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Transformer less Ethernet for DM368

Binupandian S
Prodigy 180 points
Other Parts Discussed in Thread: TLK110

Hi,

We are designing a small form factor design using DM368.

DM368 has MII interface and since the design requires Ethernet, we are looking at implementing transformerless design.

Here's what I have found on Transformerless design:

DP83848 - www.ti.com/.../snla088a.pdf

TLK110 - www.ti.com/.../slla327.pdf 

The limitations are:

1) 10Base-T is not ensured. This is  mainly current mode PHY limitation.

For proper operation, Auto negotiation is to be disabled.(forced 100Base-T mode)

2) Cable length: <= 1m

Can you recommend PHY + caps that can be used for the same?

Any better alternatives available for transformerless design?

Any suggestion regarding the same is welcome.

Regards,

Binupandian S

  • 0
    TI__Mastermind 31600 points
    Transformerless operation is typically used to connect components that are on the same board or that are connected via a backplane. Your block diagram shows a header, a cable, and an RJ-45. Presumably the RJ-45 would be on a separate board? What would be the connections on the other side of the RJ-45? Would this then be transformer coupled to another PHY?

    Patrick
  • 0 in reply to Patrick OFarrell
    Prodigy 180 points
    Hi Patrick,

    Thanks for the reply.

    In our system, the RJ45 is not on a different board.
    RJ45 comes on the housing and is then exposed to the outside world (which may be connected to external PC or network through a CAT 5 patch cable.)

    Also, I am assuming that the cable length <= 1m is from header to CAT 5 cable termination.
  • 0 in reply to Binupandian S
    TI__Mastermind 31600 points

    OK.  I think I am beginning to understand.  The RJ-45 is mounted to the equipment housing.  The cabling goes between the board and the housing.  What type of cabling would be used between the header and the RJ-45?  The signals between the PHY and the RJ-45 should have 50 Ω to ground or 100-Ω differential controlled impedance.

    On a separate note, if the equipment will be connected to an external PC or a network via CAT 5 cable, I would recommend using a transformer instead of caps.  The transformer provides DC isolation between the PHY and the far end equipment.  The transformerless configuration is best suited to applications with a shared ground.

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 180 points
    Sorry for the delayed response.

    Was out on holiday for the last week and could only reply today.

    We plan to use AWG28 twisted pair wiring between the header and the RJ45.

    We are exploring this option because of area constraints in our design. I agree that some compromises need to be made.
    But in this design is it to possible to guarantee functionality with different lan networks?.

    I also couldn't find any reference matching our use case. Can you point us to any resource?

    Regards,
    Binupandian S