High-reliability H grade and military MP grade versions of Linear Technology’s LTC3612 4-MHz synchronous buck regulator deliver up to 3 A of continuous output current at output voltages down to 0.6 V. Incorporating a constant-frequency, current-mode architecture, the device operates from an input voltage of 2.25 to 5.5 V, suiting it for single-cell Li-ion applications and 3.3- or 5-V intermediate bus systems. Switching frequency is user-programmable from 300 kHz to 4 MHz. H grade versions meet specifications over the −40 to 150°C operating junction temperature range. They come in 3- by 4-mm QFN-20 packages (LTC3612HUDC) or 20-lead, thermally enhanced TSSOPs (LTC3612HFE). MP grade versions (LTC3612MPUDC in the QFN and LTC3612MPFE in the TSSOP) meet specs over the −55 to 150°C operating junction temperature range. Internal switches with on-resistances of 45 and 70 mΩ deliver efficiencies of over 90% for high step-down ratio applications. Burst-mode operation maximizes light-load efficiency (no load requires only 70 µA). Inputs are included for tracking capability, and a DDR memory mode can source/sink at ±1.5 A.