If your design exceeds the design requirements for the chip then you cannot guarantee reliability.=20 If you say the problem in simulation - then I suggest you bite the bullet and relayout your board and add the series Rs. Best Regards Charles Grasso Senior Compliance Engineer Echostar Communications Corp. Tel: 303-706-5467 Fax: 303-799-6222 Cell: 303-204-2974 Pager/Short Message: 3032042974@xxxxxxxx Email: charles.grasso@xxxxxxxxxxxx; Email Alternate: chasgrasso@xxxxxxxx -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Edi Fraiman Sent: Wednesday, March 08, 2006 6:44 AM To: matusov@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: 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.=3D20 Best regards, Edi Fraiman=3D20 > -----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 >=3D20 > Dear experts, >=3D20 > 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? >=3D20 >=3D20 > Thanks, > = =3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D= 3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D > Mikhail Matusov > Hardware Design Engineer > Square Peg Communications > Tel.: +1 (613) 271-0044 ext.231 > Fax: +1 (613) 271-3007 > http://www.squarepeg.ca >=3D20 >=3D20 > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field >=3D20 > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list >=3D20 > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field >=3D20 > List FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ >=3D20 > List technical documents are available at: > http://www.si-list.org >=3D20 > 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 >=3D20 ------------------------------------------------------------------ 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: =20 //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 =20 ------------------------------------------------------------------ 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