SMD LED LTST-C21RKGKT Datasheet - 3.2x1.6x1.9mm - 2.4V - 75mW - Green - English Technical Documentation

1. Product Overview

This document details the specifications for a high-performance, surface-mount device (SMD) light-emitting diode (LED). The product is a top-mount chip LED utilizing an ultra-bright Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor material, emitting green light. It is designed for modern electronic assembly processes, featuring compatibility with automatic placement equipment and infrared (IR) reflow soldering. The device is compliant with RoHS (Restriction of Hazardous Substances) directives, classifying it as a green product. It is supplied in industry-standard 8mm tape on 7-inch diameter reels for efficient high-volume manufacturing.

1.1 Core Advantages

• High Brightness: Utilizes advanced AlInGaP technology for superior luminous intensity.
• Modern Manufacturing Ready: Fully compatible with automated pick-and-place systems and lead-free IR reflow soldering profiles.
• Standardized Packaging: Conforms to EIA (Electronic Industries Alliance) standards for tape and reel packaging, ensuring broad compatibility.
• Environmental Compliance: Meets RoHS requirements, making it suitable for global markets with strict environmental regulations.
• Design Flexibility: The water-clear lens provides a neutral appearance that can blend with various product designs.

2. In-Depth Technical Parameter Analysis

All parameters are specified at an ambient temperature (Ta) of 25°C unless otherwise noted. Understanding these parameters is critical for reliable circuit design and achieving expected performance.

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 operation.

• Power Dissipation (Pd): 75 mW. The maximum total power the device can dissipate as heat.
• Peak Forward Current (IFP): 80 mA. Maximum allowable current under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). Used for brief, high-intensity flashes.
• DC Forward Current (IF): 30 mA. The maximum continuous forward current for steady-state operation.
• Reverse Voltage (VR): 5 V. The maximum voltage that can be applied in the reverse direction across the LED.
• Operating Temperature Range: -30°C to +85°C. The ambient temperature range over which the device is designed to function.
• Storage Temperature Range: -40°C to +85°C. The temperature range for non-operational storage.
• Infrared Soldering Condition: 260°C for 10 seconds. The maximum thermal profile exposure during reflow soldering.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters under standard test conditions (IF = 20mA).

• Luminous Intensity (Iv): 28.0 - 180.0 mcd (millicandela). The perceived brightness of the light source as measured by the human eye (CIE curve). The wide range is managed through a binning system.
• Viewing Angle (2θ_1/2): 70 degrees (typical). The full angle at which the luminous intensity is half of the intensity at 0 degrees (on-axis). This defines the beam spread.
• Peak Emission Wavelength (λ_P): 574 nm (typical). The wavelength at which the spectral power distribution is maximum.
• Dominant Wavelength (λ_d): 567.5 - 576.5 nm. The single wavelength that perceptually matches the color of the LED, derived from the CIE chromaticity diagram. This is the key parameter for color specification.
• Spectral Line Half-Width (Δλ): 15 nm (typical). The spectral bandwidth measured at half the maximum intensity (Full Width at Half Maximum - FWHM). A smaller value indicates a more monochromatic light.
• Forward Voltage (V_F): 1.80 - 2.40 V. The voltage drop across the LED when operating at the specified forward current (20mA).
• Reverse Current (I_R): 10 μA (max) at V_R = 5V. The small leakage current that flows when the device is reverse-biased.

3. Binning System Explanation

To ensure consistent color and brightness in production, LEDs are sorted into bins based on measured characteristics. This allows designers to select parts that meet specific application requirements for uniformity.

3.1 Luminous Intensity Binning

Binned at a test current of 20mA. Tolerance within each bin is +/-15%.

• Bin N: 28.0 - 45.0 mcd
• Bin P: 45.0 - 71.0 mcd
• Bin Q: 71.0 - 112.0 mcd
• Bin R: 112.0 - 180.0 mcd

3.2 Dominant Wavelength Binning

Binned at a test current of 20mA. Tolerance for each bin is +/- 1nm.

