Decoupling capacitors

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lilimike

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This is probably a stupid question and it was probably asked before but I searched and couldn't find any occurrence.
If decoupling capacitors need to be as close as possible to the IC they are protecting, why are they not integrated to ICs?
I am sure there is a good reason and looking forward to find out.

Mike
 
Two good reasons. Size and cost. Integrating a capacitor would make the IC package much larger and more expensive since practical cap sizes used to decouple ICs are much larger than the IC chip itself.
 
Fair enough, I was under the impression that within an IC there were already some caps but I guess not.
While I am at it, is it acceptable to place a surface mount cap under a DIL IC on the same layer that is, as the IC pins are long enough for the chip to sit on the cap?

Mike
 

We usually call it a DIP, not DIL. From an electrical standpoint, there would be no reason to not do it. From a maintence standpoint, I think it would not be wise. Very often, the caps are installed on the opposite side of the board, under the IC.
 
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There are IC sockets available with a cap built in, but more expensive than a standard socket and cap.
 
Opamps have a tiny 30pf frequency compensation capacitor built-in.
30pF is 3334 times smaller than a 0.1uF supply decoupling capacitor.
 
BrownOut said:
We usually call it a DIP, not DIL. From an electrical standpoint, there would be no reason to not do it. From a maintence standpoint, I think it would not be wise. Very often, the caps are installed on the opposite side of the board, under the IC.
Click to expand...

Actually I always call it a DIP but I guess I had DIL in my head as I was just adding some devices to a schematic in Eagle and they call it DIL.

My question originated from a circuit I did with the goal to have the cap on the other layer under the chip but I forgot to switch its layer and it is when came the time to solder that I had realized my mistake, that's when I figured it still had a nice fit under a DIP chip.

About maintenance issue does a 0.1µ cap ever go bad?

MIke
 
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