[SI-LIST] Re: Overshoot / Undershoot

There are 5V tolerant 3.3V PCI devices that comply with both the 5V 
tolerant specification and the 3.3V CMOS only specification.  In these 
devices, there is either an option to tie the clamp to a different 
voltage (very rare), or to disable the 3.3V clamp for 5V tolerant 
operation.  Often, the clamp is included in the IBIS model, because the 
person doing the extraction neglected the dual-mode of clamp operation.

Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax

http://www.teraspeed.com

Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC



Tom Dagostino wrote:
> Ken
>
> I have never seen a 5V tolerant 3.3V device that had a clamp device tied to
> 3.3V.  I have seen a few 5V tolerant parts that had clamps that turned on
> past 5.5V.  99.999% of the devices we have measured have ground clamps.  If
> you have overshoot (defined as a short duration spike above the normal high
> or low level of the driver) of 2 Volts in the rising direction you will
> likely also have it on the falling edge.  You will need to control it in
> both directions.
>
> Tom Dagostino
> Teraspeed(R) Labs
> 13610 SW Harness Lane
> Beaverton, OR 97008
> 503-430-1065
> tom@xxxxxxxxxxxxx
> www.teraspeed.com
>
> Teraspeed Consulting Group LLC
> 121 North River Drive
> Narragansett, RI 02882
> 401-284-1827
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Ken Willis
> Sent: Friday, January 13, 2006 6:25 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Overshoot / Undershoot
>
>
> Hi,
>
> I had a slightly different question related to this. Some 3.3V devices
> are 5V-tolerant, and per their specs can tolerate quite a bit of
> overshoot. Let's assume for a minute that the overshoot you will see
> is within the device's spec, and is such that the timing will still be
> OK. So everything should be functional and within spec for SI/timing
> purposes.
>
> Some of the EMI folks I have worked with in hardware development have
> expressed concern about leaving a bus like this with excessive (ex. 2v)
> overshoot, even if it is within the device specs. The thinking here is
> that every time the bus switches, it can have 64 (or however many) bits
> with overshoot at their receivers, turning on their associated clamp
> diodes,
> and shooting nice spikes of current into the power/ground system. Some
> view
> this as a bunch of little noise sources, exciting the planes, and
> potentially
> lighting heatsinks, cables, other critical components, etc. nearby.
>
> So for EM compliance reasons and general robustness of the system, it
> seems
> like it may be desireable to terminate buses of this nature, even if it
> is
> OK by traditional SI/timing points of view. I was curious to see if
> folks
> are generally content to let buses like this thump away with the
> overshoot,
> or if they usually strive to terminate them in their typical
> methodologies.
>
> Ken
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Bill.Cohen@xxxxxxxxxxxxxxxx
> Sent: Thursday, January 12, 2006 7:45 PM
> To: andrew.seddon@xxxxxxxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Overshoot / Undershoot
>
> Andrew,
>
> JEDEC has an overshoot/undershoot specification for DDR2 a 1.8V
> technology.
> Older technologies relied on an absolute voltage but the newer
> technologies work on an absolute maximum and an area (above/below power)
> of stress. This area limits the overshoot stress into a maximum stress
> for a period of time. The long time reliability of the gate oxide is at
> issue here and the duty cycle of the signal also comes into play. Look
> at the DDR2 datasheet
> (JEDEC.org) and look at the stress model they have for
> undershoot/overshoot of input signals. We have incorporated this model
> into our latest specifications.
>
> Best Regards,
>
> --------------------------------------------------------------
> | Bill Cohen
> | Toshiba America Electronic Components
> | Mixed Signal Design Group
> --------------------------------------------------------------
>
>
> =20
>
>              "Andrew Seddon"
>
>              <andrew.seddon@ca
>
>              msig.co.uk>
> To=20
>              Sent by:                  <si-list@xxxxxxxxxxxxx>
>
>              si-list-bounce@fr
> cc=20
>              eelists.org
>
> =20
> Subject=20
>                                        [SI-LIST] Overshoot / Undershoot
>
>              01/12/2006 07:30
>
>              PM
>
> =20
>
> =20
>
>              Please respond to
>
>              andrew.seddon@cam
>
>                  sig.co.uk
>
> =20
>
> =20
>
>
>
>
>
> Hello,
>
>
> I was wondering if anybody had an idea of what is a typically acceptable
> bad but workable overshoot/undershoot on a 3.3V system? For example I
> see some memory IC's can take transients upto 5.5v where as the
> datasheet max is say
> +0.3. Obviously this figure is based on DC.
>
> I presume the major effect's of over/under shoot are to reduce working
> life of the IC and make the circuit potentially fail at temperature
> extremes?
>
> So when you guys analyse overshoot/undershoot how do you decide if it's
> acceptable?
>
> Kind regards,
>
> Andrew
>
> ------------------------------------------------------------------
> 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
>
>
>
>
>
> ------------------------------------------------------------------
> 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:    =20
>               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
>  =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:
> 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
>
>
>
> ------------------------------------------------------------------
> 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
>   
>
>   

------------------------------------------------------------------
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

Other related posts: