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DP83848I: Transformerless connection

Mark Guastaferro
Genius 11645 points
Part Number: DP83848I

Looking at using the DP83848I with the KSZ8895 Ethernet switch with a transformerless connection on two of the switch outputs. In one case, the PHY to PHY connection is about 3.5 inches on the same board. Second connection is about 9 inches. Both will be capacitively coupled.

Application Note AN1519 provides information on forming a transformerless connection with the DP83848 PHY so this seems possible. We have a few questions:

1. Does TI have any experience with a transformerless connection to the KSZ8895? I did see another forum post related to a transformerless connection between these two devices and it appears to be OK if run at 100 Mb/s Full duplex mode.

2. Need the PHY to come up in the proper mode from strapped settings.  I found a forum post on the DP83822 where it seemed a reserved register bit needed to be changed to output MLT-3 waveform.  Does this apply to the DP83848I?

https://e2e.ti.com/support/interface/ethernet/f/903/t/572998?tisearch=e2e-sitesearch&keymatch=transformerless 

3. Also saw this forum post about the DP838117 having issues generating MLT-3 waveform without a transformer. Just want to verify the DP83848I will not have this issue. 

https://e2e.ti.com/support/interface/ethernet/f/903/p/239397/838117?tisearch=e2e-sitesearch&keymatch=transformerless#pi239031350=1

  • 0
    TI__Mastermind 18425 points
    Hi Mark,

    1. The transformerless application was tested with TI PHY to TI PHY connection, so unfortunately we do not have test results for KSZ8895. If KSZ8895 can work in transfomer-less application then your proposed setup should work. However, the system will have to be tested for confirmation.

    2. No, the register 0x404 setting mentioned in that post was only for that particular DP83822 application. DP83848I does not need that register setting to operate in transformer-less application.

    3. As long as the design requirements for the PHY are met, it will work in transformer-less application.

    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    TI__Genius 11645 points

    Hi Aniruddha,

    I have an additional question regarding the DP83848I in a transformer-less application.  

    Would TI have recommended tests that should be performed to verify robust operation of a transformerless ethernet connection?  

    The App Note talks about running standard IEEE compliance tests and looking at critical 100Mb/s parameters like jitter, tx/rx return loss and Vod. Are there other parameters to verify?

    This planned application will not use Cat5 cabling, but a PCB board trace interconnect. One about 3.5 inches and the other about 9 inches. 

  • 0 in reply to Mark Guastaferro
    TI__Mastermind 18425 points

    Hello Mark,

    I would recommend Compliance and Bit Error Rate testing.For bit error rate testing, a MAC with packet analysis capability would be required. The MAC will need to send Ethernet packets and then analyze incoming packets for bit error.

    Other tests might also be conducted on the system but they are really dependent on customer needs. From a system level, the above two tests would help verify if the design work or not.

    -Regards,
    Aniruddha