What type of capacitor to use?

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#1
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As some of you know. I'm more a digital guy. When I look at schematics and they indicate capacitors, they seldom indicate which type. With so many out there (ceramic, electrolytic, ... etc) how do I determine which type to use?

Thanks,

-Adam
"Please don't judge my God by my inability to follow him" - Chris Mollins
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www.onecircuit.com
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Here's the standard consultant's answer"

"It depends."

I have a little blue book called "The Capacitor Handbook" that I refer to all the time. When I go home later, I will get you more info so you can get you a copy.

official AVR Consultant
www.veruslogic.com

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You might also want to take a look at this post - it has a link to a good PDF hardware design guide. There was a capacitor chart in there that had the pros and cons for the various types.

Dave

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I found an article in a muRata Mail brochure/mini-zine titled Choosing between Ceramic and Tantalum capacitors.

An interesting paragraph states

Quote:
MLCCs (multilayer ceramic capacitors) need no temperature derating... Selection of a Tantalum is different. There is a linear reduction of the working voltage above 85 deg C so that at 125 deg C the allowed DC voltage can be as low as 2/3 of the nominal value.

The last paragraph concludes:

Quote:
MLCCs have a wider frequency bandwidth and lower impedance than Tantalums, more effective in suppressing noise in power lines. The MLCC's impedance reduces by a factor of 10 when the frequency is multiplied by 10 and can be a few milli-ohms. The impedance of Tantalum capacitors remains the same above 10 KHz hundreds of milli-ohms.

"You live and learn. At any rate, you live."

Douglas Adams

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Simple question - complex answer! A good book would be "The art of electronics" by Horowitz and Hill. It's not a cheap read but should answer most of your electronic questions.

In short, for your 22pF caps used across the crystal, ceramics are the go. For the 10nF and 100nF bypass caps that are on the power rails of the micro, ceramics are the go. For bulk capacitance, electrolytics are used. It is quite an involved subject that would take many pages to describe as there are a number of different types of capacitors each with their particular application. typical requirements might be: voltage,temperature,temperature stability, tolerance, capacitance,frequency, ripple current and so on.

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in general: ceramics for bypassing (small values, guard against HF), electrolytics for charge storage, and MKTs for sensitive signals (eg audio frequency) where clarity is important.

tantalums have the unfortunate ability to fail short-circuit as well, which can lead to them glowing red hot (an obvious safety issue).

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Kartman wrote:
Simple question - complex answer! A good book would be "The art of electronics" by Horowitz and Hill. It's not a cheap read but should answer most of your electronic questions.

Hey I actually have that book from my old college days. What a great reference. Thanks for the tip... I'll dig it out and take a look.

-Adam
"Please don't judge my God by my inability to follow him" - Chris Mollins
================
www.onecircuit.com
================

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Not all ceramics are made alike. NPO/C0G have the best performance over temperature but are only available in small values. X7R is a good general purpose ceramic and has a very wide temperature range. Also the capacitance has an applied voltage factor. I try to avoid Y5V caps.

Always remember to derate the voltage on tantalums. Ceramics do not need voltage derating.

edit:
Walt Jung and Dick Marsh wrote a good article on capacitors.
http://www.waltjung.org/Classic_Articles.html