SMD LED LTST-C21TGKT Datasheet - 3.2x1.6x1.1mm - 2.8-3.8V - 76mW - Green Water Clear Lens - English Technical Document

1. Product Overview

This document provides the complete technical specifications for the LTST-C21TGKT, a surface-mount device (SMD) LED lamp. This component belongs to a family of miniature LEDs designed specifically for automated printed circuit board (PCB) assembly and applications where space is a critical constraint. The compact form factor and standardized packaging make it highly suitable for integration into modern electronic manufacturing processes.

The core application areas for this LED are broad, encompassing telecommunications equipment, office automation devices, various home appliances, and industrial control systems. Its primary functions include serving as a status indicator, providing backlighting for keypads and keyboards, enabling micro-displays, and acting as a signal or symbol luminary in indoor signage.

1.1 Key Features

• RoHS Compliance: The device is manufactured to meet the Restriction of Hazardous Substances directive, ensuring it is free from specific hazardous materials like lead, mercury, and cadmium.
• Reverse Mount Design: Features a unique chip-on-board structure where the LED chip is mounted in a reversed orientation, which can offer benefits in specific optical designs and assembly scenarios.
• Ultra-Bright InGaN Chip: Utilizes an Indium Gallium Nitride (InGaN) semiconductor material to produce a high-intensity green light output.
• Automated Assembly Compatible: Supplied in standard 8mm tape on 7-inch diameter reels, conforming to EIA standards, making it fully compatible with high-speed automatic pick-and-place equipment.
• Reflow Solderable: The package is designed to withstand standard infrared (IR) reflow soldering processes used in surface-mount technology (SMT) assembly lines.
• IC Compatible: The electrical characteristics are suitable for direct interfacing with standard integrated circuit outputs.

2. Package Dimensions and Configuration

The LTST-C21TGKT is housed in a compact, industry-standard SMD package. The lens appears water clear, while the light source itself is an InGaN-based green emitter. The typical package outline dimensions are approximately 3.2mm in length, 1.6mm in width, and 1.1mm in height, though designers must always refer to the detailed dimensional drawing for critical mechanical design. All specified dimensions are in millimeters, with a standard tolerance of ±0.1mm unless otherwise noted on the drawing.

3. Ratings and Characteristics

Understanding the absolute maximum ratings is crucial for ensuring reliable operation and preventing premature device failure. These ratings specify the limits beyond which permanent damage may occur.

3.1 Absolute Maximum Ratings (Ta=25°C)

• Power Dissipation (Pd): 76 mW. This is the maximum amount of power the device 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): 20 mA. This is the recommended maximum DC current for continuous operation.
• Operating Temperature Range (T_opr): -20°C to +80°C. The ambient temperature range over which the device is designed to function.
• Storage Temperature Range (T_stg): -30°C to +100°C. The temperature range for non-operational storage.
• Infrared Reflow Soldering Condition: Withstand 260°C peak temperature for a maximum of 10 seconds. This defines the thermal profile tolerance during PCB assembly.

3.2 Electrical and Optical Characteristics (Ta=25°C)

These parameters define the typical performance of the LED under standard test conditions.

• Luminous Intensity (I_V): Ranges from a minimum of 180.0 mcd to a maximum of 1120.0 mcd at a forward current (I_F) of 20 mA. The actual value is binned (see Section 4). Intensity is measured using a sensor filtered to match the CIE photopic eye-response curve.
• Viewing Angle (2θ_1/2): 70 degrees. This is the full angle at which the luminous intensity drops to half of its peak (on-axis) value, defining the beam spread.
• Peak Emission Wavelength (λ_P): Typically 530 nm. The wavelength at which the spectral power output is highest.
• Dominant Wavelength (λ_d): Typically 525 nm at I_F=20mA. This is the single wavelength perceived by the human eye that best represents the color of the light, derived from the CIE chromaticity diagram.
• Spectral Line Half-Width (Δλ): Approximately 35 nm. The bandwidth of the emitted spectrum measured at half the peak intensity.
• Forward Voltage (V_F): Between 2.8 V and 3.8 V at I_F=20mA. The voltage drop across the LED when conducting current.
• Reverse Current (I_R): Maximum 10 μA at a reverse voltage (V_R) of 5V. LEDs are not designed for reverse bias operation; this parameter is for test purposes only.

3.3 Important Notes on Characteristics

• Electrostatic Discharge (ESD) Sensitivity: LEDs are susceptible to damage from static electricity and voltage surges. Proper ESD controls, such as using grounded wrist straps, anti-static gloves, and ensuring all equipment is grounded, are mandatory during handling.
• Reverse Voltage Operation: The device is not designed to be operated with a reverse bias. The reverse current parameter is for informational and test purposes only.

4. Bin Ranking System

To ensure consistency in applications, LEDs are sorted (binned) based on key performance parameters. The LTST-C21TGKT uses a two-dimensional binning system.

4.1 Luminous Intensity (I_V) Bins

Green color, measured in millicandelas (mcd) at 20mA. Tolerance within each bin is ±15%.

• Bin Code S: 180.0 – 280.0 mcd
• Bin Code T: 280.0 – 450.0 mcd
• Bin Code U: 450.0 – 710.0 mcd
• Bin Code V: 710.0 – 1120.0 mcd

4.2 Hue (Dominant Wavelength) Bins

Green color, measured in nanometers (nm) at 20mA. Tolerance for each bin is ±1 nm.

