Fixed 4.8 V rail for noise-sensitive loads
The LP3985ITL-4.8/NOPB is a single-output, fixed 4.8 V linear regulator from Texas Instruments, rated for 150 mA continuous output. Its 0.1 V maximum dropout at full load means the input rail can dip as low as 4.9 V before the output falls out of regulation — a tight headroom that suits battery-powered gear where every millivolt of margin counts.
PSRR profile and noise rejection
PSRR is specified at 50 dB at 1 kHz, dropping to 40 dB at 10 kHz. This means the regulator attenuates low-frequency ripple from a switching pre-regulator by a factor of ~300 at 1 kHz, but the rejection weakens above a few kilohertz. For an analog front-end drawing 150 mA, the output noise floor will be dominated by the upstream switcher's switching frequency and its harmonics — a post-filter LC stage may be needed if the load is a sensitive ADC or PLL supply. Built-in protection covers over-current, over-temperature, and short-circuit events. The enable pin lets the system power down the regulator without disconnecting the input rail, reducing quiescent draw to near zero when the load is idle.
Package and board-fit realities
The 5-DSBGA package measures 1.41 x 1.08 mm — a wafer-level chip-scale package with no molded body. The solder balls are the only standoff; coplanarity is excellent but the package is moisture-sensitive. The tiny footprint demands a fine-pitch stencil and tight placement accuracy; a 0.4 mm aperture is typical for the 5-ball array. The 150 µA quiescent current and 250 µA max supply current keep the self-heating low even at high ambient.
It is ROHS3 compliant, free of the ten restricted substances under EU RoHS.