8.1.5 Dropout Voltage

The device uses a PMOS pass transistor to achieve low dropout. When (V_IN – V_OUT) is less than the dropout voltage (V_DO), the PMOS pass transistor is in the linear region of operation, and the input-to-output resistance of the device is the drain-to-source resistance of the PMOS pass transistor. V_DO scales with the output current and changes with temperature because the PMOS pass transistor functions like a resistor in dropout mode. For a graph of dropout voltage, see Figure 22. As with any linear regulator, PSRR and the transient response degrade as (V_IN – V_OUT) approaches dropout operation. See Figure 23 for dropout performance.