SLVSB64I November 2011 – March 2018 TPS65217
The AC and USB supplies are detected when the input is 190 mV above the battery voltage, and are considered absent when the voltage difference to the battery is less than 125 mV. This feature makes sure that the AC and USB supplies are used whenever possible to save battery life. The USB and AC inputs are both current-limited and controlled through the PPATH register.
In case AC or USB is not present or is blocked by the power path control logic (for example, in the OFF state), the battery voltage always supplies the system (SYS pin).