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DP83822I: IEEE 802.3 Compliance & LDCTRL settings

Sathya Mani
Prodigy 10 points
Part Number: DP83822I

Tool/software:

We have used DP83822I in our design. The eye pattern is not matching with 802.3 template. Need suggestions to improve the same. 

Should we try changing Rbias? Change decaps on transformer? 

Vp-p swing as per Electrical characteristics for 10BaseTe is 1.76V. But LDCTRL register mentions Swing can be 3.7V also. Is this correct?

What is the correct setting to be in LDCTRL register for 100 & 10mpbs ?

Can the 49.9m Termination resistor be 0402 (0.062W) if the any of the swing voltage is considered for 10Base-Te?

  • 0
    TI__Mastermind 39785 points

    Hello,

    Please share your setup for compliance (picture of setup), as well as layout of board. I specifically would be interested in the trace length from PHY to RJ-45.

    Has EVM been tested against the compliance software that is available to you? Our expectation is that the EVM should pass, so this would also rule out external factors such as cabling/probing.

    I would caution against component changes for now as this debug is starting, but do acknowledge this may be an option as it gets deeper.

    Electrical characteristics for 10Base-Te are Vp, not Vpp. Voltages in LDCTRL (Reg 0x403) are in Vpp. Termination resistor sizing shouldn't do much difference, so 0402 is sufficient. This resistor characteristic does match the EVM rating so this should be okay.

    Sincerely,
    Gerome

  • 0 in reply to Gerome Cacho
    Prodigy 10 points

    Hi Gerome,

    Thanks for the response.

    We used low voltage differential probe right on the RJ-45 pins.

    The magnetics is external to the connector. 

    Trace length from PHY to Magnetics --> 25mm

    Magnetics to RJ45--> 21mm

    We did not check with the EVM. Will do this.

    Do we need to keep PHY in specific test modes for checking eye pattern comparison with 802.3?

    Regards,

    Sathya 

  • 0 in reply to Sathya Mani
    TI__Mastermind 39785 points

    Hello,

    Trace length looks okay, as this is <2".

    For checking the template test for IEEE802.3 100Base-Tx testing, it is best to disable auto-negotiation and set MDI mode per SNLA266.

    Could you please provide photo of setup?

    Sincerely,

    Gerome