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Power to multiple MCU pins confusion. 2 layer board.

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  • Power to multiple MCU pins confusion. 2 layer board.

    Greeting everyone.

    Beginner here, I wanted to ask this thing which is troubling me. A micro-controller which has two VCC pins and they both require decoupling capacitors. But the VCC pins are on the opposite side of each other. Is it necessary to bring +5V power to both capacitors individually, like this :-

    First :

    Click image for larger version  Name:	2.png Views:	0 Size:	24.5 KB ID:	17896

    Or Can we do something like this :-

    Second :-

    Click image for larger version  Name:	1.png Views:	0 Size:	23.4 KB ID:	17897

    Does the second way messes with the functioning of decoupling capacitors? Is this okay?
    My board is 2 layer. I can't think of any other way.

    There is one more scenario like this in case of a voltage regulator which is confusing me.

    Click image for larger version  Name:	3.png Views:	0 Size:	32.9 KB ID:	17898

    I am taking the +5V from the output pin of the voltage regulator but not from the output capacitor. Is this bad or okay? Any opinions?

    Thanks.

  • #2
    I like the "First" screenshot more.

    This is a very simple explanation how I look at it: In the second example, the currents flowing to the second pin will "go through the first pin" so they may influence quality of the power on pin 1.

    In your power supply screenshot, I do not do that. I would place the output capacitor in the way between LDO output and rest of the circuit.

    I recommend you to watch this video, it can help:
    https://youtu.be/wbYzPwuEHPw

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    • #3
      Thanks robert for replying.

      Understood. That's what I needed to hear.

      Now I have worry about how to fan out the MCU tracks with a power trace cutting half of them. This is a big problem for me on 2 layer PCB. Considering that a 2 layer PCB is 35% cheaper here.

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