[SI-LIST] Re: Shoots
- From: "Novak David" <david.novak@xxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 11 May 2004 08:52:52 -0500
Thanks for all the great responses!
I am also of the opinion that the VDD+0.3V / VSS-0.3V specs. are =
unreasonable for AC conditions. The inductance in the lead frame will =
cause the shoots at the pin to be much larger than at the die. In =
addition, I suspect that the diode action which allows large current =
injections is slow (relatively speaking) to activate. Can anyone provide =
insight into the speed of this diode action?=20
What about the voltage at which the diode action activates? I have been =
told that the diodes are not as good as discrete diodes and won't =
actually turn on until the forward bias is about 2.0V.
Suppose I decide to let the shoots violate the VDD+0.3V / VSS-0.3V =
specs.
1) Is there a rule of thumb spec. that I should not exceed?
2) Is there an experiment that I can perform to get an idea of what a =
particular IC can withstand? For instance, I could inject a controlled =
overshoot into the IC and measure the current into the pin.
3) If a failure is going to occur, will it be developed over time? In =
other words, will I immediately see the error of my ways or will the =
product be in production when the failure occurs?
Thanks,
David
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Ingraham, Andrew
Sent: Monday, May 10, 2004 9:53 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Shoots
In my opinion, the VDD+0.3V / VSS-0.3V spec is overly conservative, and =
it
is almost definitely a DC spec where AC transients aren't included or
weren't considered. They are probably "covering their asses" so to =
speak,
and never bothered looking at their ICs in anything other than a =
carefully
controlled test environment.
In a real world environment with signals that are not point-to-point, it =
is
very difficult if not impossible to consistently maintain signal =
integrity
to that degree.
Another consideration is where the overshoots are observed. Larger
overshoot can be tolerated (and will often be present) at IC pins than =
at
the die pads.
The causes of overshoot vary, but in many cases a root cause is the =
driver
source impedance lower than the trace impedance. Sometimes this is =
desired.
If you increase the source impedance, overshoot eventually goes away, =
but
with side-effects.
Regards,
Andy
------------------------------------------------------------------
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
Other related posts:
