SMD LED Yellow Diffused Lens LTSN-B680VSST - Package Dimensions - Forward Voltage 1.8-2.4V - Luminous Intensity 710-1400mcd - English Technical Document

1. Product Overview

This document details the specifications for a surface-mount device (SMD) Light Emitting Diode (LED). The device features a diffused lens and utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material to produce yellow light. SMD LEDs are designed for automated printed circuit board (PCB) assembly processes, offering a compact form factor suitable for space-constrained applications.

1.1 Core Advantages and Target Market

The primary advantages of this LED include its compatibility with automated pick-and-place equipment and infrared (IR) reflow soldering processes, which are standard in high-volume electronics manufacturing. It is packaged on 8mm tape wound onto 7-inch diameter reels, facilitating efficient handling and assembly. The device is compliant with relevant industry standards and is designed for use in a broad range of consumer and industrial electronics. Target applications span telecommunications equipment, office automation devices, home appliances, industrial control systems, and indoor signage or display applications where reliable indicator lighting is required.

2. Technical Parameters: In-Depth Objective Interpretation

The performance of the LED is defined under specific test conditions, typically at an ambient temperature (Ta) of 25°C. Understanding these parameters is critical for circuit design and performance prediction.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation outside these limits is not advised. Key limits include a maximum power dissipation of 120 mW, a continuous DC forward current (IF) of 50 mA, and a peak forward current of 80 mA under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The maximum reverse voltage (VR) is 5 V. The device is rated for operation and storage within a temperature range of -40°C to +100°C.

2.2 Electrical and Optical Characteristics

These are the typical performance parameters under normal operating conditions. The luminous intensity (Iv), a measure of perceived brightness, ranges from a minimum of 710 mcd to a maximum of 1400 mcd when driven at a forward current of 20 mA. The viewing angle (2θ1/2), defined as the full angle where intensity drops to half its axial value, is typically 120 degrees, indicating a wide viewing pattern suitable for indicator lights. The forward voltage (VF) at 20 mA ranges from 1.8 V to 2.4 V, which is important for calculating series resistor values and power supply design. The dominant wavelength (λd), which defines the perceived color, is specified between 586.5 nm and 592.5 nm, placing it in the yellow region of the spectrum. The reverse current (IR) is typically very low, with a maximum of 10 µA at the full reverse voltage of 5V.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. This allows designers to select parts that meet specific voltage, brightness, and color requirements.

3.1 Forward Voltage (Vf) Rank

LEDs are binned based on their forward voltage drop at 20 mA. Bin codes D2, D3, and D4 correspond to voltage ranges of 1.80-2.00V, 2.00-2.20V, and 2.20-2.40V, respectively, with a tolerance of ±0.1V per bin. Selecting LEDs from the same Vf bin helps maintain current uniformity when multiple devices are connected in parallel.

3.2 Luminous Intensity (Iv) Rank

Brightness is categorized into bins V1 (710-875 mcd), V2 (875-1120 mcd), and W1 (1120-1400 mcd) at 20 mA, with an 11% tolerance per bin. This allows for matching brightness levels across an array of LEDs.

3.3 Dominant Wavelength (Wd) Rank

The color (wavelength) is binned into codes J (586.5-589.5 nm) and K (589.5-592.5 nm), with a ±1 nm tolerance. This ensures color consistency, which is crucial for applications where uniform appearance is important.

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet, typical curves for such devices provide valuable insights. The forward current vs. forward voltage (I-V) curve shows the exponential relationship, critical for determining the operating point. The luminous intensity vs. forward current curve typically shows a near-linear relationship within the operating range, but saturation can occur at higher currents. The spectral distribution curve would show a peak emission wavelength (λp) around 591 nm with a spectral half-width (Δλ) of approximately 15 nm, defining the color purity. Performance also varies with temperature; luminous intensity generally decreases as junction temperature increases.

5. Mechanical and Package Information

The LED is housed in a standard SMD package. Detailed dimensional drawings are provided, specifying the length, width, height, lead spacing, and lens geometry. These dimensions are crucial for PCB footprint design. The document includes recommended PCB land pattern (pad) designs for reliable soldering, specifying pad size and spacing to ensure proper solder joint formation during reflow. The device has a polarity marking, typically a cathode indicator on the package, which must be correctly aligned with the PCB footprint.

6. Soldering and Assembly Guidelines

6.1 Recommended IR Reflow Profile

For lead-free soldering processes, a profile compliant with J-STD-020B is recommended. Key parameters include a preheat temperature of 150-200°C, a peak body temperature not exceeding 260°C, and a time above liquidus (TAL) tailored to the specific solder paste. The total preheat time should be limited to a maximum of 120 seconds. These conditions are essential to prevent thermal damage to the LED package or the epoxy lens.

