3.3V rail LDO for medium-current loads
The LD1117S33TR is a fixed 3.3V output LDO from STMicroelectronics, delivering up to 800 mA continuous current. The maximum dropout voltage of 1.2 V at 800 mA means the input rail must stay above 4.5 V to maintain regulation — a 5 V rail with 10% tolerance still clears that headroom, but a 3.6 V battery rail will not.
Dropout is specified at 1.2 V max at the full 800 mA load. That is the worst-case figure at the temperature extremes; typical dropout is lower, but budget the max for production margin.
The SOT-223 (TO-261AA) package has a copper tab on the drain/output pin. For 800 mA continuous at 3.3 V out from a 5 V input, the dissipation is about 1.36 W. Without adequate PCB copper area on the tab, the junction temperature will climb above the 125 °C maximum in a 70 °C ambient.