1.8 V fixed LDO for clean analog rails
The LD1117AS18TR is a fixed 1.8 V output, 1 A low-dropout linear regulator from STMicroelectronics, housed in a SOT-223 (TO-261-4) surface-mount package. Output is positive and fixed at 1.8 V, with a maximum input of 15 V. The 1.3 V dropout at 1 A means the input rail needs to stay above 3.1 V to maintain regulation at full load — a 3.3 V rail works, but margin is tight under transient dips.
Dropout, quiescent current, and protection
Dropout voltage is specified at 1.3 V maximum at 1 A output — that is the headroom the input must hold above 1.8 V. On-chip protection includes over-current and over-temperature shutdown. No reverse-current protection or foldback — if the output is forced above the input, the internal pass transistor conducts backwards. A Schottky diode from output to input is cheap insurance if the load can back-drive the rail.
Active lifecycle, SOT-223 hand-soldering
The SOT-223 package has a large centre tab that acts as the thermal pad and the output connection. Hand-soldering is straightforward with a fine-tip iron and flux — the tab wets quickly. The tape-and-reel (TR) or cut-tape (CT) packaging options let you order production reels or a few pieces for prototyping.