Hello,
I was watching a webcast by Dr.Howard Johnson and he was talking about a mistake that some engineers make and overload a regulator with too much capacitance and actually kill the regulator and make it unstable. I use 78xx series a lot and till now I used to connect many digital chips that have 100nF bypass chips to the same regulator. in 78xx datasheet in output impedance vs frequency diagram even in condition of Cload = 0uF, output impedance is more than 1 Ohm at 1MHz. surely even 100nF can deteriorate this response. many digital ICs needs even faster supply so the question is, is regulator fast enough to replenish fast voltage drops and then how this problem should be addressed.I couldn't find a graph that shows output impedance vs Cload in ST datasheet of 78xx. It doesn't seem good option to place a regulator for each digital chip especially for a compact digital board that has many ICs so what do you suggest?
What about switching power supplies, I used to protect sensitive analog ICs with pi filter that has heavy weight 10uF capacitors to prevent ringing, so can presence of regulator even deteriorate the situation? I mean which one is better SMPS->Regulator->Pi-Filter->ADC or SMPS->Pi-Filter->ADC ?

Thanks,
regards