The ADP2105/ADP2106/ADP2107 are low quiescent current， synchronous， step-down dc-to-dc converters in a compact 4 mm × 4 mm LFCSP package. At medium to high load currents， these devices use a 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 ADP2105/ADP2106/ADP2107 use a pulse frequency modulation （PFM） control scheme under light load conditions that reduces switching frequency to save power. The ADP2105/ADP2106/ADP2107 run from input voltages of 2.7 V to 5.5 V， allowing single Li+/Li? polymer cell， multiple alkaline/NiMH cells， PCMCIA， and other standard power sources. The output voltage of ADP2105/ADP2106/ADP2107 is adjustable from 0.8 V to the input voltage （indicated by ADJ）， whereas the ADP2105/ADP2106/ADP2107 are available in preset output voltage options of 3.3 V， 1.8 V， 1.5 V， and 1.2 V （indicated by x.x V）。 Each of these variations is available in three maximum current levels： 1 A （ADP2105）， 1.5 A （ADP2106）， and 2 A （ADP2107）。 The power switch and synchronous rectifier are integrated for minimal external part count and high efficiency. During logic controlled shutdown， the input is disconnected from the output， and it draws less than 0.1 μA from the input source. Other key features include undervoltage lockout to prevent deep battery discharge and programmable soft start to limit inrush current at startup.