The input pins (INA, INB, and DIS) of the UCC2154x is based on a TTL and CMOS compatible input-threshold logic that is totally isolated from the VDD supply voltage of the output channels. The input pins are easy to drive with logic-level control signals (such as those from 3.3-V microcontrollers), since the UCC2154x has a typical high threshold (V_INAH) of 1.8 V and a typical low threshold of 1 V, which vary little with temperature (see and ). A wide hysterisis (V_{INA_HYS}) of 0.8 V makes for good noise immunity and stable operation. If any of the inputs are ever left open, internal pull-down resistors force the pin low. These resistors are typically 200 kΩ for INA/B and DIS (see Section 8.2). TI recommends grounding any unused inputs.

The amplitude of any signal applied to the inputs should not exceed the voltage at the VCCI pin. The UCC2154x cannot be driven from an analog controller with an output voltage greater than the VCCI voltage.