Fixed 1.8 V output, 250 mA LDO for noise-sensitive automotive rails
The LP590718QDQNRQ1 is a fixed-output positive LDO from Texas Instruments, delivering 250 mA at 1.8 V with a maximum dropout of 0.25 V at full load. The 25 µA quiescent current keeps the part efficient in always-on modules, while the PSRR profile — 90 dB at 100 Hz rolling to 60 dB at 100 kHz — means it rejects switching regulator ripple across the audio and sensor band.
PSRR and dropout — what they mean for the rail design
PSRR is specified as 90 dB at 100 Hz, dropping to 60 dB at 100 kHz. That 30 dB roll-off above 10 kHz means upstream buck converter ripple at 2 MHz will see less than 30 dB of rejection — a second-stage LC filter ahead of the LDO may be needed if the noise floor must stay below 10 µV for a 24-bit ADC supply. Below that, the pass FET enters dropout and the output tracks the input minus the dropout voltage.
Package, thermal path, and board integration
The 4-XDFN exposed-pad case requires a solderable ground plane under the pad to keep RθJA within the datasheet curve — a 1x1 mm pad on a 2-layer board with 1 oz copper typically achieves 150-180°C/W junction-to-ambient, so the 250 mA load at 3.3 V input dissipates 375 mW and stays below the 125°C limit in still air. The Enable pin allows the regulator to be shut down externally; when disabled, the supply current drops to near zero, useful for power-sequencing or low-power sleep modes.
Protection and compliance
Integrated protection features include over-current, over-temperature, and short-circuit shutdown — no external sense resistors or supervisory IC needed for basic fault handling.