LTST-E682KSTBWT Dual-Color SMD LED Datasheet - Dimensions 3.2x2.8x1.9mm - Voltage 2.4V/3.8V - Power 72mW/80mW - Yellow/Blue - English Technical Document

1. Product Overview

The LTST-E682KSTBWT is a dual-color surface-mount device (SMD) LED featuring a diffused lens. It integrates two distinct light-emitting chips within a single EIA standard package: one emitting in the yellow spectrum (AlInGaP) and the other in the blue spectrum (InGaN). This component is designed for applications requiring compact, bi-color indication or lighting solutions. Its primary advantages include compatibility with automatic placement equipment and infrared reflow soldering processes, making it suitable for high-volume manufacturing. The product is compliant with RoHS directives and is classified as a green product.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The device's operational limits are defined at an ambient temperature (Ta) of 25°C. For the yellow LED, the maximum continuous DC forward current is 30mA with a power dissipation of 72mW. The blue LED has a slightly lower maximum DC forward current of 20mA but a higher power dissipation rating of 80mW. Both share a peak forward current rating of 80mA under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The electrostatic discharge (ESD) threshold differs significantly: 2000V (HBM) for the yellow chip and 300V (HBM) for the more sensitive blue chip. The operating temperature range is from -40°C to +85°C, while storage can extend from -40°C to +100°C.

2.2 Electrical and Optical Characteristics

Key performance metrics are measured at Ta=25°C and a forward current (IF) of 20mA. The luminous intensity (Iv) for the yellow LED ranges from a minimum of 112.0 mcd to a maximum of 355.0 mcd. The blue LED's intensity ranges from 71.0 mcd to 224.0 mcd. Both LEDs feature a typical wide viewing angle (2θ1/2) of 120 degrees. The yellow LED's typical peak emission wavelength (λP) is 591nm with a dominant wavelength (λd) of 589nm and a spectral half-width (Δλ) of 15nm. The blue LED emits at a typical peak of 468nm, a dominant wavelength of 470nm, and a broader spectral half-width of 25nm. Forward voltage (VF) for the yellow LED is between 1.8V and 2.4V, while for the blue LED it is between 2.8V and 3.8V. The maximum reverse current (IR) for both is 10μA at a reverse voltage (VR) of 5V.

3. Binning System Explanation

The product utilizes a binning system to categorize LEDs based on their luminous intensity output at 20mA. This ensures consistency in brightness for production batches. For the yellow LED, bin codes range from R1 (112.0-140.0 mcd) to T1 (280.0-355.0 mcd). The blue LED uses codes from Q1 (71.0-90.0 mcd) to S1 (180.0-224.0 mcd). A tolerance of +/-11% is applied to each intensity bin. This system allows designers to select components that meet specific brightness requirements for their application.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Figure 1 for spectral measurement, Figure 5 for viewing angle), the document indicates that typical characteristic curves are provided. These would typically include plots of forward current vs. forward voltage (IV curve), luminous intensity vs. forward current, and luminous intensity vs. ambient temperature. The spectral distribution curves would show the relative radiant power versus wavelength for both the yellow and blue chips, highlighting their peak and dominant wavelengths as well as spectral width. Analyzing these curves is crucial for understanding performance under non-standard conditions, such as different drive currents or operating temperatures.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED is housed in a compact SMD package. Key dimensions include a body length of 3.2mm (0.126 inches), a width of 2.8mm (0.110 inches), and a height of 1.9mm (0.075 inches). The lens itself has dimensions of 2.2mm by 3.5mm. A dimensional drawing is provided in the datasheet with all measurements in millimeters (inches) and a general tolerance of ±0.2mm unless otherwise specified.

5.2 Pin Assignment and Polarity Identification

The device has four pins. For the LTST-E682KSTBWT model, pins 1 and 2 are assigned to the yellow LED's cathode and anode (specific order should be verified from the diagram), while pins 3 and 4 are assigned to the blue LED. The cathode is typically marked on the package. Correct polarity identification is essential to prevent reverse bias damage, especially to the blue chip which has a lower ESD tolerance.

5.3 Recommended PCB Attachment Pad

A land pattern recommendation is provided for infrared or vapor phase reflow soldering. Adhering to this recommended pad layout is critical for achieving proper solder joint formation, ensuring good thermal and electrical connection, and maintaining the correct alignment of the LED on the board.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Parameters

The device is compatible with infrared reflow soldering processes. For lead-free soldering, a profile compliant with J-STD-020B is recommended. Key parameters include a pre-heat temperature of 150-200°C, a pre-heat time of up to 120 seconds maximum, a peak temperature not exceeding 260°C, and a time above liquidus (or at peak) limited to 10 seconds maximum. Reflow should be performed a maximum of two times.

6.2 Hand Soldering

If hand soldering is necessary, the soldering iron tip temperature should not exceed 300°C, and the soldering time per lead should be limited to 3 seconds maximum. Hand soldering should be performed only once.

