LTST-C28NBEGK-2A SMD LED Datasheet - 2.8x3.5x0.25mm - Red/Blue/Green - 10-20mA - English Technical Document

1. Product Overview

The LTST-C28NBEGK-2A is a full-color, extra-thin surface-mount device (SMD) LED designed for modern, space-constrained electronic applications. This component integrates three distinct LED chips within a single, compact package, enabling the generation of red, blue, and green light from a common footprint. Its primary design goal is to facilitate automated assembly processes while providing high-brightness output suitable for a variety of indicator and backlighting functions.

1.1 Core Advantages

The device offers several key advantages for designers and manufacturers. Its ultra-thin profile of 0.25mm makes it ideal for applications where vertical space is at a premium, such as in ultra-slim mobile devices or displays. The package conforms to EIA standards, ensuring compatibility with a wide range of automated pick-and-place and infrared reflow soldering equipment, which streamlines high-volume production. Furthermore, the use of advanced InGaN (for blue/green) and AlInGaP (for red) semiconductor materials provides high luminous efficiency and excellent color purity.

1.2 Target Market and Applications

This LED is targeted at the consumer electronics, telecommunications, and industrial equipment markets. Its typical applications include, but are not limited to: status indicators and backlighting for keypads and keyboards in smartphones, tablets, and laptops; signal and symbol illumination in network equipment and home appliances; and micro-displays or decorative lighting where multiple colors from a single point source are required. Its reliability and compatibility make it a versatile choice for both portable and stationary electronic products.

2. In-Depth Technical Parameter Analysis

A thorough understanding of the electrical and optical parameters is crucial for successful circuit design and performance prediction.

2.1 Absolute Maximum Ratings

Operating the device beyond these limits may cause permanent damage. The maximum DC forward current (I_F) is specified as 10 mA for the blue and green chips, and 20 mA for the red chip, all at an ambient temperature (T_a) of 25°C. The maximum power dissipation is 38 mW for blue/green and 50 mW for red. The device can withstand a peak forward current of 40 mA under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The operating temperature range is from -20°C to +80°C, and storage conditions range from -30°C to +85°C. The component is rated for infrared reflow soldering at a peak temperature of 260°C for a maximum of 10 seconds.

2.2 Electrical and Optical Characteristics

These parameters are measured under standard test conditions (T_a=25°C, I_F=2mA). The luminous intensity (I_V) varies by color: Blue has a range of 18.0-45.0 mcd, Red from 28.0-71.0 mcd, and Green from 112.0-280.0 mcd. The typical viewing angle (2θ_1/2) is 120 degrees, providing a wide, diffuse light pattern. The forward voltage (V_F) is another critical parameter for power supply design: Blue and Green LEDs have a V_F range of 2.2V to 3.0V, while the Red LED operates between 1.2V and 2.2V at 2mA. The reverse leakage current (I_R) is guaranteed to be less than 10 μA at a reverse voltage (V_R) of 5V for all colors.

2.3 Spectral Characteristics

The color of the emitted light is defined by its wavelength. The typical peak emission wavelength (λ_P) is 465 nm for blue, 632 nm for red, and 518 nm for green. The dominant wavelength (λ_d), which more closely correlates with perceived color, has specified bins: Blue ranges from 465-475 nm, and Green from 525-535 nm. The spectral line half-width (Δλ), an indicator of color purity, is typically 25 nm for blue, 20 nm for red, and 35 nm for green. These values are derived from the 1931 CIE chromaticity diagram.

3. Binning System Explanation

To ensure color and brightness consistency in production, the LEDs are sorted into bins based on key performance metrics.

3.1 Luminous Intensity Binning

LEDs are classified by their light output at a standard test current of 2mA. Each color has specific bin codes with minimum and maximum luminous intensity values. For example, Blue LEDs are sorted into Bin M (18.0-28.0 mcd) and Bin N (28.0-45.0 mcd). Red LEDs use Bin N (28.0-45.0 mcd) and Bin P (45.0-71.0 mcd). Green LEDs, which are typically brighter, are sorted into Bin R (112.0-180.0 mcd) and Bin S (180.0-280.0 mcd). A tolerance of ±15% is applied within each intensity bin.

3.2 Hue (Dominant Wavelength) Binning

For applications requiring precise color matching, such as full-color displays, LEDs are also binned by their dominant wavelength. Blue LEDs are available in Bin B (465.0-470.0 nm) and Bin C (470.0-475.0 nm). Green LEDs are available in Bin C (525.0-530.0 nm) and Bin D (530.0-535.0 nm). The tolerance for each dominant wavelength bin is a tight ±1 nm. The specific bin code for both intensity and wavelength is marked on the product packaging, allowing designers to select components that meet their exact color and brightness requirements.

4. Performance Curve Analysis

Graphical data provides deeper insight into device behavior under varying conditions, which is essential for robust design.

