SMD LED LTST-T680UWET Datasheet - White Light, Yellow Lens - 30mA, 108mW - English Technical Document

1. Product Overview

This document provides the complete technical specifications for the LTST-T680UWET, a surface-mount device (SMD) light-emitting diode (LED). This component is designed for automated printed circuit board (PCB) assembly processes, featuring a miniature form factor suitable for space-constrained applications. The LED emits white light through a yellow-tinted lens material. Its primary function is to serve as an indicator or backlight source in a wide array of consumer electronics, computing devices, communication equipment, and signage systems.

1.1 Key Features

• Compliant with RoHS (Restriction of Hazardous Substances) directives.
• Packaged in 8mm tape on 7-inch diameter reels for automated pick-and-place machinery.
• Standard EIA (Electronic Industries Alliance) package outline.
• Electrically compatible with integrated circuit (IC) logic levels.
• Designed for compatibility with standard infrared (IR) reflow soldering processes.
• Preconditioned to JEDEC (Joint Electron Device Engineering Council) Moisture Sensitivity Level 3.

1.2 Target Applications

• Status indicators and backlighting for consumer appliances.
• General signage and display backlighting.
• Specialized and decorative lighting applications.
• Industrial equipment status and panel lighting.

2. Package Dimensions and Mechanical Data

The LTST-T680UWET utilizes a standard SMD LED package. The lens color is yellow, and the emitted light color is white. All critical dimensions for PCB footprint design and component placement are provided in the datasheet drawings. All measurements are in millimeters (mm) with a standard tolerance of ±0.2 mm unless otherwise specified. Designers must refer to the detailed dimensional drawings to ensure proper PCB pad layout and assembly clearance.

3. Ratings and Characteristics

All parameters are specified at an ambient temperature (Ta) of 25°C unless stated otherwise. Exceeding the absolute maximum ratings may cause permanent damage to the device.

3.1 Absolute Maximum Ratings

• Power Dissipation (Pd): 108 mW
• Peak Forward Current (I_F(peak)): 100 mA (at 1/10 duty cycle, 0.1ms pulse width)
• Continuous Forward Current (I_F): 30 mA DC
• Operating Temperature Range: -40°C to +85°C
• Storage Temperature Range: -40°C to +100°C

3.2 Suggested IR Reflow Profile

The component is suitable for lead-free (Pb-free) soldering processes. The recommended infrared reflow soldering profile conforms to the J-STD-020B standard. This profile defines critical parameters such as preheat ramp rate, soak time and temperature, peak reflow temperature, and cooling rate to ensure reliable solder joints without damaging the LED package.

3.3 Electrical and Optical Characteristics

The following table details the typical performance parameters when driven at a standard test current of 20mA.

• Luminous Intensity (I_V): 2100 - 3300 mcd (millicandela). Measured using a sensor filtered to match the CIE photopic eye-response curve.
• Viewing Angle (2θ_1/2): 120 degrees. Defined as the full angle where intensity drops to half of the peak axial value.
• Chromaticity Coordinates (x, y): Approximately (0.31, 0.31) on the CIE 1931 chromaticity diagram, defining the white point.
• Forward Voltage (V_F): 2.8V - 3.6V.
• Reverse Current (I_R): 10 μA maximum at a reverse voltage (V_R) of 5V. Note: This device is not designed for operation under reverse bias.

4. Binning and Ranking System

To ensure consistency in production runs, LEDs are sorted into bins based on key parameters. This allows designers to select components that meet specific application requirements for brightness, voltage, and color.

4.1 Forward Voltage (V_F) Rank

LEDs are binned by their forward voltage drop at 20mA. Bins range from D7 (2.8V - 3.0V) to D10 (3.4V - 3.6V), with a tolerance of ±0.1V per bin. This is crucial for designing current-limiting circuits and ensuring uniform brightness in multi-LED arrays.

4.2 Luminous Intensity (I_V) Rank

LEDs are categorized by their light output intensity. The primary bins are X1 (2100 - 2630 mcd) and X2 (2630 - 3300 mcd), with a tolerance of ±15% within each bin. This ranking helps achieve desired brightness levels in the final application.

4.3 Color Rank

A detailed chromaticity binning system is defined using codes (Z1-Z4, Y1-Y8, X1-X4, W1-W8). Each bin specifies a quadrilateral region on the CIE 1931 (x, y) chromaticity diagram with four corner points. This precise binning ensures tight control over the shade of white light emitted, with a tolerance of ±0.01 in both x and y coordinates. The datasheet includes a full table of these coordinate boundaries and a graphical representation of the chromaticity coordinate area.

5. Typical Performance Curves

The datasheet provides graphical representations of key relationships, which are essential for circuit design and thermal management. These curves typically illustrate:

• Forward Current vs. Forward Voltage (I-V Curve): Shows the non-linear relationship, important for determining the operating point and power dissipation.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with drive current, up to the maximum rating.
• Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as the junction temperature increases, critical for high-temperature environments.
• Relative Spectral Power Distribution: Depicts the intensity of light emitted across different wavelengths, defining the color characteristics.

6. User Guide and Assembly Instructions

6.1 Cleaning Procedures

Unspecified chemical cleaners should not be used as they may damage the LED package. If cleaning after soldering is necessary, the LED may be immersed in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute.

