RE: [SI-LIST] Re: Split gnd planes - for/against? Sol, Steve is right. There isnt any general thumb rule that we follow with respectto gnd splitting. The following link which i have gone through earlier, details example reg. Moating : http://www.national.com/an/AN/AN-1347.pdf[1] May be useful for you. Regards Vivek -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx on behalf of steve weir Sent: Tue 4/7/2009 9:41 PM To: Sol Tatlow Cc: si-list Subject: [SI-LIST] Re: Split gnd planes - for/against? Sol, unfortunately there is not a single answer. In most cases moating is a bad idea, particularly if one does not understand the caveats and how to deal with them. It's not just the moats: It's the placement, clearances, stitching, and routing that all need to be considered. Steve Sol Tatlow wrote: >I know this subject has been raised before, countless times in one >guise or another. I have also googled plenty. I'm not looking for >theoretical opinions, either, about whether or not, or when, they >should be used (specifically not, "it depends", unless you've got >REAL-LIFE examples, for and against!!!). > >This subject raised its head for me in this case due to using >2 A/Ds as well as 2 D/As, both from Analog Devices, where one >specifies a split plane, the other specifies no split. Now, I am >all too wary of relying simply on evaluation boards, where, in >general, one layout is done, and if it works, that's how everyone >should do it (_without_ comparing 2 different approaches). > >I personally have 3 concrete cases where split gnds had no positive >effect on SI, but significantly worsened EMC results (despite >sticking to all the usual guidelines, like no tracks over the >splits, etc.), but I have no concrete case FOR split ground planes. > >So, what I'm interested in is: does anyone have CONCRETE examples >which they would like to share for/against split planes? The kind >of thing I mean would be like in one of the cases I had, where I >wanted to go against the suggested approach of using a split gnd, >and persuaded my customer to pay for 2 variants of the same board >on the same manufacturing panel, one with split ground, one with >solid ground. Both variants were assembled and tested, with regards >to both SI as well as EMC: both were functionally satisfactory; at >EMC testing, however, the split-plane bombed out big time, while >the non-split sailed through. I like to think that it wasn't due >to any screw-ups on my side, that the split ground failed - I am >not a newbie to PCB layouts, and, while for sure no professional >expert on all areas of SI, I believe I avoided the typical blunders >often present in split ground layouts. > >Anyway, my customer was more than happy, but not everyone has the >money/time/desire to do as I suggested. So, any 'war stories' to >support one or the other approach would be appreciated to help >expand my knowledge and understanding of this subject - obviously, >we all respect confidentiality, so I'm not looking for circuits, >layouts and so on, but I figure many of you must have stories that >can be related regarding this subject. Or perhaps some good links >to non-confidential 'real-life' examples/studies? > >Regards, >Sol > > -- Steve Weir Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 California office (866) 675-4630 Business (707) 780-1951 Fax Main office (401) 284-1827 Business (401) 284-1840 Fax Oregon office (503) 430-1065 Business (503) 430-1285 Fax http://www.teraspeed.com[2] This e-mail contains proprietary and confidential intellectual property of Teraspeed Consulting Group LLC ---------------------------------------------------------------------------- -------------------------- Teraspeed(R) is the registered service mark of Teraspeed Consulting Group LLC ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list[3] For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net[4] List archives are viewable at: //www.freelists.org/archives/si-list[5] or at our remote archives: http://groups.yahoo.com/group/si-list/messages[6] Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu[7] --- Links --- 1 http://www.national.com/an/AN/AN-1347.pdf 2 http://www.teraspeed.com 3 //www.freelists.org/webpage/si-list 4 http://www.si-list.net 5 //www.freelists.org/archives/si-list 6 http://groups.yahoo.com/group/si-list/messages 7 http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu