Author Topic: Ground planing on mixed designs with high voltage  (Read 945 times)

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Offline Pack34Topic starter

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Ground planing on mixed designs with high voltage
« on: August 07, 2015, 07:57:13 pm »
This is sort of additional portion of the discussion I originally started in the below thread in relation to separating ground planes in a mixed signal design. It seems like a general consensus for this was to isolate the circuits such that the return path for higher switching digital signals do not cross the sensitive analog returns. I.E. do not put a buck or boost regulator on one side of the circuit board and sensitive analog on the other side. Also, to keep the rails isolated and filtered with beads, chokes, and caps.

https://www.eevblog.com/forum/beginners/separating-grounds-and-stitching-them-together/msg500271/#msg500271

A follow-up for this would be, what would be the case for higher voltages (150Vdc +)? If I had a boost regulator to send 5V up-and-up to 150- or 200-Vdc and on the same design had some logic and low-noise analog circuitry going on, would I need to isolate the ground plane for the higher voltage system? Would it be best to use traces for that instead of fills so that the noise can't propagate and reflect off the board edges?

Or like in the previous discussion, just keep everything isolated and use the appropriate filtering where needed? (Higher value caps at board inputs, 100n at Vdd pin on each chip, and a bead separating the voltage rails for the analog and digital components so switching noise doesn't propagate through the rails.)

I've noticed on some designs (particularly some motor controllers) where it seems ground planes are avoided and traces are used instead. This could just be that the outer layer that I could see was void of a fill and an internal plane was used.

So... for higher voltage and higher current designs, how does that change the game? Are different rules of thumb used, or are the same methods employed as per the previous discussion?
 


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