LTST-C150KEKT SMD LED Datasheet - 3.2x2.8x1.9mm - 2.4V - 75mW - Red - English Technical Document

1. Product Overview

The LTST-C150KEKT is a high-performance, surface-mount LED designed for applications requiring high visibility and reliability. It utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) chip, which is known for its high luminous efficiency and excellent color purity, particularly in the red spectrum. This LED is packaged in a standard EIA-compatible format, making it suitable for automated pick-and-place assembly lines commonly used in high-volume electronics manufacturing.

The primary application areas for this component include status indicators, backlighting for small displays, automotive interior lighting, and various consumer electronics where a bright, consistent red indication is required. Its design prioritizes compatibility with modern soldering processes, ensuring it can withstand the thermal profiles of infrared (IR) and vapor phase reflow soldering without degradation.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operating the LED continuously at or near these limits is not recommended.

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED package can dissipate as heat at an ambient temperature (Ta) of 25°C. Exceeding this limit risks overheating the semiconductor junction.
• Continuous Forward Current (IF): 30 mA. The maximum DC current that can be applied continuously.
• Peak Forward Current: 80 mA. This is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) to briefly achieve higher light output without overheating.
• Derating Factor: 0.4 mA/°C. For ambient temperatures above 25°C, the maximum allowable continuous forward current must be reduced linearly by this factor to prevent thermal runaway.
• Reverse Voltage (VR): 5 V. Applying a reverse voltage higher than this can break down the LED's PN junction.
• Operating & Storage Temperature Range: -55°C to +85°C. This wide range indicates robust performance in harsh environments.
• Soldering Temperature Tolerance: The LED can withstand 260°C for 5 seconds (IR/Wave) or 215°C for 3 minutes (Vapor Phase), confirming its suitability for lead-free reflow processes.

2.2 Electro-Optical Characteristics

These parameters are measured at Ta=25°C with a forward current (IF) of 20 mA, which is the standard test condition.

• Luminous Intensity (Iv): 30.0 - 50.0 mcd (millicandela). This specifies the perceived brightness of the LED as seen by the human eye (using a CIE-matched filter). The typical value is 50 mcd, indicating a very bright output for a standard indicator LED.
• Viewing Angle (2θ1/2): 130 degrees. This is a very wide viewing angle, meaning the LED emits light over a broad cone. The intensity at the half-angle (65° off-axis) is 50% of the axial (center) intensity.
• Peak Emission Wavelength (λPeak): 632 nm (typical). This is the wavelength at which the spectral power output is highest. It falls within the red region of the visible spectrum.
• Dominant Wavelength (λd): 624 nm (typical). This is derived from the CIE chromaticity diagram and represents the single wavelength that best describes the perceived color of the light. The difference between peak and dominant wavelength is characteristic of the LED's spectral shape.
• Spectral Line Half-Width (Δλ): 20 nm. This measures the spectral purity, indicating the range of wavelengths emitted at 50% of the peak intensity. A value of 20 nm is typical for a monochromatic AlInGaP LED.
• Forward Voltage (VF): 2.0V (Min) - 2.4V (Typ) at IF=20mA. This is the voltage drop across the LED when operating. It is crucial for designing the current-limiting resistor in the driver circuit.
• Reverse Current (IR): 100 µA (Max) at VR=5V. This is the small leakage current that flows when the LED is reverse-biased within its maximum rating.
• Capacitance (C): 40 pF (Typ) at VF=0V, f=1MHz. This is the junction capacitance, which can be relevant in high-frequency switching applications.

3. Performance Curve Analysis

While specific graphs are not detailed in the provided text, typical curves for such an LED would include:

• IV Curve (Current vs. Voltage): Shows the exponential relationship between forward voltage and current. The knee voltage is around 2.0V, after which current increases rapidly with small voltage increments.
• Luminous Intensity vs. Forward Current: Demonstrates that light output is approximately proportional to forward current up to a point, after which efficiency may drop due to heating.
• Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as ambient temperature increases. AlInGaP LEDs typically have good high-temperature performance compared to other technologies.
• Spectral Distribution: A plot of relative intensity vs. wavelength, showing a peak at 632 nm and a half-width of 20 nm, confirming the monochromatic red output.

4. Mechanical and Packaging Information

4.1 Package Dimensions

The LED comes in a standard surface-mount package. Key dimensions (in mm) include a body size and lead spacing compatible with automated assembly. The lens is water-clear, which maximizes light output by minimizing internal absorption.

4.2 Polarity Identification and Pad Design

The cathode is typically marked on the package. The datasheet includes suggested soldering pad dimensions to ensure a reliable solder joint, proper alignment, and sufficient thermal relief during reflow soldering.

4.3 Tape and Reel Packaging

The components are supplied on 8mm tape wound onto 7-inch (178mm) diameter reels. Each reel contains 3000 pieces. This packaging is compliant with ANSI/EIA 481-1-A-1994 standards, ensuring compatibility with standard automated feeders. The tape uses a top cover to seal empty pockets and maintain component orientation.

