This presentation was little more than a sales pitch for Fair Rite inductive components. As you might expect it suggested using beads almost on every single data line, internal and external to a circuit. Some of the "Tips" were even wrong, for example suggesting using a higher impedance bead if reducing size (say going from 1206 to 0603) to avoid saturation effects, but because higher inductance results in lower saturation current the result is probably a worse situation than just the size reduction alone.

I would like the chance to reply to this uniformed review of this presentation.

It is quite obvious that the delegate who wrote this review does not fully understand the difference between inductance and impedance when talking about ferrite. They say that (Some of the "Tips" were even wrong, for example suggesting

using a higher impedance bead if reducing size (say going from 1206 to 0603) to avoid saturation effects, but because higher inductance results in lower saturation current the result is probably a worse situation than just the size reduction alone.)

The above statement is factually wrong, the delegate did not understand this tip.

Point one. (Fair-Rite Inductive Components) ?, not once in the presentation was inductance mentioned, this presentation was about Fair-Rite Suppression Components.

Point two. It was suggested using ferrite chip impeders on many data lines, however, reasons for each and every placement was given.

Point three. (Some of the "Tips" were even wrong) This tip is quite simple - if a designer is asked to make an existing PCB smaller but with the same functionality, then more or less he has to use the same, but smaller components. So he can use smaller IC's and smaller passives, for instance changing 1206 passives to 0603 passives. Now assuming that all circuit currents remain the same, if he was using a 1206, 120ohms chip bead impeder and then changed this to a 0603, 120ohms chip bead impeder the impedance seen by that signal current would be less than seen by the same current going through the 1206 chip bead, this is due to the mass of ferrite available for energy absorption. So the current would also see less attenuation than before and thus could fail the EMC test. The solution to this problem is to use a higher impedance 0603, for instance a 150ohm, 180ohm, 220ohm 0603 chip bead. Saturation effects when using differential mode impedance are more prevalent with smaller size components, this is a fact. Thus you need to use a higher base impedance when using smaller, less massive parts (assuming you want he same impedance with the same circuit

current), this is also a fact.

I have attached a copy of the presentation for your review and await your feedback.

Rgds

Alan Keenan

Fair-Rite Europe

Editors note: We replied to Mr Keenan stating that we would print the above e-mail in full and include access to the presentation. We also e-mailed the original (anonymous) author of the review for further comment, but believe they have now moved company as we received no response. We would like to refute the accusation, however, that the review was "uninformed", the reviewer had attended the seminar and therefore was as informed as any other delegate on the day. The reviewer worked as a design engineer for a company that include inductive components in its product portfolio, hence we believed was well qualified to comment on the subject. We welcome any reviews, feedback on the site itself or items in the newsletter and when requested to be published anonymously honour such requests.