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TMS320C6678: DDR_TERM configuration

Nancy Wang
Expert 8210 points
Part Number: TMS320C6678

Hi,

The resistance connected to the PTV15 pin on the customer's hardware is 1% of 44.2Ω. It is okay to configure DDR_TERM as RZQ/6 on several of the boards, but one of them does not work, and RZQ/4 is all OK. How to configure the DDR_TERM parameter? How to calculate this parameter based on hardware?

  • 0
    TI__Expert 8210 points

    Hi,

    May I know is there any update for this case?

  • 0 in reply to Nancy Wang
    TI__Mastermind 26735 points

    Hi Nancy,

    Unfortunately, I personally do not have much experience with this device, so additional insight / confirmation from others inside TI may be required. However, it looks like the PTV15 pin is used to calibrate the drive strength to 50 Ohm. My understanding is that you would generally want to try and impedance match the drive strength, termination, and PCB trace. However, it does not look like DDR_TERM provides a 50 Ohm option, so likely using the 40 Ohm or 60 Ohm termination value would be best. Per your observations, it looks like 60 Ohm is required. You might check with the customer to better understand the trace impedance, and compare to the EVM.

    Additionally, you might run simulations with the SOC and DDR IBIS models, varying the termination to observe changes in the waveform. You might also consider probing the signals to gain more insight.

    Regards,
    Kevin