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DP83848C: Limitations of Transformerless Operation

Liam Keetch
Prodigy 20 points
Part Number: DP83848C

Hello,

I was wondering if anyone could elaborate on the following. 

Document www.ti.com/.../snla088a.pdf specifies recommendations for configuring transformerless operation. 


Specifically, it states 
"IEEE compliance testing was performed on the transformerless interface with both straight and crossover cables. The results showed compliance for critical 100 Mb/s mode parameters (jitter, tx/rx return loss, Vod). Other IEEE tests, which are designed to simulate worst-case cable loading, did not pass, thus supporting the recommendation to use short distance configurations in non-typical transformerless applications"

Is it possible to find out what specific tests failed? It recommends applications for cables less than 1 meter in length. What sort of results might one expect to see if longer cables were to be used? 

Best regards,

  • 0
    TI__Mastermind 18425 points
    Hi Liam,

    That application note was originally published a while back so tracking that data would be difficult at the moment. In general we inform customers that IEEE compliance in transformerless operation is difficult as some test pass and some don't. However, the PHY can pass BER test at 100meter cable length. For longer cable lengths, there may be degradation of BER performance and eventually at very long cable lengths there may be link issues.

    -Regards,
    Aniruddha