SMD LED LTST-T680VSWT Datasheet - Diffused Yellow AlInGaP - 50mA - 130mW - English Technical Documentation

1. Product Overview

This document provides the complete technical specifications for the LTST-T680VSWT, a surface-mount device (SMD) light-emitting diode (LED). This component belongs to a family of miniature LEDs designed for automated printed circuit board (PCB) assembly processes and applications where space is a critical constraint. The LED utilizes an Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor material to produce a yellow light output, which is diffused by its lens for a wider, more uniform illumination pattern. Its primary function is as a status indicator, signal luminary, or for front-panel backlighting in a diverse range of electronic equipment.

1.1 Core Advantages and Target Market

The LTST-T680VSWT offers several key advantages for modern electronics manufacturing. It is fully compliant with RoHS (Restriction of Hazardous Substances) directives, making it suitable for global markets with strict environmental regulations. The component is supplied in industry-standard 8mm tape on 7-inch reels, facilitating high-speed, automated pick-and-place assembly. Its design is compatible with infrared (IR) reflow soldering processes, which is the standard for lead-free (Pb-free) PCB assembly. The device is also I.C. compatible, meaning its electrical characteristics allow for direct interfacing with typical integrated circuit output pins. These features make it an ideal choice for telecommunications equipment, office automation devices, home appliances, industrial control systems, notebook computers, and network hardware where reliable, compact visual indicators are required.

2. In-Depth Technical Parameter Analysis

A thorough understanding of the electrical and optical parameters is essential for reliable circuit design and achieving consistent performance.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed. The absolute maximum ratings are specified at an ambient temperature (Ta) of 25°C.

• Power Dissipation (Pd): 130 mW. This is the maximum amount of power the LED package can dissipate as heat without exceeding its thermal limits.
• Peak Forward Current (I_FP): 100 mA. This is the maximum allowable instantaneous forward current, permissible only under pulsed conditions with a 1/10 duty cycle and a pulse width of 0.1ms. It should not be used for continuous DC operation.
• DC Forward Current (I_F): 50 mA. This is the maximum recommended continuous forward current for reliable long-term operation.
• Operating Temperature Range: -40°C to +85°C. The device is designed to function within this ambient temperature range.
• Storage Temperature Range: -40°C to +100°C. The device can be stored without applied power within this range.

2.2 Electrical and Optical Characteristics

These parameters define the typical performance of the LED under normal operating conditions, measured at Ta=25°C and a standard test current (I_F) of 20mA.

• Luminous Intensity (I_V): 710.0 - 1800.0 mcd (millicandela). This is a measure of the perceived power of the visible light emitted in a specific direction (on-axis). The wide range is managed through a binning system (see Section 3). Intensity is measured using a sensor filtered to match the human eye's photopic response (CIE curve).
• Viewing Angle (2θ_1/2): 120 degrees (typical). This is the full angle at which the luminous intensity drops to half of its on-axis value. The diffused lens creates this wide viewing angle, making the LED suitable for applications where visibility from off-axis positions is important.
• Peak Emission Wavelength (λ_P): 592 nm (typical). This is the wavelength at which the spectral power distribution of the emitted light is at its maximum.
• Dominant Wavelength (λ_d): 584.5 - 594.5 nm. This is the single wavelength that best represents the perceived color of the light, derived from the CIE chromaticity diagram. It is the key parameter for color specification.
• Spectral Line Half-Width (Δλ): 15 nm (typical). This is the spectral bandwidth measured at half the maximum intensity (Full Width at Half Maximum - FWHM). A value of 15nm indicates a relatively pure yellow color.
• Forward Voltage (V_F): 2.1V (typical), 2.6V (maximum) at I_F=20mA. This is the voltage drop across the LED when it is conducting current. It is a critical parameter for designing the current-limiting circuitry.
• Reverse Current (I_R): 10 μA (maximum) at V_R=5V. This parameter is tested for quality assurance only. The device is not designed for operation under reverse bias, and applying a reverse voltage can damage it. External protection (e.g., a diode in parallel) may be necessary in circuits where reverse voltage is possible.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance groups or "bins" based on key parameters. This allows designers to select parts that meet specific requirements for color and brightness uniformity in their application.

3.1 Forward Voltage (V_f) Rank

LEDs are binned by their forward voltage drop at 20mA. The bin code, minimum, and maximum values are as follows. The tolerance within each bin is ±0.1V.

• D2: 1.8V (Min) - 2.0V (Max)
• D3: 2.0V (Min) - 2.2V (Max)
• D4: 2.2V (Min) - 2.4V (Max)
• D5: 2.4V (Min) - 2.6V (Max)

3.2 Luminous Intensity (I_V) Rank

LEDs are binned by their on-axis luminous intensity at 20mA. The tolerance within each bin is ±11%.

