The ADP2140 includes a high efficiency， low quiescent 600 mA stepdown dc-to-dc converter and a 300 mA LDO packaged in a small 10-lead 3 mm × 3 mm LFCSP. The total solution requires only four tiny external components. The buck regulator uses a proprietary high speed current-mode， constant frequency， pulse-width modulation （PWM） control scheme for excellent stability and transient response. To ensure the longest battery life in portable applications， the ADP2140 has a power saving variable frequency mode to reduce switching frequency under light loads. The LDO is a low quiescent current， low dropout linear regulator designed to operate in a split supply mode with VIN2 as low as 1.65 V. The low input voltage minimum allows the LDO to be powered from the output of the buck regulator increasing efficiency and reducing power dissipation. The ADP2140 runs from input voltages of 2.3 V to 5.5 V allowing single Li+/Li? polymer cell， multiple alkaline/NiMH cell， PCMCIA， and other standard power sources. ADP2140 includes a power-good pin， soft start， and internal compensation. Numerous power sequencing options are userselectable through two enable inputs. In autosequencing mode， the highest voltage output enables on the rising edge of EN1. During logic controlled shutdown， the input disconnects from the output and draws less than 300 nA from the input source. Other key features include： undervoltage lockout to prevent deep battery discharge， soft start to prevent input current overshoot at startup， and both short-circuit protection and thermal overload protection circuits to prevent damage in adverse conditions. When the ADP2140 is used with two 0603 capacitors， one 0402 capacitor， one 0402 resistor， and one 0805 chip inductor， the total solution size is approximately 90 mm2 resulting in the smallest footprint solution to meet a variety of portable applications.