1A fixed 3.3V LDO with 75dB PSRR — the noise rejection angle
The LMS8117ADTX-3.3 is a fixed-output 3.3 V linear regulator delivering up to 1 A from a TO-252-3 (DPak) surface-mount package. Its 75 dB power-supply rejection ratio at 120 Hz means it attenuates 120 Hz ripple from a rectified mains supply by a factor of roughly 5600 — relevant when the regulator sits downstream of a bulk capacitor and the analog load (ADC reference, op-amp rail, sensor bias) cannot tolerate line-frequency ripple on its supply. The 1 A output current and 1.25 V maximum dropout at full load define the input rail headroom: a 4.55 V minimum input keeps the 3.3 V output in regulation at 1 A.
Active lifecycle, RoHS non-compliant — the compliance flag
Built-in protection features — over-current and over-temperature — let the regulator survive output shorts and thermal overload events without external crowbar circuitry.
TO-252-3 package — board-fit and thermal path
The tab is the ground path and the primary thermal conduction path — the junction-to-ambient thermal resistance depends heavily on the board's copper area and layer stack. A 1 A load at 3.3 V output from a 5 V input dissipates 1.7 W; without adequate copper area the junction temperature rises above the 125°C limit. The single-regulator positive-output configuration means no external resistor divider is needed for the 3.3 V rail — the fixed output voltage is set internally. Maximum input voltage is 15 V, so the part can run from 5 V, 9 V, or 12 V rails without a pre-regulator, as long as the dropout headroom is maintained.