Tool/software:
Hey High Voltage Controllers Team,
I have a customer evaluating the UCC28070 for a project and we were wondering what the minimum Dmax limit is on this regulator. From the IC electrical characteristics table, we can see that minimum limit is set to 92%. Can it be clamped even lower? If so, how much?
-Matt
Hello Matt,
Yes, the maximum duty cycle of the UC28070 gate drives can be clamped lower than 92%. Theoretically Dmax can be programmed down to 50% with Rdmx = 0R, but that is an impracticable target for this PFC controller. (See equation (4) in the datasheet.)
The datasheet minimum limit is the minimum Dmax value (92%) that can be expected when using 75kR value for Rrt and 68.1kR for Rdmx. 
With these conditions, the maximum Dmax that can be expected is 98%, but typically Dmax will be clamped close to 95%.
This specification is an indication of the worst-case expected variation around the center Dmax value over the full operating temperature range.
Regard,
Ulrich
