Difference in performance between various temperature coefficient ceramic caps?

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Michael - 28 Jul 2008 16:42 GMT

Hey there - I was just thinking about TC (Temperature Coefficients) of
ceramic capacitors. So the temperature coefficient (ie X7R, NP0, etc.)
specifies the low temp, high temp, and max capacitance change. In
general, does it affect things like ESR or anything else? For example,
would an X7R and a Y5V generally have the same ESR at 25 C? What about
the slope of the ESR with respect to temperature?

On a side note - anybody know why values are pretty much always
printed on resistors, but pretty much never on capacitors? Strikes me
as bizarre.

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MooseFET - 29 Jul 2008 02:24 GMT

> Hey there - I was just thinking about TC (Temperature Coefficients) of
> ceramic capacitors. So the temperature coefficient (ie X7R, NP0, etc.)
> specifies the low temp, high temp, and max capacitance change. In
> general, does it affect things like ESR or anything else? For example,
> would an X7R and a Y5V generally have the same ESR at 25 C? What about
> the slope of the ESR with respect to temperature?

I believe that in most cases ESR goes up with temperature. On the
high K ones, ESR is also effected by the mechanical stress etc.

> On a side note - anybody know why values are pretty much always
> printed on resistors, but pretty much never on capacitors? Strikes me
> as bizarre.

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Fred Bartoli - 31 Jul 2008 18:46 GMT

MooseFET a écrit :

>> Hey there - I was just thinking about TC (Temperature Coefficients) of
>> ceramic capacitors. So the temperature coefficient (ie X7R, NP0, etc.)
[quoted text clipped - 5 lines]
> I believe that in most cases ESR goes up with temperature. On the
> high K ones, ESR is also effected by the mechanical stress etc.

That's not my experience. I've found it to slightly decrease with
temperature and slightly increase with applied voltage.

Signature

Thanks,
Fred.

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Tom Bruhns - 29 Jul 2008 23:26 GMT

> Hey there - I was just thinking about TC (Temperature Coefficients) of
> ceramic capacitors. So the temperature coefficient (ie X7R, NP0, etc.)
[quoted text clipped - 6 lines]
> printed on resistors, but pretty much never on capacitors? Strikes me
> as bizarre.

Actually, I see capacitance codes on SMT caps fairly regularly now.
Data sheets list the codes, which are things like A3, meaning (A) 1.0
times (3) 10^3pF.

I think you'll find that the ESR is a stronger function of frequency
than of temperature. I'd expect at low frequencies that, to the
extent the ESR is determined by the resistance of the metalization, it
would follow the temperature coefficient of resistance of the
metalization material, typically around half a percent per degree C.
http://www.avx.com/docs/Catalogs/useries.pdf gives you a hint that
capacitor manufacturers can control ESR to some extent by the design
of the capacitors.

I have some empirical evidence that suggests the tempco of capacitance
of C0G caps depends on the particular batch of dielectric ceramic. I
tried heating some with a soldering iron (so they went between room
temp and at least 100C) while monitoring the capacitance, and some
varied by several PPM/C (perhaps as much as 20ppm/C), while a few
changed practically none at all--amazingly stable! The measurements
were with an HP-4274A LCR meter at 100kHz, with about one part per
10,000 resolution, thus able to resolve a 100ppm change.

You might be able to get Kemet or AVX to give you more info about ESR
vs temperature and vs various dielectrics. I'll bet they know more
than they publish in the typical data sheets. There may even be ap
notes on it in their archives.

Cheers,
Tom

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Electronics Forum / Design / July 2008

Difference in performance between various temperature coefficient ceramic caps?