Post #3706294

@gsuberland@chaos.social No, input impedance to the board doesn't count. You need a couple ohms at exactly the right point. See the red X in the schematic below. Vin, 10uF, then through a 1uH inductor with this damped cap >=4x the capacitance of the 20uF caps feeding the buck switcher. The idea is to create a phase shift relative to input voltage to feed the smaller input caps on the switcher. Electrolytics have a little ESR to begin with, and in this case a 1 ohm resistor is probably enough to damp any oscillations.