This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DP83TG720S-Q1: DP83TG720S-Q1 PSD fail ,want to Improve the MDI's driving ability

Part Number: DP83TG720S-Q1

I use the DP83TG720S-Q1, have the same problem,PSD is fail  at about 400MHz.

Is there any Reg to solve it? such as Improve the MDI's driving ability.

I have read DP83TG720S-Q1‘s datasheet and  SNLA371,just find two points as below. These way just for  CLKOUT and RGMII pads. 

For MDI, there is not mentioned.

Thanks & Best regards

shuai

  • Hi Shuai,

    Please share the MDI section of the schematic and layout. We can make a register adjustment if necessary, but adjustments required outside of SNLA371 may point to a different issue.

    Thanks,

    David

  • Hi David

    The fellow is the schematic ,and the layout is inconvenient to share.

    We've checked the code,compare with section 3 of SNLA371,the Register configuration is same ,except the last Register 0x056A is not configured.

    Now,we read the Register 0x056A is 0x1F59. And checkt the newest datasheet in TI.com, havn't saw the description.

    So,can you tell me what register can be adjusted,and how?

  • Hi Shuai,

    Your schematic is not correct, this explains the issue. Please see Figure 8-1 of the datasheet for the correct MDI circuit.

    Thanks,

    David

  • Hi david

    I'm sorry provide a wrong schematic. The correct  schematic as below.

    The different from datasheet is the MDI coupling capacitor,here is 10nF,but datasheet is 4.7nF.

  • Hi Shuai,

    Please send me the actual schematic so I can verify this is the case.

    I see several reasons this may be failing PSD compliance testing. 

    1. Your MDI is not compliant with the datasheet. Please change R3 to 100kohm and C1 to 4.7uF as recommended

    2. The presence of the FPC connector on the MDI path. How long is the trace between PHY and MDI cable?

    3. Please try removing the ESD diodes to see if this has any effect.

    Thanks,

    David

  • Hi David

    For information safety,I can't send you the actual schematic here.

    But I think My visio diagrammatic sketch is Very detailed.

    1.  The differences among 105kohm&10nF and 100Kohm&4.7nF are similar. Both failed in 400MHZ nearby.

    2.I have Marked the length in My visio diagrammatic sketch. Actually, the total layout length in my board is longer than TI's Ethernet Media Converter Board. By the way,I tested in different point have different result. I know the longer layout can bring morn losses.But in my machine,It has been Shortest.I can't let it shorter because Mechanical structure limited. so i wanna know how can I Improve the MDI's driving ability?

    3、 Removing the ESD diodes  has no effect. The ESD's diode capacitance max is 2pF .

    Notes:Above Comparison test results TEST in different Mechanical structure.

  • Hi Shuai,

    I see a passing result in number 2. Can you please explain what you mean by "By the way, I tested in different point have different result"? Please send me a picture of your setup and where you are measuring from in each case.

    Thanks,

    David

  • Hi Shuai,

    To adjust the MDI driving capability, you can write to register 0x0405. You should be reading a value of 0x5800 after configuration of the device according to SNLA371. Try increasing the value by one (write 0x5C00 to register 0x0405). Rerun the PSD test and increase this value as necessary.

    Higher swing will result in higher emissions so this may impact EMC/EMI testing. Please note TI's EMC testing was conducted using the value of 0x5800 for this register, so you will need to evaluate a higher value on your own.

    Thanks,

    David

  • Hi david

    Thanks for your answer,I willl try it and test EMC again

  • No problem. Let me know.

    -David

  • Hi david,I have tried to set this register bit15-10 to 011100b.The PSD barely PASS.And the EMC is ok.so that I will hold this configuration,is there more risks for this change?

  • Hi Shuai,

    No further risks if EMC is okay.

    Thanks,

    David