The supply voltage for the device comes from VCC pin. This pin must be bypassed with a high-frequency capacitor (greater than 0.1 μF) and tied to GND. The UCC38050 has a wide UVLO hysteresis of approximately 6.3 V that allows use of a lower value supply capacitor on this pin for quicker and easier start-up. The UCC38051 has a narrow UVLO hysteresis with of about 2.8 V, and a start-up voltage of about 12.5 V for applications where the operation of the PFC device must be controlled by a downstream PWM controller.