Other Parts Discussed in Thread: TPS2116, TPS2117
Tool/software:
I have a modular system that can consist of a single unit, or be expanded with several units connected together. Each unit can either receive power from a 5Vusb on In1 or power passed from the previous unit on In2. At first I had the power mux configured as shown below.
I found that when there was no power on In1 the power mux would select In2. At this point some of the voltage would feed back out of In1 bringing VSNS above the 0.8V limit to change that behavior of the mux to the auto switching mode. On power up of the system I would sometimes get into a state where the power mux was switching between each input so that my output was about half of what I was expecting. By removing R1 I was able to fix that switching problem for most situations. Ultimately I ended up setting the VSNS with a GPIO if I detect power in on the the 5VUSB(In1).
However, I have come across another issue. In this case I have 2 units connected together, both powered by 5VUSB(meaning that I have set VSNS High on both so that they both only use In1). This situation ends up corrupting some of the processes on the first(HEAD) box. I have found that if I add either remove the power line connecting the 2 boxes(out of the first box and IN2 of the second box) or add a Schottky diode in that same path all my problems go away. to me it seems like it might be related to the issue I described above, where I am getting some feedback from the out to the in ports of that chip. Is this a known problem, and if so what is the solution. Or is there some other drop in replacement part that might behave a little better?
