LTST-S270TGKT SMD LED Datasheet - Side Looking - Green 530nm - 3.2V - 76mW - English Technical Document

1. Product Overview

The LTST-S270TGKT is a high-brightness, side-looking Surface Mount Device (SMD) LED designed for modern electronic applications requiring compact and efficient illumination. This component utilizes an advanced Indium Gallium Nitride (InGaN) semiconductor chip, which is renowned for its high luminous efficiency and stability. The primary function of this LED is to provide a reliable and bright green light source in a package that is optimized for automated assembly processes. Its side-emitting design is particularly advantageous for applications where light needs to be directed laterally rather than perpendicular to the mounting surface, such as in edge-lit panels, status indicators on slim devices, or backlighting for membrane switches.

This LED is engineered to be a "green product," meaning it complies with RoHS (Restriction of Hazardous Substances) directives, ensuring it is free from substances like lead, mercury, and cadmium. This makes it suitable for use in consumer electronics, automotive interiors, industrial control panels, and other applications with stringent environmental and safety standards. The device is packaged on 8mm tape wound onto 7-inch reels, conforming to EIA (Electronic Industries Alliance) standards, which guarantees compatibility with high-speed pick-and-place machines used in volume manufacturing.

2. Technical Parameters Deep Objective Interpretation

2.1 Absolute Maximum Ratings

The Absolute Maximum Ratings define the stress limits beyond which permanent damage to the device may occur. For the LTST-S270TGKT, these are specified at an ambient temperature (Ta) of 25°C. The maximum continuous DC forward current is 20 mA. Exceeding this current can lead to excessive heat generation, degrading the semiconductor material and shortening the LED's lifespan. The device can handle a higher Peak Forward Current of 100 mA, but only under pulsed conditions with a strict 1/10 duty cycle and a pulse width of 0.1ms. This rating is crucial for applications involving brief, high-intensity flashes.

The Power Dissipation limit is 76 mW. This parameter, combined with the thermal resistance of the package and PCB, determines the maximum allowable operating current under different ambient conditions. The Operating Temperature Range is from -20°C to +80°C, and the Storage Temperature Range is from -30°C to +100°C. These ranges ensure the LED's mechanical and chemical integrity during both active use and inactive periods. A key specification for assembly is the Infrared Soldering Condition, which allows exposure to a peak temperature of 260°C for a maximum of 10 seconds, making it suitable for lead-free (Pb-free) reflow soldering processes.

2.2 Electro-Optical Characteristics

The Electro-Optical Characteristics are measured at Ta=25°C and an operating current (IF) of 20 mA, which is the standard test condition. The Luminous Intensity (Iv) has a wide range from a minimum of 71.0 mcd to a maximum of 450.0 mcd, with a typical value provided for reference. This variation is managed through a binning system (detailed later). The intensity is measured using a sensor filtered to match the CIE photopic eye-response curve, ensuring the value correlates with human brightness perception.

The Viewing Angle (2θ1/2) is 130 degrees. This is the full angle at which the luminous intensity drops to half of its value at the central axis (0 degrees). A wide viewing angle like this is characteristic of side-looking LEDs and provides broad, diffuse illumination. The Peak Emission Wavelength (λP) is 530 nm, and the Dominant Wavelength (λd) is 525 nm. The peak wavelength is the point of maximum radiant power in the emitted spectrum, while the dominant wavelength is the single wavelength perceived by the human eye that defines the color. The small difference indicates a relatively pure green color. The Spectral Line Half-Width (Δλ) is 35 nm, describing the spectral purity or bandwidth of the emitted light.

Electrically, the Forward Voltage (VF) ranges from 2.80V to 3.60V, with a typical value of 3.20V at 20mA. This is a critical parameter for circuit design, as it determines the voltage drop across the LED and the necessary current-limiting resistor value. The Reverse Current (IR) is specified as a maximum of 10 μA when a Reverse Voltage (VR) of 5V is applied. It is explicitly noted that the device is not designed for reverse operation; this test is for leakage characterization only.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into bins based on key parameters. The LTST-S270TGKT uses a three-dimensional binning system.

3.1 Forward Voltage Binning

Forward Voltage bins are labeled D7 through D10, each covering a 0.2V range from 2.80V to 3.60V. The tolerance within each bin is +/-0.1V. Designers can select a specific bin to achieve tighter control over the voltage drop in their circuit, which is important for power management and ensuring consistent brightness when multiple LEDs are connected in series.

3.2 Luminous Intensity Binning

Luminous Intensity bins are labeled Q, R, S, and T. Bin Q covers 71.0-112.0 mcd, and Bin T covers the highest range of 280.0-450.0 mcd. The tolerance on each intensity bin is +/-15%. This allows designers to choose LEDs suitable for their application's brightness requirements, from low-power indicators to brighter status lights.

3.3 Dominant Wavelength Binning

Dominant Wavelength bins are labeled AP (520.0-525.0 nm), AQ (525.0-530.0 nm), and AR (530.0-535.0 nm). The tolerance for each bin is a tight +/- 1nm. This precise color sorting is essential for applications where color consistency is critical, such as in multi-LED displays or color-matching applications.

