Chris, You may want to look at some of the "polymer aluminum electrolytic" capacitors from: * Cornell Dubilier. * Elna. * Jaro Components. * Kemet. * Matsushita. * NIC Components Corporation. * Nichicon. * Panasonic. * Samchung. * SDK. * etc.
I've used them on the last two controller cards that I designed for my previous employer, for the DC-DC converters and general bypassing, with very good results: * Equivalent series resistance (ESR) down to 0.015 ohms. * No worry about the capacitors catching fire in low-impedance circuits. * Priced about 1/3 of equivalent tantalums. * Readily available in quantity- no worry about being on allocation. They do tend to be a little taller than equivalent tantalums, if you are height-limited. But you don't have to derate them nearly as much as tantalums to be safe. I used the 105C-rated capacitors to ensure a longer lifetime than the more commonly available 85C capacitors. The pin-through-hole (PTH) radial versions had about 2/3 the ESR of the surface mount technology (SMT) versions when I did my last design. So we laid out my cards to use either style, with the SMT bulk capacitors turned 90 degrees from the PTH bulk capacitors, and their footprints overlaying one another for compactness. If you want to stick with tantalums, we have a bibliography for "Power Distribution on Printed Circuit Boards" at http://www.dbicorporation.com/pwr-bib.htm I just added Ken Javor's report to the bibliography, [215a], so out of the 380+ references, the following ones apply directly to the proper use of tantalum capacitors: [91] "Precautions and guidelines for users (Tantalum)," Nippon Chemi-con. (download from http://www.chemi-con.co.jp/english/support/tantal_note_e.html) [92] "Precautions in Using Tantalum Capacitors." (download from http://www.bostonaic.com/tantalum/precautions4.html) [107] "Tantalum Capacitors With Solid Electrolyte (Chip Type)," Mectron. (download from http://www.mectron.co.kr/components/tan-2.html) [145] Cain, Jeffrey, "Comparison of Multilayer Ceramic and Tantalum Capacitors." (download from http://www.avxcorp.com/docs/techinfo/mlc-tant.pdf) [180] Franklin, R. W., "Equivalent Series Resistance of Tantalum Capacitors." (download from http://www.avxcorp.com/docs/techinfo/eqtantcp.pdf) [181] Franklin, R. W., "Ripple Rating of Tantalum Chip Capacitors." (download from http://www.avxcorp.com/docs/techinfo/rpleinfo.pdf) [190] Gill, John, "Surge in Solid Tantalum Capacitors." (download from http://www.avxcorp.com/docs/techinfo/solid_ti.pdf) [215a] Javor, K., "Investigation Into the Effects of Microsecond Power Line Transients on Line-Connected Capacitors," NASA/CR-2000-209906, NASA Marshall Space Flight Center, AL 35812, February 2000. (download from http://mtrs.msfc.nasa.gov/mtrs/2000/cr209906.pdf) [271] Loh, Eugene, "Physical Interpretation of the Tantalum Chip Capacitor Life-Test Results," IEEE Transactions on Components, Hybrids, and Manufacturing Technology, vol. CHMT-3 no. 4, pp. 647-654, Dec. 1980. [280] Mattingly, David, "Increasing Reliability of SMD Tantalum Capacitors in Low Impedance Applications." (download from http://www.avxcorp.com/docs/techinfo/rel_ti.pdf) [283] Mogilevsky, Boris and Shirn, George A., "Surge Current Failure in Solid Electrolyte Tantalum Capacitors," IEEE Transactions on Components, Hybrids, and Manufacturing Technology, vol. CHMT-9 no. 4, pp. 475-479, Dec. 1986. I wrote design guidelines for, and gave a couple of informal seminars on this subject, at my former employer in 2000. My boss there has given me permission to publish the design guidelines on dBi's web site after I remove the proprietary information (about 10% of the document) and get his approval. So far I haven't had time to work on that task, but it is in my queue. John Barnes dBi Corporation http://www.dbicorporation.com/ ------------------------------------------- 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"
