STMicroelectronics LD1117D33

Overview

LD1117D33 from STMicroelectronics is a fixed-output 3.3 V low-dropout linear voltage regulator delivering up to 800 mA, featuring 1 V typical dropout at 100 mA, ±1 % output voltage tolerance at 25 °C, and 75 dB supply voltage rejection at 120 Hz - deployed in embedded power rails for microcontrollers, sensors, and industrial I/O modules.

For engineers reviewing the LD1117D33 datasheet, LD1117D33 pinout, LD1117D33 application, or LD1117D33 equivalent, key selection criteria include dropout voltage under load, thermal resistance (R_thJA = 110 °C/W in SOT-223), minimum load current (2–5 mA), stability with 10 µF ceramic output capacitor, and compatibility with standard 3.3 V logic supply domains.

Technical Context

The LD1117D33 uses an NPN pass transistor architecture to minimize quiescent current dependency on load - unlike PNP-based regulators, its bias current flows primarily into the output, improving efficiency at light loads. Internal trimming achieves tight initial accuracy without external calibration.

It integrates thermal shutdown and current limiting, with dropout voltage scaling linearly from 1.0 V (100 mA) to 1.2 V (800 mA) across temperature. The device requires only a single 10 µF output capacitor for stability and exhibits 100 µV RMS output noise (10 Hz–10 kHz) in fixed-voltage variants.

Key Specifications

Pinout & Package

LD1117D33 is supplied in SOT-223, DPAK, SO-8, and TO-220 packages. The SOT-223 variant features three signal pins plus an exposed thermal pad electrically connected to V_OUT, enabling direct PCB copper pour for enhanced thermal performance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-output LDO regulator applications.

Compared with TLV1117-33CDCR and MCP1700-3302E/TO, LD1117D33 uniquely balances high output current, low dropout, and robust protection - making it optimal for industrial and automotive 3.3 V rails where reliability under sustained load and thermal stress is critical.

Availability

LD1117D33 is available at Aetrix Electronics and suitable for industrial PLCs, automotive body control units, and IoT edge node controllers requiring stable component supply with long-term manufacturability and consistent parametric performance.

Supply support for LD1117D33 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, specializing in power management, microcontrollers, and automotive-grade analog ICs.

The LD1117 series was designed specifically for cost-sensitive, high-reliability linear regulation in industrial and automotive applications - emphasizing thermal robustness, wide input range, and minimal external component count.

FAQ

What is the minimum input voltage required for stable 3.3 V output at 800 mA?

The LD1117D33 requires a minimum input voltage of 4.5 V to maintain regulation at 800 mA, based on its maximum dropout voltage of 1.2 V at that load and temperature. At 25 °C and 100 mA, dropout drops to 1.0 V, allowing stable operation from as low as 4.3 V - but design margins should account for worst-case temperature and tolerance.

Can LD1117D33 be used with ceramic output capacitors only?

Yes - the LD1117D33 is explicitly characterized for stability with a minimum 10 µF ceramic capacitor (X5R/X7R) on the output. Unlike older LDOs, it does not require ESR-based damping, eliminating the need for tantalum or aluminum electrolytic capacitors and supporting compact, high-reliability layouts.

How does the TAB connection affect PCB layout?

The TAB is internally connected to the V_OUT pin and must be soldered to a dedicated copper pour tied to the 3.3 V net. This thermal pad conducts heat from the die to the PCB plane; omitting the connection or floating the pad degrades thermal resistance by >40 %, risking thermal shutdown under sustained 500+ mA loads.

Is there a version with improved PSRR above 10 kHz?

No - the LD1117D33's supply voltage rejection is specified only at 120 Hz (75 dB typ.). Its PSRR rolls off above 1 kHz and is not characterized beyond 10 kHz in the datasheet. For high-frequency ripple suppression (e.g., from MHz-range DC/DC converters), a second-stage RC filter or a specialized low-noise LDO like the STLQ015 should be used upstream.