Grounding in Switching Regulators

[nandopg]

Dears,
|´ve been looking on some professional layouts of switching regulators and I´ve noted that instead to use ground planes to ground related sub-systems on the board, they use traces, large traces is true, but not planes.
I can see the limit for a wide trace as a plane!!...but anyway, can anyone give a good reason for the gound be made using traces in place of planes?

Regards to all,

NandoPG

 

[IanP]

Ground traces allow the designer to isolate "quiet ground" from the "noisier power ground" whereas ground plane will spread "noise " all over the board ..
For more hints see:
"Basic Switching-Regulator-Layout Techniques"
**broken link removed**

Also, it is good practice to introduce single-point grounding and all of the individual circuit elements are returned to this point using separate ground traces ..

On the other hand, current switching at high frequencies tends to flow near the surface of a conductor (this is called "skin effect"), which means that ground traces must be very wide on a PC board to avoid problems, so, to avoid these problems some designers decide to use ground planes ..

Regards,
IanP

 

[nandopg]

Dear Ian,
Thanks for the reply and for the link.

It makes sense to me when you talked about to separate "quiet" ground from "noisy" ground, no doubts on this. But looks to me that this separated grounds should be made through planes, not traces as I've been seen.

Imagine if you do a RF grounding using traces. The circuit wouldn't never work. You would have so much inductance distributed over the ground traces that the circuit's behavior would be unpredictable.

I would imagine the same effect taking place in the case of switching regulators, where you have very fast current pulses flowing through a ground return.

...but it looks like that the practice in switching regulators design is different...

NandoPG