piclist 2000\06\05\181949a >
Thread: 5V Logic Bypass caps - SMD value/phy size recommendations?
face BY : David VanHorn email (remove spam text)

Hash: SHA1

>This suggests that lower capacitance a priori works better at higher speeds.
>My understanding of the specifications suggests the opposite: for any make
>of capacitor, higher capacitance always works better at any frequency.

That would be true if they didn't have internal inductance that is
proportional to the capacitance.

>What might be true is that certain types of capacitors are only available
>in small denominations, and these types have lower ESR and ESI so they work
>better at higher frequencies.

Smaller values of C have smaller internal inductance, in any given package.

>What's important is that the impedance of the capacitor be only 1 ohm or so
>at the frequency of interest to reduce ripple at the current draw required.

More properly, as low as possible.
A cap with a Z of 1 ohm won't do a lot in a circuit with comparable impedance.

My measurements were made in a 50 ohm system, (stripline on G-10 PCB)
Thinner tracks will be higher impedance, and a given cap will perform
better with higher track impedances. (provided of course proper layout!)

- --
Are you an ISP?  Tired of spam?
http://www.spamwhack.com  A pre-emptive strike against spam!

Where's Dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9

Version: PGPfreeware 6.5.2 for non-commercial use <http://www.pgp.com>



In reply to: <>
See also: www.piclist.com/techref/index.htm?key=logic+bypass+caps
Reply You must be a member of the piclist mailing list (not only a www.piclist.com member) to post to the piclist. This form requires JavaScript and a browser/email client that can handle form mailto: posts.
Subject (change) 5V Logic Bypass caps - SMD value/phy size recommendations?

month overview.

new search...