ZHCSLD2E may 2020 – july 2023 UCC28782
PRODUCTION DATA
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 (CREF) to AGND to decouple switching noise and to reduce the voltage transients as the controller transitions from wait state to run state. The minimum CREF value is 0.22 μF, and a high quality dielectric material should be used, such as a X7R.
The output short-circuit current (IS(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 VVDD reaches VVDD(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.