isolation caps are you referring to?  In the EVM, is this C16?  Same question for the ferrite bead filters...are you suggesting a choke after L3 on the converter bias voltage (VC) or are you suggesting a choke on the actual output voltage to the system (L2)?

    I am trying to get a handle on every part of the circuit that is switching in the case that I am coupling noise from one of these traces/planes onto adjacent signals.  Can you help point out every part of the EVM circuit that is switching at 250KHz?

    Thanks,
    Joe

  • 0 in reply to Joe Rule
    Intellectual 330 points

    Darwin,

         I am going to place a 4700pF on C20 of the EVM and I will try multiple ferrites with varying impedance in place of FB3, FB4...as well as FB1, FB2.  Can you confirm these are the areas of the reference design you were referring to?

    Joe