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GND polygons/planes layout opinions for optoisolated digital inputs

I am currently working on a design involving an ATmega48 12MHz MCU in the digital area of the PCB and 8 galvanically isolated 24V opto digital inputs located in another area of the PCB. The input isolator is a standard Sharp PC847 general purpose photocoupler.

The layout will be a 2-layer PCB with two separate areas, digital section on the left, input area on the right. I certainly will have as much GND polygon and fill areas as possible on the digital side.

Now, is it recommendable to fill the non-copper areas on the isolated input side with copper too? The 8 inputs have a common return which could be used as the potential for the copper fill.

Ricky

Reply to
H. M.
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If you need a high voltage isolation you can't fill with copper everything just because you need isolation. If your design has optocouplers just to be "interesting" and the optocoupler are isolating low level voltage signals (24-50V) then you may fill everything with copper (still using the 24V isolation between signal and ground area)

greetings, Vasile

Reply to
vasile

The inputs are low voltage 24-30V and have a common return (COM).

There is no isolation between individual inputs on the card but between the whole group of 8 inputs and the digital/microcontroller side. This isolation shall withstand 500V and there is a 2.5mm gap between these two sections on the PCB. Only the optocouplers are crossing this gap.

However the question to me is should I have also a copper pour on the isolated input side connected to the COM potential which of course will not be connected in any means to the GND of the digital side.

Ricky

Reply to
H. M.

Yes. A rule of thumb I always look at first is, you can't have too much ground plane. (or too many bypass caps, but that's a different issue.) :-)

Cheers! Rich

Reply to
Rich Grise

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