[SI-LIST] Re: Maximum Current
- From: "Muranyi, Arpad" <arpad.muranyi@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 28 Apr 2006 10:39:40 -0700
Ishan,
Aside from the fact that Tony was just joking, the reason for
those ridiculously high currents in SPICE and consequently
IBIS models is usually an omission in the SPICE process
parameters for the diode or FET parasitic diode.
The resistance properties of the material (Si) defaults to zero
in SPICE and many SPICE models do not have real data for it.
Please note that the text book equation of the diode current
is only true for the junction, and it is highly exponential.
(You can verify this by plotting it in EXCEL). But remember,
the junction is surrounded by significant amount of
***resistive*** material. As soon as you account for the
resistance, your maximum current will be limited to be no
more than Ohm's law permits.
For example, if your resistive properties would add up to
about 1 Ohm (which it not too uncommon), at -5 V you could=20
only get 5 A (if the junction is an ideal short). On the
other hand, the current of the (ideal) diode equation would
give you umpteen zillion Tera amps at -5 V...
Arpad
---------------------------------------------------------------
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Ihsan Erdin
Sent: Friday, April 28, 2006 9:05 AM
To: tony_dunbar@xxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Maximum Current
I don't think an ibis model could be the correct source for that info
especially when it is derived from spice sims. It may be because of the =
high
nonlinearity of the physical models for some devices that towards the =
end
points of the voltage sweep the current may climb to ridiculously
high values, which would melt a thin wire immediately due to =
jule-heating. I
guess that's why some vendors simply cut the current data at the runaway
point and set it to zero resulting in funny looking curves. I think
the correct answer lies in a thermal analysis. For interested, Synqor =
has a
good app. note on this topic:
http://www.synqor.com/documents/appnotes/appnt_Thermal_Relief_Study.pdf
Regards
Ihsan
On 4/27/06, Dunbar, Tony <tony_dunbar@xxxxxxxxxx > wrote:
>
> Jin,
>
> According to many IBIS models, I think it's about 50kA.
>
> Regards (and apologies),
> Tony
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