Re: gEDA-user: pcb, howto partition power planes?

[Joerg <joergsch@xxxxxxxxxxxxxxxxxxxxx>]

Stefan Salewski wrote:
> Sometimes it is necessary/recommended to partition (separate) power or
> ground planes, i.e. for ADC or DC/DC-Converters, see page 16 and 17 in
> 
> http://focus.ti.com/lit/ug/slwu028c/slwu028c.pdf
> 
> We can do this in pcb program with (adjoining) polygons.
> Disadvantage is, that if we change the size of one of the polygons we
> have to manually adjust the other sizes. A other method may be so divide
> a large polygon by copper clearing traces (with trace width zero). 
> 
> This is related to my question from
> 
> http://archives.seul.org/geda/user/Sep-2008/msg00387.html
> 
> but not identical.
> 
> What is the best way to handle this?
> 

I can't speak to that but just one word of caution: In my 20+ years in 
engineering I have yet to see one case where splitting a ground plane 
under high-speed ADCs has worked. Regardless of what application notes 
say. Usually it didn't work, lots of noise. Or it kind of worked but 
fell apart the instant somebody whipped out a GSM cell phone or BlackBerry.

Myself, I never spilt a ground place. OTOH the industry practice of 
splitting planes is providing part of my income :-)

The only time I split is where required for safety, for example patient 
isolation per 60601 (ECG, ultrasound etc.).

-- 
Regards, Joerg

http://www.analogconsultants.com/



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