Posted on October 20, 2013 at 02:47It's not so much about appropriateness, but rather one of expectations. ST does not, on the whole, participate in this forum in a meaningful way, myself and other have concluded that this is a purposeful choice, perhaps related to resources or preferred routes for customer qualification and support. The normal route for such support is direct, and managed through the sales arm, distribution, reps, etc.
This is a ''user'' forum, the ability range, again based on interactions, is anywhere from 0-40 years of experience, so you have students, hobbiest, meddlers, hackers, consultants, pros, etc. There are a couple of ST representatives that appear occasionally, and I have my own contact points. I do not work for, or represent, ST. I've been using STM32 series parts since their inception, and used STR7 and STR9 families before that, have used ARM and MIPS devices from multiple vendors, and in SoC implementations. I'm not looking to ''own'' other peoples problems, but rather try to point them in the right direction, and catch any pitfalls or obstacles I think they might stumble upon. There are perhaps only a handful of individuals here really answering the bulk of the questions.
While I can see potentials to damage parts/systems with external supplies, the most apparent problem is likely to be a powering and malfunctioning of the chip, and other subsystems attached to it.
The STM32 parts typically use VDDA to manage the POR circuits, having supplies and pins at different levels creates conduction paths, though things like pull-up resistances, ESD and clamping-diodes, which is undesirable. The levels of voltages/currents involved can reach points that could be damaging. I don't know enough about the specific implementations and structures to provide any clear direction.
