800 mA LDO with 72 dB PSRR down to 120 Hz
The LP38851SX-ADJ/NOPB is a single-output positive adjustable LDO regulator from Texas Instruments, delivering 800 mA continuous output current with a maximum dropout voltage of just 0.2 V at full load — the headroom between the input rail and the output must stay above this figure across the load range to maintain regulation. Its PSRR measures 72 dB at 120 Hz and 61 dB at 1 kHz, meaning ripple on the input rail at line frequency and the lower end of switching noise is attenuated by a factor of roughly 4000× to 1000× — relevant for post-regulation of a noisy DC-DC converter feeding sensitive analog circuitry. The adjustable output range spans 0.8 V to 1.8 V, set by an external resistor divider, suiting it for low-voltage core rails in FPGAs, ASICs, or DSPs that require tight tolerance at sub-2 V levels.
Thermal and protection envelope
Built-in protection includes over-current, over-temperature, short-circuit, and under-voltage lockout (UVLO), so the regulator can survive an output short or a brown-out input without external supervisory circuitry. Quiescent current is 300 µA typical, and maximum supply current is 9 mA — the 300 µA Iq floor means the regulator's own draw is low enough for always-on rails in battery-backed systems, though not at the ultra-low-Iq level of a dedicated micropower LDO.
Control and sourcing posture
Enable and soft-start control pins are available — the enable pin allows the output to be gated by a logic signal, and soft start limits inrush current during startup, which is useful when the output capacitor bank is large or the input supply is current-limited.