SMD LED LTST-T680QEWT Datasheet - White Diffused Lens, AlInGaP Red Source - 50mA, 2.4V, 120mW - English Technical Document

1. Product Overview

This document details the specifications for a surface-mount device (SMD) LED designed for automated printed circuit board (PCB) assembly. The component is characterized by its miniature size, making it suitable for space-constrained applications across a broad spectrum of electronic equipment.

1.1 Core Advantages and Target Market

The primary advantages of this LED include its compliance with RoHS directives, packaging tailored for automated assembly processes (8mm tape on 7-inch reels), and compatibility with standard infrared reflow soldering techniques. Its design is I.C. compatible, facilitating integration into modern digital circuits. The device is preconditioned to JEDEC Level 3 standards, enhancing its reliability for demanding applications.

The target applications span telecommunications, office automation, home appliances, and industrial equipment. It is specifically intended for use as a status indicator, for signal and symbol luminary purposes, and for front panel backlighting.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

All ratings are specified at an ambient temperature (Ta) of 25°C. Exceeding these limits may cause permanent damage.

• Power Dissipation: 120 mW. This is the maximum power the device can dissipate as heat without degradation.
• Peak Forward Current: 100 mA. This is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) to manage thermal load.
• DC Forward Current: 50 mA. This is the maximum continuous forward current recommended for reliable operation.
• Reverse Voltage: 5 V. Applying a reverse voltage beyond this limit can cause junction breakdown.
• Operating Temperature Range: -40°C to +85°C. The device is guaranteed to function within this ambient temperature range.
• Storage Temperature Range: -40°C to +100°C. The device can be stored without degradation within these limits.

2.2 Electrical and Optical Characteristics

These characteristics are measured at Ta=25°C and a forward current (IF) of 20mA, unless otherwise noted.

• Luminous Intensity (IV): Ranges from a minimum of 560 mcd to a maximum of 1400 mcd, with typical values falling within this range. Measurement uses a sensor and filter approximating the CIE photopic eye-response curve.
• Viewing Angle (2θ1/2): 120 degrees (typical). This wide viewing angle is characteristic of a diffused lens, providing a broad, even light distribution.
• Peak Emission Wavelength (λP): 633 nm (typical). This is the wavelength at which the spectral power distribution is maximum.
• Dominant Wavelength (λd): Ranges from 618 nm to 630 nm, with a typical value of 624 nm. This parameter defines the perceived color of the LED (red).
• Spectral Line Half-Width (Δλ): 15 nm (typical). This indicates the spectral purity of the emitted light.
• Forward Voltage (VF): Ranges from 1.8 V to 2.4 V at IF=20mA, with a tolerance of ±0.1V. This is a critical parameter for drive circuit design.
• Reverse Current (IR): Maximum of 10 μA at a reverse voltage (VR) of 5V.

3. Binning System Explanation

The luminous intensity of the LEDs is sorted into specific bins to ensure consistency in applications. The binning is defined as follows, measured at 20mA:

• Bin Code U2: 560 mcd (Min) to 710 mcd (Max)
• Bin Code V1: 710 mcd to 900 mcd
• Bin Code V2: 900 mcd to 1120 mcd
• Bin Code W1: 1120 mcd to 1400 mcd

A tolerance of ±11% applies to each intensity bin. This binning allows designers to select LEDs with the required brightness level for their specific application, ensuring visual consistency in products using multiple LEDs.

4. Performance Curve Analysis

The datasheet references typical performance curves which are essential for understanding device behavior under various conditions. While specific graphical data is not reproduced in text, the curves typically included in such documents analyze:

• Relative Luminous Intensity vs. Forward Current: Shows how light output increases with current, up to the maximum rated limits.
• Forward Voltage vs. Forward Current: Illustrates the diode's I-V characteristic, crucial for thermal management and driver design.
• Relative Luminous Intensity vs. Ambient Temperature: Demonstrates the derating of light output as junction temperature increases, which is vital for high-temperature or high-current applications.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the peak and dominant wavelengths and spectral width.

These curves allow engineers to predict performance in real-world operating conditions beyond the standard test point of 25°C and 20mA.

5. Mechanical and Package Information

5.1 Package Dimensions and Polarity Identification

The device conforms to an EIA standard SMD package. Key dimensional notes include: all dimensions are in millimeters, and the general tolerance is ±0.2 mm unless otherwise specified. The product features a white diffused lens with an AlInGaP (Aluminum Indium Gallium Phosphide) red light source. The cathode is typically identified by a marking on the package or a specific pad geometry on the footprint diagram. The recommended PCB attachment pad layout for infrared or vapor phase reflow soldering is provided to ensure proper solder joint formation and mechanical stability.

6. Soldering and Assembly Guidelines

6.1 Recommended Reflow Soldering Profile

For lead-free (Pb-free) soldering processes, a profile compliant with J-STD-020B is recommended. Key parameters include:

• Pre-heat Temperature: 150–200°C.
• Pre-heat Time: Maximum 120 seconds.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus: Maximum 10 seconds (maximum two reflow cycles allowed).

For hand soldering with an iron, the maximum tip temperature should not exceed 300°C, with a soldering time of 3 seconds maximum for a single operation only. It is critical to follow solder paste manufacturer specifications and perform board-specific characterization, as different designs require tailored profiles.

6.2 Storage Conditions

Proper storage is essential to prevent moisture absorption, which can cause \"popcorning\" or cracking during reflow.

• Sealed Package: Store at ≤30°C and ≤70% RH. Use within one year of packing with desiccant.
• Opened Package: Store at ≤30°C and ≤60% RH. Components should be reflowed within 168 hours (7 days) of exposure.
• Extended Storage (Opened): Store in a sealed container with desiccant or in a nitrogen desiccator.
• Rebaking: If exposed for more than 168 hours, bake at approximately 60°C for at least 48 hours before soldering.

6.3 Cleaning

If cleaning is necessary after soldering, use alcohol-based solvents such as ethyl alcohol or isopropyl alcohol. Immerse the LED at normal temperature for less than one minute. Do not use unspecified chemical liquids.

7. Packaging and Ordering Information

The device is supplied in industry-standard packaging for automated assembly:

• Tape: 8mm wide carrier tape.
• Reel: 7-inch (178mm) diameter reel.
• Quantity: 2000 pieces per reel.
• Pocket Sealing: Empty component pockets are sealed with a top cover tape.
• Missing Components: A maximum of two consecutive missing components (lamps) is allowed per the packaging specification (ANSI/EIA 481).

8. Application Recommendations

8.1 Typical Application Circuits and Design Considerations

LEDs are current-operated devices. To ensure uniform brightness when driving multiple LEDs in parallel, it is strongly recommended to use a individual current-limiting resistor in series with each LED. Driving multiple LEDs in parallel from a single current source without individual resistors is not recommended, as slight variations in the forward voltage (VF) characteristic of each LED will cause significant differences in current sharing and, consequently, brightness. A series resistor stabilizes the current for each device independently.

8.2 Electrostatic Discharge (ESD) Precautions

Like most semiconductor devices, this LED is sensitive to electrostatic discharge. Standard ESD handling procedures should be followed during assembly and handling to prevent latent or catastrophic damage. This includes the use of grounded workstations, wrist straps, and conductive containers.

9. Cautions and Intended Use

This LED is designed and intended for use in ordinary electronic equipment such as office equipment, communication devices, and household appliances. It is not specifically designed or qualified for applications where exceptional reliability is required, particularly where failure could jeopardize life or health (e.g., aviation, transportation control, medical/life-support systems, critical safety devices). For such applications, consultation with the manufacturer is required prior to design-in.

10. Technical Comparison and Differentiation

The key differentiators of this component lie in its specific combination of a white diffused lens with an AlInGaP red chip. The diffused lens provides a wide, uniform viewing angle ideal for indicator applications where visibility from multiple angles is important. The AlInGaP material system is known for its high efficiency and stability in the red/orange/amber color spectrum compared to older technologies like GaAsP. The package is designed for compatibility with high-volume, automated SMT assembly lines, including stringent IR reflow processes, which is a critical factor for modern electronics manufacturing.

11. Frequently Asked Questions Based on Technical Parameters

Q: Can I drive this LED at 50mA continuously?
A: Yes, 50mA is the maximum rated DC forward current. Ensure proper thermal management (e.g., adequate PCB copper area for heat sinking) is in place, especially at higher ambient temperatures, as power dissipation will be at its maximum (VF * IF).

Q: Why is there a binning system for luminous intensity?
A: Manufacturing variations cause slight differences in light output. Binning sorts LEDs into groups with similar performance, allowing designers to source parts with consistent brightness for their product, avoiding noticeable variations between units.

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength (λP) is where the spectral power is highest. Dominant wavelength (λd) is the single wavelength of monochromatic light that would match the perceived color of the LED. λd is more relevant for color specification in applications.

Q: How critical is the 168-hour floor life after opening the moisture barrier bag?
A: It is very important. Exceeding this time without rebaking risks moisture-induced package damage during the high-temperature reflow soldering process, potentially leading to internal delamination or cracks.

12. Practical Design and Usage Case

Scenario: Designing a status indicator panel for a network router. The panel requires multiple red power and activity LEDs visible from various angles. The designer selects the LTST-T680QEWT for its wide 120-degree viewing angle and white diffused lens, which provides a soft, evenly lit appearance. Using the typical forward voltage of ~2.1V at 20mA from the datasheet, and a 5V system supply, a series resistor value is calculated: R = (Vsupply - VF) / IF = (5V - 2.1V) / 0.02A = 145 Ohms. A standard 150 Ohm resistor is chosen. Each LED on the panel gets its own 150 Ohm resistor connected to a GPIO pin on the microcontroller, ensuring uniform brightness regardless of minor VF variations between individual LEDs. The designer specifies Bin Code V1 (710-900 mcd) to guarantee adequate and consistent brightness.

13. Operating Principle Introduction

This LED is a semiconductor photonic device. Its core is a chip made of AlInGaP materials forming a p-n junction. When a forward voltage exceeding the junction's threshold is applied, electrons and holes are injected across the junction. When these charge carriers recombine, energy is released in the form of photons (light). The specific composition of the AlInGaP layers determines the energy bandgap, which dictates the wavelength (color) of the emitted light—in this case, red. The generated light passes through a encapsulating epoxy lens. The \"white diffused\" property of the lens is achieved by adding scattering particles to the epoxy, which randomizes the direction of the light rays exiting the chip, resulting in a wide, non-directional beam pattern rather than a narrow spotlight.

14. Technology Trends

The general trend in SMD LED technology continues towards higher luminous efficacy (more light output per electrical watt), improved color consistency and stability, and smaller package sizes enabling higher density designs. There is also a focus on enhancing reliability under higher temperature and current stress to meet the demands of automotive and industrial applications. The move to lead-free and halogen-free materials in compliance with global environmental regulations is now standard. Furthermore, integration with intelligent drivers and control circuitry within modules is an ongoing area of development, moving beyond simple discrete components.