300 mA LDO, 2.8 V fixed rail
The LD39030SJ28R is a single-output positive LDO from STMicroelectronics, delivering a fixed 2.8 V at up to 300 mA continuous. The 0.3 V maximum dropout at full load means the input rail needs to stay above 3.1 V to keep the output in regulation — a 3.3 V supply with 200 mV of ripple still leaves margin. Quiescent current is 50 µA typical, rising to 85 µA maximum under load. For a battery-powered sensor that spends most of its time in a low-power state, that 50 µA overhead is comparable to the self-discharge rate of a small coin cell — the regulator isn't the dominant drain.
PSRR and noise rejection in the audio band
Power-supply rejection ratio is 62 dB from 1 kHz to 10 kHz. That flat band covers the switching frequency of most DC-DC converters and the fundamental of switch-mode audio amplifiers — the LDO attenuates upstream ripple by a factor of roughly 1,250 across that range. Above 10 kHz the PSRR typically rolls off, so if the pre-regulator switches at 2 MHz, the attenuation at that frequency will be lower than the 62 dB figure.
Package and board-fit for space-constrained layouts
The bump pitch is fine enough that a two-layer board can route the input, output, ground and enable traces without vias if the layout is tight. The enable pin lets the system shut down the LDO entirely, pulling the quiescent current to near zero when the load is idle.
Temperature grade and protection
Built-in over-current, over-temperature, and soft-start protection mean the LDO handles a shorted output or a hot environment without external clamp diodes or foldback circuits.
It is ROHS3 compliant, so it meets the current EU restriction levels for lead, mercury, cadmium and the four phthalates.