VREF is the voltage reference for the error amplifier and also for many other internal circuits in the IC. The high-speed switching logic uses VREF as the logic power supply. The 5-V reference tolerance is ±2% for the UCx84x family. The output short-circuit current is 30 mA. For reference stability and to prevent noise problems with high-speed switching transients, bypass VREF to ground with a ceramic capacitor close to the IC package. A minimum of 0.1-µF ceramic capacitor is required. Additional VREF bypassing is required for external loads on the reference. An electrolytic capacitor may also be used in addition to the ceramic capacitor.
When VCC is greater than 1 V and less than the UVLO threshold, a 5-kΩ resistor pulls VREF to ground. VREF can be used as a logic output indicating power-system status because when VCC is lower than the UVLO threshold, VREF is held low.