The ADP2105/ADP2106/ADP2107 are low quiescent current, synchronous, step-down dc-to-dc converters in a compact 4 mm x 4 mm LFCSP_VQ 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-ADJ is adjustable from 0.8 V to the input voltage, while the ADP2105/ ADP2106/ADP2107-xx are available in preset output voltage options of 3.3 V, 1.8 V, 1.5 V, and 1.2 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 A 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.