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Original question:

AM3358 DDR3 PCB length matching

AM3352: DDR3 layout max length

Tony Tang
Mastermind 30667 points

Part Number: AM3352

Customer ask why there is a MAX length requirement to A3 in the figure, they think ensure clock and control signals A1+A2 length equal to the first DDR chip, then ensure A3 between two DDR3 chip equal is adequate. 

As the Max 660mils is hard to meet in layout, customer need to extend the A3 length. is it OK? if not, please help to explain?

  • 0
    TI__Guru* 95721 points

    The restriction is necessary to ensure the timing delays to the second memory device can be programmed adequately, and will ensure the device placement distance is met.  If they exceed the requirement, there may be a timing issue in the design.  Note that A3 is only applicable if they are using two x8 devices.  Most AM335x designs use a single x16 device.

    Regards,

    james   

  • 0 in reply to JJD
    TI__Mastermind 30667 points
    JJD said:
    The restriction is necessary to ensure the timing delays to the second memory device can be programmed adequately,

    Does it relate to leveling?

  • 0 in reply to Tony Tang
    TI__Guru* 95721 points

    Yes, the software training algorithm can only adjust delays depending on bit field widths, so the trace lengths need to be constrained to accommodate this. 

    Regards,

    James