• Bin C: 567.5 - 570.5 nm
• Bin D: 570.5 - 573.5 nm
• Bin E: 573.5 - 576.5 nm

Combining intensity and wavelength bins (e.g., RC, QD) provides a precise specification for color and brightness consistency in an assembly.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet, the following analysis is based on standard LED behavior and the provided parameters.

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

The LED exhibits a typical diode I-V characteristic. The forward voltage (V_F) has a specified range of 1.80V to 2.40V at 20mA. V_F has a negative temperature coefficient, meaning it decreases slightly as the junction temperature increases. For stable operation, driving the LED with a constant current source is strongly recommended over a constant voltage source to prevent thermal runaway.

4.2 Luminous Intensity vs. Forward Current

Luminous intensity is approximately proportional to the forward current within the operating range. However, efficiency (lumens per watt) may decrease at very high currents due to increased heat. Operating at or below the recommended 20mA for testing ensures optimal efficiency and longevity.

4.3 Temperature Dependence

LED performance is temperature-sensitive. As junction temperature rises:

• Luminous Output Decreases: The light output will drop. The exact derating factor is product-specific.
• Forward Voltage Decreases: As noted in the I-V characteristic.
• Wavelength Shifts: The dominant wavelength may shift slightly, typically towards longer wavelengths (red shift) with increasing temperature.

Proper thermal management on the PCB (adequate copper area, possible thermal vias) is essential to maintain performance and reliability, especially when operating at high ambient temperatures or near maximum current ratings.

5. Mechanical & Packaging Information

5.1 Device Dimensions

The package is a standard SMD format. Key dimensions include a body size and lead configuration suitable for automated assembly. All dimensional tolerances are typically ±0.10mm unless otherwise specified. Designers must refer to the detailed mechanical drawing for precise land pattern design.

5.2 Polarity Identification

The cathode is typically indicated by a visual marker on the LED package, such as a notch, a green dot, or a cut corner on the lens. Correct polarity must be observed during placement to ensure the device functions.

5.3 Suggested Soldering Pad Layout

A recommended footprint (land pattern) is provided to ensure a reliable solder joint, proper alignment, and sufficient mechanical strength. Adhering to this layout helps prevent tombstoning (component standing up on one end) during reflow and ensures good thermal connection to the PCB.

6. Soldering & Assembly Guidelines

6.1 IR Reflow Soldering Profile

The device is compatible with lead-free (Pb-free) soldering processes. A suggested reflow profile is provided, compliant with JEDEC standards. Key parameters include:

• Pre-heat: 150-200°C
• Pre-heat Time: Maximum 120 seconds.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus: The device should be exposed to the peak temperature for a maximum of 10 seconds. Reflow should be performed a maximum of two times.

The profile must be characterized for the specific PCB design, components, solder paste, and oven used.

6.2 Hand Soldering

If hand soldering is necessary:

• Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per lead.
• Attempts: Soldering should be performed only once. Avoid repeated heating.

A temperature-controlled iron with a fine tip is recommended.

6.3 Cleaning

If cleaning after soldering is required:

• Use only specified cleaning agents. Unspecified chemicals may damage the epoxy lens or package.
• Recommended solvents are ethyl alcohol or isopropyl alcohol at normal room temperature.
• Immersion time should be less than one minute.

6.4 Storage & Handling

• ESD Precautions: LEDs are sensitive to electrostatic discharge (ESD). Use wrist straps, anti-static mats, and properly grounded equipment during handling.
• Moisture Sensitivity: As per industry standards, the device is likely moisture-sensitive. If the original sealed moisture-barrier bag is opened:
  • Store at ≤30°C and ≤60% relative humidity.
  • It is recommended to complete IR reflow within one week of opening.
  • For longer storage out of the original bag, store in a sealed container with desiccant or in a nitrogen desiccator.
  • Devices stored out of bag for >1 week should be baked at approximately 60°C for at least 20 hours before soldering to remove absorbed moisture and prevent "popcorning" during reflow.

