The LM2940SX-12 is a fixed 12 V positive-output LDO regulator from Texas Instruments, delivering up to 1 A continuous. The 66 dB PSRR at 120 Hz tells you it rejects mains-frequency ripple well — expect clean 12 V from a rectified 15–26 V input, which is the typical front-end for industrial control boards, automotive ECUs, and point-of-load supplies in telecom gear. Dropout is 1 V max at the full 1 A load, so the input rail needs at least 13 V to hold regulation. That 1 V headroom is tight for battery-backed systems but comfortable for a regulated 15 V or 24 V bus.
That means Texas Instruments will not accept new design registrations, and the part is on a path toward end-of-life. For a BOM line already using this regulator, the NRND flag means you should qualify a drop-in alternative before the next LTB window closes. The fixed 12 V output, 1 A rating, and TO-263-3 footprint narrow the search to the same LM2940 family or a pin-compatible LDO from another vendor — but no official cross-reference is published.
Package and temperature — board-fit checklist
The TO-263-4 D²Pak (3 leads plus tab) is a surface-mount power package. The exposed tab is the output and the primary thermal path. The protection features — over-current, over-temperature, reverse polarity, and short-circuit — let the regulator survive a faulted rail without external clamp diodes in most designs.