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As the IBIS spec says (pg.184) the voltage range for a GND clamp I-V characteristic must be GND-POWER...GND+POWER. For example, if the IC uses a 3.3V power, the lowest I-V characteristic voltage must be a -3.3V. The same lowest voltage must be used when we measure the I-V characteristic for a pulldown and a pullup.

But this is much more than the absolute rating of the low input voltage level (Vil) by a datasheet. If I apply this voltage to an input, the IC most likely be damage by a huge current. Also I saw in an Altera IBIS-model, that the current of the TTL3.3V input of the MAX-V CPLD is about -1A with the -3.3 input voltage.

So how to measure the pullup/pulldown I-V characteristic for an IBIS model with the full recomended voltage range and do not destroy an IC?

Arseniy
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1 Answers1

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To prevent the IC from being fried, use very short pulses with a sufficient cooldown period between them. In most cases, this allows you to go far beyond the absolute maximum ratings.

Ultimately, it does not really make sense to provide values that cannot occur. In the unlikely case that it is not possible to measure an I-V point under any circumstances, you can just extrapolate.

CL.
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