800mA fixed 1.5V LDO — dropout and PSRR for post-regulator rails
The LP3891ES-1.5/NOPB is a single-output positive LDO from Texas Instruments, delivering a fixed 1.5V at up to 800mA. Quiescent current is 30 µA typical, and the maximum supply current is 8 mA — the regulator's own draw stays low even when the load is light, which matters for always-on rails in battery-powered gear.
80dB PSRR — what it buys on a switching pre-regulator
Power-supply rejection ratio is 80 dB at 120 Hz, rolling off to 65 dB at 1 kHz. This means ripple from a 100/120 Hz rectified front-end or a 300 kHz–1 MHz switcher is attenuated by a factor of roughly 10,000 at line frequency and ~1,800 at 1 kHz. For a 50 mVpp ripple on the input, the output sees under 5 µV at 120 Hz — clean enough to feed a sensitive analog front-end or a PLL supply. The 1.5V fixed output and 5.5V maximum input give a 4V headroom window. The enable pin lets a system controller sequence the rail on and off, and the built-in protection — over-current, over-temperature, short-circuit, and UVLO — covers the common fault cases without external supervisory circuitry.
DDPAK/TO-263-5 — hand-solderable power package
The part comes in a DDPAK/TO-263-5 (5-lead plus tab) surface-mount package. The tab is electrically connected to ground (the output is positive), so no isolation mask is needed. The tube packaging is standard for prototyping and small-batch production; for reels, check the alternate order code.