[SI-LIST] Re: min/max trace length

Always solve for timing requirements.  Flight time depends on physical 
distance and effective eR.  Stripline traces see the material eR, 
microstrip see a mix of the material and air.  Once you know the fixed 
timng of your chips then you can start to build a budget for flight 
time, and SI effects like loading, ringback, crosstalk induced push-out, 
pull-in etc.  At 100MHz SDR you can likely safely tolerate at least 3ns 
flight time which would be at least 17.7".

 From a practical standpoint flash memory timing is so slow that you 
would have to have enormous trace runs before flight time becomes a 
significant issue.

Steve
bernd schuster wrote:
> Hi,
> I often read minimum and maximum trace lengths in datasheets of sdram chips
> (for example). As I figured out the length depends on the setup margin and
> hold margin.
>
> If I have a setup margin of 2ns and hold margin of 0.8ns (e.g.)  - which
> formulas will tell me the min. and max. trace length? The system is working
> at 100MHz with a fall time / rise tim of 2ns.
>
> How do I have to modify the formula when I want to calculate the timing for
> an external flash memory (without clock traces)?
>
> best regards
> Bernd
>
>
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