[SI-LIST] Re: MLCC Derating
- From: Joel Brown <joel@xxxxxxxxxx>
- To: g.h.johnson@xxxxxxxxx
- Date: Fri, 21 Nov 2014 12:29:09 -0800
TDK does a good job of this.
They have graphs for on their web site of all of their ceramic caps.
I use this a lot when selecting caps for switching regulator design.
Of course their data may not apply to other manufacturers.
Joel
On Fri, Nov 21, 2014 at 9:39 AM, Jerry Johnson <g.h.johnson@xxxxxxxxx>
wrote:
> The dielectrics in capacitors are ferroelectric and have a
> hysteresis loop very similar to magnetic materials. The
> difference
> is that the horizontal axis is Volts/thickness (e.g Volts/mil)
> and the vertical axis is the degree of polarization of the
> material.
> The permitivity is the slope of the plot at any point of the
> loop.
>
> You can have two capacitors of the same value, the same voltage
> rating, and the same material designation but have very
> different
> loss of capacitance with applied DC voltage. If they are
> constructed
> to have different spacing between the capacitor plates they will
> have a different Volts/mil for the same applied voltage.
>
> That's why you won't see much data published on the
> capacitance vs
> voltage for specific material types, since it also depends
> on the
> physical construction of each part.
>
> You can understand many other capacitor characteristics by
> understanding the hysteresis loop. The area of the loop relates
> to the loss per time you traverse the loop. There are major
> and minor loops possible. Saturation drops the permitivity to
> near zero for some materials while others (those with lower
> specified permitivity don't saturate nearly as much.
>
> (First response to the si-list in several years!)
>
> Jerry
> On 11/21/2014 11:08 AM, Ajay Dhingra wrote:
> > Hi All
> > Regarding MLCC viz X5R/X7R/Y5V
> > Is there any standard way of calculating ultimate degraded(de-rated)
> value
> > of the capacitor. Datasheets define various kind of de-ratings viz, DC
> > bias, AC Bias, Temperature, Aging, DC Bias aging etc. But it's not
> > specified if we need to account for all of them to come at final de rated
> > values. I have observed all the de-ratings are not independent and varies
> > with others.
> >
> > Does a capacitor has a saturated value? and some test to find that.
> >
> >
> > Thanks
>
>
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