Posted on Wednesday, July 6th, 2011 in partlist, parts by Ian
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.
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