Like all good designers, I try to end up with a decoupling cap ACAP to 
each VDD/VSS pair.  Typically I use a 0.1uF mono X7R cap for this 
purpose, just because I've standardized on it.  

Recently, I've had a few designs where a 0.01uF was explicitly specified 
in the datasheet for some component (for instance, the 3.3V switcher I 
use), and as such I've used 0.01uF across the board (which nowadays is 
often just a 'F886 and a single 74HC(T)), just so I didn't have to 
populate both 0.1uF's and 0.01uF's.    The reason behind this design 
choice was that I have always considered a 0.01uF to be "roughly 
equivalent" when it comes to bypassing, primarily because of my early 
TTL work - that is, either a 0.1 or 0.01uF will work, and when boards 
are hand-stuffed, it's a lot easier to make an error when there are 
mixed values on the board.

In that "other thread" going on right now, a couple of the responses 
made me worried that the 0.01uF's weren't adequate anymore.   So I dug 
around on the web and in my reference manuals a bit.   What I've dug up 
so far seems to both confirm and contradict the theory that a 0.01uF is 
sufficient.  Some documents say 0.01's are actually better, some say 
they're worse.  Some even go as far as to say 0.1uF and 1uF is the 
correct range.  And so on.

So, maybe I'm looking for some real-world experience.   Is a 0.01uF cap 
no longer sufficient for bypassing?

-forrest


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