Once the input voltage at VIN reaches about 0.8V, it seems the MPQ3431’s internal switch turns on and shorts pin 1 to GND. If I set the input voltage at V_INPUT (see attached figure) to anything greater than about 0.8V and then apply power, the input current immediately goes to my input supply current limit (2A) which drags my supply voltage down below the MPQ3431 startup voltage. However the MPQ3431 seems to keep the SW pin shorted to GND via the internal switch and I have to remove power to clear the short. If I turn my input voltage down below 0.8V and apply power the input current is 0 (but of course the MPQ3431 does not start up). Please note that in the schematic I have attached, I have added additional ceramic caps to the 22uF input and output caps to reach the 3x22uF shown in the data sheet. I also have the jumpers at JP6 all open. R2, R255 and R257 are not populated.
Could you check if the device is already damaged? If any of the pins are already shorted to GND.
Does replacing the part fix the issue?
What kind of inductor are you using? Is it damaged from the high current draw?