SMD LED LTST-E142TBKRKT Datasheet - Dual Color Blue/Red - 20-30mA - 75-76mW - English Technical Document

1. Product Overview

The LTST-E142TBKRKT is a surface-mount device (SMD) LED designed for automated printed circuit board (PCB) assembly. It features a dual-color configuration, integrating both a blue and a red LED chip within a single, compact package. This design is particularly advantageous for space-constrained applications where multiple indicator functions are required. The component is engineered for compatibility with standard infrared (IR) reflow soldering processes, making it suitable for high-volume manufacturing environments.

1.1 Core Advantages

• Miniaturized Footprint: The SMD package allows for high-density PCB layouts, saving valuable board space.
• Dual-Color Functionality: Incorporates two distinct light sources (Blue and Red) in one unit, simplifying design and reducing part count.
• Automation Compatibility: Packaged in 8mm tape on 7-inch reels, it is fully compatible with automated pick-and-place equipment.
• Environmental Compliance: The product meets RoHS (Restriction of Hazardous Substances) directives.
• Process Robustness: Withstands preconditioning to JEDEC Level 3 and is compatible with lead-free soldering profiles.

1.2 Target Markets and Applications

This LED is versatile and finds use across a broad spectrum of electronic equipment. Its primary applications include status indication, signal and symbol illumination, and front-panel backlighting. Target markets encompass telecommunications infrastructure, office automation systems, home appliances, and various industrial equipment where reliable, compact visual indicators are essential.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. For the blue LED, the maximum continuous forward current is 20mA with a power dissipation of 76mW. The red LED can handle a slightly higher continuous current of 30mA with a power dissipation of 75mW. Both share a peak forward current rating of 80mA under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The operational and storage temperature range is specified from -40°C to +100°C, indicating suitability for harsh environments.

2.2 Thermal Characteristics

Thermal management is critical for LED longevity. The maximum junction temperature (Tj) for both chips is 140°C. The typical thermal resistance from the junction to the ambient air (Rθja) is 145°C/W. This parameter is vital for calculating the necessary PCB thermal design (e.g., copper pad area) to keep the junction temperature within safe limits during operation, especially at higher drive currents.

2.3 Electrical and Optical Characteristics

These are the key performance parameters measured under standard test conditions (Ta=25°C, IF=20mA).

• Luminous Intensity (Iv): The blue LED has a minimum intensity of 140mcd and a maximum of 420mcd. The red LED ranges from 90mcd to 280mcd. This wide range is managed through a binning system.
• Viewing Angle (2θ1/2): The typical viewing angle is 120 degrees, providing a wide, diffuse light emission pattern suitable for indicator applications.
• Wavelength: The blue LED's dominant wavelength (λd) ranges from 465nm to 475nm, with a typical peak emission (λp) at 468nm. The red LED's dominant wavelength ranges from 623nm to 638nm, with a typical peak at 639nm. Spectral half-widths are 25nm (blue) and 15nm (red), indicating the color purity.
• Forward Voltage (Vf): At 20mA, the blue LED's Vf is between 2.8V and 3.8V, while the red LED's is between 1.7V and 2.5V. This difference is crucial for circuit design, particularly when driving both colors from a common voltage source.
• Reverse Current (Ir): Maximum reverse current at VR=5V is 10µA for both. The datasheet explicitly states the device is not designed for reverse operation; this test is for IR qualification only.

3. Binning System Explanation

To ensure color and brightness consistency in production, the LEDs are sorted into bins.

3.1 Luminous Intensity (Iv) Binning

Blue LEDs are binned into codes P, Q, R, and S, with intensity ranges from 140-185mcd up to 315-420mcd. Red LEDs use codes Q2, R1, R2, S1, and S2, covering ranges from 90-112mcd up to 224-280mcd. A tolerance of ±11% applies within each bin.

3.2 Dominant Wavelength (Wd) Binning

For the blue LED only, dominant wavelength bins are defined: code AC (465-470nm) and code AD (470-475nm), with a tight tolerance of ±1nm per bin. This precise control is essential for applications requiring specific blue hues.

4. Performance Curve Analysis

The datasheet references typical curves for electrical and optical characteristics. While the specific graphs are not reproduced in the provided text, they typically include:

• IV Curve: Shows the relationship between forward current (If) and forward voltage (Vf) for each color. This is used to determine the operating point and required series resistance.
• Relative Luminous Intensity vs. Forward Current: Illustrates how light output increases with current, up to the maximum rating.
• Relative Luminous Intensity vs. Ambient Temperature: Demonstrates the decrease in light output as junction temperature rises, highlighting the importance of thermal design.
• Spectral Distribution: Depicts the relative radiant power versus wavelength, showing the peak and shape of the emission spectrum for each color.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED comes in a standard EIA package. All critical dimensions (length, width, height, lead spacing) are provided in millimeters with a general tolerance of ±0.2mm. The pin assignment is clearly defined: Pins 2 and 3 are for the blue chip, and pins 1 and 4 are for the red chip. This information is essential for PCB footprint design.

