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DP83822I: is it possible to delete the pulse transformer and connect the multiple PHYs on the board

Shinichi Inoue
Guru 21646 points
Part Number: DP83822I

Dear Specialists,

My customer is considering DP83822 for EtherCAT PHY, and has a question.

I would be grateful if you could advise.

---

Generally, in EtherCAT daisy chain communication, the PHY is equipped with a pulse transformer and connect to the front and rear EtherCAT devices.

When arranging multiple EtherCAT slaves on the same board, is it possible to delete the pulse transformer and connect the PHYs on the board?

Could you please see the powerpoint file below. 

Question about DP83822I.pptx

---

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Expert 3727 points

    Hi Shinichi,

    Interesting question. I will have to bring this up with the team and get back to you, please look out for a response in the next week. 

    Best,

    Alon

  • 0 in reply to Alon Kopelman
    TI__Expert 3727 points

    Hi Shinichi,

    What is the use case here? What is being achieved by this setup?

    It is unlikely to work, however, we need more information. 

    Best,

    Alon

  • 0 in reply to Alon Kopelman
    Guru 21646 points

    Hi Alon,

    Thank you for your reply.

    The customer'd like to save pulse transformer when multiple PHYs are used on the same board.

    They use EtherCAT in a daisy chain connection.

    The purpose is motor control, and one PHY is used for each motor.

    The customer want to control multiple motors on the same board, and multiple PHYs are mounted on the board.

    Could you please let us know why it does not work.  

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    TI__Expert 3727 points

    Hi Shinichi,

    We have not tested this configuration in lab, so it is an unproven design, however in theory if the pulse transformer on the board is able to meet all the criteria for the every PHY it is connected to, then perhaps it could possibly work. 

    Can you share board schematic? Layout guidelines must also be met. 

    I have found this document: https://www.ti.com/seclit/ml/slyp788/slyp788.pdf which outlines conditions clearly for the DP83826, however it is the same concept. 

    Best,

    Alon

  • 0 in reply to Alon Kopelman
    Guru 21646 points

    Hi Alon,

    I could obtain the concept the customer consider.

    They are considering transformerless connection.

    Could you please see attached file.

    The customer's comment  is listed below.

    ---

    I will ask you a new question using a concrete example.

    As an example, the Microchip PHY LAN9252 has an application note of AN2189 --Transformerless Applications of Microchip ’s LAN9252 EtherCAT Controller.
    Is prepared. (Please refer to the attached file)

    00002189A_Transformerless Applications of Microchip's LAN9252 EtherCAT Controller.pdf

    Looking at the material, the Boot strap resistor disables Auto-Negotiation and the communication signal between the PHYs is coupled with a capacitor.

    Q1:
    Does DP83822 support such Transformerless Applications?

    Q2: 
    If the answer to Q1 is "No", please introduce a TI PHY that has Transformerless Applications and can be used with EtherCAT.

    If you can't achieve Transformerless Applications with TI PHYs, unfortunately we have to look for PHYs from other manufacturers.

    The PHY used by our company is being consolidated into DP83822 at the time of new development, so it would be nice if DP83822 supports Transformerless Applications.

    ---

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi 

  • +1 in reply to Shinichi Inoue
    TI__Expert 3727 points

    Hi Shinichi,

    The DP83822 does support transformer-less, you would need to use decoupling caps between PHY's.

    Please let us know how your design progresses. 

    Best,

    Alon

  • 0 in reply to Alon Kopelman
    Guru 21646 points

    Hi Alon,

    Thank you for your reply.

    I understand DP83822I can use for transformer‐less design with decoupling caps between PHYs.

    Could you please provide related application note, reference design or a kind of document.

    I'll share it with the customer. 

    The customer has just begun to consider new projects.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • +1 in reply to Shinichi Inoue
    TI__Expert 3727 points

    Hi Shinichi,

    We are sorry, we do not have reference designs or application notes for this design. 

    We can continue to support with questions here on E2E and more, and would like to be updated on progress with this design. 

    Best,

    Alon 

  • 0 in reply to Alon Kopelman
    Guru 21646 points

    Hi Alon,

    Thank you for your reply.

    I understand there is no reference design and application note at this time.

    When the customer has a question, I'll consult you again by the new thread,

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi