500 mA LDO with 0.73 V max dropout — the headroom decision
The LP38691QSD-2.5/NOPB is a fixed 2.5 V output LDO regulator from Texas Instruments, rated for 500 mA continuous output current. Below that headroom the output tracks the input minus the dropout, and the PSRR drops off. The quiescent current is 55 µA typical, with a maximum supply current of 100 µA. For an always-on ECU module drawing 10 mA from the output, the regulator's own draw adds less than 1% to the total load — negligible for the battery budget during key-off.
AEC-Q100 Grade 1 — the full automotive temperature band
This covers the Grade 1 temperature band used for under-hood and engine-bay electronics. A cabin module at 85°C still has 40°C of margin before the 150°C typical thermal shutdown threshold. The 10 V maximum input voltage means the part cannot be powered directly from a nominal 12 V battery system — the cold-crank dip to 6 V is within range, but the load-dump transient above 10 V requires an external clamp or a preregulator. A 5 V rail from a buck converter is the typical upstream supply.
The power-supply rejection ratio is 55 dB at 120 Hz. This is the ripple frequency from a full-wave rectified mains supply — the LDO attenuates 120 Hz ripple by a factor of roughly 560×. For an automotive audio head unit or a sensor bias supply running off a switching preregulator, the PSRR at higher frequencies (above 10 kHz) is lower and may need additional filtering ahead of the LDO.
Active lifecycle — no EOL notice on record
The package is a 6-WDFN with exposed pad (3×3 mm WSON). Supplied in tape-and-reel or cut-tape options.