2.5V fixed rail, 800mA — what the dropout and PSRR tell you
The LD1117DT25TR is a fixed-output positive LDO from ST's LD1117 family, delivering a regulated 2.5V rail at up to 800mA. Its maximum dropout of 1.2V at full load means the input needs to stay above 3.7V to hold regulation — fine for 5V rails, but tight if you're feeding it from a 3.3V bus. The 75dB PSRR at 120Hz gives decent mains-ripple rejection for analog or mixed-signal sections, though the rejection drops as frequency climbs (typical for a classic three-terminal LDO topology).
DPAK package — thermal reality for 800mA
The TO-252 / DPAK package with two leads and a tab is a common power-package choice. The tab is the output (Vout) and the main thermal path. At 800mA with a 1.2V dropout, you're dissipating nearly 1W — the DPAK can handle that with a reasonable copper area on the PCB, but without a via-stitched pad under the tab the junction will climb well above the 125°C max operating limit in still air. Plan for at least 1 square inch of copper on the top layer connected to the tab.
Protection set: over-current and thermal shutdown
Built-in over-current limiting and thermal shutdown are standard for this class of regulator. The over-current threshold is not a precision limit — it's a foldback that protects the pass transistor during a hard short. Thermal shutdown kicks in around 160°C junction, so the part survives a sustained overload as long as the board can sink the heat. No reverse-current protection, so if the output is held high while the input drops, the regulator can back-feed through the body diode.