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POWER SUPPLY to DP83848

Nick Yang1
Prodigy 50 points

Hello Sirs,

In my project, DP83848 doesn't work when 3.3V supplies to it. However, it works when 2.98V supplies.

I have checked RBIAS(1.2V, 4.87k, 1%), PFBOUT(1.8V) , reset and CRYSTAL/OSCILLATOR INPUT.

All of them seem fine.

My platform is NXP2368.

Could anyone give me some suggestions how to debug this issue?

Thanks 

Nick

  • 0
    TI__Intellectual 1885 points

    Hello Nick,

    Could you supply a few details regarding how the DP83848n is not working?

    Also, could you share your schematic for review?

    Thanks,

    John

     

  • 0 in reply to John Hamilton1
    Prodigy 50 points

    Hello John,

     

    I thank your help and I am trying to insert the schematic file, but there is an error message in this community while upload the schematic.

    Therefore, the schematic may be coming later.

    My platform is LPC2368 (NXP).

    All the functions work well except Ethernet.

    However, the Ethernet works well when I supply 2.98V but 3.3V to the system.

    And the way that I judge if Ethernet works is by using “ping” command.

    In my opinion, some components closed to DP83848 mismatch.

    Could you give me some suggestion for this? For example check which pin or voltage across some resistors.

    I appreciate your help.

     

    Nick

  • 0 in reply to Nick Yang1
    Prodigy 50 points

    The schematic is follows,..

  • 0 in reply to Nick Yang1
    TI__Intellectual 1885 points

    Hello Nick,

    Here are some DC points you can check while we are waiting for the schematic:

    Pin     Description   DC Value

    15     AGND            0 Volts

    18     PFBIN1         1.73 to 1.8 Volts

    19     AGND            0 Volts

    22     AVDD33        3.3 Volts

    23     PFBout          1.73 to 1.8 Volts

    24     RBIAS            1.19 to 1.2 Volts

    29     RESET_N     3.3 Volts

    35     IOGND          0 Volts

    36     DGND           0 Volts

    37     PFBIN2         1.73 to 1.8 Volts

    47     IOGND          0 Volts

    48     IOVDD33     3.3Volts

    Also, as per App Note 1469, did you use a 10uF cap on PFBOUT?

    Thanks,

    John

  • 0 in reply to John Hamilton1
    TI__Intellectual 1885 points

    Hello Nick,

    It appears that you are operating in RMII mode, is this correct?

    After reviewing the schematic screen shots:

    Could you also check that pin 39 is strapped to 3.3V?

    I can not be sure from the schematic that the strap resistor is connected to to pin 39.

    Can you confirm the frequency of your oscillator?

    Thanks,

    John

  • 0 in reply to John Hamilton1
    Prodigy 50 points

    Hello John,

    Thanks for your message.

    Yes, I am operating in RMII mode and I have checked the pin 39 is strapped to 3.3V.

    By the way, I have measured all the points you mentioned and list them as follows.

    Pin     Description   DC Value

    15     AGND            0 Volts                                         0V (@2.98V supplied )    0V (@3.3V supplied )  

    18     PFBIN1         1.73 to 1.8 Volts                          1.81V (@2.98V supplied )    1.81V (@3.3V supplied )

    19     AGND            0 Volts                                           0.06V (@2.98V supplied )    0.06V (@3.3V supplied )

    22     AVDD33        3.3 Volts                                       2.98V (@2.98V supplied )    3.3V (@3.3V supplied )

    23     PFBout          1.73 to 1.8 Volts                          1.81V (@2.98V supplied )    1.81V (@3.3V supplied )

    24     RBIAS            1.19 to 1.2 Volts                         1.25V (@2.98V supplied )    1.25V (@3.3V supplied )

    29     RESET_N     3.3 Volts                                       3V (@2.98V supplied )    3.34V (@3.3V supplied )

    35     IOGND          0 Volts                                             0.06V (@2.98V supplied )    0.06V (@3.3V supplied )

    36     DGND           0 Volts                                              0.06V (@2.98V supplied )    0.06V (@3.3V supplied )

    37     PFBIN2         1.73 to 1.8 Volts                              1.81V (@2.98V supplied )    1.81V (@3.3V supplied )

    47     IOGND          0 Volts                                                 0.06V (@2.98V supplied )    0.06V (@3.3V supplied )

    48     IOVDD33     3.3Volts                                                3V (@2.98V supplied )    3.34V (@3.3V supplied )

    As I mentioned before, Ethernet doesn't work at 3.3V supply but work at 2.98V.

    For another checkpoint, a 10uF cap on PFBOUT. It should be 10uF after I check the BOM but I will confirm this again.

    The frequency of my oscillator is 50MHz.

    I really appreciate your input, but I really need more check points.

    Could you give me more?

    Thank a lot.


    Nick


     

     

  • 0 in reply to Nick Yang1
    TI__Mastermind 31600 points

    Nick,

    In your schematic, I see that the DP83848 25MHz_OUT pin is connected to the MAC ENET-RX_CLK (P1.15).  Could you please confirm that this input is the RMII reference clock for the MAC?

    The 25MHz_OUT pin from the DP83848 should not be used as the RMII reference clock for the processor/MAC.  This pin will output a 50MHz clock in RMII mode, but the output clock is a simple buffered version of the input clock.  We cannot guarantee the timing of this output clock relative to the RMII data.  This connection is most likely the cause of the issues being seen.  

    The preferred connection would be to source the clock to both the processor/MAC and the Phy directly from the 50MHz oscillator.  I would suggest attempting this modification on a failing board via a jumper wire to see if it resolves the issue.

    Our RMII application note, AN-1405 (Literature Number:  SNLA076) , explicitly states that the 25MHz_OUT pin from the DP83848 should not be used as the RMII reference clock.  I have quoted the text below for your reference:

    The 25MHz_OUT signal is a delayed version of the X1/
    REF_CLK input. While this clock may be used for other
    purposes, it should not be used as the timing reference for
    RMII control and data signals.

    The direct link to the application note is:

    http://www.ti.com/lit/an/snla076/snla076.pdf

    Please let me know if modifying this connection resolves the issue.

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 50 points

    Hello Patrick,

    Thanks for your suggestion.

    This solution works and solves my problem.

    Thanks Patrick.

    Thanks John.

    Nick