The TLV755P 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 is the R_DS(ON) of the PMOS pass transistor. V_DO scales linearly with the output current because the PMOS transistor functions like a resistor in dropout mode. As with any linear regulator, PSRR and transient response degrade as (V_IN – V_OUT) approaches dropout operation. See Figure 5-13 and Figure 5-14 for typical dropout values.