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Old 10-18-2014, 06:03 PM   #1243 (permalink)
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Originally Posted by cts_casemod View Post
I can see your bottom layer (?), the blue, is not very populated. It could be a good idea to fill the empty space with a ground plane/grid. Also where the regulator will be, use a few vias, to help reduce the thermal resistance and dissipate heat to the bottom layer. The same is valid for the output amplifier.


There are components very close to the mounting hole. It may happen that if you put a screw on there its head will either touch or squash some.

If I may suggest, if you use a ground plane you could leave some exposed copper to solder some metallic adapter where the screw could safely seat.

Thanks for the suggestions!

Yes, the bottom layer - I'm trying to make this a 2 layer design - is primarily the ground, +5V supply and a few signal lines. The boards output to the mainboard run on the bottom - I'm not happy with that because of the proximity to noisy stuff.

If I make the board a 4 layer board, there will be plenty of room for a ground plane and even a bottom layer heatsink. Maybe it's worth it just to pay the extra $$$.

Regarding the mounting hole - yes; I'm working on that. Right I'm generally unhappy with it because of that spacing issue and because it needs to be a relatively small (3mm) bolt that's made of some non conductive material. The reason for this is the matching hole on the motor controller will have to fit in that space between the controller and driver boards. I want to make sure that the fastener isn't the cause for any shorting situations.

I really like the idea of using the heatsink for a fastener - I'll see what I can do there. A relatively large, thick piece of copper would be great for this. BTW, the thermal loading on the output amplifier is pretty constant. Actually the quiescent current (just running the IC, not amplifying anything) is the primary load.

Two questions regarding grounds:

On this board, there are actually two grounds - One for the +24V supply and one for the +5V supply (with is the majority of the board) Is there an issue with connecting the two grounds? Should I put a resistor or some protection device between them?

If I make a ground plane, out of the ground connections (half of the thick blue traces) and the remaining board space, what's the possibility of this becoming a noise "antenna"? How much space should I leave between signal traces and this ground? (for noise issues).

Thanks again,

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