Fixed 3 V rail with 165 mV dropout — the headroom check
The MAX8875EUK30+ is a single-output, positive-voltage linear regulator from Analog Devices / Maxim Integrated that delivers a fixed 3 V output at up to 150 mA. Key features include a maximum dropout voltage of 165 mV at full load, a quiescent current of 180 µA, and a power-supply rejection ratio of 60 dB at 100 Hz — enough to clean up 50/60 Hz mains ripple from a rectified input. Control features include Enable and Power Good pins, and the protection set covers over-temperature, reverse polarity, and short-circuit conditions.
The 165 mV maximum dropout at 150 mA sets the minimum input-to-output differential. If your rail is 3.3 V nominal, a 3 V output leaves 300 mV headroom — enough to stay in regulation through a 150 mV sag or a 3.15 V minimum input. Below that, the output starts to drop out. The 60 dB PSRR at 100 Hz means the regulator attenuates 100 Hz ripple by a factor of 1000 — useful when the input comes from a rectified transformer or a boost converter with significant line-frequency content. At higher frequencies PSRR rolls off, so keep the input bypass capacitor close to the device.
Protection set and quiescent current
Over-temperature, reverse polarity, and short-circuit protection are all built in. Reverse polarity protection is notable for battery-powered designs where the input can be accidentally reversed — the regulator survives without external blocking diodes. The 180 µA quiescent current is moderate; it is not a nanopower LDO, but it is low enough for always-on peripherals like a microcontroller's analog supply or a sensor bias rail where the PSRR and protection features justify the draw.