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EK-TM4C1294XL: Ethernet Transformer connection query

Rupesh Malavi
Prodigy 245 points
Part Number: EK-TM4C1294XL
Other Parts Discussed in Thread: TLK110

Hi Team TI,

We are using TM4C1294NCPDTI microcontroller for one of the project. we are referring TI EX-TM4C1294XL board design as a reference design. I have below query regarding transformer connection.

Generally common mode choke are kept on cable side and not on PHY side(same shown in EVK schematic), but actual board is having common mode choke towards the PHY side.

Please let me know the why the connections are like that? is there specific requirement of the PHY?

it seems symbol used in the schematic is HX1188FNL transformer and physical part used in board is HX1198FNL. Please check below attached images for better understanding.

  • 0
    TI__Guru**** 174516 points

    Hi,

    Rupesh Malavi said:
    Generally common mode choke are kept on cable side and not on PHY side(same shown in EVK schematic), but actual board is having common mode choke towards the PHY side.

      I think the pin 1-8 on the board are facing the the MCU and the pin 9-16 is facing the RJ45. When you look at the transformer where the dot is that is the pin 1 and for that entire side is pin 1-8. The CMT is pin 10 and 15 is on the other side facing the RJ45.

    Rupesh Malavi said:
    it seems symbol used in the schematic is HX1188FNL transformer and physical part used in board is HX1198FNL. Please check below attached images for better understanding.

     You are fine to use either one. We have some newer LaunchPad with the HX1198FNL in it. 

  • 0 in reply to Charles Tsai
    Prodigy 245 points

    Hi Charles,

      I think the pin 1-8 on the board are facing the the MCU and the pin 9-16 is facing the RJ45. When you look at the transformer where the dot is that is the pin 1 and for that entire side is pin 1-8. The CMT is pin 10 and 15 is on the other side facing the RJ45.

    Here TI used part is HX1198FNL and not HX1188FNL which shown is schematic.

    I want to know, Any specific reason is there to keep like that? any requirement from PHY side?

  • 0 in reply to Rupesh Malavi
    TI__Guru**** 174516 points

    Hi,

     If you read the LaunchPad user's guide, in the BOM list, it is the HX1198FNL being listed. As I said we do have LaunchPads built with either one. I don't know the history when it was changed from 1188FNL to 1198FNL. Perhaps it may have something to do with the availability/pricing of the parts in enough quantify at the time of the build.  Again, you can use either one of them.

  • 0 in reply to Charles Tsai
    Prodigy 245 points

    Hi Charles,

    Can you help me to understand , in what are the scenarios common mode choke shall be keep on PHY side.

  • 0 in reply to Rupesh Malavi
    TI__Guru**** 174516 points
    Hi Rupesh,
    I find below two threads that might explain why the common mode choke be toward the PHY side. Please note that the the internal PHY in the TM4C129 is derived from the TI TLK110 which is mentioned in the two threads.
    e2e.ti.com/.../665790
    e2e.ti.com/.../593809