I am using an LM5117 to convert 25V to 16V. I have verified 25V at Vin, 3.3V at UVLO (through divider network), Vcc is 7.6V. VCC-DIS is low. When I apply 25V to Vin, I can see the LO output switching waveforms at 7.6V, at the correct frequency (~400kHz) operating at about 3.5% duty cycle.
When I connect Vcc to HB via a diode, instead of the expected high side switching, I get a flat 1.5V at HO and the LO stays low 100% additionally, I see a strange glitch behavior when power is applied. Green is high side G-S, and blue is Low side G-S
When the diode from Vcc to HB is removed, I get the low side switching using the same scope parameters at startup. Any one have any ideas what is going on? is it possible the FET is the issue? Thanks