The ADP1821 is a versatile and inexpensive， synchronous， pulse-width-modulated （PWM）， voltage-mode， step-down controller. It drives an all N-channel power stage to regulate an output voltage as low as 0.6 V. The ADP1821 can be configured to provide output voltages from 0.6 V to 85% of the input voltage and is sized to handle large MOSFETs for point-of-load regulators. The ADP1821 is well suited for a wide range of high power applications， such as DSP and processor core power in telecommunications， medical imaging， high performance servers， and industrial applications. It operates from a 3.7 V to 5.5 V supply with a power input voltage ranging from 1.0 V to 24 V. The ADP1821 operates at a pin-selectable， fixed switching frequency of either 300 kHz or 600 kHz， minimizing external component size and cost. For noise sensitive applications， it can be synchronized to an external clock to achieve switching frequencies between 300 kHz and 1.2 MHz. The ADP1821 includes soft start protection to limit the inrush current from the input supply during startup， reverse current protection during soft start for precharged outputs， as well as a unique adjustable lossless current-limit scheme utilizing external MOSFET sensing. The ADP1821 operates over the –40°C to +125°C junction temperature range and is available in a 16-lead QSOP.