Generally speaking, 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 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 proportional to the output current because the device is operating as a resistive switch; see the Figure 6-22, Figure 6-23, and Figure 6-24 curves.

Dropout voltage is affected by the drive strength for the gate of the pass element, which is nonlinear with respect to V_IN on this device because of the internal charge pump. The charge pump causes a higher dropout voltage at lower input voltages when a bias rail is not used, as illustrated in the Figure 6-20 curve.

For this device, dropout voltage increases exponentially when the input voltage nears its maximum operating voltage because the charge pump is internally clamped to 8.0 V; see the Figure 6-20 and Figure 6-21 curves.