• V1: 710.0 mcd (Min) - 900.0 mcd (Max)
• V2: 900.0 mcd (Min) - 1120.0 mcd (Max)
• W1: 1120.0 mcd (Min) - 1400.0 mcd (Max)
• W2: 1400.0 mcd (Min) - 1800.0 mcd (Max)

3.3 Dominant Wavelength (W_d) Rank

LEDs are binned by their dominant wavelength at 20mA to ensure color consistency. The tolerance within each bin is ±1nm.

• H: 584.5 nm (Min) - 587.0 nm (Max)
• J: 587.0 nm (Min) - 589.5 nm (Max)
• K: 589.5 nm (Min) - 592.0 nm (Max)
• L: 592.0 nm (Min) - 594.5 nm (Max)

4. Performance Curve Analysis

Graphical data provides insight into how the LED's characteristics change with operating conditions. The datasheet includes typical curves for the following relationships (all at 25°C unless noted).

4.1 Forward Current vs. Forward Voltage (I-V Curve)

This curve shows the non-linear relationship between the current flowing through the LED and the voltage across it. It is essential for selecting an appropriate current-limiting method (resistor or constant current driver). The curve will show the "turn-on" voltage and how V_F increases with I_F.

4.2 Luminous Intensity vs. Forward Current

This curve illustrates how the light output (in mcd) scales with the drive current. It is typically linear over a range but will saturate at higher currents. This helps designers balance brightness requirements against power consumption and thermal management.

4.3 Luminous Intensity vs. Ambient Temperature

This curve demonstrates the thermal derating of light output. As the ambient temperature increases, the luminous efficiency of the LED decreases, leading to lower intensity for the same drive current. This is a critical consideration for applications operating in high-temperature environments.

4.4 Relative Spectral Power Distribution

This graph plots the intensity of emitted light across the visible spectrum. It shows the peak wavelength (λ_P~592nm) and the spectral half-width (Δλ~15nm), confirming the narrowband yellow emission characteristic of AlInGaP technology.

5. Mechanical and Packaging Information

5.1 Package Dimensions

The LED conforms to an EIA standard SMD package outline. All critical dimensions, including length, width, height, and lead spacing, are provided in the datasheet drawings with a general tolerance of ±0.2mm. The lens is described as "Diffused," which scatters the light to achieve the specified 120-degree viewing angle.

5.2 Polarity Identification and PCB Pad Design

The component has an anode and cathode. The datasheet includes a recommended PCB land pattern (footprint) for infrared or vapor phase reflow soldering. Adhering to this pad layout is crucial for achieving reliable solder joints, proper alignment, and managing heat dissipation during the soldering process. The polarity is typically indicated by a marking on the component body or an asymmetric feature in the package.

6. Soldering, Assembly, and Handling Guidelines

6.1 Recommended IR Reflow Profile (Pb-Free)

The device is qualified for lead-free soldering processes according to J-STD-020B. A sample reflow temperature profile is provided, which includes key parameters:

• Pre-heat Temperature: 150-200°C
• Pre-heat Time: Maximum 120 seconds.
• Peak Body Temperature: Maximum 260°C.
• Time Above Liquidus (TAL): Recommended to follow JEDEC guidelines, typically 60-150 seconds.
• Maximum Number of Passes: Two times through reflow is the maximum allowed.

Because board design, solder paste, and oven characteristics vary, this profile should be used as a target and fine-tuned for the specific assembly line.

6.2 Hand Soldering

If hand soldering is necessary, extreme care must be taken:

• Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per lead.
• Number of Times: One time only. Repeated heating can damage the package and semiconductor.

6.3 Cleaning

If post-solder cleaning is required, only specified solvents should be used to avoid damaging the plastic package. Acceptable methods include immersion in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Unspecified chemical cleaners must be avoided.

6.4 Storage and Moisture Sensitivity

The LEDs are packaged in a moisture-barrier bag with desiccant. While sealed, they should be stored at ≤30°C and ≤70% Relative Humidity (RH) and used within one year. Once the bag is opened, the components are exposed to ambient moisture. They are rated to Moisture Sensitivity Level (MSL) 3, which means they must be IR-reflowed within 168 hours (7 days) of exposure to factory floor conditions (≤30°C/60% RH). If this time is exceeded, the components require a baking procedure (approximately 60°C for at least 48 hours) to remove absorbed moisture before soldering to prevent "popcorning" or package cracking during reflow.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LTST-T680VSWT is supplied in standard 8mm wide embossed carrier tape on 7-inch (178mm) diameter reels. Each reel contains 2000 pieces. The tape pockets are sealed with a top cover tape. The packaging conforms to ANSI/EIA-481 specifications. The maximum allowable number of consecutive missing components in the tape is two.

