I am using the TPS51315 using the schematic above and have some problems with a reliable output. I started out by depopulating R7 and R8 and using a 5k pot at J9. If I have the wiper all the way to one side where R7 becomes ~0Ohm, it outputs ~0.75V correctly, and then as I turn the pot I can get the output to rise to about 2V and then the output shuts off. The power-good LED stays on the whole time. I have this behavior with 12V input and either open circuit output or a 20Ohm load. Another point of interest is that the switching frequency is ~2MHz regardless of what I set R3 to. I have tried values from 150KOhm to 500KOhm. If I look at the scope, I can see that the duty cycle increases slightly before the output shuts off, but the frequency never deviates from 2MHz much until complete shutoff. Finally, the TPS5135 IC gets pretty hot to the touch even when running without a load. I have the center pad connected to a large copper pour on the back of the PCB by multiple vias. I have also tried adding an RC component to R11 to hold it low briefly when the system powers up, with same result.
Is there something obviously wrong with my circuit or how can I proceed to troubleshoot? I plan to test for shorts between pins when I get home, however, the board seems to operate up to ~2V output. Thank you in advance!
