Why does this 5V circuit use two of the EXACT same value capacitors?
It's not needing a larger capacitance issue considering 100nF is relatively small.
Here is the full schematic: Arduino Leonardo
Electronic – What’s the purpose of having two of the same value caps in parallel
capacitorpower supply
Related Solutions
The two capacitors used in the LM317 typical application are described on page five of this datasheet. An identical schematic to the one you provided is given:
Along with a helpful note about why the capacitors are needed:
Note: 3. \$C_i\$ is required when the regulator is located an appreciable distance from power supply filter. \$C_O\$ is not needed for stability; however, it does improve transient response. Since \$I_{ADJ}\$ is controlled to less than 100 μA, the error associated with this term is negligible in most applications.
The best practice, for either capacitor, is to always include them. Specifically for \$C_i\$, place it as close to the input pin on the LM317 as reasonable.
If you have determined that you know what you're doing, you can decide to omit or alter the suggested schematic. In determining that, for \$C_i\$, an appreciable distance in on the order of centimeters, but you should also factor in the level of noise you expect on the input supply and how much the load the LM317 will be changing. For \$C_O\$, you can likely omit it if you have decoupling capacitors at the inputs of any ICs and relatively high current draw devices, anywhere things are going to be changing how much current they're drawing in a short amount of time.
Do check out the related questions and answers regarding how to use decoupling capacitors and how to select the type of capacitors to use.
The various size, style and values of capacitors shown are selected because of the advantages of each type.
Normally the smaller non-polarized capacitor will have better performance at high frequencies.
The larger valued capacitors that are polarized will have ability to work at lower frequency and smooth larger current flows at those frequencies.
Note also that one capacitor is isolated from the others via a ferrite bead so there is not a direct combination possible anyway.
So as you can see there is a disadvantage to combine all the values to a single capacitor.
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Best Answer
Because they're decoupling caps for two different ICs or supply paths. On the schematic they're side-by-side, but on the actual board they're over by the ICs they're decoupling.