SMD LED LTST-T680QSWT Datasheet - Diffused Yellow AlInGaP - 20mA - 130mW - English Technical Document

1. Product Overview

This document provides the technical specifications for a surface-mount device (SMD) LED. The component is designed for automated printed circuit board (PCB) assembly processes, featuring a miniature form factor suitable for space-constrained applications. The LED utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material to produce a diffused yellow light output. Its primary function is as a status indicator, signal luminary, or for front-panel backlighting in various electronic systems.

1.1 Features

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

1.2 Applications

The LED is intended for use in a broad range of consumer, commercial, and industrial electronic equipment. Typical application areas include telecommunication devices (e.g., cordless/cellular phones), office automation equipment (e.g., notebook computers, network systems), home appliances, and general industrial control panels. Its specific roles are as status indicators, signal or symbol illumination, and front panel backlighting.

2. Technical Parameters: In-Depth Objective Interpretation

The following sections provide a detailed analysis of the LED's key performance parameters under standard test conditions (Ta=25°C).

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed and should be avoided for reliable long-term performance.

• Power Dissipation (Pd): 130 mW. This is the maximum amount of power the package can dissipate as heat.
• Peak Forward Current (I_F(peak)): 100 mA. This is the maximum allowable instantaneous forward current, typically specified under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) to prevent overheating.
• Continuous Forward Current (I_F): 50 mA. This is the maximum recommended DC current for continuous operation.
• Reverse Voltage (V_R): 5 V. Applying a reverse bias voltage exceeding this value can cause junction breakdown.
• Operating Temperature Range: -40°C to +85°C. The ambient temperature range over which the device is designed to function.
• Storage Temperature Range: -40°C to +100°C. The temperature range for non-operational storage.

2.2 Electro-Optical Characteristics

These parameters define the device's performance under normal operating conditions (I_F = 20mA, Ta=25°C).

• Luminous Intensity (I_V): 710 - 1400 mcd (millicandela). This is the perceived luminous power per unit solid angle. The wide range indicates a binning system is used (see Section 3). Measurement follows the CIE photopic eye-response curve.
• Viewing Angle (2θ_1/2): 120° (typical). This is the full angle at which the luminous intensity is half the value at the optical axis (0°). A 120° angle indicates a wide, diffused emission pattern suitable for wide-area illumination.
• Peak Emission Wavelength (λ_P): 592 nm (typical). The wavelength at which the spectral radiant intensity is 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). The spectral width of the emission at half its maximum intensity. A value of 15nm is characteristic of AlInGaP materials, indicating a relatively pure yellow color.
• Forward Voltage (V_F): 2.1V (typical), 2.6V (maximum) at 20mA. The voltage drop across the LED when conducting the specified forward current.
• Reverse Current (I_R): 10 μA (maximum) at V_R=5V. The small leakage current that flows when the device is reverse-biased within its maximum rating.

3. Binning System Explanation

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

3.1 Forward Voltage (V_f) Rank

LEDs are binned based on their forward voltage drop at 20mA. This is critical for designing current-limiting circuits and ensuring uniform brightness in parallel arrays.

• Bin D2: 1.8V - 2.0V
• Bin D3: 2.0V - 2.2V
• Bin D4: 2.2V - 2.4V
• Bin D5: 2.4V - 2.6V
• Tolerance per bin: ±0.1V

3.2 Luminous Intensity (I_V) Rank

This binning ensures a minimum brightness level for a given product code.

• Bin U2: 710 mcd - 900 mcd
• Bin V1: 900 mcd - 1120 mcd
• Bin V2: 1120 mcd - 1400 mcd
• Tolerance per bin: ±11%

3.3 Dominant Wavelength (W_d) Rank

This binning controls the precise shade of yellow emitted by the LED.

• Bin H: 584.5 nm - 587.0 nm
• Bin J: 587.0 nm - 589.5 nm
• Bin K: 589.5 nm - 592.0 nm
• Bin L: 592.0 nm - 594.5 nm
• Tolerance per bin: ±1 nm

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet, typical performance trends for AlInGaP LEDs can be described.

4.1 Current vs. Voltage (I-V) Characteristic

The forward voltage (V_F) exhibits a logarithmic relationship with forward current (I_F). Below the turn-on voltage (~1.8V for AlInGaP), current is minimal. Above this threshold, V_F increases relatively linearly with I_F, with a slope determined by the dynamic resistance of the diode. Operating at the recommended 20mA ensures stable performance within the typical V_F range.

4.2 Luminous Intensity vs. Forward Current

The luminous intensity (I_V) is approximately proportional to the forward current (I_F) in the normal operating range. However, efficiency may decrease at very high currents due to increased junction temperature and other non-linear effects. Driving the LED at or below the specified continuous current (50mA) is essential for maintaining rated output and longevity.

4.3 Temperature Characteristics

The performance of LEDs is temperature-dependent. Typically, the forward voltage (V_F) has a negative temperature coefficient, decreasing as junction temperature rises. Conversely, luminous intensity generally decreases with increasing junction temperature. Proper thermal management in the application (e.g., adequate PCB copper area for heat sinking) is crucial to maintain consistent optical output and device reliability over the specified operating temperature range.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED is housed in a standard surface-mount package. All critical dimensions are provided in millimeters with a general tolerance of ±0.2mm unless otherwise specified. The package includes a diffused lens which creates the wide 120° viewing angle.

5.2 Recommended PCB Attachment Pad Layout

A land pattern design is provided for infrared or vapor phase reflow soldering. Adhering to this recommended footprint ensures proper solder joint formation, self-alignment during reflow, and reliable mechanical attachment. The pad design also aids in heat dissipation from the LED package.

5.3 Polarity Identification

Surface-mount LEDs typically have a marking or a shaped feature (like a notch or a beveled corner) on the package to indicate the cathode (negative) terminal. Correct polarity orientation on the PCB is mandatory for the device to function.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Profile (Pb-Free Process)

The datasheet references a profile compliant with J-STD-020B. A typical lead-free reflow profile includes:

• Preheat/Ramp: A gradual ramp to ~150-200°C to activate flux and minimize thermal shock.
• Soak Zone: A plateau typically between 150-200°C for up to 120 seconds to allow temperature equalization across the PCB.
• Reflow Zone: A rapid temperature increase to a peak of 260°C maximum. The time above liquidus (e.g., 217°C) should be controlled.
• Cooling: A controlled cool-down phase to solidify solder joints.
• Note: The specific profile must be optimized for the actual PCB assembly, considering board thickness, component density, and solder paste specifications.

6.2 Storage and Handling

• Sealed Package: Store at ≤30°C and ≤70% RH. Use within one year of packing date when in a moisture-barrier bag with desiccant.
• Opened Package: For components removed from their dry-pack, the recommended storage ambient is ≤30°C and ≤60% RH. Components should be subjected to IR reflow within 168 hours (1 week) of exposure. For longer exposure, a 48-hour bake at 60°C is recommended prior to soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

6.3 Cleaning

If post-solder cleaning is required, use alcohol-based solvents such as isopropyl alcohol (IPA) or ethyl alcohol. Immersion should be at normal temperature and for less than one minute. Avoid unspecified chemical cleaners that may damage the LED lens or package material.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The components are supplied in embossed carrier tape with a protective cover tape, wound onto 7-inch (178mm) diameter reels. Standard reel quantities are 2000 pieces per reel. The packaging conforms to ANSI/EIA-481 specifications to ensure compatibility with automated assembly equipment.

8. Application Suggestions

8.1 Typical Application Circuits

LEDs are current-driven devices. A series current-limiting resistor is mandatory when connecting to a voltage source. The resistor value (R_s) can be calculated using Ohm's Law: R_s = (V_supply - V_F) / I_F. For uniform brightness when driving multiple LEDs in parallel, it is strongly recommended to use a separate current-limiting resistor for each LED, rather than a single resistor for the entire parallel array. This compensates for natural variations in the forward voltage (V_F) between individual LEDs.

8.2 Design Considerations

• Thermal Management: Ensure the PCB layout provides adequate thermal relief, especially when operating near maximum current ratings. Copper pours connected to the thermal pad of the LED can help dissipate heat.
• ESD Protection: While not explicitly stated for all LEDs, implementing basic ESD protection on signal lines connected to LEDs is good design practice for sensitive environments.
• Optical Design: The diffused lens provides wide viewing. For directed light, external optics (reflectors, light pipes) may be required.

9. Technical Comparison and Differentiation

This AlInGaP-based yellow LED offers specific advantages. Compared to older technology like GaAsP (Gallium Arsenide Phosphide) yellow LEDs, AlInGaP provides significantly higher luminous efficiency, resulting in brighter output at the same drive current, and better color stability over temperature and lifetime. The wide 120° viewing angle with a diffused lens is a key feature for applications requiring broad, even illumination rather than a focused beam, differentiating it from LEDs with narrow viewing angles designed for directed light.

10. Frequently Asked Questions (Based on Technical Parameters)

10.1 What resistor value should I use with a 5V supply?

Using the typical V_F of 2.1V at 20mA: R = (5V - 2.1V) / 0.02A = 145 Ohms. The nearest standard value of 150 Ohms would result in I_F ≈ 19.3mA, which is acceptable. Always calculate using the maximum V_F (2.6V) to ensure the minimum current is sufficient for your brightness requirement: R_min = (5V - 2.6V) / 0.02A = 120 Ohms.

10.2 Can I drive this LED without a current-limiting resistor using a constant current source?

Yes, a constant current driver set to 20mA is an excellent method to drive an LED, as it ensures precise current regulation independent of forward voltage variations. This is often preferred for critical brightness applications.

10.3 Why is there a peak current rating (100mA) higher than the continuous current (50mA)?

The peak current rating allows for brief pulses of higher current, which can be useful for multiplexing schemes or creating short, bright flashes. The low duty cycle (1/10) ensures the average power dissipation and junction temperature remain within safe limits, preventing thermal damage.

11. Practical Use Case Example

Scenario: Front Panel Status Indicator for a Network Router
A designer needs multiple yellow status LEDs on a router's front panel to indicate power, internet connectivity, and Wi-Fi activity. They choose this LED for its wide viewing angle, ensuring the light is visible from various angles. The LEDs are driven at 15mA (below the 20mA test condition for a longer lifespan) via GPIO pins on a microcontroller. A 150-ohm series resistor is used for each LED, connected to the 3.3V rail. The diffused lens provides a soft, non-glaring light suitable for a home/office environment. The LEDs are placed on the PCB according to the recommended pad layout and assembled using a standard lead-free reflow profile.

12. Operating Principle Introduction

An LED is a semiconductor diode. When a forward voltage exceeding the material's bandgap energy is applied, electrons and holes recombine at the p-n junction. In an AlInGaP LED, this recombination event releases energy in the form of photons (light). The specific composition of the Aluminum, Indium, Gallium, and Phosphide layers determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, in the yellow spectrum (~590nm). The diffused epoxy lens surrounding the semiconductor chip scatters the light, creating the wide emission pattern.

13. Technology Trends

The general trend in LED technology is toward higher efficiency (more lumens per watt), improved color rendering, and greater reliability. For indicator-type LEDs, miniaturization continues while maintaining or increasing light output. There is also a focus on broadening the color gamut available in SMD packages. The use of AlInGaP for yellow, amber, and red LEDs represents an established, high-performance technology. Future developments may involve new material systems or nanostructures to achieve even narrower spectral emission or higher efficiency at high temperatures.