5. Soldering and Assembly Guidelines

5.1 Reflow Soldering Conditions

The LED is qualified for lead-free soldering processes. The recommended profile peaks at 260°C for 5 seconds for infrared or wave soldering, and at 215°C for 3 minutes for vapor phase soldering. It is critical to follow these thermal profiles to avoid damaging the epoxy lens or the internal wire bonds due to excessive thermal stress.

5.2 Cleaning

If cleaning is necessary after soldering, only specified solvents should be used. The datasheet recommends immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Using unspecified or aggressive chemicals can damage the plastic package, leading to cracking or discoloration.

5.3 Storage Conditions

Components should be stored in their original moisture-barrier bags at temperatures between -55°C and +85°C and at low humidity to prevent moisture absorption, which can cause \"popcorning\" during reflow soldering.

6. Application Suggestions and Design Considerations

6.1 Typical Application Circuits

The most common drive method is a simple series resistor. The resistor value (R) is calculated using Ohm's Law: R = (Vcc - VF) / IF, where Vcc is the supply voltage, VF is the LED forward voltage (use 2.4V for design margin), and IF is the desired forward current (e.g., 20mA). For a 5V supply: R = (5 - 2.4) / 0.02 = 130 Ohms. A standard 130 or 150 Ohm resistor would be suitable. For constant brightness over a range of supply voltages or temperatures, a constant current driver is recommended.

6.2 Thermal Management

Although the power dissipation is low (75mW max), proper thermal design is still important for longevity and stable performance, especially when operating at high ambient temperatures or near maximum current. Ensure the PCB has adequate copper area connected to the LED's thermal pad (if applicable) or leads to act as a heat sink. Follow the current derating guideline of 0.4 mA/°C above 25°C.

6.3 Optical Considerations

The wide 130-degree viewing angle makes this LED ideal for applications where the indicator needs to be seen from a wide range of positions. For more directed light, external lenses or light pipes can be used. The water-clear lens provides the highest possible light output but may appear as a bright point source; diffused lenses are available in other variants if a more uniform appearance is desired.

7. Technical Comparison and Differentiation

The LTST-C150KEKT's key differentiators are its AlInGaP technology and high brightness. Compared to older GaAsP (Gallium Arsenide Phosphide) red LEDs, AlInGaP offers significantly higher luminous efficiency, meaning more light output for the same electrical input power. It also maintains its color and intensity better at elevated temperatures. The wide viewing angle and compatibility with automated, high-temperature soldering processes make it a modern, cost-effective choice for mass-produced electronics.

8. Frequently Asked Questions (FAQ)

Q: Can I drive this LED directly from a 3.3V microcontroller pin?
A: Possibly, but it depends on the pin's current sourcing capability. The LED's VF is ~2.4V, leaving only 0.9V across a current-limiting resistor at 3.3V. To achieve 20mA, the resistor would need to be 45 Ohms (0.9V/0.02A). Check if your microcontroller pin can source 20mA. A buffer transistor is often a safer and more reliable solution.

Q: What is the difference between Peak Wavelength and Dominant Wavelength?
A: Peak Wavelength is the physical peak of the emitted light spectrum. Dominant Wavelength is a calculated value based on human color perception (CIE chart) that best matches the perceived color. They are often close but not identical, especially if the spectrum is not perfectly symmetrical.

Q: How do I interpret the \"Typical\" values in the datasheet?
A: \"Typical\" values represent the most common or expected performance under specified conditions. They are not guaranteed. For design purposes, always use the \"Min\" and \"Max\" limits to ensure your circuit will function correctly across all possible component variations.

9. Practical Design and Usage Examples

Example 1: Status Indicator on a Power Supply: Use the LED with a 150-ohm resistor in series connected to a 5V rail. Its high brightness ensures clear visibility even in well-lit environments. The wide viewing angle allows the status to be seen from various angles in a rack or on a bench.

Example 2: Backlight for a Membrane Switch Panel: Multiple LEDs can be arranged behind a translucent panel. The consistent color (624 nm dominant wavelength) and brightness ensure uniform illumination. The compatibility with reflow soldering allows all LEDs and other SMD components to be soldered in a single pass, reducing assembly cost.

10. Operating Principle Introduction

An LED is a semiconductor diode. When a forward voltage is applied across its PN junction, electrons from the N-type material recombine with holes from the P-type material in the active region. This recombination releases energy in the form of photons (light). The specific wavelength (color) of the light is determined by the bandgap energy of the semiconductor material. AlInGaP has a bandgap corresponding to red, orange, and yellow light. The water-clear epoxy package acts as a lens, shaping the light output and protecting the delicate semiconductor chip.

11. Technology Trends

The trend in indicator LEDs like this one is towards ever-higher efficiency (more lumens per watt), allowing for the same brightness at lower current, which saves power and reduces heat. There is also a drive towards miniaturization while maintaining or improving optical performance. Furthermore, enhanced reliability and broader qualification for automotive and industrial temperature ranges are common goals. The use of materials like AlInGaP represents an ongoing shift from older, less efficient technologies to provide better performance in standard packages.