Hi Larry; How does manufactoring verify the decoupling design works on the production PCBs? I foresee two issues 1. the right capacitors are not always installed. 2. the design objectives are determined by ESR. seems that the ESR of capacitors is a typically value. it is not specified or guaranteed( ie measured). a deviant batch of capacitors could cause havoc. is this perception correct? Are there other concerns? suggestions? Craig -----Original Message----- From: Larry Smith [mailto:Larry.Smith@xxxxxxx] Sent: June 4, 2002 7:58 PM To: Larry.Smith@xxxxxxx; mibrown@xxxxxx Cc: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Decoupling capacitors Mike - For SI purposes, there is not much you can do at the PCB level to help the PDS impedance above the package corner frequency. However, there may (probably will) be EMI reasons to use capacitors on the core power planes to knock down emissions at higher frequencies. We use 3 capacitors per decade to make the PDS impedance sufficiently flat. The fifteen values of ceramic X5R/X7R capacitors that we most commonly use are: 100uF 47uF 22uF 10uF 4.7uF 2.2uF 1uF 470nF 220nF 100nF 47nF 22nF 10nF 4.7nF 2.2nF This menu is usually sufficient for SI caps. We mount these caps on pads that are much less than 1nH so the series resonant frequencies (SRF) range from 360kHz to 150 MHz. Five decades of capacitance value covers about 2.5 decades of frequecy because the SRF goes as the square root of capacitance. The ESR's range from 2 mOhms to 300 mOhms, with the lower valued caps having the highest ESR. 1uF and below is available in 0603 case sizes. 100uF caps are now available in 1812 size. Our power planes generally have more than 10 nF capacitance. The ESR of the capacitors below 10nF is so high that many, many capacitors are required in parallel to reach target impedance. It is best to use power plane capacitance above about 100 MHz rather than try to do it with discretes. There may be a few well defined EMI frequencies that you want to attack with carefully chosen high quality capacitors, but that is a different issue. regards, Larry Smith Sun Microsystems > From: "Brown, Mike (AUS)" <mibrown@xxxxxx> > To: <Larry.Smith@xxxxxxx> > Cc: <si-list@xxxxxxxxxxxxx> > <snip> > > range. Individual capacitors have an impedance vs frequency profile > that look like a "V". By selecting the optimum number of capacitors > with different values, it is possible to combine a lot of these "V's" > together to approach a flat curve over a broad frequency range. That > essentially presents a resistance to the load over the frequency > range. > > <snip> > = = = = = > Larry, > > It would appear that I don't have to worry about board impedance above the > package corner frequency, where the package X exceeds the target impedance. > I may need a bunch of different cap values and resonances to keep the board > and PDS impedance flat up to that frequency, however. > > What is an acceptable spacing between the series-resonant "V's" to avoid > unacceptably high parallel resonance impedance peaks? 1 per decade? 1 per > octave? > > I know, I know. "It Depends." On what? > > > Thanks > > Mike > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu