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Original question:

LMR38010: LMR38010 FSS EMI % Q1 difference?

LMR38010: INDUCTOR GND LAYOUT

kwon
Intellectual 850 points
Part Number: LMR38010
Other Parts Discussed in Thread: LMR38020EVM

HI~

The link below says, “GND should not be placed under the INDUCTOR.”

https://techweb.rohm.com/product/power-ic/dcdc/dcdc-design/3254/

However, DATASHEET 11.2 LAYOUT EXAMPLE has GND under INDUCTOR.

1) In DATASHEET LAYOUT, only GND COPPER exists without VIA.

2) Place a VIA connected to BOTTOM GND under the INDUCTOR in LMR38020EVM LAYOUT.

3) Without GND.

Which is most effective for EMI?

Best Regards,

KWON.
  • +1
    TI__Genius 16335 points

    Hi kwon

    Placing Ground under the inductor is more effective for EMI.

    When laying copper at the inductor’s bottom, the magnetic field generated by inductors or other high-frequency circuits creates an eddy current at the copper layer. This current weakens the original magnetic lines, resulting to reduce the inductance of the inductor, and increase the loss.  But the impact is small, and can be eliminated if use a shielded inductor, where there are few leaked magnetic induction lines.

    The advantage for placing ground under inductor: an electromagnetic shield can block the magnetic field’s downward transmission, to reduce the high-frequency magnetic field’s impact on other components.

     No need to have vias.

  • +1 in reply to Gui He
    Intellectual 850 points

    Hi Gui.

    Thanks for the reply.

    Does this mean that gnd copper+gnd via and only gnd copper have the same emi effect?

    Best Regards,

    KWON.
  • +1 in reply to kwon
    TI__Genius 16335 points

    Hi kwon

    Yes with/without vias have little impact on the emi. But vias can help improve thermal performance if the inductor is hot.

    Thanks and Best regards.

  • +1 in reply to Gui He
    Intellectual 850 points

    Hi Gui.

    Thank you for the detailed explanation.

    Best Regards