Arduino with voltage regulator

  • Hi All,
    first of all sorry if its way basic question but i need bit of advise before i go crazy over voltage regulator and how people are using it.
    if you look at typical applications for the mic5219 regulator it has no capacitor on input and on output it 2.2uf tantalum and 470pf but when i look at all arduino board design and schematics i see 10uf on input, and on output 10uf, 0.1uf capacitor. Can someone with better hardware understanding shed some light on this for me

    sparkfun schematic

    voltage regulator data-sheet

  • Filtering the power lines on input and output is generally not a critical issue when it comes to the value of the capacitors unless you plan to produce a large number of boards when cost of components become the issue.

    If you are looking for a trouble-free operation it is better to be safe than sorry and to be conservative in the dimensioning. So 10 uF on the output is better than 2.2 since it provides more filtering of low frequency noise. 0.1 uF is better than 470 pF since it provides more filtering of high frequency noise. 10 uF on the input also filter out spikes in the input power, should there be any, so that they do not pass through the regulator. It is good practice to have both a 10 uF and a 0.1 uF capacitor on the output since they have different electrical capabilities to filter low and high frequency noise.

    So in essence, the value of filtering capacitors is not that critical most of times. Too little filtering could give you issues with the radio, which is sensitive to noise on the power lines. This is why there always should be a capacitor of at least 4.7 uF close to the radio power input.

  • @bgunnarb thank you for explaining

  • Hero Member

    @pihome Maybe because the Pro Mini doesn't necessarily have a radio attached to it, Sparkfun didn't care as much about noise. It would appear that Sparkfun's Pro Mini design, by default, assumes no radio is connected.

    Details from the datasheet tell the tale:

    • "Reference Bypass: Connect external 470pF capacitor to GND to reduce
      output noise. May be left open." i.e. The 470pF relates specifically to the bypass pin and noise reduction.
    • " The minimum size of the output capacitor
      is dependent upon whether a reference bypass capacitor is
      used. 1µF minimum is recommended when CBYP is not used
      (see Figure 5). 2.2µF minimum is recommended when CBYP
      is 470pF (see Figure 6). For applications <3V, the output
      capacitor should be increased to 22µF minimum to reduce
      start-up overshoot. "

  • thank you guys for explaining this, some times asking question is easy then googling around and finding contradicting answers.