Ceramic Cap with DC Bias derating

Is it possible to use the Variable Charge Storage element to make a capacitor that derates its capacitance as its DC Bias voltage increases. For example, a 22uF X5R ceramic capacitor in 0402 case would derate as about: Ceffective = 22u * EXP( -Vbias / 3) The charge storage element is in coulombs, so how do I simulate it. Frankly, I wish it was in farad units because then it would be much more obvious.

by swagon
January 28, 2015

I tied using the model with the all-critical "*V()" to convert coulombs into farads, but after a few 100us, it crashes my simulation. I'm using it at the output of a switching regulator. Not sure if that matters or not. Anyway, when the simulation crashes, the voltage goes to kilovolts or negative kilovolts, and capacitance becomes near zero. It happens even if I put a small fixed capacitor in parallel. I'm using formula as Q = 22u * V() * EXP(-V()/3).

by swagon
January 29, 2015

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