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AM3352 DDR3 routing

Jan Switzky
Prodigy 125 points

On page 185 of the AM335X datasheet, it talks about length matching / topologies for the various net classes.  In the diagrams, it shows A1, A2, AS, and AT sections.  Can you tell me what those represent?  I can’t find any reference to them telling what they are.  FYI, I am using a single (x16) DDR3 device, and am not planning to use any termination.

 Thanks.

  • 0
    TI__Guru**** 393215 points
    Hi,

    A1 and A2 are resp. vertical and horizontal segments to first DDR chip. AS is the stump from the trace to the chip and AT is the termination segment. If you use a single chip point-to-point topology you don't need to worry about these. You only need to match total trace lengths within the class.

    I would suggest that (if possible) you copy the Beaglebone Black stack-up and layout directly, as this is a proven design. You can find the PCB files in several formats here: elinux.org/Beagleboard:BeagleBoneBlack
  • 0 in reply to Biser Gatchev-XID
    Prodigy 125 points
    Biser,

    Thanks for your quick reply. This does answer my question. You may want to revise the data sheet to remove that figure from the section on routing to a single DDR3, as it is confusing.

    Regards,

    Jan
  • 0 in reply to Jan Switzky
    TI__Guru**** 393215 points

    Please note that there is a paragraph in section 7.7.2.3.3.9, which says:

    "Figure 7-48 provides an example DDR3 schematic with a single 16-bit DDR3 memory device that does not have VTT termination on the address and control signals. A typical DDR3 point-to-point topology may provide acceptable signal integrity without VTT termination. System performance should be verified by performing signal integrity analysis using specific PCB design details before implementing this topology."