Part Number: TPS2121
In the circuit above, both sources (IN1 & IN2) are 5V and the output is 5V.
There is a normal source that is DC buck derived (IN2) and the battery (IN1) is to take over when the IN2 disappears.
I have tested in the lab, and I see various results. I can take either source away, and then on the restoral of that source, I see one of three results; 1) normal operation, 2) the device will reboot (temporary loss of power), and 3) an unending oscillation (where the output is going up and down). When the circuit goes into oscillation, the recovery is to remove both voltage sources and start anew.
Looking for help on where to look next