piclist 2002\07\06\081345a >
Thread: .1uf between Vcc and gnd ???
picon face BY : Spehro Pefhany email (remove spam text)

At 09:24 PM 7/5/02 -0700, you wrote:
>I have a product on the market with NO caps across Vcc and Gnd.
>It is a PIC12C672 run with a 3.6V lithium battery.
>Thousands sold and around the world and not seen any issues from leaving
>caps off.
>I decided to do this to save parts count/cost.  Normally I use a 0.1uF, but
>in this case I left it off due to the battery being very close to the PIC
>(short track).
>I'm sure someone on this list will tell me that what I did was wrong, but
>since it works fine I'd be happy to hear from someone at to why it is a bad

If you don't have any output lines, or there is some resistance in series
with them, then there is less need of bypass capacitors. PICs are pretty
tolerant of bypass caps being left off, but I don't do it except on the
bench. As someone else has already mentioned, the internal resistance of
the cell will go up as the battery gets older, so any problems would tend
to manifest themselves nearer the end of battery life. Some batches of
chips will be less tolerant than others to the resulting noise on the Vdd
line. Future mask revisions may be less or more tolerant. It doesn't seem
worth gnawing away at margins for the sake of a penny part that uses no
port pins and little space.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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