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

• Reel Size: 7-inch diameter.
• Tape Width: 8mm.
• Quantity per Reel: 3000 pieces (standard full reel).
• Minimum Pack Quantity: 500 pieces for remainder quantities.
• Packaging Standard: Compliant with ANSI/EIA-481 specifications.
• Cover Tape: Empty component pockets are sealed with a top cover tape.
• Missing Components: A maximum of two consecutive missing lamps (empty pockets) is allowed per specification.

8. Application Recommendations

8.1 Typical Application Scenarios

This LED is suitable for a wide range of applications requiring a compact, bright green indicator, including but not limited to:

• Status and power indicators on consumer electronics (routers, chargers, appliances).
• Backlighting for keys on keyboards or control panels.
• Display panel status lights.
• Automotive interior lighting (non-critical functions, subject to further qualification).
• Portable electronic devices.

It is intended for ordinary electronic equipment. For applications requiring exceptional reliability where failure could jeopardize safety (aviation, medical, transportation safety systems), specific consultation and qualification are mandatory.

8.2 Circuit Design Considerations

• Current Limiting: ALWAYS use a series current-limiting resistor or a dedicated constant-current LED driver circuit. The value is calculated using Ohm's Law: R = (V_supply - V_F) / I_F. Use the maximum V_F from the datasheet (2.40V) to ensure current does not exceed limits even with a low-V_F part.
• Parallel Connections: Avoid connecting LEDs directly in parallel. Slight variations in V_F can cause current imbalance, where one LED hogs most of the current and fails prematurely. Use separate current-limiting resistors for each LED or a constant-current driver with multiple channels.
• Series Connections: Connecting LEDs in series ensures identical current through each device, which is preferable for uniform brightness. Ensure the supply voltage is sufficient for the sum of all V_F drops plus headroom for the current regulator.
• Thermal Management: For continuous operation at high currents or in high ambient temperatures, consider the PCB layout. Providing a small copper pad under the LED's thermal pad (if present) or connecting the cathode pads to a larger copper plane can help dissipate heat.
• Reverse Voltage Protection: While the LED can withstand up to 5V in reverse, it is good practice in circuits where reverse polarity is possible (e.g., user-installable modules) to include protection, such as a diode in series or a shunt diode across the LED.

9. Technical Comparison & Differentiation

Compared to older LED technologies like standard GaP (Gallium Phosphide) green LEDs, this AlInGaP-based device offers significant advantages:

• Higher Brightness: AlInGaP material provides substantially higher luminous efficiency, resulting in greater light output for the same input current.
• Better Color Purity: The spectral half-width is relatively narrow (15nm typical), producing a more saturated and pure green color compared to broader-spectrum alternatives.
• Modern Process Compatibility: The package and materials are specifically engineered for compatibility with lead-free, high-temperature IR reflow processes, which is essential for contemporary RoHS-compliant manufacturing.
• Standardization: The EIA package and tape-and-reel format ensure seamless integration into automated assembly lines, reducing setup time and placement errors compared to non-standard or bulk-packed components.

10. Frequently Asked Questions (FAQs)

10.1 What is the difference between Peak Wavelength and Dominant Wavelength?

Peak Wavelength (λ_P) is the physical wavelength where the LED emits the most optical power. Dominant Wavelength (λ_d) is the perceptual color match—the single wavelength that a human eye would perceive as the same color as the LED's mixed output. For monochromatic LEDs like this green one, they are often close, but λ_d is the key parameter for color specification in design.

10.2 Can I drive this LED without a current-limiting resistor if my power supply is exactly 2.0V?

No, this is not recommended and is risky. The forward voltage (V_F) varies from 1.80V to 2.40V. If you have a 2.0V supply and an LED with a V_F of 1.85V, a small 0.15V difference will cause a large, uncontrolled current to flow (limited only by the LED's dynamic resistance and parasitic circuit resistance), likely exceeding the maximum current and damaging the LED. Always use a current-limiting mechanism.

