SN74LVC1G123: How does Rexr, Cext, RL and CL included in the calculation of pulse duration ?

Hello,

The K value you have determined is incorrect -- for a 28 pF timing capacitor, you can expect K to be approximately to 3.3.

Note that decreasing the capacitor value increases the K value significantly.

t_w = K * R * C = 3.3 * 28pF * 2kohm = 184.8 ns

This would be a good starting point for a design, but after selecting these values, I would highly recommend building a prototype to determine if your components produce the pulse width you expected.