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Thread: Decoupling capacitor
face picon face BY : Olin Lathrop email (remove spam text)

I'm a beginner in PIC programming, and I just want to know what's the real
of a decoupling capacitor. How does it affect the operation of the PIC? What
capacitance value should I use? What should I use, an electrolytic cap or a
ceramic (non-polarized) cap?

Sounds like you should go find a good basic electronics book.  You are never
far from the hardware in an embedded system.

Digital ICs can often change the amount of current they draw by a large
factor very rapidly.  The regulator in the power supply can take care of
longer term variations in the current demand, but there is a frequency
beyond which it can not respond to fluctuations anymore.  Also, wires or PC
board traces are not perfect conductors.  They have some finite resistance
and inductance.  All these effects together make it so that a digital chip
can cause significant glitches on the power supply voltage near the chip.  A
capacitor accross the power supply leads right at the chip will attenuate
these transients, thereby "decoupling" the chip from other chips being fed
from the same power supply.

Decoupling capacitors are commonly 10 to 100 nF ceramic.

Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, KILLspamolin.....spamembedinc.com, http://www.embedinc.com

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