Fixed 4.7V rail for noise-sensitive loads
The Texas Instruments LP3985IM5-4.7/NOPB is a 150 mA fixed-output LDO delivering 4.7 V from a maximum 6 V input rail. The 0.1 V dropout at full load means the input needs only 4.8 V to stay in regulation — useful when the upstream rail is a 5 V bus with tolerance.
PSRR and noise rejection across the band
PSRR is specified at 50 dB at 1 kHz, rolling to 40 dB at 10 kHz. That's a 10 dB drop over a decade — the regulator rejects low-frequency ripple well but becomes less effective above a few kilohertz. If the load is an audio or ADC front-end drawing switching noise from a DC-DC converter upstream, the PSRR profile means you'll want a post-filter above 10 kHz to keep the supply clean.
Quiescent current and enable for battery duty
Quiescent current is 150 µA typical, with a maximum supply current of 250 µA. The Enable pin lets the system shut the regulator down entirely — pulling it low drops the load current to near zero, which matters for a battery-powered device that spends most of its time in sleep. The protection block includes over-current, over-temperature, and short-circuit shutdown, so a momentary load fault won't cascade into a rail collapse.
SOT-23-5 footprint and temp grade
The part is in a SC-74A / SOT-23-5 package (supplier device package SOT-23-5). The package is surface-mount, so the copper pad area and PCB stack-up set the thermal resistance — for 150 mA continuous at high ambient, a few vias under the pad help keep the junction below the 125°C limit.