Fixed 5V rail for industrial and mixed-signal boards
The STMicroelectronics LD1117S50CTR is a single-output positive fixed LDO regulator delivering a regulated 5V output at up to 800mA. With a maximum dropout voltage of 1.3V at full load, it needs at least 6.3V on the input to hold regulation — a practical consideration when sizing the upstream rail. The 75dB PSRR at 120Hz makes it a reasonable choice for cleaning up rectified mains ripple in power supplies feeding analog or logic circuits.
Dropout and input headroom — what the 1.3V max means
The 1.3V maximum dropout at 800mA is the number to check when you're running from a 6.5V or 7V rail. At lower loads the dropout drops, but the worst-case figure governs the design margin. If your input rail dips below 6.3V during brownout or cold-crank, the output follows — no headroom left. The 15V absolute maximum input gives plenty of room for 12V or 9V rails, but the dropout spec is what determines the minimum operating input.
Protection and quiescent draw
Built-in over-current and over-temperature protection are standard for this class of LDO. The quiescent current sits at 10 mA — not a micropower part, but acceptable for always-on industrial rails where the load current dominates the power budget.
Package and footprint — SOT-223 reality
The SOT-223 package (supplier device package designation) is a common three-terminal surface-mount footprint with a large tab for heat sinking. Without a decent ground-plane thermal path, the junction temperature climbs quickly above 800mA continuous in a 85°C ambient.
No LTB risk or successor part is indicated.