I'm fairly new to the topic and about to design my own first pcb, soldering my own MCU onto it, finally moving on from arduino boards and breadboards.
I am very confused about when reading a datasheet or a tutorial and they recommend a capacitor. Schematics, descriptions and explanations only account for the amount of capacitance the capacitor is supposed to(!) have. Nowhere do they say anything about which type ("class?" - at least for ceramic capacitors) you are supposed to use.
My knowledge so far:
I would guess, unless specified, a ceramic capacitor type is almost always the way to go. If a datasheet calls for something else, that will actually be told.
Capacitors are (mostly) used as a buffer (to provide energy for sudden higher currents), and also used to filter out noise (by filtering out noise from other components but also preventing noise from being generated by acting as a buffer as I just mentioned so voltage does remain stable).
Capacitors of different capacitance have difference impedance curves.
Ceramic capacitors have two classes. One is more accurate and temperature stable (as in the capacitance is) (class 1) than the other (class 2).
I saw various videos and slideshows, and read numerous articles on this topic. However I actually feel more confused, as most of these seem to be focused on showing and telling why people with more advanced and in-depth electronics knowledge have been choosing the wrong capacitors and less about hands-on approaches on what type to pick when. They also introduce a lot of different concepts and terminologies very quickly and abundantly that I am not yet familiar with. There doesn't seem to be a step by step approach that gradually gives me more information which makes it very difficult for me to ease into this.
My questions:
When reading a datasheet or some other source and a capacitor of a specific size is recommended, how do I know...
What class of capacitor to use?
And/or
Which submaterial type(?) to use? NP0, X7R, Z5U, etc.? (I notice some if not all are designated to a specific class, hence I am phrasing these "two" questions as "and/or")
Some datasheets/situations where I would like some advice which we can use as exemplary situations to explain this to me:
The ATTiny 162* datasheet and it's power supply schematic.
I would go for a class 2 capacitor for the higher value cap(s), and a class 1 capacitor for the lower valued cap. I'm not sure why, I would guess because of the higher rating accuracy of the capacitance of the larger one(s) is not that critical. Although I could easily understand that given two/three differently sized caps are used to have higher impedance spread out across the board (figuratively) both should be class 1 capacitors. (General question: When in doubt, is it advised to go for a class 1 capacitor?)
Plus it says "High Frequency" for C2, so I see this as a keyword for using an NPO/COG (class 1) capacitor.
I would go for a class 1 capacitor here simply because the capacitor and resistor are used as a oscillating circuit and accuracy is advised here.
A "simple" momentary switch debouncing circuit. I would say a class 2 cap because of the size, and also because it is advised to add another resistor so the cap itself doesn't induce any noise (if I recall correctly?)
Type isn't critical. Max voltage and capacitance are the critical params.
Normally sort for voltage and value on DigiKey or Mouser (JameCo is DOWN) and buy whatever physical size and cost you feel is appropriate. Ceramics and electrolytics are common. If no spec is listed most any part will do. We're not designing UHF front ends where parasitics etc. are important. This is POWER supply and bypass caps, ESR etc. just isn't important at these levels.
If there is a specific part needed, the schematic should call out the spec. No spec, use what you got.
Never really come across "class" as a description of a capacitor, in over 50 :years in electronics, so it is either wrong or new.
This describes various types of capacitors.
Well worth a read. The dielectric is the stuff between the plates of a capacitor and has a lot to do with, temperature coefficient, that is if the capacitor increases or decrease with an increase in temperature, and by how much. So while you can get a ceramic capacitor there are a myriad of different dielectric that can be in them. So for example with a decoupling capacitor you are not so much interested in the actual value but in the amount of inductance it has because the self resonant point, the frequency where it stops looking like a capacitor and starts looking like an inductor determines the maximum frequency it can filter out.
On the other hand if you want a stable capacitance with a low temperature coefficient for something like an RC oscillator then your choices are governed by the frequency you are using. For high frequencies the best capacitor to use is the silver mica type, but these are limited to how big you can get the capacitance.
Remember the best capacitor for the job is not always needed, with the exception of decoupling capacitors which have to be ceramic for them to be effective.
Basically it comes down to knowing what you are doing and what you want from a capacitor.
The designations NP0, X7R, Z5U specify the change in capacitors over temperature.
NPO is the most stable but the most costly. Unless you are using it for a timing circuit its never worth the $$.
X7R is a "medium" stable capacitance over temperature. This is all I use for hobby use.
Voltage:
Ceramic capacitors capacitance drops with higher voltages and its relatively easy to make capacitors that are well above what we use for Arduino circuits and 12v power. I usually use 50V. but higher is OK, lower to 25V is OK for Arduino but I wouldn't recommend 25V for a 12V circuit.
Package size:
I usually pick 0805 because its the smallest I like to solder. 0605 is a PIA to solder. 1206/1210 are getting hard to get at the 0.01 and 0.1 µf range.
Usually you can get by with a 0.1µf nearly everywhere***. For circuits (usually regulator circuits) requiring 1µ or 10µF I have been using ceramics. Often tantalum are suggested but these are costly and lately the 10µ ceramics are reasonable.
This touches on only a small part of capacitors, however for Arduino typical circuits it should be enought.
*** for crystal circuits you must use the values specified by the mfg.
Thank for your replies!
So I see there seems to be a tendency towards the direction of "X7R is almost always good", "get a higher voltage rating because of capacitance drop".
@JohnRob
So you recommend 25V and higher rated capacitors for MCU-voltage regions?
@Smajdalf
As far as I understand the materials are tied to specific classes.
What is your take on materials then?
Yes, if you look at the offerings of ceramic capacitors you will find 25 and 50 volt are most common from the more well know mfg. You only go below that if:
you are in the 10µf and higher capacities (a specialty at the moment)
I've been doing some reading (and watching) based on all of your suggestions.
Right now I feel like I have understood enough, however, if I have any more questions, I will just leave another post here.
