Other Parts Discussed in Thread: LM25085
I am using the LM25085A buck converter to regulate a 24-30V input (29V nominal) to a 12V output with a max load of 8A. I put my design requirements into the WEBENCH online tool and selected all external components as recommended. The only component that I chose myself was the PFET, for which I am using the DMPH6023SK3.
After assembling my PCB and testing with a 29VDC power supply, I found that the output voltage is incorrect. The circuit outputs almost exactly 29V, the same as VIN. I probed the pins on the LM25085A with an oscilloscope and found that it is not switching the PFET on and off at all. The PGATE pin on the LM25085A supplies a constant voltage equal to VCC (or ~21.3V). I read in the datasheet that the output of PGATE is supposed to oscillate between VIN = 29V (PFET off) and VCC ~ 21.3V (PFET on). This is not happening and the PFET is just constantly switched on. Any help figuring out what's wrong would be much appreciated!
