What decoupling capacitor to use.

Discussion in 'General Electronics Chat' started by TheCircuitsHaveEyes, Apr 26, 2016.

  1. TheCircuitsHaveEyes

    Thread Starter New Member

    Mar 19, 2016
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    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.
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    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.
     
  3. TheCircuitsHaveEyes

    Thread Starter New Member

    Mar 19, 2016
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    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.
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    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.
     
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  5. SLK001

    Well-Known Member

    Nov 29, 2011
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    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.
     
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  6. TheCircuitsHaveEyes

    Thread Starter New Member

    Mar 19, 2016
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    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.
     
  7. wayneh

    Expert

    Sep 9, 2010
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    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.
     
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  8. TheCircuitsHaveEyes

    Thread Starter New Member

    Mar 19, 2016
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    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
     
  9. SLK001

    Well-Known Member

    Nov 29, 2011
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    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.
     
  10. takao21203

    Distinguished Member

    Apr 28, 2012
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    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.
     
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  11. TheCircuitsHaveEyes

    Thread Starter New Member

    Mar 19, 2016
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    Thanks for all the information guys. This thread has fulfilled its purpose. How do I close it?
     
  12. wayneh

    Expert

    Sep 9, 2010
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    Just walk away! :D
     
  13. ian field

    Distinguished Member

    Oct 27, 2012
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    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.
     
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  14. dl324

    Distinguished Member

    Mar 30, 2015
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    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.
     
  15. RichardO

    Well-Known Member

    May 4, 2013
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    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.
     
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  16. Tesla23

    Active Member

    May 10, 2009
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    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.
     
  17. dannyf

    Well-Known Member

    Sep 13, 2015
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    I typically use .1u but some times up to 4.7uf electroltics as well.
     
  18. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    Atleast you guys have a store to get parts from cause where I live we only have mail order parts..
     
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