6.2 Recommended PCB Pad Layout

A suggested land pattern (footprint) for the PCB is provided to ensure proper solder fillet formation and mechanical stability during infrared or vapor phase reflow soldering. Adhering to this pattern is vital for reliable assembly.

6.3 Tape and Reel Packaging Specifications

The components are supplied in industry-standard embossed carrier tape with a protective cover tape. Detailed dimensions for the tape pockets, pitch, and overall tape width are specified to ensure compatibility with automated assembly equipment.

6.4 Reel Specifications

LEDs are wound onto 7-inch (178mm) diameter reels. Each reel contains 2000 pieces. The packaging conforms to ANSI/EIA-481 standards. Specifications include the maximum allowable number of consecutive empty pockets (two) and requirements for sealing the tape.

7. Important Cautions and Application Notes

7.1 Intended Use and Reliability

This LED is designed for use in standard electronic equipment such as office devices, communications gear, and household appliances. It is not intended for applications where failure could directly jeopardize life or health (e.g., aviation, medical life-support, critical safety systems) without prior consultation and specific qualification.

7.2 Storage and Handling Conditions

Sealed Package: The moisture-sensitive devices are packed with desiccant in a moisture-barrier bag. They should be stored at ≤30°C and ≤70% relative humidity (RH) and used within one year of the bag seal date.

Opened Package: Once the original bag is opened, the ambient storage conditions must not exceed 30°C and 60% RH. Components exposed to ambient conditions should undergo IR reflow soldering within 168 hours (7 days). For longer storage after opening, LEDs must be stored in a sealed container with desiccant or in a nitrogen-purged desiccator to prevent moisture absorption, which can cause "popcorning" during reflow.

8. Design Considerations and Application Suggestions

When integrating the LTST-T680UWET into a design, several factors must be considered. The forward voltage binning requires careful design of the current-limiting resistor or driver circuit to ensure consistent current and brightness across multiple LEDs, especially when connected in parallel. The wide 120-degree viewing angle makes it suitable for applications requiring broad illumination rather than a focused beam. Thermal management is critical; the maximum junction temperature must not be exceeded, which involves considering the PCB's thermal conductivity, ambient temperature, and the LED's power dissipation. For best soldering results, follow the provided reflow profile precisely to avoid thermal shock or solder defects.

9. Technical Comparison and Differentiation

Compared to generic SMD LEDs, this component offers defined and controlled binning for luminous intensity, forward voltage, and chromaticity. This level of categorization provides designers with predictable performance, which is essential for products requiring consistent visual appearance and brightness. The preconditioning to JEDEC Level 3 indicates a robust package capable of withstanding standard surface-mount assembly processes with a specified floor life, reducing the risk of assembly-related failures.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED at its maximum continuous current of 30mA?
A: While possible, operating at the absolute maximum rating reduces lifetime and increases junction temperature. For optimal reliability and longevity, derating to a lower current (e.g., 20mA) is recommended.

Q: What is the purpose of the detailed color binning table?
A: It allows for precise color matching in applications where multiple LEDs are used side-by-side (e.g., backlight arrays, signage). Selecting LEDs from the same color bin ensures a uniform white appearance without noticeable color shifts.

Q: Why is the 168-hour floor life after bag opening important?
A: SMD LED packages can absorb moisture from the air. During the high-temperature reflow process, this trapped moisture can vaporize rapidly, causing internal delamination or cracking ("popcorning"). The 168-hour limit is the safe exposure time for the specified moisture sensitivity level.

11. Practical Design and Usage Examples

Example 1: Status Indicator Panel: In a network router, several LTST-T680UWET LEDs could be used behind translucent plastic caps to indicate power, network activity, and port status. Their wide viewing angle ensures visibility from various angles. Using LEDs from the same V_F and I_V bin ensures all indicators have equal brightness when driven by a common current-limiting resistor network.

Example 2: Backlight for Membrane Switch: The LED can be mounted on a flexible PCB behind a silicone rubber keypad to provide even backlighting. The yellow lens can help create a warm white or specific colored light when combined with the overlay graphics. The compatibility with IR reflow allows it to be soldered simultaneously with other SMD components on the flex circuit.

12. Operational Principle

An LED is a semiconductor diode. When a forward voltage exceeding its characteristic threshold is applied, electrons recombine with holes within the device's active region, releasing energy in the form of photons (light). The color of the light is determined by the energy bandgap of the semiconductor materials used. A white LED typically uses a blue-emitting semiconductor chip coated with a phosphor layer. The phosphor absorbs a portion of the blue light and re-emits it as yellow light. The mixture of the remaining blue light and the converted yellow light is perceived by the human eye as white. The yellow external lens further modifies the final color output and viewing characteristics.

13. Technology Trends

The general trend in SMD LED technology continues toward higher luminous efficacy (more light output per watt of electrical input), enabling brighter displays or lower power consumption. There is also a drive for improved color rendering index (CRI) and more precise color consistency across production batches. Packaging is evolving to allow for higher power density and better thermal management from ever-smaller footprints. Furthermore, integration with intelligent drivers and control circuitry directly into the LED package is an area of ongoing development for smart lighting applications.