The ADP2121 is a high frequency, low quiescent current, step-down, dc-to-dc converter optimized for portable applications in which board area and battery life are critical constraints. Fixed frequency operation at 6 MHz enables the use of tiny ceramic inductors and capacitors. Additionally, the synchronous rectification improves efficiency and results in fewer external components. At high load currents, the device uses a voltage regulating pulse-width modulation (PWM) mode that maintains a constant frequency with excellent stability and transient response. In forced PWM mode, the converter continues operating in PWM for light loads. At light load conditions in auto mode, the ADP2121 can auto-matically enter a power saving mode that uses pulse-frequency modulation (PFM) to reduce the effective switching frequency and ensure the longest battery life in portable applications. During logic controlled shutdown (EN ≤ 0.4 V), the input is disconnected from the output and draws less than 0.3 μA current (typical) from the source.