4.1 Current vs. Voltage (I-V) and Luminous Intensity

The forward voltage (V_F) of an LED is not constant; it increases with forward current (I_F). The typical curves show the relationship for each color chip. The red LED typically has a lower forward voltage for a given current compared to the blue and green LEDs, which is consistent with its different semiconductor material (AlInGaP vs. InGaN). Similarly, the luminous intensity increases super-linearly with current before potentially saturating at higher currents. Designers must use these curves to select appropriate current-limiting resistors or constant-current drivers to achieve desired brightness while staying within the device's thermal and electrical limits.

4.2 Temperature Dependence

LED performance is significantly affected by junction temperature. As temperature increases, the forward voltage typically decreases slightly for a given current, while the luminous output decreases. The datasheet provides typical derating curves that show the relative luminous intensity as a function of ambient temperature. Understanding this relationship is critical for applications that operate over a wide temperature range or in environments with poor thermal management, as it affects long-term brightness stability and color point.

4.3 Spectral Distribution

The spectral power distribution curves illustrate the relative intensity of light emitted across different wavelengths for each color. The blue and green InGaN chips typically show a narrower, more Gaussian-like distribution centered around their peak wavelength. The red AlInGaP chip may have a slightly different spectral shape. These curves are important for applications involving color sensors, filters, or where specific spectral content is required, as they show not just the dominant color but also the amount of light emitted at neighboring wavelengths.

5. Mechanical and Package Information

5.1 Package Dimensions and Pin Assignment

The LTST-C28NBEGK-2A conforms to a standard SMD footprint. The package dimensions are provided in a detailed drawing with all critical measurements in millimeters. The tolerance for most dimensions is ±0.1 mm. The device has four pins. Pin 1 is the common anode for all three LED chips. Pin 2 is the cathode for the Red chip, Pin 3 is the cathode for the Blue chip, and Pin 4 is the cathode for the Green chip. The lens is water clear, allowing the native chip color to be visible.

5.2 Recommended PCB Pad Design

For reliable soldering and optimal thermal performance, a specific land pattern is recommended for the PCB. This pattern includes the solder pad dimensions and spacing, which are designed to facilitate good solder fillet formation during reflow without causing bridging or tombstoning. Adhering to this recommended layout helps ensure strong mechanical attachment and efficient heat dissipation away from the LED junction.

6. Soldering and Assembly Guidelines

6.1 Infrared Reflow Soldering Profile

The device is compatible with lead-free (Pb-free) infrared reflow soldering processes. A suggested temperature profile is provided, which typically includes a pre-heat stage (e.g., 150-200°C), a controlled ramp-up, a time above liquidus (TAL), a peak temperature not exceeding 260°C, and a controlled cooling phase. The critical parameter is that the component body should not be exposed to temperatures above 260°C for more than 10 seconds. It is emphasized that the optimal profile may vary depending on the specific PCB assembly, solder paste, and oven used, and board-level characterization is recommended.

6.2 Storage and Handling Precautions

Proper handling is essential to prevent damage from electrostatic discharge (ESD). It is recommended to use wrist straps or anti-static gloves and ensure all equipment is grounded. For storage, unopened moisture-sensitive devices (MSL 3) should be kept at ≤30°C and ≤90% relative humidity (RH) and used within one year. Once the original sealed packaging is opened, the LEDs should be stored at ≤30°C and ≤60% RH. Components removed from their dry pack for more than one week should be baked at approximately 60°C for at least 20 hours before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. Immersing the LED in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute is acceptable. The use of unspecified or aggressive chemical cleaners can damage the plastic package or lens, leading to reduced light output or reliability issues.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied packaged in 8mm wide embossed carrier tape on 7-inch (178mm) diameter reels, in accordance with ANSI/EIA-481 specifications. Each reel contains 3000 pieces. The tape has a pocket pitch and dimensions designed for compatibility with standard automated feeders. A top cover tape seals the component pockets. The packaging specifications also note that a minimum of two consecutive missing components (empty pockets) is the maximum allowed, and the minimum order quantity for remainder lots is 500 pieces.

8. Application Notes and Design Considerations

8.1 Circuit Design

Each color channel (Red, Green, Blue) must be driven independently via its own current-limiting circuit connected to the common anode (Pin 1) and the respective cathode pin. Due to the different forward voltage characteristics, separate current-setting calculations are required for each color to achieve uniform perceived brightness or specific color mixes. A constant-current driver is often preferred over a simple series resistor for better stability over temperature and supply voltage variations, especially in battery-powered devices.

8.2 Thermal Management

Although the power dissipation is relatively low (38-50 mW per chip), effective thermal management is still important for maintaining performance and longevity, especially when driving the LEDs at or near their maximum rated current. The PCB acts as the primary heat sink. Ensuring a good thermal connection via the recommended pad design and, if necessary, using thermal vias or a copper pour under the package, helps conduct heat away from the LED junction.

