117 dB PSRR across 120 Hz to 10 MHz — the noise floor decision
The LT3042MPDD#PBF is an adjustable positive LDO from Analog Devices delivering 200 mA output with a PSRR that starts at 117 dB at 120 Hz and rolls off to 56 dB at 10 MHz. That bandwidth coverage means it suppresses both line-frequency ripple and the switching noise from a downstream DC-DC converter — the regulator itself becomes the filter, not just a post-regulator. For a precision analog rail feeding a 16-bit ADC or a VCO, the 117 dB at 120 Hz is what keeps 50/60 Hz hum out of the signal chain.
This is the same die as the industrial-grade LT3042IDD#PBF (-40°C to 125°C), but the extended low end matters for cold-start avionics or outdoor telecom gear that sees -40°C ambient with self-heating margin. The high end at 150°C junction gives headroom in a 105°C ambient enclosure with the regulator dissipating near its thermal limit. Without it, the junction-to-ambient thermal resistance rises and the 150°C rating becomes academic at any real load.
Protection set: over-temp and reverse polarity, not just current limit
The LT3042MPDD#PBF includes current limit, enable, and power-good output, plus over-temperature shutdown and reverse-polarity protection. The reverse-polarity feature is unusual for an LDO — it protects the regulator and downstream load if the input rail is accidentally reversed, which saves an external Schottky diode in battery-powered or field-wired designs. Lifecycle status is active per Analog Devices — this is a current-production part suitable for new designs.