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Bypass caps for devices

Other Parts Discussed in Thread: SN74LVCH244A

In referencing an old app note from TI (The bypass capacitor in high-speed environments) it states two ways to calculate the bypass cap required

 

C = (I x N x delta t) / delta V

where the number of outputs switching (N)

the time required for the capacitor to charge the line (delta t)

the drop in VCC that can be tolerated (delta V)

delta t and delta V can be assume.  i.e. 3ns, and 0.1V. 

So if I have a SN74LVCH244A, my estimation of the bypass cap required is

So would i use 24mA for I (worst case), 8 for the number of outputs?  What about delta t? How do I find out about this. 

 

I see most designs use either a 0.1uF or 1.0uF.  Besides being a rule of thumb I am curious about how to actually calculate the real value. 

 

I am also using SN65LBC173AD, SN65LBC174A16DW, and a LM139AD. Would the caps be any different?