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DDR2 Memory Hardware Question

tdipson
Prodigy 20 points
Other Parts Discussed in Thread: TMS320DM6467

We are working on our senior design project at school that centers around  TMS320DM6467. We are having a hard time getting DDR2 memory chips for this processor becuase most suppliers are requesting that we order large quanties which of course we cannot afford nor do we need.

My question is does the memory interface on TMS320DM6467 require a minimum amount of pins to be connected to the memory chip? The reason for asking this is that most 1.8V 3ns DDR2-667 we are coming across have either 84 or 60 pins. It's looking like we might be able to get the 60-pin (BGA) from Micron (part # MT47H128M8HQ-3 IT:E), but I am a little concerned about the lesser number of pins on the chip especially when compared to the memory chip that was used on the evaluation board which had 92-pins.

Second question, is there a memory density (size) limitation on with  TMS320DM6467? We are thinking of using the 2Gb modules instead of the 1Gb memory density used on the evaluation board. Will this be a problem?

Thanks.

  • 0
    TI__Mastermind 37340 points

    Most of these questions are covered in either the main data sheet or the DDR2 Controller user guide.

    Key points:

    - Must comply with "JESD79D-2A"  standards, which I believe imply other requirements stated in the data-sheet

         - JEDEC 16x DDR2 devices with up to 667 speed grades

         - min ball count of 84 to max of 92, 92 being for legacy purposes

    - also has mx addressable space of 256 MB, or 2048 Gb; however, to reach 2048Gb, I believe you will need two 1024 Gb parts.

    In general, DDR2 layout is very difficult, if PCB traces are too long or not the same length for all data lines you can violate specification real easily; distance between traces can also cause havoc...  We do put out collateral such as http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=spraav0a to help you in this effort. 

        

  • 0 in reply to Juan Gonzales
    Genius 3575 points

    I think you are out of luck on the lower pin count devices.  If you look at the ddr2 chip datasheet, you will see that the difference between the low count and high count devices is the data bus size.  The low ones are 8 bits wide, incompatible with your part.

    DDR2 lead times are outrageous right now, everyone cut their manufacturing capability when the economy tanked and they are starting to run out of inventory just in time for demand to increase.  You might have better luck with very small quantities using a distributor like arrow, digikey, newark, etc.