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I'm looking for a power supply filter for this mcu. In page 1789 and 1790 referred that lots of the power supply pins needs decoupling capacitor filtering. Some of those pins need an additional inductor for LC filtering. The question is:

  • Why Cut-Off Frequency starts from few KHz (e.g. 10kHz) and not with value closest to Zero (0Hz)?
  • Why Frequency ends at few MHz (e.g. 10MHz) and not continues beyond of that boundary?
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A low cut-off frequency means that you need to use large components. Not only are have these components large dimensions and are heavy, they also become less ideal. Large capacitors and inductors have larger ESR than smaller capacitors/inductors.

High frequency behavior degrades in similar ways. The self-resonance frequency of inductors and capacitors for such filters is in the range of a few MHz at most, unless you use very expensive RF components (if those are available at all). Over this frequency and inductor shows capacitive behavior and a capacitor inductive behavior.

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Different frequency components are handled in different parts of the power distribution network.

If you have a switched power supply with 100kHz switching frequency on the input side, this will handle frequencies below 10kHz as a simple change in current draw of the entire assembly, so no further stabilization of the voltage is required.

Higher frequencies need decoupling capacitors, because the PSU would be too slow to react to these, as it does not continuously sample the output voltage.

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