8.3 Optical Integration

The wide 120-degree viewing angle makes this LED suitable for applications requiring broad, even illumination rather than a focused beam. For backlighting panels or light guides, the optical coupling and diffusion materials must be selected to work effectively with the LED's emission pattern and color points. Designers should also consider the potential for color mixing when multiple LEDs are placed close together, which can be used to create secondary colors like cyan, magenta, yellow, or white.

9. Technical Comparison and Differentiation

The LTST-C28NBEGK-2A differentiates itself in the market through its combination of features. Its primary advantage is the integration of three high-brightness, distinct-color chips into an industry-standard, extra-thin (0.25mm) package. This is contrasted with alternatives such as using three separate single-color LEDs (consuming more board space), or a single white LED with color filters (which is less efficient and offers less saturated colors). The use of AlInGaP for red provides higher efficiency and better thermal stability compared to older technologies like GaAsP, resulting in brighter and more consistent red output. Its compliance with automated assembly and reflow standards makes it a cost-effective choice for mass production compared to LEDs requiring manual soldering.

10. Frequently Asked Questions (Based on Technical Parameters)

10.1 Can I drive all three colors simultaneously at their maximum current?

No, not without exceeding the package's total power dissipation limits. If all three chips were driven at their maximum DC current (Red: 20mA, Blue: 10mA, Green: 10mA) and typical forward voltages, the total power could approach or exceed the combined thermal capacity of the small package, leading to overheating and reduced lifespan. The design must consider the duty cycle and thermal environment. For full-white light (all three on), it is common to drive each channel at a lower current to manage total heat.

10.2 Why is the forward voltage different for each color?

The forward voltage is a fundamental property of the semiconductor material's bandgap energy. Blue and green LEDs use Indium Gallium Nitride (InGaN) which has a larger bandgap, requiring a higher voltage (typically ~2.8V) to \"push\" electrons across it and cause light emission. Red LEDs use Aluminum Indium Gallium Phosphide (AlInGaP), which has a smaller bandgap, resulting in a lower forward voltage (typically ~1.8V).

10.3 How do I interpret the bin codes when ordering?

When placing an order, you can specify the desired bin codes for luminous intensity and dominant wavelength for each color. For example, ordering \"Blue: Bin N, Bin B\" requests Blue LEDs with luminous intensity between 28.0-45.0 mcd and a dominant wavelength between 465.0-470.0 nm. Specifying bins allows for tighter control over color consistency and brightness matching across multiple units in your product, which is critical for display and indicator applications.

11. Practical Design and Usage Case Study

Consider a portable gaming device that uses the LTST-C28NBEGK-2A for multi-color status indication around its control buttons. The design challenge involves providing vibrant, user-selectable colors (Red, Green, Blue, Cyan, Magenta, Yellow, White) while minimizing power consumption from the device's battery. The engineer selects a low-quiescent-current, triple-output constant-current LED driver IC. Using the V_F and I_V curves from the datasheet, they program the driver to supply 5mA to the Red channel and 3mA to the Blue and Green channels to create a balanced white light at the lowest total current. They choose LEDs from Bin P for red and Bin S for green to ensure high brightness, and specify tight wavelength bins (B for blue, C for green) to guarantee consistent color across all units. The PCB layout follows the recommended pad design and includes a small thermal relief connection to a ground plane for heat dissipation. The final assembly uses the specified IR reflow profile, resulting in reliable, bright, and consistent indicator lights that enhance the user experience.

12. Operational Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light through a process called electroluminescence. When a forward voltage is applied across the p-n junction of the semiconductor material, electrons from the n-type region gain enough energy to cross the junction and recombine with holes in the p-type region. This recombination event releases energy. In an LED, the semiconductor material is chosen so that this energy is released primarily in the form of photons (light particles). The specific wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material: a larger bandgap produces shorter wavelength (bluer) light, and a smaller bandgap produces longer wavelength (redder) light. The InGaN material system is used for blue and green LEDs, while AlInGaP is used for high-efficiency red and amber LEDs. The SMD package encapsulates the tiny semiconductor chip, provides electrical connections via metal leads, and includes a molded plastic lens that shapes the light output.

13. Technology Trends and Developments

The field of SMD LEDs continues to evolve driven by demands for higher efficiency, smaller size, better color rendering, and lower cost. Trends observable in components like the LTST-C28NBEGK-2A include the ongoing miniaturization of packages while maintaining or increasing light output (higher efficacy in lumens per watt). There is a continuous improvement in the materials science behind InGaN and AlInGaP chips, leading to reduced efficiency droop at higher currents and better performance at elevated temperatures. Another significant trend is the integration of more functionality, such as combining RGB LEDs with a dedicated driver IC or control logic into a single package (\"smart LED\"). Furthermore, advancements in phosphor technology for white LEDs and the pursuit of micro-LEDs for next-generation displays represent parallel development paths that influence the broader optoelectronics ecosystem in which multi-color SMD LEDs operate.