[IBIS-Users] I/O model with dynamically changing pullup

Dear all,

 

I have a special case where the pullup of an I/O pin changes dynamically.
This is how it works:

 

1.       The I/O has a 100kOhm resistor pullup in parallel with the clamp 

2.       While the pin is HIGH, it can be pulled LOW externally - behaving
like a open-drain I/O with a 100K pullup

3.       When the pin is pulled LOW by the device - it is a strong pull-down

4.       Here is the problem:

When this pin is pulled HIGH from a LOW state - a strong internal pullup
acts on it for (~)1us - after this time, the strong pullup is disabled and
it acts like the point 2 above.

 

Sequence:

Pin is LOW -> Pulled high with a strong pullup (20Ohm) for 1us -> Strong
pullup is disabled and pin acts as an open-drain I/O with an weak internal
pullup

 

Any ideas on how this pin needs to be modeled?

I understand that the resistive pullup should be accounted for in the Clamp
currents. However, how do I account for the fact that the pull-up table
changes dynamically.

 

Your help would be greatly appreciated.

 

Thanks,

Gaurav


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