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C674x mDDR / LPDDR

Mike B
Prodigy 120 points
Other Parts Discussed in Thread: OMAP-L138, TMS320C6748

Hello everyone,

 

I’m a little confused about the specification for mDDR memory which can be used with the C674x DSPs. According to the datasheet for the C6746, one must use a -400 speed-grade part (see section 6.11.3.2). However, the maximum clock speed allowed is 133MHz for mDDR, suggesting an LPDDR266 part or better is all that is really required.

Looking at the OMAP-L138/TMS320C6748 EVM from LogicPD, they’re using an mDDR/LPDDR chip which has a data rate of “LPDDR333”. Thus I assume the -400 requirement only applies to DDR2, and not to mDDR. Can you please confirm that an LPDDR333 memory is suitable? We had hoped to use a LPDDR333 part.

Thanks,

Mike

 

 

  • 0
    TI__Mastermind 27585 points

    Yes that is acceptable. Currently we just list one number for mDDR and DDR2, but since the mDDR is run at a slower clock rate, the LPDDR333 can be used.

    Jeff

  • 0 in reply to jc-ti
    TI__Genius 13045 points

    JC,

    Thanks for the information.  So, I'm still a little confused.  Maybe it's because of my unfamiliarity with DDR in general. 

    The DS for C6746 in Table 6-24, Parameter 1: JEDEC DDR2/mDDR Device Speed Grade states Min spec as DDR/mDDR-400.  I am interpretting this to mean that you need to use -400 or higher speed.  Whereas you statement on -333 speed LPDDR seems to be a lower speed grade.  Am I misunderstanding the spec, or is there a typo?

    Thanks.

  • 0 in reply to TommyG
    TI__Mastermind 27585 points

    Yes you can use the -333 speed LPDDR, as it looks like the datasheet did not breakout separate entries for mDDR and DDR2.

    Jeff

  • 0 in reply to jc-ti
    TI__Genius 13045 points

    Jeff,

    Thanks for the feedback.  Does this mean that the DS needs to be updated to say -400 min for DDR2 and -333 min for mDDR?

    Regards.

  • 0 in reply to TommyG
    Prodigy 120 points

    Thanks, everyone. Regarding the datasheet updates:For mDRR, wouldn't it be a minimum of LPDDR200 (with a clock frequency of 100MHz as per datasheet table 6-22) or LPDDR266 (with a clock frequency of 133MHz)? I agree the minimum for DDR2 is DDR2-400, since that is the lowest DDR2 speed grade defined in JESD79.