Alex, If I had a dime for every time a serial device or it's cable caused fits during EFT...Well I'd still be on the EMC-PSTC group; but I'd be doing it from the comforts of my woodshop at home because I wouldn't have to work anymore. (Reference my recent rantings regarding mice, keyboards...)
I sympathize with your situation completely. I recommend a few ideas for consideration: 1. Go down the hallway and whack the marketing guy who came up with the idea of running an external I2C device. Just kidding, we don't whack people, we hand out a little rubber pig for such occassions. 2. Is there any way that you can shield the cable and possibly tie the cable shield to PCB ground? 3. Do you feel comfortable with the "electrical mass" of your product's ground plane? Is it a large plane or just a trace or a grid of traces? Would there be any way to prototype a small "extra" ground plane within your device using copper tape or foil? If there is a way, try to stuff one in there, connect it to your digital ground at a few points and connect your I2C filter caps to it. If you try to shield the cable, connect this cable shield to your extra ground plane. If this works out, there are all sorts of places that can make you a piece of die cut metal foil to fit in your box. (Orion Industries in Massachusetts comes to mind.) My feeling based upon some experience (which pales in comparison to most of the "Old Ones" on the listserver) is that "electrical mass" is the key to EFT. It seems to work better than ferrite, TVS diodes and other solutions. "Electrical Mass" is a simple idea...more copper equals more free electrons which makes it harder for your product's RF potential to change. Minimizing RF potential changes is good for EFT, ESD radiated emissions and your hairline. (Reference Dr. Howard Johnson's article "Not All EMC Guys are Bald" in a recent issue of Digital Design News.) 4. Are you sure that your product is being upset? Or, is the peripheral being upset and then hanging the I2C bus which then hangs up your product? You may have to try filtering at the peripheral end with ferrites ... at least during testin in order to figure out what is goint on. 5. If none of these solutions are possible, a software fix may be the only solution. Perhaps you can change your interrupt servicing routine so that a hung up I2C line can be reset or at least ignored? Serial peripherals are a PAIN!!!!! and I wish you the best. Please let me know if something pans out for you. After all, they're still a pain for me and I'm always eager to know what works. Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | > -----Original Message----- > From: Alex McNeil [SMTP:alex.mcn...@ingenicofortronic.com] > Sent: Tuesday, January 29, 2002 12:40 PM > To: emc-p...@majordomo.ieee.org > Subject: EFT problem with I2C Serial Bus > > > Hi Group, > > To those of you who are familiar with the I2C Serial Bus. > Have you experienced a similar problem, as described below, with > EN55024 > mains EFT noise? > > I know it can be misleading to try and resolve a problem over the > internet, > but you can never tell....... > > I need to attach a 4way 2metre lengfh of cable to my product I2C Bus > output > to supply a peripheral. > > When I apply the mains EFT pulse at > 500V the product, with this new > cable > only attached and no peripheral, hangs. I have diagnosed the problem > down to > this cable picking up the EFT radiated noise from the AC SELV output > cable > (input to the product) of the 230Vac/10Vac power supply. > When I remove the I2C i.e. the SDA and SLC lines, within the product, > the > product passes the EFT. When I re-attach either of these signals the > system > hangs. This was just to further prove the I2C bus was causing the > problem. > The product passed the EFT 2KV pulse with no I2C cable attached. Also, > I > cannot alter the power supply. > > I have tried various solutions on the PCB, all to my disappointment: > Ferrites on cables > Varied series resistor values on the SDA and SLC (22R to 330R) > Varied series ferrite values on the SDA and SLC > BAV99 (2 serial "fast" signal diodes package hanging on the lines) > 100pf caps hanging on the lines > > Note: My product is a Class II (no earthing), all plastic. > > I would appreciate any comments? > > Kind Regards > Alex McNeil > Principal Engineer > Tel: +44 (0)131 479 8375 > Fax: +44 (0)131 479 8321 > email: alex.mcn...@ingenicofortronic.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: > Michael Garretson: pstc_ad...@garretson.org > Dave Heald davehe...@mediaone.net > > 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: > No longer online until our new server is brought online and the > old messages are imported into the new server. ------------------------------------------- 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: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net 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: No longer online until our new server is brought online and the old messages are imported into the new server.