8. Application Notes and Design Considerations

8.1 Drive Method

An LED is a current-driven device. To ensure uniform brightness, especially when multiple LEDs are connected in parallel, each LED should be driven by its own current-limiting resistor or, preferably, by a constant current source. Driving LEDs in parallel directly from a voltage source is not recommended due to variations in forward voltage (V_F) from unit to unit, which can cause significant differences in current and thus brightness.

8.2 Thermal Management

While the power dissipation is relatively low (130mW max), proper thermal design extends LED life and maintains stable light output. Ensure the PCB pad design provides adequate thermal relief and avoid operating the LED at its absolute maximum current (50mA) continuously in high ambient temperatures without evaluation.

8.3 Application Scope and Reliability

This LED is designed for use in standard commercial and industrial electronic equipment. It is not specifically designed or tested for applications where failure could directly jeopardize life or health, such as in critical medical, aviation, transportation, or safety systems. For such high-reliability applications, consultation with the component manufacturer for specific qualification data is mandatory.

9. Technology and Principle Introduction

The LTST-T680VSWT is based on Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor technology. This material system is highly efficient for producing light in the red, orange, amber, and yellow regions of the spectrum. When a forward voltage is applied, electrons and holes recombine in the active region of the semiconductor, releasing energy in the form of photons. The specific composition of the AlInGaP layers determines the bandgap energy and thus the wavelength (color) of the emitted light. A yellow phosphor is not used; the color is inherent to the semiconductor material, resulting in high color purity and stability. The diffused epoxy lens encapsulates the semiconductor die, providing mechanical protection, shaping the light output beam, and improving the viewing angle.

10. Practical Design and Usage Examples

10.1 Example: Status Indicator for a Network Switch

In a 24-port network switch, each port may have multiple LEDs (e.g., link, activity, speed). The LTST-T680VSWT, with its wide 120-degree viewing angle, is an excellent choice for front-panel status indicators. A designer would:

1. Determine the required brightness based on viewing distance and ambient light. Select an appropriate I_V bin (e.g., V2 for medium brightness).
2. Choose a drive current, typically 10-20mA, to balance brightness and power. Using a constant current driver IC for all LEDs ensures perfect uniformity.
3. Design the PCB footprint exactly as per the datasheet recommendation to ensure proper soldering.
4. Follow the MSL-3 handling guidelines: keep opened reels in a dry cabinet and ensure boards are assembled within 168 hours of opening the reel.

10.2 Example: Backlighting for a Membrane Switch Panel

For illuminating symbols on a control panel, uniform off-axis visibility is key. The diffused lens of this LED is advantageous.

1. The LED would be mounted behind a translucent or laser-etched icon on the panel.
2. The wide viewing angle ensures the icon is evenly lit even if the LED is not perfectly centered behind it.
3. To achieve a specific yellow hue, the designer would specify a tight Dominant Wavelength bin (e.g., K: 589.5-592.0nm) to match other indicators or branding colors.
4. A simple series resistor can be used for current limiting if only one or two LEDs are powered from a regulated voltage rail.

11. Frequently Asked Questions (Based on Technical Parameters)

Q1: Can I drive this LED with 3.3V logic without a resistor?
A: No. The typical V_F is 2.1V, but it can be as high as 2.6V. Connecting it directly to 3.3V would force a current limited only by the LED's dynamic resistance and the source, likely exceeding the absolute maximum DC current of 50mA and destroying the device. A current-limiting resistor or regulator is always required.

Q2: What is the difference between Peak Wavelength and Dominant Wavelength?
A: Peak Wavelength (λ_P) is the single wavelength where the LED emits the most optical power. Dominant Wavelength (λ_d) is the single wavelength of monochromatic light that would appear to have the same color as the LED's light to the human eye. λ_d is the parameter used for color specification and binning.

Q3: Why is there a 168-hour floor life after opening the bag?
A: The plastic LED package can absorb moisture from the air. During the high-temperature reflow soldering process, this trapped moisture can vaporize rapidly, creating steam pressure inside the package that can cause delamination or cracking ("popcorning"). The 168-hour limit and baking procedure are safeguards against this failure mode.

Q4: How do I interpret the bin codes when ordering?
A: You would specify the part number LTST-T680VSWT followed by codes for the specific V_f, I_V, and W_d bins you require (e.g., for medium brightness and a specific yellow shade). Consult the manufacturer's ordering guide for the exact format. If no bin is specified, you will receive parts from standard production bins.