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I am looking at the datasheet of nc7wz04 UHS dual inverter. The propagation delay specified is 2.3ns. The rise time/ fall time of input pulse in the fig 6 is 3ns. But in recommended operating conditions table, for 5V output, tr & tf is 25ns. What should be my input pulse rise time?

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The 3ns rise and fall time is a specified test condition in Figure 6 used as a reference point for measuring the propagation delays for tPHL and tPLH. You will only realize the specified propagation delays if your input rise and fall time are 3ns or less. A longer input rise or fall time will result in different propagation delays (usually longer times).

The 25ns time that you found in the recommended operations conditions table is from the 5V at 5ns/V specification. This is the recommended slowest input rise time that the manufacturer specifies for the part so that you can realize good performance over normal operating conditions. Note that at this slowest recommended rise/fall time you will not obtain the nominal 2.3ns propagation delay.

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  • \$\begingroup\$ The maximum input transition time for this part is also due to it being CMOS and if the input transition time is slower than this, significant conduction may occur reducing the life of the component. \$\endgroup\$ Mar 26, 2017 at 13:30

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