Electronics > Beginners
Creating controller for LED display, help / review needed
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Eka:

--- Quote from: Lt_Flash on July 27, 2018, 09:26:51 pm ---Just a thought, though. In regards to 3V3 rail - you often have different cover of the polygon over capacitor contacts, like at C1 or C5 - it's just a tiny 10mil trace, actually, even though you have a whole huge polygon next to it. Just cover the half of capacitor with that polygon everywhere, right to the middle of each cap, not the way you have it - different for each capacitor, that'd be good. Otherwise - seems good to me. Polygons can be optimized a bit, but nothing to be stressed about.

--- End quote ---
The short traces between solder pad and flood fill polygon* is done is for easier soldering, and if mass produced it would be much less likely to have gravestones. Electrically it means very little because the traces are so short.

* I forget what they are called.
Lt_Flash:

--- Quote from: Eka on July 28, 2018, 05:06:04 am ---
--- Quote from: Lt_Flash on July 27, 2018, 09:26:51 pm ---Just a thought, though. In regards to 3V3 rail - you often have different cover of the polygon over capacitor contacts, like at C1 or C5 - it's just a tiny 10mil trace, actually, even though you have a whole huge polygon next to it. Just cover the half of capacitor with that polygon everywhere, right to the middle of each cap, not the way you have it - different for each capacitor, that'd be good. Otherwise - seems good to me. Polygons can be optimized a bit, but nothing to be stressed about.

--- End quote ---
The short traces between solder pad and flood fill polygon* is done is for easier soldering, and if mass produced it would be much less likely to have gravestones. Electrically it means very little because the traces are so short.

* I forget what they are called.

--- End quote ---
Yes, I know what relief connect is for, but usually you would want to pour polygon around pad so there would be three short traces to polygon from a pad. It may be important for power rails.
muktupavels:

--- Quote from: Lt_Flash on July 27, 2018, 05:05:03 pm ---Maybe just cover 3V3 output of the regulator with polygon? Till the middle of capacitor, as that's your primary 3V3 joint.

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Did I understand this correctly? Please check new attachment...


--- Quote from: Lt_Flash on July 27, 2018, 05:11:47 pm ---Also it may be a good idea to add a lot of thermal vias around and under voltage regulator for better thermal performance.

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Added only under regulator, is that ok?


--- Quote from: Lt_Flash on July 27, 2018, 09:26:51 pm ---Just one more thing, I can see you've got a 5V trace running from connector, why don't you flip C7 upside down and then create a solid polygon for 5V rail? Just a thought, though.

--- End quote ---

Is not trace big enough?


--- Quote from: Lt_Flash on July 27, 2018, 09:26:51 pm ---In regards to 3V3 rail - you often have different cover of the polygon over capacitor contacts, like at C1 or C5 - it's just a tiny 10mil trace, actually, even though you have a whole huge polygon next to it. Just cover the half of capacitor with that polygon everywhere, right to the middle of each cap, not the way you have it - different for each capacitor, that'd be good.

--- End quote ---

Done. Is that what you meant?


--- Quote from: Lt_Flash on July 27, 2018, 09:28:04 pm ---Here's a good video from Dave about bypass caps and where to place them, just for information.



--- End quote ---

Thanks, but I have seen that video. :) The real question is whether I have learnt something from it...  Probably should watch again.

In few places I have put vias to connect top gnd polygons that are split by 3v3. Is that needed?
Lt_Flash:
Yes, you did understand correctly, now you have a solid 3-wire connections for each 3V3 rail! Thermal vias are good too, there's a solid polygon around that regulator and now with thermal vias even if regulator would get hot - these vias will help to dissipate heat. In regards to 5V rail - yes, trace is usually enough, I just got used to use polygons where possible with power rails, usually that's better, it also dissipates heat and has better conductivity too. In regards to GND vias - usually you would want to have them as that shortens your current return path, thus reducing impedance of a trace.
Lt_Flash:
Just one more thing - you probably would want to cover pin 3 of regulator with 3V3 polygon, that's why I included Dave's video, it says that you should have decoupling capacitor as close to regulator output as possible even if that's a polygon pour, but in your case it's just a short thick trace and then a huge polygon, so current would flow through that trace first. It's better to have a polygon and a cap close to the source of current, as I suggest.
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