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DCP010505B: Input filter operation

Nam, Dino
Expert 4275 points
Part Number: DCP010505B

Dear team, 

The customer are trying to add bead at input line like below for solving EMC issue(CE). Please review below concept/layout and let me know your opinion regarding side effect. 

Thank you. 

  • +1
    TI__Mastermind 25580 points

    Dino,

    I'd recommend populating the GND ferrite with a 0-ohm resistor for first tests. That ferrite will create a voltage difference between the GND of the supply and the GND of the device (and the rest of the board) which may cause worse common-mode noise.

    You may also want some damping (bulk cap with ESR or ceramic cap with series resistor) to prevent any undesired oscillations on the input.

    Other than that, yes, a ferrite bead is a great way to improve EMI.

    -Sam

  • 0 in reply to Samuel Jaffe
    TI__Expert 4275 points

    Hello Samuel, 

    I have a related question. 

    As above question, the customer are trying to add bead to solve EMI Issue (Conducted Emission) but the issue is not clear. 

    Have you seen this issue(CE fail) in other projects? There is noise at switching frequency of DCP010505BP(about 780KHz ~ 800KHz) and harmonic frequency.  

    Please review above schematic and layout again and let me know your opinion regarding debug point to solve EMI issue(CE)

    Thank you.  

  • 0 in reply to Nam, Dino
    TI__Mastermind 25580 points

    Dino,

    Yes, all switchers will create EMI at their switching frequency and its harmonics. Reduce this EMI by adding input capacitance and more series impedance (inductor or ferrite) with the supply.

    If you have further questions, please attach the EMI plot.

    -Sam

  • 0 in reply to Samuel Jaffe
    TI__Expert 4275 points

    Hi Samuel,

    Thank you for your prompt response.

    please review attached EMI plot and let me know your opinion.

    - Would you recommend input capacitance and series impedance?

    - Adding ferrite on output path, Will this effect CE result?

    DCP010505B EMI(CE)result_210422.pptx

    Thank you.

  • 0 in reply to Nam, Dino
    TI__Mastermind 25580 points

    Dino,

    2MHz - 15MHz is relatively low frequency so adding capacitance may do the trick. If it's not enough, add a series inductor or ferrite bead.

    -Sam

  • 0 in reply to Samuel Jaffe
    TI__Mastermind 25580 points

    Adding a ferrite on the output path may not help considerably but it may be worth a quick test if this is a more convenience solution.


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