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### Topic: Tolerance tolerance... (Read 633 times)previous topic - next topic

#### 2n3904

##### Feb 05, 2018, 03:41 pm
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%?

#### Koepel

#1
##### Feb 05, 2018, 04:38 pm
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 But then the specifications in the datasheet are no longer valid.

#### Delta_G

#2
##### Feb 06, 2018, 12:38 am
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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.
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#### 2n3904

#3
##### Feb 06, 2018, 01:53 am
Guys thank you! That's all i needed to know.

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