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DP83848 Transmit level question.

Daniel Chilinski
Prodigy 60 points

I have 2 DP83848's set up in a capacitor coupled setup similar to the AN-1519 App note.  in figure 6 an figure 8 of the application note it shows voltage levels for capacitor coupled and transformer coupled setups.  I am seeing that the transmit of one of the phys is at the correct 1.8V to 2.8V for capacitor coupled Phy's but the transmit of the other DP83848 is at the voltage levels of the transformer coupled phys 2.8V to 3.8V.


This is causing an issue where only 1 of the phy's is reporting link and the other is not and I cannot get communication up and running.


Any thoughts on what the cause may be and what I can do to fix it?

Thank you,

  • 0
    TI__Mastermind 31600 points

    Could you share a schematic of your application?

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 60 points

    unfortunatly current process with my company does not allow me to post my schematic but I can say that I have 2 instances of the circuit with 1 of them working and the other not.  i am starting to think that one of the phy's has failed but I want to be sure before I have any parts replaced. 

  • 0 in reply to Daniel Chilinski
    TI__Mastermind 31600 points

    Would you company policy allow you to share the schematic directly via email?  If so I can provide you an email address.

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 60 points

    email would be great.  I was able to look at 2 boards 1 is working correctly and the other is not so I am assuming a component failure but have not completely convinced myself.

    a quick run down of what I am seeing. 

    Both phy's are on the board with Tx tied to Tx and Rx tied to Rx so auto-negotiation will need to happen to determine Rx and Tx.

    On the working board

    both phys report link

    Phy 1 Pin 11 is seeing the waveform centered around ~2V with Phy 2 Pin11 seeing the waveform around ~3V

    Phy 1 Pin12 is seeing the waveform centered around ~2V with Phy 2 Pin12 seeing the waveform around ~3V

    Phy 1 Pin14 is seeing the waveform centered around ~3V with Phy 2 Pin14 seeing the waveform around ~2V

    Phy 1 Pin15 is seeing the waveform centered around ~3V with Phy 2 Pin15 seeing the waveform around ~2V

    This shows that auto negotiation as happend and Phy 1 is transmitting out pins 14 and 15 and recieving on 11 and 12

    On the failed board I see the exact opposite in terms of voltage and only phy 2 reports seeing link.

    Phy 1 Pin 11 is seeing the waveform centered around ~3V with Phy 2 Pin11 seeing the waveform around ~2V

    Phy 1 Pin12 is seeing the waveform centered around ~3V with Phy 2 Pin12 seeing the waveform around ~2V

    Phy 1 Pin14 is seeing the waveform centered around ~2V with Phy 2 Pin14 seeing the waveform around ~3V

    Phy 1 Pin15 is seeing the waveform centered around ~2V with Phy 2 Pin15 seeing the waveform around ~3V

    This shows that auto negotiation as happened and Phy 1 is transmitting out pins 11 and 12 and recieving on 14 and 15 but for some reason Phy 1 is not reporting it has link.

    Any insight on what to look a for would be appreciated.  we are running both boards with the same software so that should not be a factor.

    Thank you,