VC is the bias supply for the DC-DC controller. The MOSFET gate drivers run directly from VC. VB is regulated down from VC, and is the bias voltage for the rest of the converter control. A start-up current source from VDD1 to VC is controlled by a comparator with hysteresis to implement the converter bootstrap start-up. VC must be connected to a bias source, such as a converter auxiliary output, during normal operation.
A minimum 0.47 μF-capacitor, located adjacent to the VC pin, should be connected from VC to COM to bypass the gate driver. A larger total capacitance is required for start-up to provide control power between the time the converter starts switching and the availability of the converter auxiliary output voltage.