The DIS/EN pin has a 1.2-V typical threshold which can be used to disable the TPS4021x. With DIS/EN forced above this threshold voltage, the device is disabled and switching is inhibited even if VVDD is above its UVLO threshold. Hysteresis on the DIS/EN pin threshold gives a typical turnon threshold of 1.05 V. If the DIS/EN is left floating or is pulled below the 1.05-V threshold while VVDD is above its UVLO threshold, the device becomes active. Switching is enabled and the soft-start sequence is initiated. The TPS4021x will ramp up the output voltage at the rate determined by the external capacitor at the soft-start pin.