Tag
decoupling
3 articles.
- Your 2.2 µF is 0.68 µF: DC bias and the capacitance you did not buy
Class 2 ceramics lose capacitance when you put voltage across them. Würth measured a 25 V X7R part losing 69 % of its value at its own rated voltage — and the datasheet headline never mentions it.
- The via is the decoupling: 40 dB from layout alone
Würth built one board with the same ferrite and the same two 100 nF capacitors in every channel, and changed only the layout. The worst channel is more than 40 dB down on the next best. The capacitor was never the variable.
- Why 100 nF, and the frequency where it stops being a capacitor
The value is inherited, not derived. What actually decides whether a decoupling capacitor works is its inductance — and above a few tens of megahertz your 100 nF is an inductor.