0
\$\begingroup\$

I'm trying to source parts to build my own Huzzah32 (ESP-WROOM32 Dev board) and have grabbed the BOM from Eagle:

BOM:

enter image description here

I've found certain parts that are more 'unique' to me, at least, such as the USB-UART Bridge CP2104. But I want to be sure I'm getting the right capacitors, resistors etc. I have a general understanding of how these SMD components work but want to do my research to ensure I'm in good shape.

When searching on Mouser I see a wide range of 10uF ceramic caps in the 0805 package with different voltage ratings, etc. I know that just about everything on the Huzzah and ESP chip is 3.3v, but don't see caps specifically rated for 3.3v? I'm sure there's a general discipline on what parts to use, and was hoping someone had some wisdom to impart on it.

\$\endgroup\$
1
\$\begingroup\$

Generally for capacitors, any significantly higher voltage rating than the operating voltage will be fine. So you might use a 6.3 or 10V rated part. Bypass capacitors are not very critical as to capacitance value, as long as it exceeds the minimum. You should look at the circuit schematic and try to estimate the actual working voltage. For example, for an RS-232 driver chip powered from 5V you might need some capacitors rated at 16V rather than 6.3V.

If you are redesigning it to use physically smaller capacitors you have to be a bit careful because of voltage coefficients.

\$\endgroup\$
4
  • \$\begingroup\$ Got it. I'll look at the schematic to see about calculating that. If that is the case generally, is it a bad practice to hit, say 50V, to ensure you're above the threshold? \$\endgroup\$
    – AndrewL
    Oct 27 '20 at 12:23
  • \$\begingroup\$ For parts like small NP0 capacitors (pF up to maybe 1nF or even 10nF) it is okay or might be okay, but for higher values you'll end up paying more and may not be able to find the part in the package you want at any price. That is why they are offered in different voltage ratings. \$\endgroup\$ Oct 27 '20 at 13:53
  • \$\begingroup\$ I've found a 0805 1uF at 50VDC then. No major concerns there? Is the only major concern with how much the parts will cost rather than the function? \$\endgroup\$
    – AndrewL
    Oct 28 '20 at 13:45
  • \$\begingroup\$ To get high capacitance and high voltage rating in a small package sometimes otherwise inferior dielectrics must be used. Inferior characteristics might include temperature coefficient, aging, and voltage coefficient. \$\endgroup\$ Oct 28 '20 at 14:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.