The California Micro Devices SmartORTM CMPWR280 is a fully protected Dual-Input low dropout CMOS regulator that also provides the necessary control signal for driving an external auxiliary Pchannel MOSFET switch. The SmartORTM device automatically selects one of three possible inputs on a priority basis: VCC (1.5A), VSBY (375mA) or VAUX via the drive signal used to control an external switch. VCC is given first priority. In the event of the VCC supply being powered down, the device will automatically deselect the VCC prior to regulator dropout and immediately select VSBY (second priority) as its power source.