Other Parts Discussed in Thread: TPS54160,
Hello team,
Please see below question from a customer:
After some integration work coupling some heretofore unconnected external components to our system, I have discovered a startup problem with the TPS54160 controller I have on my board and wanted to get your thoughts on what might be the best way to solve it.
First, we have a 5V controller, powered by a nominal 28V. Upon application of 28V, we use a reset supervisor to allow the 5V (LM5576) to turn on first, then ~40ms later, the 3.3V (54160) to turn on, powered by the 5V rail.
When the 5V comes up, it is used to tie to the top of some external-to-our-system 10K POTs. The wiper of the 10K POTs are fed back into our system to be filtered and attenuated by some op-amp circuits driven by the same 5V rail. The op-amp outputs feed some A/D converter pins on the processor. Since the 3.3V rail is not up yet, the op-amp signals backfeed into the 3.3V rail causing it to rise. If the POTs are turned to the low end, the 3.3V rail does not come up very much and the supply starts. If the POTs are turned to the high end, as much as 2.2V is on the 3.3V rail before it starts and this seems to prevent the 54160 from starting.
Once not started, turning the POTs back towards the low end mostly, but not always allows the startup to occur.
The only pins that would seem to be directly effected are the BOOT (through a cap), VSNS, PH, and PWRGD. I am guessing something about the backfeed is causing the shutdown condition to prevent the startup, but it might be something else.
I doubt it is the PWRGD as it is an open drain.
Got any ideas about which pin(s) on the 54160 need protecting and how to best do it?
