A few tips:
Connect all 4 holes to chassis AND DGND and to the ground plane in the PCB. Don’t use resistor, just plan connect. If you can, use more holes. It is worth the effort. Especially place a hole very close to the center tap and connect it to it. Use the famous 1NF 2kV capacitor to galvanically (?!) isolate the ethernet bus from GND Keep distance between transformer and chassis (steel) overall including hole stud and cap and routing less than 1 inch. Reserve place for 2 small CM coils at the outputs of the chipset. Keep the routing of the transmit and receive pairs as short as possible but keep them parallel and symmetrical (mandatory). Use the right resistor values from the datasheets. Add 2 x 2 15 ohm resistors at the chip side of the transformer. Remove any serial R win series with the center tap. (some designs have 50 or 100 ohm there) If nothing helps, change magnetic for a better brand, or add a good quality CM choke after the transformer. Last resort: change chipset. Keep your ground plane contiguous, no gaps larger then a soldering hole, and keep ground between any standard 0.1” drill pattern such as used standard IC’s. Especially be aware of ground gaps caused by rows of vias. The inside layer clearing in the PAD stack is most of the time too large. And needless to say. DO NOT USE THE GROUND LAYER TO SOLVE ROUTING PROBLEMS: AT NO COST! Regards, Ing. Gert Gremmen [email protected] <mailto:[email protected]> www.cetest.nl Kiotoweg 363 3047 BG Rotterdam T 31(0)104152426 F 31(0)104154953 Before printing, think about the environment. Van: [email protected] [mailto:[email protected]] Namens deepak Engineer Verzonden: Thursday, September 30, 2010 10:19 AM Aan: John Woodgate CC: [email protected] Onderwerp: Re: [PSES] EMI issue with Ethernet Hello Team(Gert,John,Rob,Gary), Thanks for sharing the knowledge/experience... I am still hesitating to take a decision on chassis ground.. On my board, I have four mouting holes for chasis... I cannot use the chassis ground on all four mounting hole, becasue of layout restriction.. Three holes are connected to signal/digital ground while fourth is connector to Ethernet Chassis ground... In whole system, Chasiss ground and signal ground are linked/communicating through only two points.. 1. throught zero ohms resistor between RJ45 jack and signal ground 2. through chassis, where ethernet cable ground will be passed to chassis(thru mounting hole) and mix with singal ground... would it effect the system... is it stable approach.. Cheers, Deepak On 30 September 2010 09:43, John Woodgate <[email protected]> wrote: In message <[email protected]>, dated Thu, 30 Sep 2010, "ce-test, qualified testing bv - Gert Gremmen" <[email protected]> writes: No John, while what you state is correct, the coupling from CM currents out of the ground via the center tap of the transformer is one common way of creating problems. Now I'm completely confused. Earlier in this thread, you wrote: Most of the time the problem is that the ground point center-tap of the Ethernet transformer is insufficiently grounded. Now you seem to be saying that the equipment 'ground' can be a source of CM energy, and I agree it can be. Therefore, it would be better NOT to ground the centre-tap. And much more likely then balancing problems. Balancing problems will immediately be detected by poor transfer rates and errors. CM current will go unnoticed. I don't think so. The balance has to be a long way off before it noticeably affects the signal transfer, but only a little way off to significantly increase emission levels. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk <http://www.jmwa.demon.co.uk/> and www.isce.org.uk <http://www.isce.org.uk/> John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK If at first you don't succeed, delegate. But I support unbloated email http://www.asciiribbon.org/ - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]>
