Partlist Wednesday: Ceramic capacitors

in partlist, parts by Ian | 5 comments

Every Wednesday we highlight a component from the updated partlist. This week: surface mount ceramic capacitors.

Ceramic capacitors are cheaper than aluminum and tantalum SMD caps, but come in smaller values. Typical values are in the pF to 1uF range, but we’ve noticed some 2uF+ ceramic caps at Mouser recently. Most have a maximum rating between 25 and 50volts.

Unlike electrolytic capacitors, ceramic caps are unpolarized. There’s no + or – side, they can’t go in backwards on accident.

Our favorite packages are 0805 and 0603. We recently standardized on the smaller 0603 because it can be 30-50% cheaper than 0805.

Here are some rules of thumb for ceramic capacitors:

  • Value: pF, nF, uF, F, etc. Usually taken from a schematic, partlist, or datasheet.
  • Voltage: We choose something at least double the operating voltage. A 0.1uF cap decoupling a 3.3volt power pin should be rated for at least 6.6volts.
  • Tolerance: How close to actual value is any given capacitor. Not really important unless it is an audio or analog application, and the datasheet will specify. We don’t worry about this for digital stuff.
  • ESR: How ‘fast’ is a capacitor. For most digital hobby stuff this is never important, maybe switch mode power supplies. If it is, the design probably says what to do.
  • 100nF is the same as 0.1uF. A 0.1uF ceramic capacitor is generally used on every power pin of a digital chip. Commonly called a decoupling capacitor because it lessens the effect of a digital chip on a circuit power supply.
  • 18pF, 0.1uF, and 1uF ceramic caps are most common in our projects, we buy them by the reel. Get a cheap capacitor kit from eBay so you have a couple of the other values available too.
This entry was posted in partlist, parts and tagged , .

Comments

  1. James Hudson says:

    I have now started using these parts Murata GRM31CR61E106KA12L. 10uF X5R 25V in a 1206 package. They are MLCC construction. One third the size of a similar tant and non-polarized. The GRM series even has 100uF parts but only in a 6.3V part. The 10uF parts I use are great for the input and output on voltage regulators. Mouser sells them for $0.21 at 100 pieces.

  2. erdabyz says:

    Oh well, 2uF+ ceramic capacitors are really reaaally common. I have a nice stock of 10uF 10V 0805, 10uF 16V 0805, 4,7uF 0805…. and lots more, and I use them a lot, as they are cheaper, smaller, safer and for lots of uses better than tantalum ones. They are available at up to 47uF in 0805 I think, and they should be easily available at up to 22uF 0603.

    These capacitors have however some drawbacks, and one must know how to choose them. Generally you’ll have to look at the dielectric material, and get always X5R or X7R type, which are the best ceramics which are still very cheap. These tend to have capacitance variations of less than 15% over the entire temperature range. It’s capacitance varies with the applied voltage. Most times they have 110% rated capacitance at small voltages, 95-100% at half the rated voltage and around 80% at the rated voltage, so one must take that into account.

    They also use ceramics that are piezoelectric, so these capacitors tend to suffer from microphonics (the higher the capacity density, the higher the micrphonics).

    Apart from these drawbacks, they tend to have really low ESR and also verly low inductance. And they are way cheaper than tantalum caps of the same ratings, and smaller.

  3. kmmankad says:

    I was just about to hit ‘submit’ on the importance of choosing the dielectric part (erdabyz already mentions).THAT PART IS IMP. Do read!

  4. Ian says:

    Great info, thanks! I have always designed with tantalum caps above 2uF, but that part is a drop-in replacement for an A-case. I just ordered some and will try them on the next prototype.

  5. Brian says:

    Ian I was looking at your part list. I use an ABM7 XTAL on Eridani. I noticed there is now ABM2 which are slightly bigger but cost about 0.50 for the quantity you would be building at Seeed. Might be of use to you for a size/price tradeoff.

    EG:
    http://www.mouser.com/ProductDetail/ABRACON/ABM2-16000MHZ-D4Y-T/?qs=sGAEpiMZZMsBj6bBr9Q9aV1JZYJL70sAJWRjCEl9sgc%3d

    On caps I too prefer to use ceramic whenever possible at least up to 10 uF. Normally electrolytic (Al) for anything above that.

Leave a Comment

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>

Notify me of followup comments via e-mail. You can also subscribe without commenting.