I am developing a circuit for a dsPIC30fxxxx microcontroller. In the documents I found a picture that depicts the Vdd circuits, see attachment.
What does the picture say?
Do I need 3 capacitors for each Vdd?

enter image description here B

  • 1
    \$\begingroup\$ There's some subjective religion about this and usually not much in the way of science. Depending on the input impedance of the pins, each of these caps form a low pass filter of sorts. If there are any particular frequency you wish to avoid, then different cap values may be suitable. For generic EMC it probably doesn't make much sense, since emissions could be from anywhere between a few MHz up to many GHz. If this is part of a RF product then it might be sense to adapt values to your own fundamental + harmonics. But smacking on multiple decoupling cap values is still mostly black magic... \$\endgroup\$
    – Lundin
    May 4, 2021 at 13:04

1 Answer 1


Probably yes. Note how C6, C7 and C8 are different values: they are meant to work as a group to provide a low impedance at different frequencies. I read the schematic as instructing you to place one group of three close to each pin (order them by capacitance with the smallest closest to the pin)

Now, it's quite possible that in practice you can use a different configuration. See if you can find the schematics for an evaluation board as these are often more concrete than the chip's datasheet.


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