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DP83867IR: 125MHz EMI noise

Part Number: DP83867IR

Dear Team,

My customer is evaluating DP83867IRRGZT on their trial board. When they measured EMI of the trial board, there was 125MHz EMI noise on it. When they unplugged LAN cable, that 125MHz EMI noise was reduced. Then, they judged that it to be the DP83867IR application related noise.
I asked them to try to disable CLK_OUT by CLK_O_DISABLE = 1 (= Disable clock output on CLK_OUT pin), but the 125MHz EMI noise was not reduced.

Could you suggest me which part of the DP83867IR application to check to reduce the 125MHz EMI noise?

Thank you.

Best Regards,

Koshi Ninomiya

  • Hi Ninomiya,

    Can you try setting bit[10] of register 0x0000 to enable MII Isolate mode and see that reduces the noise?

    If that does not work, can you share the register dump file?

    Regards,

    Adrian Kam

  • Hi Adrian-san,

    The customer tried setting bit[10] of register 0x0000 to enable MII Isolate mode, but the noise was not reduced.

    The register dump file is as follows,
    *The numbers after "registers for MII PHY 0:" are the register values from 0x00 to 0x1F.

    *********************************************************************

      registers for MII PHY 0:

        1140 796d 2000 a231 05e1 cde1 006f 2001

        6001 0200 7800 0000 0000 401f 00a8 3000

        d048 bc02 0000 1c80 29c7 0000 0000 0040

        6150 4444 0002 0000 0000 0000 0202 0000

    *********************************************************************

    Please review their register settings and suggest measures to reduce the 125MHz noise.
    Thank you.

    Best Regards,

    Koshi Ninomiya

  • Hi Ninomiya,

    I would like to double confirm something. Was CLK_OUT also disabled when the customer enabled MII isolate mode? Also, I did not see any outstanding issues with the register configurations.

    In order to potentially locate the source of the noise, try the following experiments and let me know of the results:

    1. With the cable inserted, MII isolate mode enabled, and CLK_OUT disabled, measure RX_CLK. Does the customer see a 125 MHz clock?
    2. With the cable inserted, MII isolate mode enabled, and CLK_OUT disabled, reduce the speed of operation from 1000 Mbps to 100 Mbps. Does the customer still see the 125 MHz noise?

    Regards,

    Adrian Kam