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Proper decoupling capacitor practices, and why you should leave 100nF behind
Ever wondered why 100nF is a go-to value for decoupling capacitors? This number has pervaded in datasheets and electronics advice going back to the 1980s, and is still widely present in the datashe…
This is partly due to more modern MOSFET construction techniques that improve switching speeds and efficiency, but also came as a side-effect of die shrinks, where manufacturers use physically smaller transistors in order to squeeze more chips out of a silicon wafer. If you take the exact same circuit design and replace the ICs with modern equivalents that have undergone die shrinks, suddenly the EMI will look a lot worse. Consult the datasheet and the part vendor’s simulation tools for exact details, but as a rule of thumb physically moving the large MLCCs away from those areas by a small distance will drastically improve the phase margin, because the parasitic inductance in the traces acts to decouple that extra capacitance from the control loop.
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