8.2.2.3 Dropout Voltage

The TPS795 uses a PMOS pass transistor to achieve a low dropout voltage. When (V_IN – V_OUT) is less than the dropout voltage (V_DO), the PMOS pass device is in its linear region of operation and r_DS(on) of the PMOS pass element is the input-to-output resistance. Because the PMOS device behaves like a resistor in dropout, V_DO approximately scales with the output current.

As with any linear regulator, PSRR degrades as (V_IN – V_OUT) approaches dropout. This effect is illustrated in Figure 9 through Figure 12.