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TM4C1294NCPDT: M4 ethernet connect

user1359349
Intellectual 450 points

Part Number: TM4C1294NCPDT

hello 

  i have used the TM4C1294NCPDTI for the SC card which communication with linecard，the SC card have completed 3 years ago,and the linecard just finished in this year,for some historical reasons,the SC card must be used capacitor for AC couple,but the OTDR module have a transformer inside it ,so,i must used a transformer connected to OTDR module back to back on linecard ,now it's working well,please refer the below figure

on the M4 side ,i have added 49.9ohm pull up resistor to 3V3, but on linecard ,there are only 5V power supply on it,so ,i connected the CT of transformer to 5V(because,it's AC couple,i think,  it's not important that add different voltages at both side of capacitor)

is there any risk in the linecard design,if change the voltage of CT to 2.5V or 3.3V,whether is better than now? 

please check it ,and give me your advise,thanks 

  • 0
    TI__Guru**** 191886 points

    Hi,

      Since it is AC coupled, I will agree with you to connect the center tap to 5V is the right thing to do on the linecard side. If you still have some doubt, I will suggest you contact your transformer vendor on the linecard for recommendation. 

  • 0 in reply to Charles Tsai
    Intellectual 450 points

    thanks for your replay,for current design,whether the M4 can work safely and communication is stable?

  • 0 in reply to user1359349
    TI__Guru**** 191886 points

    Hi,

      In our TM4C129 system design guideline, we show the recommended connection to the external transformer and protection diode. Since you have mentioned that it is working well, I have no reason that it will not work. One thing I'm not sure is if you have the protection diode. Please refer to the system design guideline for details. I also strongly suggest you contact the transformer vendor if they have any comments with the CT connecting to 5V.