Analog Devices ADP5301 features high efficiency, ultra-low quiescent current step-down regulators using only 180nA quiescent current to regulate the output at no load. The ADP5301 regulators operate from an input startup voltage range of 2.15V to 6.50V, enabling the use of multiple alkaline or NiMH, Li-Ion cells, or other power sources. The output voltage is user-selectable from 0.8V to 5.0V by an external VID resistor and factory fuse. The total solution requires only four tiny external components. The regulator in hysteresis mode achieves excellent efficiency at a power of less than 1mW and provides up to 50mA of output current. The regulator in PWM mode produces a lower output ripple and supplies up to 500mA of output current. The flexible configuration capability during operation of the device enables very efficient power management to meet both the longest battery life and low system noise requirements.