Electronic – How to discover reliable speed to use a logic gate

clock-speeddatasheetdigital-logic

It seems to be very hard to get consistent numbers for the performance of logic chips. I am interested in using the SN74F574 component (8 bit register).

Looking at DigiKey, when I search for the component it shows a results grid with a clock frequency of 100Mhz and max propagation delay of 8.5ns. This is inconsistent as 8.5ns is equal to 117Mhz, a not insignificant difference in my opinion. Should I take the lower of these two numbers?

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So I open up the datasheet of the component and inside it has a grid showing the propagation delays. The maximum value in the grid is 35ns and so surely the only safe way to use the part is to ensure you can handle the maximum. So that would give an actual speed of 28Mhz.

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So do I clock at 28Mhz, 100Mhz or 117Mhz? Why don't datasheets make your life easy and specify a clock speed (or the matching ns) that it can be clocked at?

Best Answer

Here's a clip from just a few inches above the part your clipped:

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