5V fixed LDO — 100 mA ceiling, 0.37 V dropout
The LP2981A-50DBVR is a single-output positive LDO from Texas Instruments, delivering a fixed 5 V at up to 100 mA. The 95 µA quiescent current sets the always-on drain — for a battery-powered sensor waking once a minute, the LDO's own draw is the floor the system sleeps on.
Power-supply rejection ratio is 63 dB at 1 kHz, meaning the output ripple from a switching pre-regulator at that frequency is attenuated by a factor of roughly 1400. For an RF front-end or an analog sensor bridge powered off a noisy DC-DC rail, this LDO cleans the supply before it reaches the load. Protection features include over-current, over-temperature, and short-circuit — the part folds back rather than latching off, so a transient overload on the output doesn't require a power cycle to recover. The Enable pin lets a microcontroller gate the output, cutting the 95 µA quiescent draw to near zero in sleep mode. Operating temperature spans -40°C to 125°C, covering the industrial and under-hood automotive band. The SOT-23-5 package (SC-74A) fits a 2.9 mm × 1.6 mm footprint — board space is tight, but the thermal pad under the die carries the heat to the PCB copper pour.