6.2 Storage Conditions

The LEDs are moisture-sensitive. When stored in their original sealed moisture-barrier bag with desiccant, they should be kept at ≤ 30°C and ≤ 70% RH, with a recommended use-within period of one year. Once the bag is opened, the storage environment should be ≤ 30°C and ≤ 60% RH. Components exposed to ambient conditions for more than 168 hours should be baked at approximately 60°C for at least 48 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. Unspecified chemicals may damage the package material or lens.

7. Packaging and Ordering Information

The standard packaging consists of LEDs placed in embossed carrier tape (8mm pitch) and sealed with a cover tape. This tape is wound onto a standard 7-inch (178 mm) diameter reel. Each full reel contains 2000 pieces. For quantities less than a full reel, a minimum pack quantity of 500 pieces may be available. The packaging conforms to ANSI/EIA-481 specifications.

8. Application Suggestions

8.1 Typical Application Circuits

LEDs are current-driven devices. To ensure stable and uniform brightness, especially when multiple LEDs are used, each LED should be driven with a current-limiting resistor in series. The resistor value (R) is calculated using the formula: R = (Vcc - VF) / IF, where Vcc is the supply voltage, VF is the forward voltage of the LED (use max value for worst-case current calculation), and IF is the desired forward current (e.g., 20 mA). Driving LEDs in parallel without individual resistors is not recommended due to variations in VF, which can lead to significant current imbalance and uneven brightness.

8.2 Design Considerations

Consider the thermal environment. Operating at or near the maximum current rating will generate more heat, potentially reducing luminous output and lifespan. Adequate PCB copper area or thermal vias may be necessary for heat dissipation in high-current or high-ambient-temperature applications. Ensure the PCB layout matches the recommended pad geometry for reliable soldering. Account for the wide viewing angle (120°) when designing light guides or bezels.

9. Technical Comparison and Differentiation

Compared to older through-hole LEDs, this SMD type offers significant space savings, better suitability for automated assembly, and often improved reliability due to the absence of wire bonds. Within the SMD yellow LED category, key differentiators for this part include its specific combination of high luminous intensity (up to 1400 mcd), wide viewing angle, and the use of AlInGaP technology, which typically offers higher efficiency and better temperature stability compared to some other semiconductor materials for yellow light. The detailed binning structure provides designers with precise control over color and brightness consistency.

10. Frequently Asked Questions Based on Technical Parameters

Q: What resistor value should I use for a 5V supply?
A: Using the maximum VF of 2.4V and a target IF of 20mA: R = (5V - 2.4V) / 0.020A = 130 Ohms. A standard 130 or 150 Ohm resistor would be appropriate, checking the actual power dissipation in the resistor.

Q: Can I drive this LED at 50 mA continuously?
A: While the absolute maximum rating is 50 mA DC, operating at this limit may reduce longevity and increase junction temperature, potentially lowering light output. For optimal reliability and performance, driving at or below the typical test current of 20 mA is recommended.

Q: How do I ensure uniform brightness in an array?
A: Use individual current-limiting resistors for each LED and, if possible, specify LEDs from the same luminous intensity (Iv) and forward voltage (Vf) bins during procurement.

Q: Is this LED suitable for outdoor use?
A: The datasheet specifies applications including indoor signage/display. For outdoor use, factors like UV resistance of the lens, wider temperature cycling, and waterproof sealing are critical and not explicitly covered here. It is primarily designed for indoor/benign environments.

11. Practical Design and Usage Case

Scenario: Designing a status indicator panel for a network router. The panel requires ten yellow indicator lights to show link activity and system status. The designer selects this LED for its brightness, wide viewing angle, and compatibility with automated assembly. Each LED is connected between a 3.3V microcontroller GPIO pin and ground via a 56 Ohm series resistor (calculated for ~20mA at a typical VF of 2.2V). The PCB layout uses the recommended pad footprint. The designer specifies bin code D3 for Vf and V2 for Iv to ensure consistent brightness and current draw from the microcontroller pins. The LEDs are placed behind a lightly diffused acrylic panel. The assembled board undergoes IR reflow using the specified lead-free profile, resulting in reliable solder joints and fully functional indicators.

12. Principle Introduction

Light emission in this LED is based on electroluminescence in a semiconductor p-n junction made of AlInGaP materials. When a forward voltage is applied, electrons and holes are injected into the active region where they recombine. The energy released during this recombination is emitted as photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, which in turn defines the wavelength (color) of the emitted light, in this case, yellow. The diffused lens contains scattering particles that help spread the light, creating a wider, more uniform viewing angle compared to a clear lens.

13. Development Trends

The general trend in SMD LEDs continues toward higher luminous efficacy (more light output per watt of electrical input), enabling brighter displays or lower power consumption. Package sizes are constantly miniaturizing while maintaining or improving optical performance. There is also a focus on improved color consistency and tighter binning tolerances to meet the demands of high-quality display applications. Furthermore, enhanced reliability under higher temperature and humidity conditions is an ongoing area of development to expand the range of suitable applications. The drive for broader compatibility with lead-free, high-temperature soldering processes remains standard.