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TDA2: DDR3 Interface pullup resistors of Address/Data Bus

Joseph Wang Wang
Intellectual 520 points
Part Number: TDA2
Other Parts Discussed in Thread: DRA756, , , TPS51200-Q1

We study TDA2H/TDA2S/TDA2P reference schematics, we found difference between DDR3 interface schematics:

1. There are not pullup resistors with VTT on TDA2H/TDA2S reference schematics, but some technical support engineers recommend we add pullup resistors for TDA2H/TDA2S/DRA756 schematics;

2. The reference schematics of TDA2P-ACD and TDA2P-ABZ include the following pullup resistors.

Would you please help us to explain following schematic usage and function ?

  • 0
    TI__Mastermind 18640 points

    Hi Joseph,

    These resistors are terminations to VTT.

    If the memory type is DDR3/3L, TI has validated and supports only the fly-by topology of the C/A bus for each EMIF, with termination to VTT at the bus end. This implies that a dedicated VTT source (stand-alone regulator IC, or part of a complex DDR power solution) is employed in the design and that it is supplying the termination resistors of both EMIFs (the recommended automotive-qualified part is the TPS51200-Q1; it generates also the VREF voltage). If the ECC lane of EMIF1 has been utilized in the design, usage of the VTT-terminated fly-by topology is almost unavoidable for a 32-bit system (due to the odd number of memory chips and very difficult balancing otherwise).

    Regards,

    Stan