I have found removal of inductance at power pins often REDUCES emissions. When this is so, it is because designers who put it in did not insure there was sufficient local capacitance to hold up Vcc while the isolated device switches. This has happened to me often enough that when I see series inductance at a device power pin, I question the designer, and persuade him to add capacitance or remove the inductor (sometimes both - grin).
Power filtering can be estimated based on data sheets and measurements on sketch boards. But designers need to do at LEAST that much, and they often do not. I consider this important enough that when I interview engineer candidates (that's when I am not one myself!) I ask them to show me how they will calculate the capacitance needed to support a digital device driving some number of loads. This is not rocket science, but many have not thought of it at all. Cortland Richmond ------------------------------------------- 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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"
