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Original question:

AM5748: IBIS question, how to select proper model for DDR drive strength?

TDA3LX: Buffer model "resistor termination value"

Jin Hui Wong
Prodigy 60 points
Part Number: TDA3LX

Referring to the thread title, i have here a bunch of buffer models for one of the pins of the TDA3LX.

SR000_DRV48_1P8_M#100 

SR011_DRV40_1P8_M#101 

SR010_DRV40_1P8_M#102 and etc....

I have a few questions regarding these buffer models:

1) If i would like to run a signal integrity simulation, for a DDR3L SRAM I/O type of trace, which models do i choose? (I have other buffer names that don't start with SRXXXX, but are DDR3L_ODT_60_1P5_M#118, DDR3_ODT_120_1P5_M#120 etc, so am looking for something like a general guideline to choosing buffer models.)

2) If the standard termination value is recommended to be 50ohms, should a 40 ohm or 60 ohm, or even higher, be chosen? (The list i have doesn't show any buffers with a 50 ohm termination, be it on die or without on-die termination?

3) What is the standard procedure in selecting the MOST appropriate buffer model for a selected trace such as the the mentioned DDR3 trace?

Thanks.

  • 0
    TI__Mastermind 38170 points

    Hi,

    The models named DDR*_ODT_* should be used for input (READS), and the models named SR*_DRV*_1P* should be used for output (WRITES).

    For the output models,

    • SR* defines the slew rate setting, where SR000 is the fastest, and SR111 is the slowest. 
    • DRV* is the drive strength (34 ohms,  40 ohms, ...)
    • 1P* is the IO voltage (1.8V, 1.5, 1.35). You should use a model ending in 1P35 if using DDR3L.

    For the input models,

    • ODT is the on-die termination strength.

    Best regards,
    Kevin

  • 0 in reply to Kevin S
    Prodigy 60 points

    Hello.

    Thanks for the clarification.

    A few follow up questions about the clarification:

    1) Regarding the On Die Termination strength, if PCB termination value is 50 ohm, which ODT value should be chosen?

    2) What is Drive Strength?

  • 0 in reply to Jin Hui Wong
    TI__Mastermind 38170 points

    Hi,

    As a suggestion, you may start with 60 ohm ODT and compare the simulation results against other settings. 

    Best regards,
    Kevin