Active production — 1.8V fixed LDO for automotive power rails
The BU18SD2MG-MTR is an active-production linear regulator from ROHM Semiconductor, part of the Automotive AEC-Q100 series. It delivers a fixed 1.8V output at up to 200mA from a maximum 6V input rail. The 0.29V maximum dropout at 100mA means the input-to-output headroom needs to stay above that threshold across load and temperature to keep the output in regulation — a 3.3V rail feeding this LDO has about 1.2V of margin at full load.
68dB PSRR at 1kHz — what it means for noise-sensitive loads
The 68dB power-supply rejection ratio at 1kHz attenuates ripple on the input rail by a factor of roughly 2500 — a 100mVpp switching ripple at 1kHz appears as about 40µVpp on the output. This matters when powering analog front-ends, sensor bias, or reference circuits in an automotive ECU where the 12V bus carries alternator whine and DC-DC switching artifacts. Quiescent current is 80µA typical — the LDO's own draw is low enough that it doesn't dominate the sleep-mode budget in a body-control module or battery-backed domain.
AEC-Q100 qualification and temperature range
AEC-Q100 Grade 2 qualification means the part is characterized and reliability-tested for -40°C to +105°C ambient — the under-hood and cabin-temperature band for automotive electronics. The SC-74A (SOT-753) 5-pin surface-mount package fits standard reflow profiles and is suited for automated assembly. Protection features include over-current and over-temperature shutdown — the LDO folds back or latches off before the junction exceeds the safe operating area, which is useful when the downstream load shorts or the ambient spikes above the rated range.
The Enable pin allows the output to be gated by a logic-level signal — useful for sequencing multiple rails or shutting down the regulator in standby to save the 80µA quiescent draw.