SMD LED LTST-B680VSKT Datasheet - Yellow AlInGaP - 20mA - 120mW - English Technical Document

1. Product Overview

The LTST-B680VSKT is a surface-mount device (SMD) light-emitting diode (LED) designed for automated printed circuit board (PCB) assembly. It belongs to a family of miniature LEDs suitable for space-constrained applications. The device utilizes an Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor material to produce yellow light, encapsulated in a water-clear lens package. Its primary design goals are compatibility with high-volume manufacturing processes and reliability in various electronic environments.

1.1 Core Advantages and Target Market

The key advantages of this LED include its compliance with RoHS (Restriction of Hazardous Substances) directives, making it environmentally friendly for modern electronics. It is packaged on 8mm tape wound onto 7-inch diameter reels, which is a standard (EIA) format compatible with automated pick-and-place equipment. This feature significantly streamlines assembly lines. The component is also designed to be compatible with infrared (IR) reflow soldering processes, which is the dominant method for attaching SMD components. Its primary target markets are telecommunications equipment, office automation devices, home appliances, industrial control systems, and indoor signage or display applications where reliable, compact indicator lighting is required.

2. Technical Parameters: In-Depth Objective Interpretation

This section provides a detailed analysis of the LED's operational limits and performance characteristics under standard conditions.

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the stress limits beyond which permanent damage to the device may occur. These ratings are specified at an ambient temperature (Ta) of 25°C. The maximum continuous DC forward current (IF) is 50 mA. For pulsed operation, a peak forward current of 80 mA is permissible under a strict 1/10 duty cycle with a 0.1ms pulse width. The maximum reverse voltage (VR) that can be applied is 5V. The device can dissipate up to 120 mW of power. The operational and storage temperature range is specified from -40°C to +100°C, indicating robustness for use in harsh environments.

2.2 Electrical and Optical Characteristics

These parameters are measured under typical operating conditions (Ta=25°C, IF=20mA) and represent the expected performance. The luminous intensity (Iv) has a typical range from 900 mcd (millicandela) to 1800 mcd, indicating a bright output suitable for indicator purposes. The viewing angle (2θ1/2) is 120 degrees, providing a very wide beam pattern. The peak emission wavelength (λp) is typically 591 nm, falling within the yellow region of the visible spectrum. The dominant wavelength (λd), which defines the perceived color, is specified between 584.0 nm and 594.0 nm. The forward voltage (VF) at 20mA ranges from a minimum of 1.8V to a maximum of 2.4V, with a typical value implied within this range. The reverse current (IR) is very low, with a maximum of 10 μA at 5V reverse bias.

3. Bin Ranking System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. This allows designers to select components that meet specific threshold requirements for their application.

3.1 Forward Voltage (Vf) Rank

LEDs are binned based on their forward voltage drop at 20mA. The bins are: D2 (1.80V - 2.00V), D3 (2.00V - 2.20V), and D4 (2.20V - 2.40V). A tolerance of ±0.1V is applied to each bin. Selecting LEDs from the same Vf bin helps maintain current uniformity when multiple LEDs are driven in parallel from a common voltage source.

3.2 Luminous Intensity (Iv) Rank

The luminous output is categorized into three bins: V2 (900 - 1120 mcd), W1 (1120 - 1400 mcd), and W2 (1400 - 1800 mcd). A tolerance of ±11% applies to each intensity bin. This ranking is crucial for applications requiring consistent brightness levels across multiple indicators.

3.3 Dominant Wavelength (Wd) Rank

The color (dominant wavelength) is sorted into four bins: H (584.0 - 586.5 nm), J (586.5 - 589.0 nm), K (589.0 - 591.5 nm), and L (591.5 - 594.0 nm). Each bin has a tolerance of ±1 nm. This ensures color consistency, which is vital for multi-LED displays or status indicators where color matching is important.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet, their implications are described here. Typical curves would include the relationship between forward current (IF) and forward voltage (VF), showing the diode's exponential I-V characteristic. Another key curve would plot relative luminous intensity against ambient temperature, typically showing a decrease in output as temperature increases. A spectral distribution curve would illustrate the narrow bandwidth of light emission centered around 591 nm, which is characteristic of AlInGaP technology and results in a saturated yellow color.

5. Mechanical and Package Information

The LED comes in a standard SMD package. The lens color is water clear, and the light source color is yellow from the AlInGaP chip. All package dimensions are provided in millimeters with a standard tolerance of ±0.2 mm unless otherwise noted. The datasheet includes detailed dimensional drawings for the LED itself, the recommended PCB attachment pad layout for infrared or vapor phase reflow soldering, and the packaging (tape and reel dimensions).