5.2 Recommended PCB Attachment Pad

A land pattern recommendation is provided to ensure proper soldering, mechanical stability, and optimal thermal performance. Following this guideline helps prevent tombstoning and ensures reliable electrical connections.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Profile

A suggested reflow profile compliant with J-STD-020B for lead-free processes is included. Key parameters include a pre-heat temperature of 150-200°C, a peak temperature not exceeding 260°C, and a total time above liquidus tailored to ensure proper solder joint formation without exposing the LED to excessive thermal stress.

6.2 Storage Conditions

Strict storage conditions are mandated due to the moisture sensitivity of the package (Level 3). Unopened reels should be stored at ≤30°C and ≤70% RH and used within one year. Once the moisture barrier bag is opened, components should be stored at ≤30°C and ≤60% RH and subjected to reflow soldering within 168 hours. If this window is exceeded, a bake-out at 60°C for 48 hours is required prior to assembly.

6.3 Cleaning

If cleaning is necessary after soldering, only specified alcohol-based solvents like ethyl alcohol or isopropyl alcohol should be used at room temperature for less than one minute. Unspecified chemicals may damage the LED package.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The components are supplied on 8mm wide carrier tape wound onto 7-inch (178mm) diameter reels. Each reel contains 4000 pieces. Detailed dimensions for the tape pockets and the reel are provided to ensure compatibility with automated assembly equipment. The packing follows ANSI/EIA 481 specifications.

8. Application Suggestions

8.1 Typical Application Circuits

When designing a drive circuit, the different forward voltages of the blue and red chips must be considered. A common design uses a constant current source or a voltage source with a current-limiting resistor in series with each LED anode. The cathode of both LEDs can be connected to ground. Independent control of each color is achieved by switching the voltage to their respective anodes.

8.2 Design Considerations

• Current Limiting: Always use a series resistor or active current control to prevent exceeding the maximum DC forward current (20mA for blue, 30mA for red).
• Thermal Design: Use the recommended PCB pad layout and ensure adequate copper area to dissipate heat, especially if operating near maximum ratings or in high ambient temperatures.
• ESD Protection: While not explicitly stated, standard ESD precautions should be observed during handling.

9. Technical Comparison and Differentiation

The primary differentiation of this component lies in its dual-color, single-package design. Compared to using two separate SMD LEDs, it reduces the PCB footprint by approximately 50%, simplifies the bill of materials (BOM), and requires only one pick-and-place operation during assembly, increasing throughput. The wide 120-degree viewing angle is a standard feature for indicator-type LEDs, providing good off-axis visibility.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive the blue and red LEDs simultaneously from the same current source?
A: Not directly in a simple series circuit, due to their different forward voltage characteristics. They would require separate current-limiting paths (e.g., individual resistors) to ensure each receives the correct current.

Q: What is the meaning of the bin codes in the part number?
A> The part number LTST-E142TBKRKT likely includes fixed bin codes for intensity and wavelength. For specific projects requiring tight color or brightness matching, engineers should consult the full binning tables (sections 4.1 and 4.2) and may need to specify exact bin codes when ordering.

Q: Is this LED suitable for outdoor applications?
A: The operating temperature range (-40°C to +100°C) suggests it can handle wide ambient swings. However, the datasheet does not specify an ingress protection (IP) rating. For outdoor use, additional environmental sealing (conformal coating, enclosures) would be necessary to protect against moisture and dust.

11. Practical Use Case

Scenario: Dual-State Status Indicator on a Network Router. A single LTST-E142TBKRKT can indicate multiple system states: Off (no power), Solid Blue (system powered and operating normally), Solid Red (system error or booting), and Blinking Red (network activity or specific fault). This consolidates what might have required two separate LEDs into one, creating a cleaner front-panel design. The drive circuit would involve two GPIO pins from a microcontroller, each connected through an appropriate current-limiting resistor to the anode of one LED color, with the common cathodes grounded.

12. Principle Introduction

Light emission in LEDs is based on electroluminescence in a semiconductor material. When a forward voltage is applied across the p-n junction, electrons and holes recombine, releasing energy in the form of photons. The color of the light is determined by the bandgap energy of the semiconductor material. The blue LED uses an Indium Gallium Nitride (InGaN) chip, which has a wider bandgap, producing higher-energy (shorter wavelength) blue light. The red LED uses an Aluminum Indium Gallium Phosphide (AlInGaP) chip, which has a narrower bandgap, producing lower-energy (longer wavelength) red light. The package incorporates a clear lens that shapes the light output into the specified viewing angle.

13. Development Trends

The general trend in SMD LEDs for indicators and backlighting continues toward higher efficiency (more light output per watt of electrical input), increased miniaturization, and greater integration. Multi-chip packages (like this dual-color unit) and even RGB (Red-Green-Blue) packages are becoming more common, enabling full-color programmability in a tiny footprint. Furthermore, advancements in packaging materials and phosphor technology are constantly improving reliability, color consistency, and resistance to thermal and environmental stress. The drive for lower power consumption in all electronic devices also pushes LED manufacturers to develop components that deliver required brightness at ever-lower currents.