• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 101 subscribers
  • Views 580 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

Original question:

AM5726: tpiu trace

AM3874: DDR3 VTT termination resistor remove

shigehiro tsuda
Mastermind 9490 points
Part Number: AM3874

Hi,

Our customer is troubled with DDR3 access failure.

The cause of DDR3 access failure is known to be due to waveform distortion of the DDR3 power supply(VTT).
As a workaround, we are considering removing the termination resistor where the DDR3 address/command signal is pulled up by VTT via the termination resistor.

This workaround has passed the DDR3 compliance test, and the DDR3 input signal is within the rating of the IC.
I know that it is recommended to pull up VTT with a termination resistor in the wiring of AM3874 and DDR3, but if there is no problem in the compliance test etc., can I think that the above workatound are satisfactory as AM3874?
If you have any other concerns or items to be confirmed, please let us know.

Best Regards,
Shigehiro Tsuda

  • 0
    TI__Guru**** 170625 points

    Hi Shigehiro,

    Below you can find some Questions and Answers I have found in some internal sources:

    Question: for customers with limited board space, we wonder if the DDR could be implemented without serial termination resistors at all?

    Answer: DDR3 will require parallel termination to VTT for the address and control bus. No terminators are required on the DDR3 data bus due to ODT. The problem is the DDR3 bus cannot be made short enough to be short from an SI point of view.  In this case, what most people call short is really medium, which is really bad because there is little loss.  Thus, without termination, the lines will ring really bad.  Longer traces are actually better because they have enough loss to dampen some of the ringing. That said, the address termination for DDR3 should not take up that much space.

    Question: Can we avoid DDR VTT termination on this design? If so, how can we implement it?

    Answer: Yes, this is possible, but at your own risk (you will need precise SI and timing simulation), as TI does not recommend DDR topology which do not have VTT terminations.

     


    We have also some info in below e2e threads:

    I would also suggest you to make DDR3 memory stress test. You can adjust below test for your custom board:

    Regards,
    Pavel