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Problem with connection between two PHY (KSZ9031RNX)

Pavel Babkin
Prodigy 60 points
Other Parts Discussed in Thread: AM5728

Hi everybody!

We have a custom boards (absolutely identical) we designed with the Micrel KSZ9031RNXIA. Everything is ok when we connect our board to notebook (stabile and fast connection in RGMII mode - Advertise 1000BASE-T full-duplex only). But if we want to connect our boards to each other they try to connect, the consumption current is changed, sometimes the LED blinks and after a few minutes sometimes it may make a connection and then everything is stable but only sometimes.

Any ideas?

Any help would be greatly appreciated.

  • 0
    Prodigy 60 points

    I read this post: https://e2e.ti.com/support/arm/sitara_arm/f/791/t/488872

    Symptom: Gigabit auto negotiation link goes up and down forever and doesn't ever link. However, if you manually set the link speed to 100Mb or 10Mb everything works fine.

    Cause: This problem relates to a dirty power supply on the 1.2V (DVDDL pins) rail of the KSZ9031 when using the LDO pin to drive an external FET as seen in the AM5728 reference design and the beagle board X15. If you look at the difference between the AM5728 reference design and the X15 you will notice that the X15 has quite a few more decoupling caps on the DVDDL lines of both KSZ9031's. If you made a custom board based on the TI reference design, chances are you are having this same issue.

    Resolution / Testing: Put a big electrolytic cap on before and after the FET, something like 100uF. Do not try to load an operating system or boot. Just power up the board while plugged into a Gigabit router / switch / hub. You should get your link LED's to come up and stay up. Once you have verified that this is your issue, you can take a closer look at adding some more filtering caps to your design.

    Good luck.

    I will try... may be it helps....

  • 0 in reply to Pavel Babkin
    TI__Mastermind 19780 points
    Hi Pavel,

    Does your board consist of a KSZ9031 connected to an AM5728? If so, this belongs in the AM5728 forum. I can assist you in moving it if you still need assistance.

    Best Regards,