10.3 Why is there a binning system, and which bin should I choose?

Manufacturing variations cause slight differences in color and brightness. Binning sorts LEDs into groups for consistency. Choose a bin based on your application:

• For single indicators, any bin is usually fine.
• For multiple LEDs that need to look identical (e.g., a row of status lights), specify the same intensity and wavelength bin (e.g., all "QD") to ensure visual uniformity.
• For the brightest output, specify the highest intensity bin (R). For a specific green hue, specify the corresponding wavelength bin (C, D, or E).

10.4 The datasheet mentions a 75mW power dissipation. How do I calculate this?

Power dissipation (P_d) in an LED is primarily calculated as: P_d ≈ V_F * I_F. For example, at the maximum continuous current (I_F = 30mA) and a typical V_F of 2.1V, P_d = 0.030A * 2.1V = 63mW, which is below the 75mW maximum. Always use the maximum V_F for worst-case calculation: 0.030A * 2.40V = 72mW. This leaves a small safety margin. Ensure your operating conditions, including ambient temperature, allow for this dissipation without overheating.

11. Practical Design & Usage Examples

11.1 Example 1: Simple 5V Indicator Circuit

Goal: Power a single LED from a 5V DC supply at I_F = 20mA. Calculation: Assume worst-case V_F = 2.40V. Required voltage drop across resistor: V_R = 5V - 2.40V = 2.60V. Resistor value (Ohm's Law): R = V_R / I_F = 2.60V / 0.020A = 130 Ω. Component Selection: Choose the nearest standard resistor value, e.g., 130Ω or 150Ω. A 150Ω resistor would yield I_F ≈ (5V - 2.40V)/150Ω = 17.3mA, which is safe and still bright. Resistor Power Rating: P_resistor = I² * R = (0.020)² * 150 = 0.06W. A standard 1/8W (0.125W) or 1/4W resistor is more than sufficient.

11.2 Example 2: Driving Multiple LEDs from a 12V Supply

Goal: Power three LEDs in series from a 12V supply at I_F = 20mA. Calculation: Total LED V_F (worst-case max): 3 * 2.40V = 7.20V. Voltage drop across resistor: V_R = 12V - 7.20V = 4.80V. Resistor value: R = 4.80V / 0.020A = 240 Ω. Advantage: Series connection guarantees identical current through all three LEDs, ensuring uniform brightness even if their V_F values differ. Only one current-limiting resistor is needed, improving efficiency compared to three separate resistors.

12. Technology Introduction

12.1 AlInGaP Semiconductor Principle

AlInGaP (Aluminum Indium Gallium Phosphide) is a III-V compound semiconductor material used primarily for high-brightness red, orange, yellow, and green LEDs. By precisely adjusting the ratios of aluminum, indium, gallium, and phosphorus in the crystal lattice during epitaxial growth, engineers can "tune" the bandgap of the material. The bandgap energy determines the wavelength (color) of light emitted when electrons recombine with holes across the junction. AlInGaP offers higher quantum efficiency and thermal stability for colors in the yellow-to-red spectrum compared to older materials, resulting in brighter and more reliable devices. The green emission from this specific part is achieved by pushing the composition towards a higher bandgap energy.

13. Industry Trends

13.1 Evolution of Indicator LEDs

The trend in SMD indicator LEDs continues towards:

• Increased Efficiency: Development of new semiconductor materials and chip structures (like flip-chip designs) to deliver more lumens per watt, reducing power consumption for a given brightness.
• Miniaturization: Packages are becoming smaller (e.g., 0402, 0201 metric sizes) to save valuable PCB real estate in increasingly compact devices like wearables and ultra-thin smartphones.
• Enhanced Reliability & Robustness: Improved packaging materials and processes to withstand higher reflow temperatures, harsher environmental conditions, and provide better moisture resistance.
• Integrated Solutions: Growth of LEDs with built-in current-limiting resistors or IC drivers ("LED drivers in package") to simplify circuit design and reduce component count.
• Broadening Color Gamut: Ongoing research into materials like gallium nitride (GaN) on different substrates and quantum dot technology to achieve purer and more saturated green and cyan colors, which are valuable for full-color displays and lighting.

Devices like the one documented here, with their RoHS compliance, reflow compatibility, and high brightness, represent the current mainstream standard for general-purpose indicator applications.