6. Soldering and Assembly Guidelines

6.1 Recommended IR Reflow Profile

For lead-free soldering processes, a reflow profile compliant with J-STD-020B is recommended. Key parameters include a pre-heat temperature between 150°C and 200°C, a pre-heat time up to 120 seconds maximum, and a peak package body temperature not exceeding 260°C for a maximum of 10 seconds. It is critical to note that the optimal profile depends on the specific PCB design, solder paste, and oven used.

6.2 Storage Conditions

Unopened moisture-proof bags containing desiccant should be stored at ≤30°C and ≤70% Relative Humidity (RH), with a recommended shelf life of one year. Once the original packaging is opened, LEDs should be stored at ≤30°C and ≤60% RH. It is strongly recommended to complete the IR reflow process within 168 hours (7 days) after opening. For storage beyond this period, baking at approximately 60°C for at least 48 hours before soldering is necessary to remove absorbed moisture and prevent \"popcorning\" damage during reflow.

6.3 Cleaning

If cleaning is required after soldering, 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 chemical cleaners must be avoided as they may damage the package material.

7. Packaging and Ordering Information

The standard packaging is 8mm tape on 7-inch (178mm) diameter reels. A standard 13-inch reel contains 8000 pieces. The minimum order quantity for remnants is 500 pieces. The packaging follows ANSI/EIA 481 specifications, with a maximum of two consecutive missing components (empty pockets) allowed in the tape.

8. Application Suggestions

8.1 Typical Application Circuits

LEDs are current-driven devices. For reliable operation and uniform brightness when driving multiple LEDs in parallel, it is essential to use a individual current-limiting resistor in series with each LED. This compensates for minor variations in the forward voltage (Vf) of each device, preventing current hogging where one LED draws more current and appears brighter while others are dim. A simple series resistor circuit is the recommended and most reliable drive method.

8.2 Design Considerations

Designers must consider thermal management. While the device can operate up to 100°C, luminous output decreases with increasing junction temperature. Adequate PCB copper area or thermal vias may be necessary for high-current or high-ambient-temperature applications. The wide 120-degree viewing angle makes this LED suitable for applications where the indicator needs to be visible from a broad range of positions, but not for focused beam applications.

9. Technical Comparison and Differentiation

Compared to older technologies like Gallium Phosphide (GaP), AlInGaP LEDs offer higher efficiency and brighter output for colors in the red to yellow range. The water-clear lens, as opposed to a diffused or tinted lens, provides the highest possible light output from the chip, maximizing luminous intensity. The combination of a standard EIA package, tape-and-reel packaging, and IR reflow compatibility makes this device highly suitable for modern, automated electronics manufacturing, offering advantages in cost and assembly speed over through-hole LEDs.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED directly from a 3.3V or 5V logic supply?
A: No. You must always use a series current-limiting resistor. The required resistor value can be calculated using Ohm's Law: R = (V_supply - Vf_LED) / I_desired. For example, with a 5V supply, a Vf of 2.2V, and a desired current of 20mA, R = (5 - 2.2) / 0.02 = 140 Ohms.

Q: Why is there a binning system for Vf, Iv, and Wd?
A: Semiconductor manufacturing has natural variations. Binning sorts parts into performance groups, allowing designers to choose the consistency level needed for their application, ensuring predictable behavior in the final product.

Q: What happens if I exceed the absolute maximum ratings?
A: Exceeding these limits, even momentarily, can cause immediate or latent damage, reducing lifespan or causing catastrophic failure. Always design with a safety margin.

11. Practical Use Case Example

Consider designing a control panel for an industrial appliance with multiple yellow status indicators. The designer selects LEDs from the W1 intensity bin (1120-1400 mcd) and the K wavelength bin (589.0-591.5 nm) to ensure uniform brightness and color. The LEDs are placed on the PCB with the recommended pad layout. A microcontroller GPIO pin, configured as an open-drain output, drives each LED through a 150-ohm series resistor connected to a 3.3V rail. This setup provides approximately 18mA of current ((3.3V - 2.2V)/150Ω ≈ 7.3mA, recalc needed for actual Vf), ensuring reliable operation within specifications. The panel is assembled using an IR reflow process with a profile adhering to the datasheet guidelines.

12. Operating Principle Introduction

An LED is a semiconductor p-n junction diode. When a forward voltage exceeding the diode's threshold is applied, electrons from the n-type region recombine with holes from the p-type region within the active layer (in this case, made of AlInGaP). This recombination process releases energy in the form of photons (light). The specific wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material. AlInGaP has a bandgap corresponding to light in the red, orange, amber, and yellow spectral regions.

13. Technology Trends

The general trend in SMD LED technology is toward ever-higher luminous efficacy (more light output per watt of electrical input), improved color rendering and saturation, and increased power density in smaller packages. There is also a continuous drive for higher reliability and longer operational lifetimes. Furthermore, integration with control electronics, such as built-in current regulators or pulse-width modulation (PWM) drivers, is becoming more common in advanced LED packages, though the device described here is a basic, discrete component.