Using 1206 will force you to have (probably significantly) larger inductance than with 0805 or 0603. Inductance is the most important parameter above about a couple of MHz, because that will determine the decoupling impedance. Therefore you may decide to use all one value (except for the bulk caps) or to properly stagger the values of the caps (without creating parallel resonance, thus the values should not be far apart), but keep the inductance low. That criterion may force you to use smaller package than 1206. In addition, this will greatly depend on how you connect the caps, so keep low-inductance regardless of the cap size.
Neven > Hi all, > > I've just come from a discussion of decoupling capacitance.... > > In a nutshell, we have a combination of DSP and A-D/D-A conversion going on.. > I have recommended that we use a single 4.7 microfarad 1210 packaged cap in > place of the more traditional 0.1 and 0.001 microfarad 0805 caps in parallel. > I believe that the data shows a better compromise favoring the single chip. > Further, the need for BIG board entry caps is diminished. > > This is on an 8 layer board. > > Thoughts? > > Thanks, > > Derek Walton > L F Research EMC Design and Test Facility ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
