40 V input ceiling sets the supply headroom
Its 40 V maximum input and 500 mA output cover the common ground for powering analog rails, sensor supplies, and low-power logic from unregulated or semi-regulated DC buses. Output adjusts from 1.25 V up to 37 V with two external resistors — the classic LM317 topology. Single regulator, positive output configuration.
Ripple rejection at line frequency
PSRR is specified at 80 dB to 65 dB at 120 Hz. That 65 dB floor is the design-in number for a 60 Hz full-wave rectified supply — it tells you how much 120 Hz ripple bleeds through to the output. For a clean 5 V analog rail, that is still about 1.8 mV ripple from a 1 Vpp input ripple, which is acceptable for most 12-bit ADC references but marginal for a 16-bit precision chain.
SOT-223-4 — rework and thermal reality
The SOT-223-4 package (TO-261-4 equivalent) is surface-mount with a large centre tab. The tab is the thermal path and the output pin — it needs a solid copper pour and vias to the ground plane to keep junction temperature under 125°C at 500 mA with a moderate input-output differential.
Protection features and quiescent current
Built-in over-current, over-temperature, and short-circuit protection. Quiescent current is 10 mA typical — not a low-Iq part, so not for battery-powered always-on rails, but fine for line-powered industrial and automotive circuits.