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SN74AHC123A: Tw Design calculation and Observed output is not matching

Sandeep NS
Intellectual 400 points
Part Number: SN74AHC123A

Hi,

I am designed a timing circuit with SN74AHC123A

Requirements are Tw=22uS, VCC=3.3V

As per the calculation I have selected 1nF(1000pF) and 22.1K resistance.

But when I am observing , the output is around 50uS pulse width.

If I changed the capacitor to 10nF(10nF*22K=220uS), I am getting around 220uS.

Again if i Change the resistor to 2.2K and 10nF(calculated value 22uS) , again I am getting 50uS.

What can be the reason for this behavior?