• Bin Code AP: 520.0 – 525.0 nm
• Bin Code AQ: 525.0 – 530.0 nm
• Bin Code AR: 530.0 – 535.0 nm

A full part number typically includes these bin codes to specify the exact performance grade.

5. Typical Performance Curves

Graphical data provides deeper insight into device behavior under varying conditions. While specific curve plots are not rendered here, the datasheet typically includes the following essential graphs for design analysis:

• Relative Luminous Intensity vs. Forward Current (I_V / I_F): Shows how light output increases with current, often becoming sub-linear at higher currents due to heating and efficiency droop.
• Forward Voltage vs. Forward Current (V_F / I_F): Illustrates the diode's I-V characteristic, crucial for designing the current-limiting circuitry.
• Relative Luminous Intensity vs. Ambient Temperature (I_V / T_a): Demonstrates the thermal dependence of light output, which generally decreases as junction temperature rises.
• Spectral Power Distribution: A plot of relative intensity versus wavelength, showing the peak at ~530nm and the ~35nm spectral width.
• Viewing Angle Pattern: A polar plot depicting the spatial distribution of light intensity, confirming the 70-degree viewing angle.

6. Assembly and Handling Guidelines

6.1 Recommended PCB Attachment Pad Layout

A suggested land pattern (footprint) for the PCB is provided to ensure proper solder joint formation, mechanical stability, and thermal management. This pattern typically includes pad dimensions and spacing slightly larger than the device terminals to facilitate good solder wetting and fillet formation.

6.2 Soldering Process

The device is qualified for lead-free (Pb-free) soldering processes. A suggested IR reflow profile is provided, adhering to JEDEC standards. Key parameters include:

• Pre-heat: 150°C – 200°C.
• Pre-heat Time: Maximum 120 seconds to allow for uniform heating and paste activation.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus (at peak): Maximum 10 seconds. The device should not be subjected to more than two reflow cycles.

For manual rework with a soldering iron, the tip temperature should not exceed 300°C, and contact time should be limited to 3 seconds maximum for a single repair event only. It is critical to follow the solder paste manufacturer's guidelines and characterize the profile for the specific PCB design.

6.3 Cleaning

If post-solder cleaning is required, only specified alcohol-based solvents like ethyl alcohol or isopropyl alcohol should be used. The LED should be immersed at normal temperature for less than one minute. Unspecified chemical cleaners may damage the epoxy lens or package.

6.4 Storage and Moisture Sensitivity

The LEDs are packaged in a moisture-barrier bag with desiccant. While sealed, they should be stored at ≤ 30°C and ≤ 90% Relative Humidity (RH) and used within one year. Once the original bag is opened, the components are rated at Moisture Sensitivity Level (MSL) 3. This means they must be subjected to IR reflow soldering within one week of exposure to factory ambient conditions (≤ 30°C / 60% RH). For storage beyond one week outside the original bag, they must be stored in a sealed container with desiccant or in a nitrogen ambient. Components exposed for more than one week require a bake-out at approximately 60°C for at least 20 hours before assembly to remove absorbed moisture and prevent \"popcorning\" damage during reflow.

7. Packaging Specifications

The product is supplied in a tape-and-reel format compatible with automated assembly equipment.

• Tape Width: 8 mm.
• Reel Diameter: 7 inches (178 mm).
• Quantity per Reel: 3000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Pocket Sealing: Empty pockets in the tape are covered with a top cover tape.
• Missing Components: A maximum of two consecutive missing LEDs is allowed per the packaging standard.
• Standard: Packaging conforms to ANSI/EIA-481 specifications.

8. Application Notes and Design Considerations

8.1 Drive Method

An LED is a current-controlled device. To ensure consistent and stable luminous intensity, color, and longevity, it must be driven by a constant current source, not a constant voltage source. The forward voltage (V_F) has a tolerance and a negative temperature coefficient (it decreases as temperature increases). Using a simple series resistor with a voltage supply is common for basic indicators, but for applications requiring stable brightness, a dedicated LED driver IC or a more sophisticated current-regulating circuit is recommended. The design must respect the absolute maximum ratings for continuous (20mA) and pulsed (100mA) current.

8.2 Thermal Management

Although the power dissipation is relatively low at 76mW, effective thermal management is still important for maintaining performance and reliability, especially in high ambient temperatures or when driven near maximum ratings. The PCB copper pads act as the primary heat sink. Following the recommended pad layout, using thermal vias under the pad (if applicable to the package), and ensuring adequate airflow contribute to keeping the LED junction temperature within safe limits, thereby preserving luminous output and operational life.

8.3 Optical Integration

The 70-degree viewing angle provides a wide, diffuse emission pattern suitable for area illumination and status indicators. For applications requiring a more focused beam, secondary optics such as lenses or light guides may be necessary. The water-clear lens allows the true chip color (green) to be emitted without tinting.

8.4 Polarity and Orientation

As a diode, the LED has an anode (+) and cathode (-). The package includes a polarity indicator, typically a notch, a green dot, or a cut corner on the cathode side. Correct orientation on the PCB is essential for the device to illuminate. The reverse mount design may have specific implications for how light is extracted from the package, which should be considered in the optical design.

9. Reliability and Application Scope

The LEDs described are intended for use in standard commercial and industrial electronic equipment, including office automation, communications, network systems, and home appliances. For applications requiring exceptional reliability where failure could jeopardize safety, health, or life—such as in aviation, transportation, medical, or critical safety systems—special qualification and consultation are necessary prior to design-in. The provided cautions on storage, handling, and soldering are fundamental to achieving the expected reliability in the intended applications.