The UCC28220D is a PWM controller for step-up/step-down applications, supporting flyback and forward converter topologies. It provides two transistor-driver outputs with a 75% maximum duty cycle and a 200kHz to 2MHz switching frequency range.
The 200kHz to 2MHz range lets you trade off transformer size against switching losses. At the low end, you get wider flux swing and simpler magnetics; at 2MHz, the transformer shrinks but you need careful layout and snubbing. The 75% maximum duty cycle is a practical ceiling for flyback and forward converters — it limits the off-time available for resetting the transformer core, so the turns ratio and output voltage range are constrained accordingly. If you need higher duty cycle for a wide-input design, this part isn't the fit.