I've seen two PCBs where a TL431 is used to regulate a flyback SMPS. Near the TL431, there was a SMT capacitor going from ground-to-ground. Yes, the same net on each pin of the cap as best as I can measure.
In one case the cap was not stuffed, and on the other the cap was 10nF.
I've not seen this before, and I'm not sure what this cap would be doing. A cap was a 0402 to 0805 package with short traces going to a via on each side, so I can't imagine any substantial voltage difference between the terminals of the cap (and what else would the cap do?). This is a multi-layer board with internal planes, so it's hard to know if something clever might happen in an internal layer.
Has anyone else seen this? What could be the purpose of a capacitor in this location?
