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AM335x DDR2 termination resistor distance

Emmanuel Trinidad - Alicea
Genius 10260 points
Other Parts Discussed in Thread: AM3359

Hi Team,

I have been searching the AM3359 datasheet for information regarding DDR2 Signal Termination.  I have found a good souce in Section 5.5.2.2.2.9 (page 157) regarding the amount of resistance necessary.  Unfortunately, the documentation goes on to state:

     "Placement of serial terminations for ADDC_CTRL net class signals should be close to the AM335x device." 

It does not specify a recommended distance between the resistor and the device.  I have also searched within the TRM but have not found any information on the proper spacing.  I would like to be sure the resistors are the proper distance from the device.  Can you please provide me with some recommended spacing measurments (in mm or mils)?

Thanks in advance,

-- Emmanuel

 

 

  • 0
    TI__Guru 62855 points

    Series termination resistors for uni-directional signals should always be located as close as possible to the source.  This is the case for ADDR_CTRL net class signals.

    We realize there are design specific physical limitations that need to be considered when designing a PCB.

    For example, you may need to place decoupling capacitors around the perimeter of the device because they also perform best when located as close as possible to the respective power terminals.  In this case it may be more important to place the high frequency decoupling capacitors in their best popsition first then place the series termination resistors followed by the low frequency bulk capacitors.

    There may be other design details that also need to be considerd which are unique to your specific design, so it is difficult to provide a firm requirement.

    Our recommendation is to locate series terminations for ADDR_CTRL net class signals as close as possible to the AM335x terminals.  However, you may need to apply your best engineering judgement or analyze system performance when evaluating various design trade-offs.

    Using series termination resistors on bi-directions signals may not be as effective as using series termination resistors on uni-directions signals.  Also the location of series termination resistors on bi-directions should be based on the results of signal integrity analysis.

    Regards,
    Paul