Capacitance versus voltage for X7S caps?

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Tried the major mfgs and the typical datasheet looks like this:

http://www.avx.com/docs/Catalogs/cx7s.pdf

Quote "Capacitance for X7S varies under the influence of electrical
operating conditions such as voltage and frequency."

Then under diagrams ... nada, zip, zilch. Great.

One paper listed X7S with the same voltage coefficient as X7R but that
doesn't sound right. Anyone have a link to some hard data, with a graph
in there and preferably no marketing hype?

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: Capacitance versus voltage for X7S caps?




Joerg wrote:
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Joerg,

Not too long ago I was also looking for C(V) dependencies for different
capacitor types; didn't find much useful information either. One of the
reasons for that is C(V) behavior of particular cap is strongly affected
by electrostatic mechanical (!) effects; thus, at low frequencies, it is
too much of dependency from everything.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

Re: Capacitance versus voltage for X7S caps?


Joerg a écrit :
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I looked at that recently but for X7R/X5R. Data sheets often have
nothing, but the good manufacturers offer some 'simulation' program with
lots of curve fitting,...

IIRC TDK has some web base one too.
I think Kemet, AVX, Murata, Taiyo have what you're after.


--
Thanks,
Fred.

Re: Capacitance versus voltage for X7S caps?


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I've been through those. My impression was that a lot of docs I used to
see there have been "cleaned out". I need something in the form of a
document, not a simulator. Also, other than SPICE and beam field
simulators I don't trust them. For example, National has flagged all my
first switchmode converter ideas as "can't be done". And all went into
mass production without a hitch ...

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: Capacitance versus voltage for X7S caps?


On Wed, 24 Mar 2010 16:22:59 -0700, Joerg

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I seem to recall reading that C0G and NP0 dielectrics have
the lowest cap-vs-temp dependance and that pretty much
everyone "understands" that X7R dielectrics have large
coefficients and are pretty much unsuitable where it matters.
They pack a lot of capacitance into a small space and that
makes them great for decoupling jobs and not so much else.

But I don't know remember reading anything about X7S,
specifically.  If they are the same as X7R, they are crap if
what else I read was right.

Jon

Re: Capacitance versus voltage for X7S caps?


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The lousy ones are Y5V and Z5U. X7R is actually pretty good.

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: Capacitance versus voltage for X7S caps?


On Wed, 24 Mar 2010 17:41:39 -0700, the renowned Joerg

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For low values of "pretty good". I suppose losing 20% of capacitance
due to voltage and/or 5% due to temperature and/or a few more percent
due to aging is better than -80% or whatever..

NP0 are now available (though a bit pricey and bulky) even in fairly
large values like 0.1uF 1206.


Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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Re: Capacitance versus voltage for X7S caps?


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Exactly. We only go to about 50% of rated voltage under normal operating
conditions and I'd be perfectly happy if the capacitance loss there
would be 20%.


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But not 4.7uF/100V :-)

Oh, and it can't be taller than 0.100".

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: Capacitance versus voltage for X7S caps?


On Wed, 24 Mar 2010 17:41:39 -0700, Joerg

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X7R is bad enough that it distorts like hell in an audio
amplifier (used as the Miller cap) and I know I certainly
can't even come close to using them in integrators, from
actual (hilarious, for a moment) experience.  Decoupling is
what they are good for.

Jon

Re: Capacitance versus voltage for X7S caps?


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Unsurprisingly, the integration curve (step input) looks just like a high
permeability, ungapped ferrite inductor's.

You're just tracing out the D-E curve instead of the B-H curve.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms



Re: Capacitance versus voltage for X7S caps?


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That's what I am needing them for :-)

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: Capacitance versus voltage for X7S caps?



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That is relatively easy.  Polystyrene, polyethylene, or20%
polyethylenterephthalate [PET / Mylar] are normal materials20%
of choice.  Of course if you have atypical size constraints20%
you may have real difficulty obtaining any parts of reasonable20%
price.

Re: Capacitance versus voltage for X7S caps?


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Atypical? A 4.7uF/100V film cap is going to be humongous.

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: Capacitance versus voltage for X7S caps?



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About 1/2 cubic inch any way you pack it.
Alternatively i might try the aluminum polymer electrolytics.

Re: Capacitance versus voltage for X7S caps?


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  "Electrolytic" makes an alarm bell go off in my head against
expectation of capacitance refusing to vary with voltage.

  Is there a reason for polymer to fix this for aluminum electrolytics?

 - Don Klipstein ( snipped-for-privacy@misty.com)

Re: Capacitance versus voltage for X7S caps?


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Tantalums are quite excellent (typically 10%, stable enough e.g. for long
period timing), but they have a tendancy to explode.

By removing the moist electrolyte from the capacitor, replacing it with a
conductive organic polymer, the alpos get tantalum grade performance without
the risk of incineration.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms



Re: Capacitance versus voltage for X7S caps?


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Do you know how they take hardcore freezes, like north of the Klondike
in January?

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: Capacitance versus voltage for X7S caps?



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Oscon aluminum organic polymer are characterized to -55degC., with
less than 10% cap reduction. At 4.7uF, ESR is in the 80mR range.

Later developers tend to follow this.

RL

Re: Capacitance versus voltage for X7S caps?


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I have used Oscons on another project. They are very expensive and in
this case I need 100V and the height cannot be more than 2.5mm or around
0.100".

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: Capacitance versus voltage for X7S caps?



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I'm not sure if you've actually stated your requirement at some time
or another. You seem to be merely floating generalized but limited
questions regarding part characteristics.

What is the actual requirement?

RL

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