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?