STMicroelectronics LD1117AS18TR

Overview

LD1117AS18TR from STMicroelectronics is a fixed-output 1.8 V low-dropout linear voltage regulator delivering up to 1 A output current with 1.15 V typical dropout at 1 A and ±2% output voltage tolerance at 25 °C. It features 5 mA typical quiescent current, 80 dB supply voltage rejection at 120 Hz, and stable operation with only a 10 µF output capacitor - used in power rails for microcontrollers, FPGAs, and USB peripherals requiring clean, regulated 1.8 V.

For engineers reviewing the LD1117AS18TR datasheet, LD1117AS18TR pinout, LD1117AS18TR application, or LD1117AS18TR equivalent, key selection criteria include dropout voltage under full load, thermal resistance in SOT-223 package, line/load regulation performance, and compatibility with standard 1.8 V logic supply domains in embedded and industrial control systems.

Technical Context

The LD1117AS18TR employs an NPN pass transistor architecture enabling low dropout while maintaining high PSRR and thermal stability. Its internal reference is trimmed to 1.25 V, and output voltage is set by factory-trimmed resistors - no external components required for fixed 1.8 V operation.

It integrates thermal shutdown and current limiting, operates across 0–125 °C junction temperature, and achieves 0.08–0.2 %/W thermal regulation. The device supports input voltages up to 15 V DC but requires minimum VIN ≥ VO + VD (e.g., ≥2.95 V at 1 A) for regulation.

Key Specifications

Pinout & Package

LD1117AS18TR is supplied in SOT-223 package with exposed thermal pad connected internally to VOUT. This configuration enhances heat dissipation in compact layouts and requires PCB copper pour under the tab for optimal thermal performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TLV1117-18CDCYR and MCP1703T-1802E/MB, LD1117AS18TR uniquely balances 1 A output, industrial temperature range, and high PSRR in a cost-optimized SOT-223 package - making it the preferred choice for thermally constrained 1.8 V power rails in embedded controllers and programmable logic.

Availability

LD1117AS18TR is available at Aetrix Electronics and suitable for industrial control panels, automotive body electronics modules, and medical diagnostic equipment requiring stable component supply with long-term manufacturability and RoHS-compliant packaging.

Supply support for LD1117AS18TR 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, Switzerland, designing and manufacturing silicon solutions for automotive, industrial, and consumer markets since 1987.

The LD1117A series was developed to deliver high-reliability, low-cost LDO regulation for space-constrained embedded systems - emphasizing thermal robustness, minimal external components, and compatibility with standard PCB assembly processes.

FAQ

What is the minimum input voltage required for LD1117AS18TR to maintain regulation at 1 A load?

The minimum input voltage is determined by dropout voltage: VO + VD = 1.8 V + 1.30 V (max) = 3.1 V. At 1 A and 125 °C, worst-case dropout reaches 1.30 V per datasheet Table 5, so VIN must exceed 3.1 V to sustain regulation. For margin, 3.3 V input is recommended.

Can LD1117AS18TR be used with ceramic output capacitors?

Yes - the device is stable with 10 µF ceramic capacitors (X5R/X7R) as confirmed in Section 4 (Schematic Application) and Table 4–6 of the datasheet. ESR independence eliminates need for added series resistance, simplifying design and improving transient response.

How does the SOT-223 package's thermal performance compare to DPAK or TO-220 for LD1117AS18TR?

SOT-223 has RthJA = 110 °C/W, versus 100 °C/W for DPAK and 50 °C/W for TO-220. At 1 A and 1.15 V dropout (1.15 W dissipation), SOT-223 junction temperature rises ~127 °C above ambient - requiring careful PCB copper area design. TO-220 allows higher continuous current without heatsink.

Is LD1117AS18TR pin-compatible with other LD1117A fixed-voltage variants?

Yes - all LD1117A fixed versions (1.2 V, 1.8 V, 3.3 V) share identical SOT-223 pinout (IN–OUT–GND), allowing footprint reuse across voltage options. This simplifies BOM consolidation and design scalability for multi-rail systems using the same regulator family.