Wondering if anyone could help me rectify my understanding of decoupling capacitors and their role in suppressing high frequency voltage spikes (particularly increases in supply voltage).
The answer provided above does not explain to me the inherit nature as to why a decoupling capacitor will suppress these surges.
From my understanding, a capacitor placed at an input pin should shunt excess current through the capacitor proportional to the rate of change of voltage.
If such a transient spike travels down the supply line, shouldn't the voltage seen by the decoupling capacitor and the input pin be identical? The decoupling capacitor serves to shunt current, but the voltage is effectively unchanged.
If the incoming transient spike is seen by the node at the capacitor, shouldn't this same voltage be seen by the input pin?
Forgive my confusion, any insight would be great. Thanks.
Best Answer
That is precisely how it works but all supply lines will have inductance and some resistance and this makes the capacitor effective in restricting the rise of the voltage spike. A capacitor on its own has no effect; it is the capacitor in conjunction with series components such as L and R that make it effective against fast transients.
However, for a continuous or long term change the capacitor is ineffective.