3 A fixed 5 V LDO — what it brings to the rail
The Texas Instruments LM1085ISX-5.0/NOPB is a single-output, positive fixed 5 V LDO regulator rated for 3 A continuous output. It is built for industrial and automotive-grade environments, with a junction temperature range of -40°C to 125°C and protection features including over-current and over-temperature shutdown. The 1.5 V maximum dropout at 3 A means it holds regulation through input dips down to 6.5 V — relevant for 5 V rails fed from a 12 V bus that sees cold-crank or transient sag. The 68 dB PSRR at 120 Hz makes it a natural choice for post-rectifier smoothing in AC-fed supplies or for cleaning up ripple in audio / instrumentation rails where line-frequency rejection matters.
Dropout and PSRR — the numbers that decide fit
Dropout is quoted as 1.5 V max at 3 A, so the input must stay above 6.5 V to maintain a clean 5 V output at full load. That is a tighter headroom requirement than the LP5907 series (which operates down to 5.5 V input but only delivers 250 mA), but the LM1085 is in a different load tier — 3 A continuous versus 250 mA. The 68 dB PSRR at 120 Hz is a solid figure for a 3 A LDO; it attenuates full-wave-rectified ripple by roughly 99.96%, which simplifies downstream filtering for sensitive analog circuits.
Active lifecycle — no obsolescence risk
The LM1085ISX-5.0/NOPB carries an Active lifecycle status, meaning TI continues to manufacture and support it for new designs. No end-of-life notice or last-time-buy window is in effect. ROHS3 compliant per the listing. This part is a stable line item for production BOMs.
Package and mounting — DDPAK/TO-263-3
Supplied in Tape & Reel (TR) or Cut Tape (CT), surface-mount DDPAK/TO-263-3 (3 leads plus tab). The exposed tab is the output, so the PCB copper pour serves double duty as a thermal spreader. For 3 A continuous dissipation, a via-stitched thermal pad under the tab is necessary — without it the junction temperature climbs quickly above 400 mA.