I have some challenges with the circuit UCC28950. I'm using it in a DC-DC converter design, in a similar configuration as depicted on page 1 and page 8 in the UCC28950 datasheet (SLUSAG4 – APRIL 2011). My challenge is related to the (adaptive) delay between OUTA and OUTB. I would like to increase TABSET to several hundred ns, but is not able to get it above 75ns delay in the case between OUTB going low and OUTA going high. In the opposite case, the delay becomes slightly larger. I have set KA=0, by shorting ADEL to GND, and increased RAB to 90kOhm. The only effect it has is to increase the delay TABSET from 50ns to 75ns, and NOT to 1750ns as it should have been according to the datasheet. I am measuring the OUTA and OUTB directly on the UCC28950, to be sure that the problem is not related to the small difference in PCB routing distance. I have tested 3 different different UCC28950 circuits to eliminate the possibility that the problem is related to one specific circuit.
What could possibly be wrong?
