What decoupling capacitor to use.

Thread Starter

TheCircuitsHaveEyes

Joined Mar 19, 2016
16
I'm using an Atmel microcontroller together with an LCD Display, a 16-button keyboard and some LEDs. I'm using a 5V wall adapter to power all this on my breadboard.

However, I'm not sure what kind of decoupling capacitors to use or their size. From what I've read, 0.1uF ceramic caps are the best for this job, but the store in my city only has very low capacity ceramic ones, with 10nF being the largest. They do have 0.1uF polyester ones though.

What is the best one in my case? Also, does voltage rating matter at all, because the ceramic ones are rated to a massive 500 V.
 

dl324

Joined Mar 30, 2015
11,282
0.01uF or 0.22uF would also work. Is mail order an option?

Voltage rating will affect the size of the cap. Anything with a rating of at least 10V; don't think you'll find many ceramic caps rated below 25-50V.
 

Thread Starter

TheCircuitsHaveEyes

Joined Mar 19, 2016
16
0.22uF would be ideal, but like I said, 0.01uF is the largest ceramic they have. Are you sure that's enough? I think I'm going to wait for some more answers.

Also, considering transportation would cost about 30 times as much as the capacitor itself, I really do not want to mail order if I can help it.
 

dl324

Joined Mar 30, 2015
11,282
Are you sure that's enough? I think I'm going to wait for some more answers.
That's certainly your prerogative.

Sometimes you can get away with no additional supply decoupling. Sometimes 0.1uF isn't optimal. It really depends on the frequency of the supply noise you're addressing.

On a breadboard, you're going to have all sorts of coupling. I can't remember ever putting a decoupling cap on each IC on a breadboard.
 

SLK001

Joined Nov 29, 2011
1,548
Only having a 0.01μF capacitor in stock? I would find another store. The recommended decoupling capacitor is 0.1μF. If you only use the 0.01μF, you risk issues from the digital switching noise.

The choice, of course, is up to you.
 

Thread Starter

TheCircuitsHaveEyes

Joined Mar 19, 2016
16
There's only two electronic stores here and the one I usually shop from was the one I mentioned. The other one only has electrolytic capacitors :((.

Is the polyester capacitor so bad at decoupling? There was a datasheet for one that mentioned decoupling as one typical application.
 

wayneh

Joined Sep 9, 2010
16,399
I'd buy some of 0.1µ ceramics by mail-order in a pack of 50-100 or so. When you place them on every IC and use them for miscellaneous other chores, you go through them like candy. Figure out what other components you might need and pool your order to minimize shipping charges. A pack of resistors is handy to have on hand.

It's rare I can find what I want in local stores anymore.
 

Thread Starter

TheCircuitsHaveEyes

Joined Mar 19, 2016
16
Okay so apparently I'm a noob and also the store's website categories are confusing. I just checked in the "Multilayer capacitors" and they look exactly like the ceramic ones. There I found 100nF caps. Some are also labelled "monolithic" within the "Multilayer capacitors". Shouldn't multilayer and monolithic be entirely different things?

In any event, this is the one : Y5V, CM-100N
 

SLK001

Joined Nov 29, 2011
1,548
Shouldn't multilayer and monolithic be entirely different things?

In any event, this is the one : Y5V, CM-100N
Monolithic means "one piece". Most ceramic chips are multilayer. Buy any generic 0.1μF ceramic capacitor, be it leaded or surface mount and use that in your design. Buy extras, 'cause as wayneh says, you will use them like candy.
 

takao21203

Joined Apr 28, 2012
3,695
Metal film is a bit inductive so as for high frequency spikes, the capacitance this signal sees is smaller.

For low frequency electrolytic works or just any kind but above 30 mhz you need the correct parts. You could use 4.7uf ceramic. But high frequency circuits often use a smaller additional capacitor.
 

ian field

Joined Oct 27, 2012
6,539
0.22uF would be ideal, but like I said, 0.01uF is the largest ceramic they have. Are you sure that's enough? I think I'm going to wait for some more answers.

Also, considering transportation would cost about 30 times as much as the capacitor itself, I really do not want to mail order if I can help it.
Aside from special RF types - ceramic decoupling capacitors have the advantage of being lossy at high frequency, that is the supply rail spikes are to some extent dissipated as heat. On a technical level; the loss factor appears as a resistive component that functions as a Q spoiler. That reduces the chances of distributed decoupling capacitance resonating with any parasitic inductance in the supply traces.

Most foil types are probably OK, but will take up a lot more space than ceramic. You should avoid any types that are normally used for RF work.

0.1uF is a common value for supply decoupling - but on high end gear, you'll probably find 0.22uF.

Multilayer ceramic chip capacitors are very small for any given capacitance and weigh in at among the lowest ESR. Most are SMD, but some manufacturers will supply resin dipped leaded parts - I've seen brochures offering values as high as 180uF.
 

dl324

Joined Mar 30, 2015
11,282
The rule of thumb value will not work for all cases. You have to consider ESR/ESL of the caps (and power nets) and the frequencies that require bypassing. The topology of the power supply net(s) and whether ground planes are used should also be considered.

I just noticed that this recent post is coming up as a similar thread.
 

RichardO

Joined May 4, 2013
2,271
In any event, this is the one : Y5V, CM-100N
These caps sound like they will work... But, be warned that the Y5V dielectric is very sensitive to temperature. At temperature extremes (which are not very extreme) the capacitance can all but dissapear.

If you are only using the circuit at "comfortable temperatures" then the Y5U caps are fine. I would recommend that you plan on using caps with X5R and X7R dielectrics in the future. These caps will be a bit bigger but the larger size is worth it.
 

Tesla23

Joined May 10, 2009
406
These caps sound like they will work... But, be warned that the Y5V dielectric is very sensitive to temperature. At temperature extremes (which are not very extreme) the capacitance can all but disappear.
I had an understanding that these things were pretty temperature dependent (i.e. don't use them where you want a stable capacitance), but that comment sent me looking for data. From the Vishay datasheet:

y5utemp.PNG

Thanks Richard.
 
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