Capacitance versus voltage for X7S caps?
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From: qrk on 25 Mar 2010 12:41 If you can't find data, send me a sample and I can run it on our HP4194 impedance analyzer. -- Mark On Thu, 25 Mar 2010 08:02:15 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Robert Baer wrote: >> Joerg wrote: >>> 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? >>> >> I know that the rating system of ceramic capacitors allow "X7S" but i >> have never seen (anything)(anything)S even sold... >> So why the question? > > >Because distributors sell them and I'd like to use this one: > >http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=445-5211-2-ND
From: Joerg on 25 Mar 2010 12:48 qrk wrote: > If you can't find data, send me a sample and I can run it on our > HP4194 impedance analyzer. > Thanks for the offer, Mark. I have a HP4191 here so I could also do that. But this project is too fast-track. Needs to go into layout ideally by tonight or tomorrow morning, no time to get samples here. It blows my mind that maufacturers do not furnish such data. This time that could cost the sales since w may go hi-rel electrolytic, to be on the safe side. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: whit3rd on 25 Mar 2010 14:35 On Mar 25, 9:48 am, Joerg <inva...(a)invalid.invalid> wrote: > qrk wrote: > > If you can't find data, send me a sample and I can run it on our > > HP4194 impedance analyzer. > > Thanks for the offer, Mark. I have a HP4191 here so I could also ... > It blows my mind that maufacturers do not furnish such data. I think there's an important point being missed here: capacitance is a term in a linear equation, and the behavior of these capacitor materials is NONLINEAR. The 'capacitance' change is undefined unless you specify a full test setup. The nonlinearity of these materials includes hysteresis and memory effects and acoustic emission and sensitivity. They don't have 'capacitance versus voltage', they have nonlinearity. The manufacturer has good reasons to only specify a few limits.
From: Fred Bartoli on 25 Mar 2010 16:09 whit3rd a �crit : > On Mar 25, 9:48 am, Joerg <inva...(a)invalid.invalid> wrote: >> qrk wrote: >>> If you can't find data, send me a sample and I can run it on our >>> HP4194 impedance analyzer. >> Thanks for the offer, Mark. I have a HP4191 here so I could also ... >> It blows my mind that maufacturers do not furnish such data. > > I think there's an important point being missed here: capacitance is > a term in a linear equation, and the behavior of these capacitor > materials > is NONLINEAR. The 'capacitance' change is undefined unless you > specify a full test setup. > > The nonlinearity of these materials includes hysteresis and memory > effects and acoustic emission and sensitivity. They don't have > 'capacitance versus voltage', they have nonlinearity. The > manufacturer > has good reasons to only specify a few limits. Well, in fact that's even worse because some relaxation time factors in too. -- Thanks, Fred.
From: Joerg on 25 Mar 2010 16:17
Fred Bartoli wrote: > whit3rd a �crit : >> On Mar 25, 9:48 am, Joerg <inva...(a)invalid.invalid> wrote: >>> qrk wrote: >>>> If you can't find data, send me a sample and I can run it on our >>>> HP4194 impedance analyzer. >>> Thanks for the offer, Mark. I have a HP4191 here so I could also ... >>> It blows my mind that maufacturers do not furnish such data. >> >> I think there's an important point being missed here: capacitance is >> a term in a linear equation, and the behavior of these capacitor >> materials >> is NONLINEAR. The 'capacitance' change is undefined unless you >> specify a full test setup. >> >> The nonlinearity of these materials includes hysteresis and memory >> effects and acoustic emission and sensitivity. They don't have >> 'capacitance versus voltage', they have nonlinearity. The >> manufacturer >> has good reasons to only specify a few limits. > > Well, in fact that's even worse because some relaxation time factors in > too. > Those factors are all minor when using capacitors for bypassing. For all traditional ceramics such as X7R, Z5U or Y5V (the latter two having much higher non-linearity) the manufacturers give capacitance versus voltage spec. For X7S they don't. Somehow that smells like a "Marketing didn't like the graphs" situation. All I need to know is how much C will be left at 50% voltage, roughly. I don't care whether it's non-linear. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |