Fixed 2.5V LDO — what the 1A output and dropout mean for your rail
The LD1117ADT25TR is a fixed-output positive LDO regulator from STMicroelectronics, delivering 2.5V at up to 1A. The 1.3V maximum dropout at full load means the input rail must stay above 3.8V to maintain regulation — factor that into your headroom budget when the input comes from a 5V bus or a battery that sags under load.
PSRR and protection — where the 80dB at 120Hz matters
80dB PSRR at 120Hz gives ripple rejection for feeding analog circuits from a rectified supply. The integrated over-current and over-temperature protection means the regulator folds back or shuts down before the die exceeds its safe operating area.
ST has marked the LD1117ADT25TR as Obsolete. Stock that exists in the channel is new-old-stock or surplus, sourced via independent distribution. We quote and procure to order against an RFQ — confirm the quantity and date-code window at quote time. For a BOM that needs a production-lifetime guarantee, look at the active LD1117 family variants (adjustable or other fixed voltages) that share the same DPAK footprint and pinout.
DPAK package — surface-mount assembly notes
The TO-252-3 (DPAK) package has a large exposed tab that carries the ground / output current. The tab is soldered to the PCB copper island — that copper area sets the thermal resistance. For 1A continuous output, plan a minimum of 1 square inch of 2oz copper on the top layer tied to the tab pad.