150mA fixed 3.3V LDO — what the dropout and PSRR mean on your board
The LT1121IS8-3.3#TRPBF is a single-output positive LDO from Analog Devices, delivering a fixed 3.3V at up to 150mA. Maximum dropout is 0.7V at full load, so the input rail needs to stay above 4.0V to keep the output in regulation — a 5V bus with a 0.5V diode drop still leaves enough headroom. PSRR is 58dB at 120Hz, which means it knocks down line-frequency ripple from a rectified AC supply by a factor of roughly 800 — useful when this LDO is post-regulating a noisy 5V rail in an industrial controller or a battery charger. Quiescent current is 50µA typical, so in always-on applications like a sensor node or a keep-alive rail the regulator's own draw won't dominate the battery budget.
8-SOIC package — board fit and rework
Housed in an 8-SOIC (0.154-inch wide, 3.90mm body width), the LT1121IS8-3.3#TRPBF uses a standard footprint that solders with a basic iron or hot-air station — no thermal pad, no exposed paddle, so rework on a populated board is straightforward.
ROHS3 compliant, so it meets the current EU restriction directive without an exemption.