3V fixed LDO for noise-sensitive rails
The STMicroelectronics LD39020ADTPU30R is a single-output, positive fixed linear regulator delivering 3V at up to 200 mA from a maximum 5.5V input rail. It belongs to the LD39020 family of low-dropout regulators in a compact 4-DFN (1x1 mm) package. With a PSRR of 80 dB at 1 kHz rolling off to 55 dB at 100 kHz, this LDO attenuates switching noise from upstream DC-DC converters — critical for powering analog front-ends, ADC reference rails, or RF VCO supplies where supply ripple directly degrades signal-to-noise ratio.
Dropout, quiescent current, and thermal range
Maximum dropout voltage is 0.35V at the full 200 mA load — the input rail must stay at least 350 mV above 3V to maintain regulation. The 40 µA typical quiescent current keeps the regulator's own draw low enough for battery-powered sensors that spend most of their time in light-load or shutdown states. The Enable pin allows external control of the output; protection features include over-current, over-temperature, and soft-start to limit inrush on power-up.
The fixed 3V output variant is pin-compatible with other LD39020 output voltages (0.8V, 1.1V, 2.5V) in the same package — a BOM change between rails requires only swapping the regulator, not the PCB layout.