Chris if you search on USB Chokes and Filtered USB Connectors you will find many with 4 wire common mode chokes. Even if you build your own you will find data and app notes on these sites answering many of your questions.
Fred Townsend Chileshe, Chris wrote: >Group, > >Simple query. > >I have a product which features two PCBs connected via 4-wire serial (RS-485) interface. >The signal assignments are Vcc, GND, A, B > >I have been performing radiated immunity tests and have had good results over most of the band >between 10KHz and 1GHz. I have had minor susceptibility at around 800MHz and major susceptibility >at around 18MHz. > >My product currently features differential line filtering (chip ferrite) for the Vcc and Gnd lines >and a 2-wire common mode choke on A and B. The circuits are identical on both boards so A and >B exit one board through a CM choke and enter the second through a CM choke. The ferrite/cap >filters are mirrored so Vcc and GND exit one board through chip beads and enter the second through >chip beads (I have an illustration I can send if required) > >I have traced some of the susceptibility to the 4-wire harness ( 27cm long). I am thinking about using >a common mode choke on the Vcc and Gnd lines. > >My questions are; > >Is there an established EMI filter strategy for 4-wire interfaces similar to that described above? >Would I be better off using a single 4-way CM choke or two 2-way CM chokes? > >Any advice or pointers to sources of information most appreciated > >Rgds > >- Chris > >p/s I have googled! > >---------------------------------------------------------------- >This message is from the IEEE Product Safety Engineering Society >emc-pstc discussion list. Website: http://www.ieee-pses.org/ > >To post a message to the list, send your e-mail to [email protected] > >Instructions: http://listserv.ieee.org/listserv/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: > > Richard Nute: [email protected] > Jim Bacher: [email protected] > >All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > > > > This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/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: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
