Generally, the dropout voltage often refers to the minimum voltage difference between the input and output voltage (V_DO = V_IN – V_OUT) that is required for regulation. When V_IN – V_OUT drops below the required V_DO for the given load current, the device functions as a resistive switch and does not regulate output voltage. Dropout voltage is linearly proportional to the output current because the device is operating as a resistive switch, see Figure 6-4 and Figure 6-5.

Dropout voltage is also affected by the drive strength for the gate of the pass element, which is nonlinear with respect to V_BIAS on this device because of the inherited nonlinearity of the pass element gate capacitance, see Figure 6-7.