Overview

The STMicroelectronics LD1117S18CTR is a low-dropout (LDO) linear voltage regulator designed to provide a fixed 1.8 V output voltage with a high output current capability, typically up to 800 mA. It is part of the LD1117 series, known for excellent load regulation, thermal stability, and low dropout voltage, making it well-suited for powering modern low-voltage digital circuits, microcontrollers, and other sensitive components. Its compact SOT-223 package and internal protection features simplify design while ensuring robust, reliable operation in various applications including consumer electronics, embedded systems, and communication devices.

Key Features

* Fixed output voltage of 1.8 V with tight regulation
* Output current capability up to 800 mA continuous
* Low dropout voltage typically 1.1 V at full load, minimizing power dissipation
* Wide input voltage range up to 15 V, enabling flexibility in power supply design
* Internal current limiting and thermal shutdown for device protection and reliability
* Very low quiescent current for power-efficient operation
* Excellent line and load regulation for stable output voltage under varying conditions
* Output voltage tolerance typically ±2%
* Fast transient response to load changes
* Low noise output suitable for sensitive analog and digital circuits
* SOT-223 surface-mount package enabling compact PCB layouts and good thermal performance
* Compatible with standard bypass capacitors for stable operation
* Operating junction temperature range up to 125°C

Electrical Specifications

* Output Voltage: Fixed 1.8 V ±2%
* Maximum Output Current: 800 mA continuous
* Input Voltage Range: 2.6 V minimum to 15 V maximum
* Dropout Voltage: Typically 1.1 V at 800 mA load current
* Line Regulation: 0.2% typical over input voltage range
* Load Regulation: 0.4% typical from 10 mA to 800 mA
* Quiescent Current (Iq): Approximately 5 mA typical
* Output Noise: Low, suitable for analog circuits (typically in microvolts range)
* Operating Temperature Range: −40°C to +125°C junction temperature
* Thermal Shutdown Threshold: Typically around 150°C with hysteresis
* Package: SOT-223, lead-free and RoHS compliant

Functional Description

The LD1117S18CTR is a linear regulator that steps down an input voltage to a stable 1.8 V output with high precision and low noise. The device incorporates an internal pass transistor and error amplifier to maintain a regulated output voltage, even under varying input voltage and load current conditions. The low dropout voltage allows efficient operation when the input voltage is close to the output voltage, reducing power loss and heat dissipation.

Protection circuitry including current limiting and thermal shutdown safeguards the regulator and downstream components against overloads and thermal stress, ensuring system reliability. The device requires minimal external components—a standard input and output capacitor—to guarantee stability and optimal transient response.

Package and Mechanical Details

The LD1117S18CTR comes in the SOT-223 package, a compact surface-mount package widely used in power regulation due to its efficient heat dissipation and small PCB footprint.

* Package Type: SOT-223
* Dimensions: Approximately 6.5 mm × 3.7 mm × 1.5 mm
* Lead Pitch: 1.27 mm
* Thermal Resistance Junction-to-Ambient (RθJA): Approximately 60°C/W on a standard PCB layout
* RoHS compliant and lead-free finish

Typical Applications

* Low-voltage digital circuits and microcontrollers requiring 1.8 V supply
* Battery-powered devices and portable electronics
* Power management in embedded systems
* Consumer electronics such as smartphones, tablets, and media players
* Communication devices and networking equipment
* Analog and mixed-signal circuits requiring low noise power supply
* Instrumentation and measurement systems

Reliability and Protection Features

The device includes internal current limiting to prevent damage during overload conditions or short circuits. Thermal shutdown protects the device against overheating by disabling the output when the junction temperature exceeds a safe threshold, automatically restoring operation once cooled. These features improve overall system robustness and safety without requiring external protection components.

The LD1117S18CTR exhibits stable operation with standard ceramic or tantalum capacitors at input and output, providing reliable transient response and minimizing output voltage deviations during rapid load changes.

Typical Application Circuit

A typical implementation involves connecting the input to a DC power source, the output to the load requiring 1.8 V, and placing a bypass capacitor (typically 10 µF) close to the regulator output to ensure stability. An input capacitor is also recommended (usually 1 µF) to filter input voltage noise and enhance transient performance. The compact SOT-223 package facilitates thermal dissipation on the PCB, often supplemented by a copper area or heat sink pad.

Summary of Key Parameters

| Parameter | Value |
| ---------------------- | ------------------------------ |
| Output Voltage | 1.8 V ±2% |
| Maximum Output Current | 800 mA |
| Input Voltage Range | 2.6 V to 15 V |
| Dropout Voltage | 1.1 V (typical at 800 mA load) |
| Line Regulation | 0.2% typical |
| Load Regulation | 0.4% typical |
| Quiescent Current | 5 mA typical |
| Operating Temperature | −40°C to +125°C junction |
| Package | SOT-223 |

The STMicroelectronics LD1117S18CTR offers a reliable, efficient, and compact solution for delivering a stable 1.8 V power rail in a broad range of electronic systems, balancing low dropout, robust protection, and ease of integration for demanding modern applications.