An LDO (Low Drop Out regulator) is a DC regulator designed to operate from a supply voltage only slightly above the output voltage. They find use in many places; among the most popular are core voltage regulators for FPGA’s, CPLD’s, uP’s or complex digital ASICs. There is at least one in every cell phone. As we shall see, the logic in a cell phone can provide a challenging load to an LDO.