SMD LED Green Dome Lens LTST-C930TGKT Datasheet - 2.8x3.2V - 76mW - English Technical Document

1. Product Overview

The LTST-C930TGKT is a high-brightness, surface-mount device (SMD) light-emitting diode (LED) utilizing an Indium Gallium Nitride (InGaN) semiconductor material to produce green light. It features a distinctive dome-shaped lens, which is designed to enhance light output and viewing angle characteristics compared to flat-lens alternatives. This component is engineered for compatibility with automated pick-and-place assembly systems and standard reflow soldering processes, making it suitable for high-volume manufacturing environments. Its primary applications include status indicators, backlighting for small displays, panel illumination, and various consumer electronics where reliable, consistent green illumination is required.

1.1 Core Advantages and Target Market

The key advantages of this LED stem from its material and package design. The InGaN chip technology provides efficient green emission, which is often more challenging to achieve with high brightness compared to red or blue LEDs. The dome lens acts as a primary optic, effectively increasing the light extraction from the semiconductor chip and providing a wider, more uniform viewing angle. The device is packaged on 8mm tape for 7-inch reels, adhering to EIA standards, ensuring seamless integration into automated production lines. The target market encompasses a broad range of electronic equipment manufacturers, particularly those in office automation, communication devices, and household appliances, where the LED serves as a reliable visual indicator component.

2. In-Depth Technical Parameter Analysis

This section provides a detailed breakdown of the electrical, optical, and thermal parameters specified for the LTST-C930TGKT, offering context for design engineers.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. They are not intended for normal operation.

• Power Dissipation (Pd): 76 mW. This is the maximum amount of power the LED package can dissipate as heat at an ambient temperature (Ta) of 25°C. Exceeding this limit risks overheating the semiconductor junction.
• DC Forward Current (IF): 20 mA. The recommended continuous operating current for reliable long-term performance.
• Peak Forward Current: 100 mA. This is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) and should not be used for DC operation.
• Derating Factor: 0.25 mA/°C above 50°C. This critical parameter indicates that the maximum allowable DC forward current must be reduced linearly by 0.25 mA for every degree Celsius the ambient temperature rises above 50°C. For example, at 70°C, the maximum DC current would be 20 mA - (0.25 mA/°C * 20°C) = 15 mA.
• Reverse Voltage (VR): 5 V. Applying a reverse bias voltage greater than this can cause breakdown and failure of the LED junction.
• Operating & Storage Temperature: -20°C to +80°C and -30°C to +100°C, respectively. These define the environmental limits for operation and non-operating storage.
• Soldering Conditions: Specific profiles are provided for wave (260°C for 5s), infrared reflow (260°C for 5s), and vapor phase reflow (215°C for 3 minutes). Adherence to these time-temperature limits is crucial to prevent package cracking or solder joint issues.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters measured at Ta=25°C and IF=20mA, unless stated otherwise.

• Luminous Intensity (Iv): Ranges from 710.0 mcd (minimum) to 2000.0 mcd (typical). This is the perceived brightness of the light source as measured by a sensor filtered to match the human eye's photopic response (CIE curve). The actual intensity for a specific unit depends on its bin code.
• Viewing Angle (2θ1/2): 25 degrees (typical). This is the full angle at which the luminous intensity drops to half of its value measured on-axis (0°). A 25-degree angle indicates a relatively focused beam pattern, characteristic of a dome lens designed for higher axial intensity.
• Peak Emission Wavelength (λP): 530 nm (typical). This is the wavelength at which the spectral power output is maximum. It is a physical property of the InGaN material.
• Dominant Wavelength (λd): 525 nm (typical at IF=20mA). This is derived from the CIE chromaticity diagram and represents the single wavelength that best describes the perceived color of the light. It is the key parameter for color specification.
• Spectral Line Half-Width (Δλ): 35 nm (typical). This measures the bandwidth of the emitted spectrum at half its maximum power. A value of 35nm is common for green InGaN LEDs and indicates a moderately pure green color.
• Forward Voltage (VF): 2.80V (Min), 3.20V (Typ), 3.60V (Max) at 20mA. This is the voltage drop across the LED when operating. Its variation is managed through the voltage binning system.
• Reverse Current (IR): 10 μA (Max) at VR=5V. A small leakage current under reverse bias.
• Capacitance (C): 40 pF (Typ) at VF=0V, f=1MHz. This junction capacitance can be relevant in high-frequency switching applications.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. The LTST-C930TGKT uses a three-dimensional binning system.

