Hi, You may have already tried this: 1. Is it possible to vary the driver impedance in the DRAM ( OCD / other driver impedance control in EMRS reg) then set it to weak/ low. 2. Is it possible to operate the DRAM at its lowest allowable Vdd (3.3V - 10%) that may get you some margin in the overshoots? regards, Jai --- Mikhail Matusov <matusov@xxxxxxxxxxxx> wrote: > Edi, > > Thanks for your suggestion. We have actually tried > this. It does help, but > only a tiny bit compared to what is needed... > > ======================= > Mikhail Matusov > Hardware Design Engineer > Square Peg Communications > Tel.: +1 (613) 271-0044 ext.231 > Fax: +1 (613) 271-3007 > http://www.squarepeg.ca > > > > > ----- Original Message ----- > From: "Edi Fraiman" <Edi.Fraiman@xxxxxxxxxxxxx> > To: <matusov@xxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx> > Sent: Wednesday, March 08, 2006 8:43 AM > Subject: RE: [SI-LIST] Effects of > overshoot/undershoot on long-term > reliability > > > > Hi, > > > > I could suggest you maybe another way solve the > overshoot/undershoot > > problem. > > Try simulating the SDRAM interface with different > traces thickness (I > > think that more narrow traces should dump the > overshoot/undershoot).If > > you achieve better overshoot/undershoot results > during simulation than > > you will ask from PCB manufacturer only change the > traces thickness > > without relayout and adding serial resistors. > > > > Best regards, > > Edi Fraiman > > > > > -----Original Message----- > > > From: si-list-bounce@xxxxxxxxxxxxx > > [mailto:si-list-bounce@xxxxxxxxxxxxx] > > > On Behalf Of Mikhail Matusov > > > Sent: Friday, March 03, 2006 5:34 PM > > > To: si-list@xxxxxxxxxxxxx > > > Subject: [SI-LIST] Effects of > overshoot/undershoot on long-term > > > reliability > > > > > > 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 > > > > > > > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in > the Subject field > > or to administer your membership from a web page, go > to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the > Subject field > > List FAQ wiki page is located at: > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > List technical documents are available at: > http://www.si-list.org > > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are > viewable at: > http://www.qsl.net/wb6tpu > > > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu