SMD LED LTST-C990TGKT Datasheet - Ultra Bright Green - 20mA - 76mW - English Technical Document

1. Product Overview

This document provides the complete technical specifications for a high-performance, surface-mount LED. Designed for automated assembly processes, this component is suitable for a wide range of space-constrained electronic applications requiring reliable and bright indicator lighting.

1.1 Key Features and Advantages

The LED offers several key advantages for modern electronics manufacturing:

• Compliance with environmental regulations (RoHS).
• Utilizes an Ultra Bright InGaN (Indium Gallium Nitride) semiconductor chip, known for high efficiency and brightness in the green spectrum.
• Features a dome lens design which typically provides a wider viewing angle and improved light extraction compared to flat lenses.
• Packaged on 8mm tape mounted on standard 7-inch diameter reels, compatible with high-speed automated pick-and-place equipment.
• Designed to be compatible with standard integrated circuit (I.C.) drive levels.
• Withstands infrared (IR) reflow soldering processes, making it suitable for standard Surface Mount Technology (SMT) assembly lines alongside other components.

1.2 Target Applications and Markets

This LED is engineered for versatility across multiple sectors:

• Telecommunications & Office Equipment: Status indicators in routers, modems, phones, and printers.
• Consumer Electronics: Backlighting for keypads, keyboards, and micro-displays in portable devices.
• Home Appliances & Industrial Equipment: Power, mode, or fault indicators.
• General Signage: Small-scale indoor signal and symbol illumination.

2. Technical Parameters: In-Depth Objective Interpretation

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

2.1 Absolute Maximum Ratings

These are stress limits that must not be exceeded under any conditions, even momentarily. Operation beyond these limits may cause permanent damage.

• Power Dissipation (Pd): 76 mW. This is the maximum amount of power the device can dissipate as heat.
• Peak Forward Current (I_FP): 100 mA. Permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). Not for continuous DC operation.
• DC Forward Current (I_F): 20 mA. The recommended continuous operating current for standard brightness and longevity.
• Operating Temperature Range: -20°C to +80°C. The ambient temperature range over which the device is guaranteed to function.
• Storage Temperature Range: -30°C to +100°C.
• Infrared Soldering Condition: Withstands 260°C peak temperature for 10 seconds, compliant with lead-free (Pb-free) process requirements.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters under normal operating conditions (I_F = 20mA).

• Luminous Intensity (I_V): 2240 - 4500 mcd (millicandela). This is the perceived brightness to the human eye, measured with a filter matching the CIE photopic response curve. The wide range indicates a binning system is used (see Section 3).
• Viewing Angle (2θ_1/2): 75 degrees. Defined as the full angle at which luminous intensity drops to half of its on-axis (0°) value. The dome lens contributes to this relatively wide viewing angle.
• Peak Emission Wavelength (λ_P): 518 nm (typical). The wavelength at which the spectral power output is maximum.
• Dominant Wavelength (λ_d): 515 - 535 nm. This is the single wavelength that best represents the perceived color (green) of the LED, derived from the CIE chromaticity diagram.
• Spectral Line Half-Width (Δλ): 35 nm (typical). The bandwidth of the emitted light measured at half the peak intensity, indicating the spectral purity.
• Forward Voltage (V_F): 1.9 - 3.4 V. The voltage drop across the LED when driven at 20mA. This range is also subject to binning.
• Reverse Current (I_R): 10 μA (max) at V_R = 5V. The device is not designed for reverse bias operation; this parameter is for test purposes only.

2.3 Thermal Considerations

While not explicitly graphed in the provided data, thermal management is implicit in the specifications. Exceeding the maximum junction temperature, influenced by forward current, ambient temperature, and PCB thermal design, will reduce luminous output and lifespan. The 76mW power dissipation rating and 80°C maximum operating temperature are key thermal design constraints.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted (binned) based on key parameters. This allows designers to select parts that meet specific application needs for color, brightness, and forward voltage.

3.1 Forward Voltage (V_F) Binning

Bins ensure LEDs in a circuit have similar voltage drops, promoting uniform current sharing when connected in parallel. Tolerance per bin is ±0.1V.

• G2: 1.9V - 2.2V
• G3: 2.2V - 2.5V
• G4: 2.5V - 2.8V
• G5: 2.8V - 3.1V
• G6: 3.1V - 3.4V

3.2 Luminous Intensity (I_V) Binning

Bins group LEDs by brightness output. Tolerance per bin is ±15%.

• X2: 2240 mcd - 2800 mcd
• Y1: 2800 mcd - 3550 mcd
• Y2: 3550 mcd - 4500 mcd

3.3 Hue / Dominant Wavelength (λ_d) Binning

This binning ensures color consistency. A shift of just a few nanometers can be perceptible. Tolerance per bin is ±1nm.

• AN: 515 nm - 520 nm
• AP: 520 nm - 525 nm
• AQ: 525 nm - 530 nm
• AR: 530 nm - 535 nm

4. Performance Curve Analysis

While specific graphical data is referenced, typical curves for such LEDs provide essential design insights.

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

The I-V characteristic is exponential. A small increase in voltage beyond the nominal V_F causes a large increase in current. Therefore, driving an LED with a constant current source (or a voltage source with a series current-limiting resistor) is mandatory to prevent thermal runaway and destruction.

4.2 Luminous Intensity vs. Forward Current

Luminous intensity is approximately proportional to forward current up to a point. However, efficiency (lumens per watt) often peaks at a current lower than the maximum rating, and excessive current leads to increased heat and accelerated lumen depreciation.

4.3 Temperature Dependence

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

• Forward Voltage (V_F): Decreases slightly (negative temperature coefficient).
• Luminous Intensity (I_V): Decreases. The output can drop significantly as temperature approaches the maximum operating limit.
• Dominant Wavelength (λ_d): May shift slightly, potentially affecting perceived color, especially in tight-binned applications.

4.4 Spectral Distribution

The emitted light is not monochromatic but has a Gaussian-like distribution centered around the peak wavelength (518 nm). The spectral half-width (35 nm) defines the spread of this distribution. A narrower half-width indicates a more saturated, pure color.

5. Mechanical & Package Information

5.1 Device Dimensions and Polarity

The LED conforms to a standard EIA package footprint. Key dimensional notes:

• All dimensions are in millimeters.
• Standard tolerance is ±0.1 mm unless otherwise specified.
• The package features a dome-shaped, water-clear lens.
• Polarity is indicated by a cathode mark (typically a notch, green dot, or cut corner on the package). Correct orientation is crucial for operation.

5.2 Recommended PCB Attachment Pad Layout

A suggested land pattern (copper pad design) is provided to ensure proper soldering, mechanical stability, and potentially aid in heat dissipation. Following this recommendation helps achieve reliable solder fillets and prevents tombstoning during reflow.

5.3 Tape and Reel Packaging Specifications

The device is supplied in industry-standard embossed carrier tape.

• Tape Width: 8 mm.
• Reel Diameter: 7 inches.
• Quantity per Reel: 3000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• The packaging includes a top cover tape to seal component pockets and follows ANSI/EIA-481 specifications for compatibility with automated equipment.

6. Soldering, Assembly, and Handling Guidelines

6.1 IR Reflow Soldering Process

The device is qualified for lead-free (Pb-free) soldering processes. A suggested reflow profile is critical:

• Pre-heat: 150°C to 200°C.
• Pre-heat Time: Maximum 120 seconds to allow for uniform heating and solvent evaporation.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus (at peak): Maximum 10 seconds. The device can withstand this profile a maximum of two times.

Important Note: The optimal profile depends on the specific PCB assembly (board thickness, component density, solder paste). The provided values are guidelines; process characterization for the specific application is recommended.

6.2 Hand Soldering (If Required)

If manual rework is necessary:

• Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per pad.
• Apply heat to the PCB pad, not directly to the LED body, to minimize thermal stress on the component.

6.3 Cleaning

Post-solder flux residue cleaning must use compatible solvents:

• Use only alcohol-based cleaners such as ethyl alcohol or isopropyl alcohol (IPA).
• Immersion time should be less than one minute at normal temperature.
• Avoid unspecified chemical cleaners which may damage the epoxy lens or package.

6.4 Storage and Moisture Sensitivity

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

• Sealed Package (Original): Store at ≤30°C and ≤90% RH. Use within one year.
• Opened Package: Store at ≤30°C and ≤60% RH. For components removed from moisture-proof bags, it is recommended to complete IR reflow within one week (Moisture Sensitivity Level 3, MSL 3).
• Extended Storage (Out of Bag): Store in a sealed container with desiccant or in a nitrogen desiccator.
• Rebaking: If stored out of the original packaging for more than one week, bake at approximately 60°C for at least 20 hours before soldering to remove absorbed moisture.

6.5 Electrostatic Discharge (ESD) Precautions

LEDs are sensitive to electrostatic discharge. Always:

• Use a grounded wrist strap or anti-static gloves when handling.
• Ensure all workstations, equipment, and tools are properly grounded.
• Use conductive foam or trays for storage and transport of loose devices.

7. Application Design Considerations

7.1 Drive Circuit Design

Constant Current Drive: The preferred method. Use a dedicated LED driver IC or a simple current-limiting circuit (voltage source + series resistor). The resistor value is calculated as: R = (V_source - V_F) / I_F. Use the maximum V_F from the bin or datasheet to ensure current never exceeds 20mA under worst-case conditions.

PWM Dimming: For brightness control, Pulse Width Modulation (PWM) is highly effective. It switches the LED at full current (e.g., 20mA) at a high frequency (typically >100Hz) and varies the duty cycle. This method maintains color consistency better than analog (current reduction) dimming.

7.2 Thermal Management on PCB

To maintain performance and longevity:

• Use the recommended PCB pad layout, which may include thermal relief connections.
• Incorporate adequate copper area around the LED pads to act as a heat sink.
• Avoid placing the LED near other significant heat sources on the board.
• Ensure adequate ventilation in the end-product enclosure.

7.3 Optical Integration

The 75-degree viewing angle makes it suitable for direct viewing. For light-piping or diffusion applications, the wide angle helps couple light into the guide. The water-clear lens is optimal for uncolored output; for a colored appearance, an external colored diffuser or filter is typically used.

8. Technical Comparison and Differentiation

Key differentiators of this component in its class include:

• Ultra-Bright InGaN Chip: Offers higher luminous efficiency compared to older technologies like AlGaInP for green, resulting in greater brightness at the same drive current.
• Wide Viewing Angle (75°): Provides good off-axis visibility, beneficial for status indicators that may be viewed from various angles.
• Comprehensive Binning: The three-parameter binning (V_F, I_V, λ_d) allows for precise selection for applications demanding uniformity in brightness, color, and electrical behavior.
• Robust Reflow Compatibility: Withstands 260°C peak temperature, making it fully compatible with modern, lead-free, high-temperature SMT assembly processes.

9. Frequently Asked Questions (Based on Technical Parameters)

Q1: Can I drive this LED at 30mA for more brightness?

A: No. The Absolute Maximum Rating for DC forward current is 20mA. Exceeding this rating increases junction temperature, leading to rapid lumen depreciation, color shift, and potential catastrophic failure. Always operate at or below the recommended DC current.

Q2: Why is my LED dimmer than expected when I apply 2.5V?

A: LEDs are current-driven devices, not voltage-driven. The forward voltage (V_F) has a range (1.9V-3.4V). Applying a fixed 2.5V may under-drive an LED with a high V_F bin (e.g., G5/G6) or over-drive an LED with a low V_F bin (e.g., G2). Always use a series resistor or constant-current driver to set the current to 20mA regardless of V_F variation.

Q3: Can I use this LED for outdoor applications?

A: The specified operating temperature range is -20°C to +80°C. While it may function in some outdoor environments, prolonged exposure to UV radiation, moisture, and temperature extremes beyond the rating is not recommended without additional protective measures (conformal coating, sealed enclosures). The datasheet specifies applications for ordinary electronic equipment; consult the manufacturer for high-reliability applications.

Q4: What is the difference between Peak Wavelength and Dominant Wavelength?

A: Peak Wavelength (λ_P) is the physical wavelength where the spectral power output is highest. Dominant Wavelength (λ_d) is a calculated value that represents the perceived color by the human eye on the CIE chart. λ_d is more relevant for color specification in visual applications.

10. Operational Principles and Technology Trends

10.1 Basic Operating Principle

This LED is a semiconductor photonic device. When a forward bias voltage exceeding its bandgap energy is applied, electrons and holes recombine in the active region of the InGaN chip. This recombination releases energy in the form of photons (light). The specific composition of the Indium Gallium Nitride (InGaN) semiconductor material determines the bandgap energy and thus the wavelength (color) of the emitted light, in this case, green.

10.2 Industry Trends

The use of InGaN technology for green LEDs represents a significant trend towards higher efficiency and brightness across the visible spectrum. Ongoing developments in materials science and chip design continue to push the boundaries of luminous efficacy (lumens per watt), allowing for brighter displays and more energy-efficient indicator lighting. Furthermore, advancements in packaging aim to improve thermal management, color uniformity, and reliability under harsh operating conditions. The move towards tighter binning tolerances and digital (addressable) LED interfaces are also notable trends in the industry.