Subject: RE: [IBIS-Users] FW: Extreme currents????
From: Mohan, Prabhu (Prabhu.Mohan@actel.com)
Date: Thu Jul 11 2002 - 18:01:40 PDT
Hi all,
I've come across a few kilo Amps(!) in the -3.3V region while generating
IBIS models. In all the cases the reason was the clamp-diodes (with zero R).
Here is what I do. For all the transistors that are directly connected to
the PAD, I just stick a resistor (say 5ohms) between substrate and ground
(or power). This brings the current down to "reasonable" levels. Once some
silicon measurements are done I just tune the resistors that I inserted.
Please tell me if there is anything wrong with the above method.
Ofcourse, this means sifting through the spice netlist but it has worked
quite well so far.
Prabhu/~
-----Original Message-----
From: dbcox [mailto:dbcox@micron.com]
Sent: Thursday, July 11, 2002 11:59 AM
To: 'Kim Helliwell'; Lynne Green
Cc: Chris.Dewitt@motorola.com; ibis-users@eda.org
Subject: RE: [IBIS-Users] FW: Extreme currents????
Well it looks like everyone has put in their 2 cents worth on this subject.
For what it is worth I loved the model that had 900 AMPS at -3.3V. It was
my favorite. Aside from all the other obvious comments that have been made
How wide would the trace on the PCB have to be to carry this type of load?
Would this device be classified as a fuseable lead frame? It is obvious that
model makers could do a better job in QA'ing their data. There is something
to
be said also about ibis itself here. If the specification allows unrealistic
data to be acceptable then model makers will continue to provide it. Perhaps
extremely high currents should be changed to an error instead of a warning.
This would force correction to this issue at the source. Couldn't resist
commenting on this issue it is one of my favorites........BC
-----Original Message-----
From: Kim Helliwell [mailto:kimgh@apple.com]
Sent: Wednesday, July 10, 2002 4:50 PM
To: Lynne Green
Cc: Chris.Dewitt@motorola.com; ibis-users@eda.org
Subject: Re: [IBIS-Users] FW: Extreme currents????
Frankly, I wish that suppliers of models (whether IBIS
or SPICE) would stop using these "ideal" diodes that
allow such large currents. I don't understand how anyone
can look at such results and think that's OK to ship to
customers!
Maybe they just don't look, but that's hardly an acceptable
excuse, either.
There, I feel better now!
Kim
On Wednesday, July 10, 2002, at 03:19 PM, Lynne Green wrote:
> Hello, Chris,
>
> Different EDA tools have different upper limits on currents that can be
> handled
> by the simulator.
>
> The warning is needed because "Spice" models that use the default series
> resistance (0.0 ohms) for diodes and junction leakage currents result
> in large
> IBIS table currents (often above 1 MegAmp). Most EDA tools don't go
> quite
> _that_ high.
>
> Best regards,
> Lynne
>
>
>
> -----Original Message-----
> From: John Angulo [mailto:jangulo@innoveda.com]
> Sent: Tuesday, July 09, 2002 6:02 PM
> To: ibis-users@eda.org
> Subject: [IBIS-Users] FW: Extreme currents????
>
>
> The following is forwarded on behalf of Chris DeWitt at Motorola TCG.
> Please send all private replies to Chris.Dewitt@motorola.com.
>
> John Angulo
> IBIS Open Forum Postmaster
> -----------------------------------
>
> If I run IBISCHK3 on many models I download I get an "Extreme currents
> present" warning.
>
> What are the limits on currents in the VI tables? I can't find it
> documented anywhere.
>
> Thanks
>
> Chris DeWitt
> Principal Staff Engineer
> Motorola TCG
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Apple Computer
kimgh@apple.com
408 974 9936
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