Fixed 3.3 V rail in a DPAK — what this LDO delivers
The STMicroelectronics LD1117DT33 is a positive fixed-output LDO regulator delivering 3.3 V at up to 800 mA from a maximum input of 15 V. The output is fixed — no external resistor divider needed — and the single regulator channel is protected against over-current and over-temperature events.
The maximum dropout voltage is 1.2 V at the full 800 mA load. That means the input rail must stay above 4.5 V to maintain regulation at the output — a 3.3 V rail from a 5 V supply has 1.7 V of headroom, which is comfortable. If the input dips below 4.5 V under load, the output follows it down. PSRR is 75 dB at 120 Hz, which is the typical rectified line-frequency ripple. That level of rejection cleans up the 120 Hz hum from a mains-derived supply.
The LD1117DT33 is listed as Obsolete. STMicroelectronics no longer manufactures it in volume.
Sourcing posture — how to get this part today
Because the part is obsolete, it is not available through the factory or franchised distributors in new-production quantities. No stock-holding claim; every lot is verified before shipment.