The input pins (IN+ and IN–) of the UCC53x0 family are based on CMOS-compatible input-threshold logic that is completely isolated from the VCC2 supply voltage. The input pins are easy to drive with logic-level control signals (such as those from 3.3-V microcontrollers), because the UCC53x0 family has a typical high threshold (VIT+(IN)) of 0.55 × VCC1 and a typical low threshold of 0.45 × VCC1. A wide hysteresis (Vhys(IN)) of 0.1 × VCC1 makes for good noise immunity and stable operation. If any of the inputs are left open, 128 kΩ of internal pulldown resistance forces the IN+ pin low and 128 kΩ of internal resistance pulls IN– high. However, TI still recommends grounding an input or tying to VCC1 if it is not being used for improved noise immunity.
Because the input side of the UCC53x0 family is isolated from the output driver, the input signal amplitude can be larger or smaller than VCC2 provided that it does not exceed the recommended limit. This feature allows greater flexibility when integrating the gate-driver with control signal sources and allows the user to choose the most efficient VCC2 for any gate. However, the amplitude of any signal applied to IN+ or IN– must never be at a voltage higher than VCC1.