6.3 Storage Conditions

For sealed moisture-proof bags with desiccant, LEDs should be stored at ≤30°C and ≤70% RH and used within one year. Once the original packaging is opened, the storage environment must not exceed 30°C and 60% RH. Components exposed beyond 168 hours should be baked at approximately 60°C for at least 48 hours before soldering to remove moisture and prevent \"popcorning\" during reflow.

6.4 Cleaning

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

7. Packaging and Ordering Information

The LEDs are supplied in 8mm tape on 7-inch diameter reels, in accordance with ANSI/EIA 481 specifications. Each reel contains 2000 pieces. For quantities less than a full reel, a minimum packing quantity of 500 pieces applies for remainders. The tape uses a cover tape to seal empty pockets, and the maximum number of consecutive missing components on a reel is two. The part number LTST-E682KSTBWT specifies the device with a diffused lens, yellow (AlInGaP) and blue (InGaN) chips.

8. Application Recommendations

8.1 Typical Application Scenarios

This dual-color LED is ideal for status indication in consumer electronics, office equipment, communication devices, and household appliances. It can be used to signal different operational states (e.g., power on/standby, network activity, charge status) using the two distinct colors. Its wide viewing angle makes it suitable for front-panel indicators.

8.2 Design Considerations

Designers must consider the different forward voltage requirements of the two chips when designing the drive circuit. A current-limiting resistor must be used for each LED chip independently to ensure proper current and brightness. The significant difference in ESD sensitivity (2000V vs. 300V HBM) necessitates careful handling and board-level ESD protection for the blue LED, especially during assembly and testing. Thermal management should be considered if operating near maximum current ratings or in high ambient temperatures.

9. Technical Comparison and Differentiation

The key differentiator of this component is the integration of two chemically distinct semiconductor materials (AlInGaP and InGaN) in one package, providing yellow and blue emission. Compared to using two separate single-color LEDs, this saves board space and simplifies assembly. The wide 120-degree viewing angle is a common advantage for indicator applications. The disparity in ESD robustness between the two chips is an important factor compared to some single-material dual-color LEDs which might have more uniform characteristics.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive both LEDs simultaneously at their maximum DC current?

A: It is not recommended to drive both at absolute maximum current (30mA yellow, 20mA blue) simultaneously without careful thermal analysis, as the combined power dissipation (152mW) may exceed the package's ability to shed heat, especially in confined spaces. Derating according to application temperature is advised.

Q: Why is the ESD rating for the blue LED so much lower?

A: InGaN-based blue LEDs are generally more sensitive to electrostatic discharge than AlInGaP-based yellow LEDs due to the material properties and the device structure. This is a common characteristic in the industry and necessitates stricter ESD control measures for the blue chip.

Q: How do I interpret the bin code on an order?

A: The bin code (e.g., R1, S2) specifies the guaranteed range of luminous intensity for that batch. You must specify the desired bin code(s) for yellow and blue when ordering to ensure your brightness requirements are met. If not specified, you may receive components from any production bin within the product's overall range.

11. Practical Design and Usage Case

Consider a portable device needing a multi-state charge indicator: off (no light), charging (blue light), and fully charged (yellow light). A microcontroller can control two GPIO pins, each connected through an appropriate current-limiting resistor to the anode of one LED chip, with the cathodes connected to ground. The resistor values are calculated separately based on the supply voltage and the desired forward current (e.g., 15mA for adequate brightness) for each color, taking into account their different forward voltage drops (e.g., 2.1V for yellow, 3.3V for blue). The board layout must follow the recommended pad pattern and ensure sufficient clearance from other heat-generating components.

12. Operating Principle Introduction

Light emission in LEDs is based on electroluminescence in a semiconductor p-n junction. When a forward voltage is applied, electrons and holes are injected into the active region where they recombine, releasing energy in the form of photons. The color (wavelength) of the emitted light is determined by the bandgap energy of the semiconductor material. The yellow LED uses an Aluminum Indium Gallium Phosphide (AlInGaP) compound, which has a bandgap corresponding to yellow/red-orange light. The blue LED uses Indium Gallium Nitride (InGaN), which has a wider bandgap suitable for blue/green emission. A diffused lens is molded over the chips to scatter the light, creating a wider, more uniform viewing angle.

13. Technology Trends

The development of SMD LEDs continues towards higher efficiency (more lumens per watt), increased reliability, and smaller package sizes. For multi-color packages, trends include tighter color and intensity binning for better consistency, improved ESD protection integrated into the device, and packages that enable higher power density and better thermal management. There is also a growing focus on precise spectral tuning for specialized applications beyond simple indication, such as sensor systems and backlighting. The underlying material science for both AlInGaP and InGaN continues to advance, pushing the limits of efficiency and lifetime.