3.1 Forward Voltage Binning

Units are sorted based on their forward voltage (VF) at 20mA. The bin codes (D7, D8, D9, D10) correspond to specific voltage ranges with a tolerance of ±0.1V per bin. For example, a D8 bin LED will have a VF between 3.00V and 3.20V. This allows designers to select LEDs with matched voltage drops for circuits where current regulation is critical, especially when multiple LEDs are connected in parallel.

3.2 Luminous Intensity Binning

This is arguably the most critical bin for brightness consistency. The bins (V, W, X, Y) define minimum and maximum luminous intensity values, each with a ±15% tolerance. For instance, a 'W' bin LED has an intensity between 1120.0 mcd and 1800.0 mcd. Selecting LEDs from the same intensity bin is essential for applications requiring uniform brightness across multiple indicators.

3.3 Dominant Wavelength Binning

This binning ensures color consistency. The bins (AP, AQ, AR) define ranges for the dominant wavelength (λd) with a tight tolerance of ±1 nm. An 'AQ' bin LED, for example, will have a λd between 525.0 nm and 530.0 nm. Using LEDs from the same wavelength bin guarantees a consistent shade of green across a product.

4. Performance Curve Analysis

While specific graphs are referenced in the datasheet (Fig.1, Fig.6), their implications are standard. The Relative Luminous Intensity vs. Forward Current curve would show a near-linear relationship at lower currents, tending to sub-linear at higher currents due to efficiency droop and heating. The Forward Voltage vs. Forward Current curve exhibits an exponential turn-on characteristic, stabilizing in the operating region. The Relative Luminous Intensity vs. Ambient Temperature curve is crucial; it typically shows a negative temperature coefficient, meaning light output decreases as junction temperature increases. This reinforces the importance of thermal management and current derating. The Spectral Distribution curve (referenced by λP and Δλ) would show a Gaussian-like shape centered around 530nm.

5. Mechanical & Packaging Information

The device conforms to a standard SMD LED footprint. The datasheet includes detailed package dimension drawings (all in mm) with a general tolerance of ±0.10mm. Key mechanical features include the dome lens geometry and the cathode identification mark. The suggested soldering pad layout is provided to ensure a reliable solder fillet and proper alignment during reflow. The polarity is clearly marked on the device, typically with a notch or a green dot on the cathode side, which must be observed during assembly to prevent reverse connection.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profiles

The datasheet provides two suggested infrared (IR) reflow profiles: one for standard SnPb solder processes and one for Pb-free (e.g., SnAgCu) processes. Both profiles emphasize controlled ramp-up, a sufficient preheat/soak zone to activate flux and equalize board temperature, a defined time above liquidus (TAL), a peak temperature not exceeding 260°C, and a controlled ramp-down. Following these profiles prevents thermal shock to the epoxy package and the semiconductor die.

6.2 Storage and Handling

LEDs are moisture-sensitive devices. If removed from their original moisture-barrier packaging, they should be reflow-soldered within one week. For longer storage outside the original bag, they must be stored in a dry environment (e.g., a sealed container with desiccant or a nitrogen desiccator). If exposed to ambient humidity for more than a week, a bake-out at approximately 60°C for 24 hours is recommended before soldering to drive out absorbed moisture and prevent \"popcorning\" during reflow.

6.3 Cleaning

Only specified cleaning agents should be used. Isopropyl alcohol (IPA) or ethyl alcohol are recommended. The LED should be immersed at normal temperature for less than one minute. Harsh or unspecified chemicals can damage the epoxy lens material, causing clouding or cracking.

7. Packaging and Ordering Information

The standard packaging is 1500 pieces per 7-inch diameter reel, with components on 8mm wide embossed carrier tape. The tape has a cover tape to seal empty pockets. Minimum order quantities for remainder reels are 500 pieces. The packaging conforms to ANSI/EIA-481-1-A standards. The part number LTST-C930TGKT itself follows a likely internal coding scheme where 'LTST' may denote the product family, 'C930' the specific series/package, 'TG' indicating the color (Green) and lens type, and 'KT' possibly denoting the binning or other variant.

8. Application Design Recommendations

8.1 Drive Circuit Design

Critical Consideration: LEDs are current-driven devices, not voltage-driven. The most reliable method to operate an LED is with a constant current source. In a simple voltage-driven circuit, a series current-limiting resistor is absolutely mandatory. The datasheet strongly recommends using a separate resistor for each LED when multiple units are connected in parallel (Circuit Model A). Using a single resistor for multiple parallel LEDs (Circuit Model B) is discouraged because small variations in the forward voltage (VF) characteristic between individual LEDs will cause significant imbalance in current sharing, leading to uneven brightness and potential overstress of the LED with the lowest VF.

