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C6457 board routing and layout questions, SERDES and DDR.

Bryan Busacco
Expert 1215 points

 

C6457 board routing and layout questions, SERDES and DDR.

We are going to be using the TMS320C6457CGMH2 DSP. SERDES implementation guide spraay1a.pdf Section 2.2 table 2 gives a minimum trace width of of 4mils for a 10inch trace. We are going to limit the trace length to 4inches or less. Can we use a trace width of 3.3-3.8mils? (probably 3.6mils) We wil be using 370HR(~FR4) material and 0.5oz copper ]

We are going to be using the TMS320C6457CGMH2 DSP. The DDR guidelines require a continuous ground plane. Our PCB will be ~3" square. I will need to use routing layers as small ground planes to get the number of controlled impedance layer needed for this route. TOP/GND1/SIG1/SIG2/GND2/BOT Can I route on SIG1 and add a GND3 puddle on the SIG2 layer?]

Thank you, Bryan Busacco

 

  • 0
    TI__Mastermind 46460 points

    SERDES question:

    We are going to be using the TMS320C6457CGMH2 DSP. SERDES implementation guide spraay1a.pdf Section 2.2 table 2 gives a minimum trace width of of 4mils for a 10inch trace. We are going to limit the trace length to 4inches or less. Can we use a trace width of 3.3-3.8mils? (probably 3.6mils) We wil be using 370HR(~FR4) material and 0.5oz copper ]

    Response:

    Due to the skin effect, narrower traces result in increased loss.  However, since your maximum length is only 4inches.  You will have plenty of margin.

     

    DDR2 routing / board stackup question:

    We are going to be using the TMS320C6457CGMH2 DSP. The DDR guidelines require a continuous ground plane. Our PCB will be ~3" square. I will need to use routing layers as small ground planes to get the number of controlled impedance layer needed for this route. TOP/GND1/SIG1/SIG2/GND2/BOT Can I route on SIG1 and add a GND3 puddle on the SIG2 layer?]

    Response:

    Placing a copper pour on SIG1 that is either GND or the DDR2 Supply voltage is a good way to isolate these DDR signal routes.  If the pour is GND, make sure there are multiple vias between it an the other GND planes and the connected decoupling.