How do I choose a feed through (feedthrough/feed-through?) capacitor to replace a ferrite bead pi-filter circuit? Manufacturers quote capacitance figures but what value should I choose this to be?
The reference design of a CPU design filters out, from a common VDD, various filtered power inputs (several pins per input). Per input, a pi-filter is given plus 100nF per pin. I have read good things about the feed through capacitors and want to replace the pi-filter with one. I am unclear what value of capacitance should be chosen though.
Filter is currently Power->1uF cap->120R@100M FB-> 10uF cap
1uF 0201 caps will be used per pin.
Best Answer
All filters are voltage-dividers, having a SERIES reactance followed by a SHUNT reactance. What are your needs for these two reactances? Define those needs first.
The preceding components, and the components that follow your filter, must be considered.
And WIRES are part of the SERIES reactances. At 1uH per meter, if not part of twisted-pair or coax or over ground/power plane or metal chassis.