Subject: More on series R

From: [email-masked] (Bob Ward)
Date: Wed, 16 Mar 94 6:54:21 CST

Kellee -

You both did and didn't miss something :-).  From the picture given with
the proposal for series resistance, it is the bond wire, pin, bond pad,
and bond lead resistance lumped into one and added in series with the
leadframe.  But in the course of discussion it was mentioned that this was
intended to be a silicon resistance or an element resistance in the case
of a through resistor pack.  That got me thinking about the series
resistance we use as part of some of our ESD networks that appears exactly
in series with the output lead, between the bond pad and the output
transistor ( pair ).  In that case the resistor is saturable in the sense
that the voltage across it continues to increase, but the current through
it limits at some value.  Thus the resistance is a function of the voltage
between the pin, neglecting leadframe and bondwire drop, and the output
point of the driver circuit.  Our situation is somewhat as follows:

                          -----+-----Vcc
                               |
                             |_|
                             |
                        |---o|
                        |    |_
                        |    | |
                        |      |   | Vdrop  |
                        |      |   |<------>|
                  ------|      +-----/\/\/\------ Output pin
                        |      |     Rseries
                        |      |        I|              .   . .
                        |    |_|         |        .
                        |    |           |
                        |----|           |   .
                             |_          | .
                             | |         |.
                               |         |___________________
                         ------+-----Vss                Vdrop

Where the IV curve is that of Vseries.  A similar situation exists on
input pins.

Now I have thought about whether or not this non-linearity would be
captured as part of the normal driver IV curve, and so far have built
about an equal case in my mind that it will and that it won't.  I lean
toward the notion that it will.  In that case, the whole thing is a moot
point anyway.  According to my mail, Bob Ross is also coming down on this
side of the question, which DOES add fuel to that fire.  But if it be not
correctly captured, then perhaps there is a problem here that needs to be
addressed.  I plan to ask my trusty Spice simulator about it tomorrow
( probably today as you read this ). Yes, there is, in theory some
temperature effect on the resistance, but the effect of importance is the
voltage dependence rather than temperature or some even more exotic
effect.

Now I ask the forum for the advice of collective wisdom ... should this be
dealt with as a separate element in the ibis model when the information to
do so is available, or should it lumped into the driver IV curve?  Or
should that question wait until this evening after some simulation
experiments?  :-)
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