The MC33565 Low Dropout Regulator is designed for computer peripheral card applications complying with the instantly available requirements as specified by ACPI objectives. The MC33565 permits glitchfree transitions from "sleep" to "active" system modes and has internal logic circuitry to detect whether the system is being powered from the motherboard main 5V power supply or the 3.3V aux supply. The MC33565 provides a regulated output voltage of 3.3V via either an internal low drop out 5.0Vto3.3V voltage regulator or an external Pchannel MOSFET, depending on the operating status of the system in which the card is installed. During normal operating mode (5V main supply available) the 3.3V output is provided from the internal low dropout regulator at an output current of 200mA. When the motherboard enters sleep mode, the MC33565 operates from the 3.3V aux supply and routes the aux current to the output via the external Pchannel MOSFET bypass transistor controlled by the drive out pin. As a result, the output voltage provided to the peripheral card remains constant at 3.3V even during transitions to and from sleep mode.