2013-10-19 03:37 PM
Does anyone know if it's guaranteed safe to apply a voltage to an analog input on a TMS32F0xxx if power is not present on the VDD and VDDA supply pins? Our system monitors an independently powered external sensor. It will routinely happen that the processor won't have power, but, the sensor will still be applying a voltage to an analog input.
Thanks! Norman2013-10-19 04:29 PM
Damage is a strong word, the effect is likely that current will find a path, and back feed into the chip supply, and potentially cause the chip to start/function, perhaps in an undesirable fashion.
These are all question you're going to want to pose to your local ST FAE, this is a user forum, and I have no interest in the kinds of liability issues with aberrant or out-of-spec operation, and advice revolving about such.2013-10-19 04:56 PM
Hi Clive,
Thank you for the reply. Please accept my apologies for making an inappropriate post. I'm new here. So that I don't repeat the mistake, what's the distinction between a ''user'' and a circuit designer such as myself? Is there a policy you can direct me to that describes what questions are appropriate and what are not? For the record, I wouldn't in a million years consider legal action on the basis of a forum post. It's my sole responsibility to ensure my designs work. I was just looking for feedback from people with more experience than myself with the ST32 ecosystem. Thanks again, Norman2013-10-19 05:47 PM
It'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.2013-10-19 07:20 PM
Hi Clive,
Thank you again for the reply. I was clearly confused. The way you're talking, it sounds like this forum is at arm's length from ST. I reached it from the ST main site, and frankly, can't tell where one ends and the other begins. I appreciate your assistance and wish you all the best. Best regards, Norman