The RoHS status is non-compliant, so this part carries the legacy lead-bearing finish. If your BOM requires RoHS exemption or you are maintaining a legacy assembly line that accepts tin-lead solder, this is the right version. For RoHS-compliant builds, the lead-free variant (LP5900SD-1.5/NOPB) is the drop-in alternative.
150mA at 1.5V fixed — the rail it powers
The LP5900SD-1.5 delivers a fixed 1.5V output at up to 150mA. That is a common core voltage for low-power MCUs, RF transceivers, and sensor front-ends that run on a 1.5V rail. The output is positive and regulated by a single internal LDO. Maximum dropout is 150mV at full load. That means the input rail needs to stay above 1.65V to keep the output in regulation at 150mA — a 200mV headroom is safe. Below that, the output follows the input minus dropout, and you lose regulation.
85dB PSRR — noise rejection across the spectrum
Power supply rejection ratio is 85dB at 100Hz, rolling off to 40dB at 100kHz. At 100kHz the rejection drops to 40dB, which still knocks down switching-regulator ripple by 100x. If your upstream rail is a noisy buck converter, the LP5900SD-1.5 cleans it up well into the hundreds of kilohertz.
50µA quiescent — always-on battery budget
Quiescent current is 50µA typical, with a maximum supply current of 230µA. For a battery-powered device that spends most of its life in a low-power state, the 50µA Iq is the floor draw of the regulator itself — it does not disappear in sleep mode unless the enable pin pulls the output to zero. The enable pin lets you gate the regulator off entirely, cutting the quiescent draw to near zero when the load is idle.
6-WSON package — footprint and thermal path
The LP5900SD-1.5 comes in a 6-WDFN exposed pad package, supplier device package 6-WSON measuring 2.2mm x 2.5mm. Without that pad connection, the junction temperature rises faster under load, and the 125°C junction limit is reached at a lower ambient. Mounting type is surface mount. The package is small enough for space-constrained designs but requires a decent solder paste stencil aperture for the thermal pad to avoid voids.
That covers industrial enclosures, outdoor telecom cabinets, and under-hood automotive environments. The protection features — over-temperature and short-circuit — are built in: if the junction exceeds the thermal limit, the regulator shuts down; if the output is shorted to ground, current is limited until the fault clears or the thermal trip engages.
Bulk packaging — tubes, not reels
The LP5900SD-1.5 ships in bulk packaging, meaning tubes or anti-static trays rather than tape-and-reel. For prototype runs, small-batch production, or repair-stock replenishment, bulk is convenient — you are not paying for a full reel you will never use. For high-volume pick-and-place, the tape-and-reel variant (LP5900SD-1.5/NOPB or the lead-free version) is the standard order code.