[SI-LIST] Re: Split gnd planes - for/against?
- From: "Vivekkumar M-TLS,Chennai" <Vivekkumarm@xxxxxx>
- To: "Sol Tatlow" <Sol.Tatlow@xxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 7 Apr 2009 22:16:46 +0530
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
>
>
--
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