Hello!
In the datasheet SLUS794E on p. 28 says:
"PFC Start-Up Hold Off: An additional feature designed into the UCC28070 is the “Start-Up Hold Off” logic that prevents the device from initiating a soft-start cycle until the VAO is below the zero-power threshold (0.75 V). This feature ensures that the SS cycle will initiate from zero-power and zero duty-cycle while preventing the potential for any significant inrush currents due to stored charge in the VAO compensation network."
However from the functional block diagram on the p. 10 can be seen that this is true only when S-R flip-flop is set (e.g. during first start from the grid). If controller is disabled by pulling down SS pin below 0.6 V the ZeroPwr comparator has no effect and VAO can remain high, thus causing long duty cycles and large inrush current after enabling SS, in contrary to stated "Start-up hold off" in p. 28.
Can somebody please clear this?
