The LM1086CS-2.5/NOPB is a 2.5V fixed output low-dropout (LDO) Linear Regulator with a maximum dropout of 1.5V at 1.5A of load current. The device circuit includes a zener trimmed bandgap reference, current limiting and thermal shutdown. The topology is basically that of the LM317 except for the pass transistor. Instead of a Darlington NPN with its two diode voltage drop, the LM1086 uses a single NPN. This results in a lower dropout voltage. The structure of the pass transistor is also known as a quasi LDO. The advantage of a quasi LDO over a PNP LDO is its inherently lower quiescent current.
