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Doubt in RM57L843 demo board (TMDXRM57LHDK)

EASHWAR ARIVAZHAGAN
Intellectual 315 points
Other Parts Discussed in Thread: RM57L843

Dear Friends,

I am designing a board using RM57L843 in which i have a requirement to interface SDR - SDRAM  and FRAM (1No.). I have connected all the required address, data and control signals directly to the memory device without any buffer in between. Now when I referred Hercules RM57Lx demo kit (TMDXRM57LHDK), I found that : EMIFNDQM1_ETMD14, EMIFNDQM0_ETMD15, EMIF_CKE & EMIF_nCS0 go through U47 (SN74CBTLV3245ARGY).

Kindly suggest me if a buffer or a FET switch is required or not.

  • 0
    TI__Guru**** 184496 points

    HI Eashwar,


    Please refer to the IBIS model for LC4357. 

    http://www.ti.com/lit/zip/spnm063



    You can use IBIS models to simulate the drive of the signal and for the purposes of signal integrity. 

    Can't answer your question as is. You really need to consider the speed of the SDRAM  as well as the physical layout (i.e. distance and loading on traces between the EMIF and your SDRAM). Most likely answer is that you don't need extra buffering - you probably have more of a need for termination than buffering.

  • 0 in reply to Charles Tsai
    TI__Guru 68830 points
    Charles,

    The CBT is actually a crossbar switch - no buffering.

    Eashwar,

    That much said - Charles answer still applies except I'd say likely the answer is no CBT needed if you are careful in your layout and keep traces short (try for < 2in). Termination resistors probably are needed and you can use the IBIS to analyze this aspect.
  • 0 in reply to Anthony F. Seely
    Intellectual 315 points

    Thank you Charles and Anthony F. Seely for your kind reply. I made sure that trace length are within 2in and implemented series termination.

    I need a clarification on TMDXRM57LHDK sch. I found that  in part U1F (RM57L843) pin no. V19 & W18 have names which mismatches with datasheet. Please clarify.

  • 0 in reply to EASHWAR ARIVAZHAGAN
    TI__Guru**** 184496 points
    Hi Eashwar,
    V19 and W18 are both AD2IN[24]. This is correct. V19 and W18 are the corner pins. Normally the corner pins are used for power pins. The corner pins are also more susceptible to stress concern. Since we want to bring out additional ADC inputs on LC4357 we use the corner pins. We use 2 corner pins to address the stress concern.