The output of the internal 5-V regulator of the controller is connected to the REF pin. REF provides bias current to most of the functional blocks in the UCC28782. It requires a high-quality ceramic by-pass capacitor (C_REF) to AGND to decouple switching noise and to reduce the voltage transients as the controller transitions from wait state to run state. The minimum C_REF value is 0.22 μF, and a high quality dielectric material should be used, such as a X7R.

The output short-circuit current (I_S(REF)) of the REF regulator is self-limited to approximately 17 mA. 5-V bias is only available after the under-voltage lock-out (UVLO) circuit enables the operation of UCC28782 after V_VDD reaches V_VDD(ON). This pin can be used to perform an external shutdown function. A small-signal switch can be used to pull this pin voltage below the power-good threshold of 4.5V, so the controller will stop switching, force a VDD restart cycle, and turn off the REF current.