SBVS233B January 2016 – June 2021 TPS7A84
Generally speaking, the dropout voltage often refers to the minimum voltage difference between the input and output voltage (VDO = VIN – VOUT) that is required for regulation. When VIN drops below the required VDO 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 VIN 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.