LTC36xx/LTC7149 Series Step-Down Buck Regulators Analog Devices Inc. LTC36xx/LTC7149 Series Synchronous Step-Down Buck Regulators are high efficiency, monolithic, and excellent for inverting output applications. The LTC3623 and LTC3600 are programmed with a single external resistor. The LTC3649 and LTC7149 feature single resistor programmable output voltage, with high efficiency over a wide VOUT range.