The ADP2147 is a high efficiency， low quiescent current， stepdown （buck） dc-to-dc regulator with an output voltage that can be switched between two different settings under the control of a select pin. The total solution requires only three tiny external components. The buck regulator automatically switches operating modes， depending on the load current level， to maximize efficiency. At high output loads， the buck regulator operates in PWM mode. When the load current falls below a predefined threshold， the regulator operates in power save mode （PSM）， improving the light-load efficiency. The ADP2147 runs on input voltages of 2.3 V to 5.5 V， which allows for single lithium or lithium polymer cells， multiple alkaline or NiMH cells， PCMCIA， USB， and other standard power sources. The maximum load current of 800 mA is achievable across the input voltage range. The ADP2147 is available with fixed output voltages from 0.8 V to 3.3 V. All versions include an internal power switch and synchronous rectifier for minimal external part count and high efficiency. The ADP2147 has an internal soft start and is internally compensated. During logic controlled shutdown， the input is disconnected from the output， and the ADP2147 draws less than 0.2 μA （typical） from the power source. Other key features include undervoltage lockout to prevent deep battery discharge and soft start to prevent input current overshoot at startup. The ADP2147 is available in a 6-ball WLCSP.