The AT73C239 is a 4-channel Power Supply Power Management Unit (PMU) available in a QFN 3 x 3 mm package. It is a fully integrated, low cost, combined Power Management device for wireless modules, GPS and WLAN devices. It integrates four Linear Low Drop Out (LDO) Regulators, three of which provide high-accuracy RF performance and one (LDO4) with very low quiescent current that is supplied by an external backup battery. A Low Power Bandgap (LPBG) requiring no external capacitor for decoupling, is used as reference voltage for LDO4 and starts when VBAT is present. LDO4 regulates output voltage with extremely low quiescent current, maximizing the lifetime of the backup battery. An Internal State Machine manages the startup of the other LDOs in the order of LDO3 then LDO1 then LDO2. An economic High Power Bandgap (HPBG) provides highly accurate, low noise voltage reference to LDOs 1, 2, 3. HPBG operates in switching mode thereby decreasing its current consumption and becomes inactive when not directly supplied by VIN current. When the RF LDOs are in idle mode, quiescent current is decreased to a minimum.