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

[Jai Shanker <jswarrier@xxxxxxxxx>]

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:
> http://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:     
>               http://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:
http://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:     
                http://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