LTC3638 & LTC3639 Step-Down Regulators Analog Devices Inc. LTC3638 and LTC3639 High-Efficiency Step-Down Regulators maintain a regulated output voltage at no load with an internal power switch at only 12μA typical DC supply current. The LTC3638 and LTC3639 incorporate low quiescent current, integrated power switch, Burst Mode® operation, and programmable peak current limit creating high efficiency over a broad range of load currents. A programmable peak current limit creates a simple method for optimizing efficiency and for reducing output ripple and component size.