2.5 V fixed rail for sensor and MCU bias
The LD2985BM25R is a fixed 2.5 V output LDO from STMicroelectronics, delivering up to 150 mA from a 16 V maximum input. That 2.5 V rail is a common bias for analog front-ends, low-voltage MCU I/O banks, or as a clean reference for a local ADC supply — the 45 dB PSRR at 1 kHz knocks down switching ripple from a buck converter feeding the input. A 5 V rail gives comfortable headroom.
Dropout and quiescent — the real trade-offs
Quiescent current is 150 µA typical — not ultra-low for a battery always-on rail, but reasonable for a general-purpose LDO that also carries an enable pin to shut down the output completely when the load is idle. The 4 mA maximum supply current at full load is the total drawn from the input, including the output current. The 45 dB PSRR at 1 kHz means the output ripple is about 0.56 % of the input ripple at that frequency — adequate for powering a 10-bit ADC reference but marginal for a 16-bit converter without additional post-filtering. At higher frequencies the rejection rolls off; the datasheet curve (not reproduced here) shows the slope. Operating temperature spans -40°C to 125°C, so the part handles under-hood automotive ambient or a warm enclosure near a power stage without derating the output current.
Package and pinout — SOT-23-5 layout notes
Housed in a SOT-23-5 (SC-74A) package, the LD2985BM25R shares the same footprint as the LD2985BM18R — the 1.8 V output sibling in the same family. The pinout is identical: input, ground, enable, output, and a no-connect or bypass pin depending on the variant. A board laid out for one output voltage accepts the other without a spin. The enable pin is active-high; tying it to the input rail keeps the regulator on. The over-current and over-temperature protection circuits are internal — no external sense resistor needed.
It is ROHS3 compliant, so it passes the current EU restriction directive without exemption claims. No minimum order threshold beyond the reel increment.