Hello,
We have a circuit that generates signals with an extremely slow rise/fall time (milliseconds). This circuit should feed a digital IO sampler that has a CMOS input (AHCT245/645...), and it's known that slow rise/fall times are bad for CMOSes (forcing them to spend long time in a conducting state, thus generating power and heat that may cause damage).
The common solution for this problem is placing a shcmidt trigger (74VHC14) on the circuit's output, to feed a fast signal to the CMOS.
However, one engineer presented the following appnote: "Implications of Slow or Floating CMOS Inputs"
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and claims that this article doesn't mention that Schmidts themselves don't suffer from the slow input problem, and that a Schmidt may be damaged from inputs as slow as 1 ms. He proposes to use a comparator (that has hystheresis) as the most robust design. On the contrary, many people say that the Schmidt is enough, and 74VHC14'th data sheet poses no limit on the rise time.What is your opinion ? It's an important subject that surely raises in many designs.
Eli