• Locked Locked
  • Replies 3 replies
  • Subscribers 33 subscribers
  • Views 1408 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DP83867ERGZ-R-EVM: Gigabit + PoE Ethernet RJ45 jack compatibility

Frankie Myers
Prodigy 20 points
Part Number: DP83867ERGZ-R-EVM

Our design includes a gigabit PoE ethernet interface based around the DP83867 PHY, and we're currently unable to establish a network link of any kind. We have confirmed that we are able to communicate with the PHY and read its configuration registers from our MPU. Below is our schematic. 

The PHY datasheet discusses requirements for the magnetics and mentions that the center taps on the PHY side must all be isolated and individually bypassed with 0.1 uF capacitors. The RJ45 jack we have chosen does not bring these center taps out individually and instead busses them all together, so we are thinking this may be the culprit here. But I was hoping for some clarification on this because it's hard to see how bussing these center taps would affect the differential signals going in and out of the PHY.

Here's the excerpt from the PHY datasheet:

  • TI__Mastermind 19621 points

    Hi Frankie,

    I see that you are able to perform register reads/writes, but are unable to get any kind of link. We have a troubleshooting guide available for the DP83867, I believe this would greatly help debug the issue you are facing.

    I also took a look at the transformer that you are using, the TRJG0926HENL (link is where I found the specs for this part) and it meets the requirements listed in Table 9-1 Magnetic Isolation Requirements of the data sheet. Please follow the troubleshooting guide and let me know if it helps find the issue or if there is something missing from the guide that we could add.

    Regards,

    Alvaro

  • in reply to Alvaro (Al-vuh-roe) Reyes
    Prodigy 20 points

    Alvaro, thank you for your reply. I went through much of the troubleshooting guide and I didn't find anything that looked particularly concerning. I did make the 100 ohm terminated RJ45 cable and confirmed that the auto-negotiation pulses are appearing on the bidirectional pins of the jack.

    I replaced our RJ45 connector with a non-PoE connector (TE 6-2301994-2). that has individual capacitors on the center taps, and it worked.

    I also tried using our current connector (Trxcom TRJG0926HENL) while removing all PoE related components from the board, and it did not work.

    I'm still not clear why our current jack does not work. Do you have any more thoughts on this?

    In any case, I'm searching for a compact form-factor PoE compatible 1000Mbps jack which will work for the DP83867 PHY.

    Here is our current connector (Trxcom TRJG0926HENL):

    Here is the connector that works (TE 6-2301994-2)

  • in reply to Frankie Myers
    TI__Mastermind 19621 points

    Hi Frankie,

    Thank you for providing the information so clearly. The Center taps bussed together never works, even without the POE circuitry. 

    We have a POE reference design board here: https://www.ti.com/tool/TIDA-010083 

    The schematics and BOM are available on that page, used a Wurth Electronics 749023010A. 

    The DP83867 is a voltage line driver (for the MDI side communication), where the line transmitting data are sensitive to DC voltage. On your current connector, try probing CT 4 & 5 and see what voltage you get and compare that to P1 on the connector that works. 

    Regards,

    Alvaro