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Creating controller for LED display, help / review needed

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Lt_Flash:
One more thing - it's best to have a 'star' or 'single point' power traces design, coming from same point, while yours are almost all serial, that leads to higher resistance, impedance and antenna effect, have a look at these articles:

https://www.maximintegrated.com/en/app-notes/index.mvp/id/3630

And this one is the best, I think, have a look at 2.2.2

http://www.ti.com/lit/an/szza009/szza009.pdf

muktupavels:

--- Quote from: Lt_Flash on May 03, 2018, 05:45:44 pm ---I'd created a solid ground plane on both sides of the board.

--- End quote ---

Why? What do I gain by doing it? Or what problems I could have not doing it so?


--- Quote from: Lt_Flash on May 03, 2018, 05:45:44 pm ---Also, have a look at this article in regards to bypass capacitors.

--- End quote ---

Thanks for your reply. May I ask at least for little explanation what is wrong with way I have done it or why it is wrong. The linked question itself is about capacitor placement on 4 layer PCB, but I use only two layers (not sure if that changes anything, I have not read comments and answers yet).

Lt_Flash:
Ground plane is basically a big shielding, it reduces any EMI effects and also structurally it makes the board more sturdy as most of the copper stays on it. In regards to power lines - you've got a very long power trace going from one current user to another, each trace has resistance and impedance, so effectively after each device that consumes current you're getting a small voltage drop, as any trace has resistance. Also, any trace has impedance and capacitance and impedance is basically acting as a resistor, trying not to change magnetic field and thus not allowing for current to flow, this also reduces current. Yes, it's all very small values but it's still not recommended to have a power trace, that's why we have 4 layer boards - basically they have signal traces on both sides and then a solid ground and power planes in the middle.

In regards to bypass capacitors you should take into account the same - your power traces design is in series and if your MCU is switching it's outputs fast and you connect VCC points from bypass cap to next bypass cap on next chip and so on - capacitors may not charge fast enough and that would cause troubles for MCU as it will not have enough power. Bypass caps are basically devices that can provide current fast when it's required. Here's another example from TI about bypass layout. In your case you can just put traces up and down from the cap, not sideways, as you did. Also, if you have ground plane on top (don't forget to put multiple vias connecting it to bottom ground plane) - you just need to connect power line and the other end of capacitor will have perfect connection to ground.

http://slideplayer.com/slide/4662087/15/images/31/Bypass+Capacitor+Routing.jpg

Lt_Flash:
Have a look at this picture too:


--- End quote ---

Lt_Flash:
And another good example why you would want to have a signal layer GND plane. Also, by the way, it dissipates heat very well, so, for example, for all my LiPo charger designs I'm always using GND planes on both sides with as many vias as I can put close to charger IC and power polygons instead of just traces. Here you can see a 'Signal ground' which is just a top ground plane, and you can see VCC lines for capacitors.

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