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LM5116: Radiated emission between 30MHz and 50MHz

anais bercker
Prodigy 10 points
Part Number: LM5116

Tool/software:

Hello 

I have a design for a DC/DC converter based on LM5116. (Q1 and Q2 reference is FDD86102) 

We have issues in radiated emission in the bandwidth 30MHZ to 50MHZ.

We added 10Ohm,(then 33Ohm) serial resistor on LO and HI signal but it didn't solve the issue. 

What can we change on our design to solve this issue? 

Best regards  

Anaïs 

  • 0
    TI__Guru 58171 points

    Hello Anais 

    Please try these items on by one.  

    30M-50MHz noise is also affected by the PCB layout. If possible please send me the layout for my review . 

    -EL

  • 0 in reply to EricLee
    Prodigy 10 points

    Hello Eric 

    I already tuned the snubber because I found that there was noise around 130MHz. There was ringing noise at SW node at 130MHZ. So I tuned the snubber and now the value is R=3.3Ohm and C=560pF. It allows to reduce the noise at 130MHz but it has no impact on range 30MHz-50MHz. 

    I changed the switching transistor with this reference with lower input capacitor value (IPD80R1K2P7ATMA1) . I noticed that at LO pin the signal is sometimes on sometimes I see just a peak I'm not surE that the LM5116 is fully functionnal.

    I added a schottcky diode in parallel with Q2 but it doesn't solve the issue. 

    I can send you the gerber files by email ( I am not sure I achieved to put them in attachement)

    Best regards 

  • 0 in reply to anais bercker
    TI__Guru 58171 points

    Hello Anais

    Please attach the Gerber file here for my review.

    -EL 

  • 0 in reply to EricLee
    Prodigy 10 points

    Hello Eric 

    You will find the gerber files in attachments.

    Best regards

     A5Q00071862-02-ZA.zip

  • 0 in reply to anais bercker
    TI__Guru 58171 points

    Hello Anais 

    • Make the SW node copper are as small as possible
    • Rotate the inductor 90degree CCW and make the SW node copper area as small as possible. (For example, 3 x 3 =9 < 2 x 6 = 12)
    • Use physically smaller inductor
    • Connect the VCC capacitor ground directly to the PGND pin
    • Locate the HB capacitor as close as possible to the IC
    • Route HO-SW traces in parallel to the high-side MOSFET. 

    -EL