250 mA LDO, 1.8 V fixed — dropout and headroom
The LP2992AIM5X-1.8 is a 250 mA fixed-output LDO from Texas Instruments, delivering 1.8 V from an input up to 16 V. Quiescent current is 95 µA typical, making it suitable for always-on rails in battery-powered equipment where the LDO's own draw is a fraction of the load current. The 4 mA maximum supply current includes the pass-element drive.
PSRR and noise rejection bandwidth
PSRR is 45 dB at 1 kHz — this is the mid-band rejection figure. Below 1 kHz the PSRR is higher (the LDO's error amplifier has more loop gain at lower frequencies); above 1 kHz it rolls off. For a design where the upstream switching regulator runs at 500 kHz, the LDO's rejection at that frequency will be lower than the 1 kHz spec — the switching frequency should be checked against the PSRR vs. frequency curve in the datasheet.
Industrial temperature grade and protection
The SOT-23-5 package's thermal resistance (junction-to-ambient, ~250°C/W on a standard 2-layer board) limits the allowable power dissipation: at 85°C ambient, the maximum internal dissipation before hitting the 125°C junction limit is about 160 mW. The Enable pin allows the output to be gated by a logic signal, reducing quiescent draw to near zero when the rail is unused.