8.2 Electrostatic Discharge (ESD) Protection

The LED is susceptible to damage from electrostatic discharge. Proper ESD controls must be implemented in the handling and assembly environment: use grounded wrist straps and work surfaces, employ ionizers to neutralize static charges that can build up on the plastic lens, and ensure all equipment is properly grounded.

8.3 Thermal Management

Although power dissipation is low (76mW max), effective heat sinking through the PCB pads is important to maintain LED performance and longevity. The derating curve (0.25 mA/°C above 50°C) must be applied in designs where the ambient temperature around the LED is expected to be high. Ensuring adequate copper area around the solder pads on the PCB helps dissipate heat.

9. Technical Comparison & Differentiation

The primary differentiation of the LTST-C930TGKT lies in its combination of a dome lens and InGaN technology for green light. Compared to flat-lens LEDs, the dome provides higher axial luminous intensity and a more controlled viewing angle. Compared to older technologies like Gallium Phosphide (GaP) for green, InGaN offers significantly higher brightness and efficiency. Its compatibility with lead-free (Pb-free) reflow processes makes it suitable for modern, RoHS-compliant electronics manufacturing.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED directly from a 5V supply?
A: No. You must use a series current-limiting resistor. With a typical VF of 3.2V at 20mA, using Ohm's Law (R = (Vsupply - Vf) / If), the resistor value would be (5V - 3.2V) / 0.02A = 90 Ohms. A standard 91 or 100 Ohm resistor would be appropriate, and its power rating should be at least I^2 * R = (0.02^2)*90 = 0.036W, so a 1/10W or 1/8W resistor is sufficient.

Q: Why is the luminous intensity given as a range (710-2000mcd)?
A: This is the overall specification spread. Actual production units are sorted into tighter bins (V, W, X, Y). For consistent brightness in your design, specify the required intensity bin when ordering.

Q: What happens if I exceed the absolute maximum DC forward current of 20mA?
A: Operating above 20mA continuously will increase the junction temperature beyond safe limits, accelerating lumen depreciation (the LED dims over time) and potentially causing catastrophic failure. Always design the drive circuit to limit current to the rated value or lower, especially at elevated ambient temperatures.

11. Design and Usage Case Study

Scenario: Designing a status indicator panel with 10 uniformly bright green LEDs.
1. Circuit Design: Use a regulated voltage source (e.g., 5V). Place ten individual current-limiting resistors, one in series with each LED. Do not share one resistor among multiple LEDs.
2. Component Selection: Order all LEDs from the same Luminous Intensity bin (e.g., all 'W' bin) and the same Dominant Wavelength bin (e.g., all 'AQ' bin) to guarantee uniform brightness and color. The Forward Voltage bin is less critical here as each LED has its own resistor.
3. PCB Layout: Follow the suggested soldering pad dimensions from the datasheet. Include a small thermal relief connection to the cathode/anode pads if they are connected to large copper pours, to aid soldering.
4. Assembly: Follow the recommended Pb-free IR reflow profile. Ensure the assembly area has ESD controls.
5. Result: A reliable, professional-looking indicator panel with consistent color and brightness across all 10 LEDs.

12. Operating Principle Introduction

An LED is a semiconductor p-n junction diode. When a forward voltage is applied, electrons from the n-type region and holes from the p-type region are injected into the junction region. When these charge carriers recombine, they release energy. In a standard silicon diode, this energy is released primarily as heat. In a direct bandgap semiconductor like InGaN, a significant portion of this recombination energy is released as photons (light). The specific wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material. Indium Gallium Nitride (InGaN) alloys allow engineers to tune this bandgap to produce light in the blue, green, and ultraviolet parts of the spectrum. The dome-shaped epoxy lens surrounding the chip serves to protect it and to shape the light output, improving extraction efficiency and defining the viewing angle.

13. Technology Trends

The field of LED technology, particularly for green emission, continues to evolve. Key trends include:
- Increased Efficiency (Lumens per Watt): Ongoing material science research aims to reduce \"efficiency droop\" in InGaN LEDs, especially for green wavelengths, which historically have been less efficient than blue or red.
- Color Consistency and Binning: Advances in epitaxial growth and manufacturing control are leading to tighter intrinsic parameter distributions, reducing the spread within bins and the need for extensive sorting.
- Miniaturization: The drive for smaller, denser electronics continues to push for LEDs in even smaller package footprints while maintaining or improving light output.
- Reliability and Lifetime: Improvements in package materials, die attach methods, and phosphor technology (for white LEDs) are extending operational lifetimes and performance under harsh environmental conditions.