FreeLists / si-list / [SI-LIST] Re: Effects of overshoot/undershoot on long-term reliability

["Dimiter Popoff" <dp@xxxxxxxxxxx>]

I guess it would depend not just on the peak voltage but on
the energy in that peak (i.e. peak area).
 I don't know what technology the DSP is - overshoots
like this should matter somewhere about 130 nm and below,
if older, chances are you will face no problems (but
we'll know for sure after several years :-).
If 130 nm and below, it would really be an interesting
experiment to have one board constantly on until it fails  - after
days, months or years ? Really interesting, if you make such an
experiment please keep us posted.

Dimiter


------------------------------------------------------
Dimiter Popoff               Transgalactic Instruments

http://www.tgi-sci.com
------------------------------------------------------


>  -------Original Message-------
>  From: Mikhail Matusov <matusov@xxxxxxxxxxxx>
>  Subject: [SI-LIST] Effects of overshoot/undershoot on long-term reliability
>  Sent: Mar 03 '06 17:34
>  
>  Dear experts,
>  
>  I designed a card based on the ADI TS201 TigerSHARC EZ-KIT evaluation board
>  schematics. The TS201 has 2.5V 3.3V-tolerant I/Os . On this board it is
>  directly connected to a 3.3V Micron SDRAM.  Unfortunately, we had not
>  simulated this interface before going into the layout. When we did we found
>  that there is a huge overshoot on SDRAM read reaching almost 5V at the DSP
>  pins. Our SI subcontractor recommends adding series terminations at the
>  SDRAM pins. At this point it would mean major PCB redesign. I pulled an
>  EZ-KIT card and captured the read cycle to verify the simulation results and
>  found that the board behaves exactly as in simulation, i.e. the DSP chip is
>  constantly subjected to this huge overshoot. However, the board works fine.
>  So, I was wondering how I could estimate the risk of leaving the design as
>  is?
>  
>  
>  Thanks,
>  =======================
>  Mikhail Matusov
>  Hardware Design Engineer
>  Square Peg Communications
>  Tel.: +1 (613) 271-0044 ext.231
>  Fax: +1 (613) 271-3007
>  http://www.squarepeg.ca
>  
>  
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