Tolerance tolerance...

On the atmega32u4 datasheet it says:

  • Serial resistors on USB Data lines must have 22 Ohms value (+/- 5%).
  • Ucap capacitor should be 1µF (+/- 10%) for correct operation.

Can someone explain what those tolerance mean? What if I use parts with lesser tolerance like +/-1%?

It is only an indication. There are different types of resistors and capacitors. Sometimes a metalfilm resistor is needed or a special capacitor with low ESR of a special type of capacitor.
A 5% resistor and a 10% capacitor means just normal components. You can use of course 1% components. That means that the 22 Ω is probably closer to 22 Ω.

±5% means that the 22 Ω can be 20.90 up to 23.10 Ω
±1% means that the 22 Ω can be 21.78 up to 22.22 Ω

Perhaps it will still work when that value is 0 Ω to 120 Ω. But then the specifications in the datasheet are no longer valid.

Ucap capacitor should be 1µF (+/- 10%) for correct operation

That means that the cap will have 1uF of capacitance lus or minus 10%. So the real capacitance of that capacitor is between 0.9 and 1.1 uF. If yours has a 1% tolerance then it is certainly within that spec right? Your says that it is something between 0.99 and 1.01 uF.

Guys thank you! That's all i needed to know. :slight_smile: