I suppose this applies to any chip in the DSBGA package, but I'm wondering how the LM3691 behaves when exposed to light. From the part's datasheet:
The DSBGA package is optimized for the smallest possible size in applications with red or infrared opaque cases. Because the DSBGA package lacks the plastic encapsulation characteristic of larger devices, it is vulnerable to light. Backside metallization and/or epoxy coating, along with front side shading by the printed circuit board, reduce this sensitivity. However, the package has exposed die edges. In particular, DSBGA devices are sensitive to light, in the red and infrared range, shining on the package’s exposed die edges.
Specifically, I'd like to use it, or something similar, to get 3.3V from USB on a board that is exposed to ambient light. If doing so would be unwise without some sort of case/coating, I would welcome alternate part suggestions. Otherwise, what happens to the part and its performance?