4. Performance Curve Analysis

While the PDF references typical electrical/optical characteristic curves, the specific graphs for IV (Current vs. Voltage), relative luminous intensity vs. temperature, and spectral distribution are not provided in the extracted text. Typically, such curves would show the following:

The IV curve would demonstrate the exponential relationship between forward voltage and current, highlighting the turn-on voltage and dynamic resistance. The relative luminous intensity vs. ambient temperature curve would show a negative correlation; as temperature increases, the luminous output generally decreases. This is a fundamental characteristic of semiconductor light sources and must be accounted for in thermal management. The spectral distribution graph would plot radiant power against wavelength, showing a peak at or near 530 nm with the defined 35 nm half-width, confirming the green color emission.

5. Mechanical and Packaging Information

The LED is housed in a standard SMD package. The exact dimensions (length, width, height) are detailed in the package dimensions drawing referenced in the datasheet. Key features of this side-looking package include a molded lens that directs light output from the side of the component. The datasheet includes suggested soldering pad dimensions and a recommended soldering direction to ensure optimal solder joint formation and mechanical stability during the reflow process. Polarity is indicated by the package marking or cathode/anode identification, which is crucial for correct orientation during assembly to prevent reverse bias.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Profile

A suggested Infrared (IR) Reflow Profile for Pb-free processes is provided. This profile typically includes several zones: preheat, soak, reflow, and cooling. The critical parameters are a peak temperature not exceeding 260°C and a time above liquidus (e.g., 217°C) of around 60-90 seconds, with the time at peak temperature limited to a maximum of 10 seconds. Adhering to this profile is essential to prevent thermal shock, delamination, or damage to the LED's epoxy lens and internal wire bonds.

6.2 Storage and Handling

LEDs are moisture-sensitive devices. If the original sealed moisture-proof bag with desiccant is unopened, they should be stored at ≤30°C and ≤90% Relative Humidity (RH) and used within one year. Once the bag is opened, the storage environment should not exceed 30°C and 60% RH. Components exposed to ambient humidity for more than one week should be baked at approximately 60°C for at least 20 hours before soldering to drive out absorbed moisture and prevent "popcorning" during reflow.

6.3 Cleaning

If cleaning is necessary after soldering, only specified solvents should be used. The datasheet recommends immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Harsh or unspecified chemicals can damage the plastic package, leading to discoloration, cracking, or reduced light output.

6.4 Electrostatic Discharge (ESD) Precautions

The LED is sensitive to electrostatic discharge. It is recommended to use a wrist strap or anti-static gloves when handling. All equipment, including soldering irons and placement machines, must be properly grounded to prevent ESD events that can degrade or destroy the semiconductor junction.

7. Packaging and Ordering Information

The standard packaging is 8mm embossed carrier tape on 7-inch (178mm) diameter reels. Each reel contains 4000 pieces. For quantities less than a full reel, a minimum packing quantity of 500 pieces is available for remainders. The tape and reel specifications comply with ANSI/EIA-481 standards, ensuring compatibility with automated feeders. The tape has a cover seal to protect components, and the maximum allowable number of consecutive missing components (empty pockets) in the tape is two.

8. Application Suggestions

8.1 Typical Application Scenarios

This side-looking green LED is ideal for a variety of applications: Status indicators on consumer electronics (routers, printers, chargers), backlighting for slim buttons and keypads, edge-lighting for decorative panels or signage, and as a source in opto-isolators or optical sensors where side emission is beneficial. Its RoHS compliance makes it suitable for global markets.

8.2 Design Considerations

Circuit Design: A current-limiting resistor is mandatory. Its value can be calculated using Ohm's Law: R = (Vsupply - VF) / IF. Use the maximum VF from the datasheet (3.60V) for a worst-case design to ensure the current does not exceed 20mA. For example, with a 5V supply: R = (5V - 3.6V) / 0.02A = 70 Ohms. A standard 68 or 75 Ohm resistor would be appropriate.

Thermal Management: Although power dissipation is low, proper PCB layout is important. Ensure adequate copper area around the LED pads to act as a heat sink, especially if operating at high ambient temperatures or near the maximum current.

Optical Design: Consider the 130-degree viewing angle. For applications requiring a more focused beam, external lenses or light guides may be necessary. The side-looking nature means the primary light output is parallel to the PCB plane.

9. Technical Comparison and Differentiation

Compared to standard top-emitting LEDs, the primary differentiation of the LTST-S270TGKT is its side-emitting optical design, which solves space constraints in ultra-thin devices. Compared to other side-emitting LEDs, its advantages include the use of a high-efficiency InGaN chip for brighter output, a well-defined binning system for color and intensity consistency, and explicit compatibility with aggressive Pb-free IR reflow profiles (260°C peak), which is a requirement for modern electronics assembly.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED with a 3.3V supply without a resistor?

A: No. Even if the supply voltage is close to the typical forward voltage (3.2V), the actual VF can vary from 2.8V to 3.6V. Without a current-limiting resistor, the current could become uncontrolled and exceed the maximum rating, damaging the LED. Always use a series resistor.

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

A: Peak Wavelength is the physical point of highest energy output in the spectrum. Dominant Wavelength is a calculated value based on human color perception (CIE chart) that best represents the perceived color. They are often close but not identical.

Q: The LED is rated for 20mA continuous current. Can I run it at 15mA to make it last longer?

A: Yes, operating below the maximum rated current is a common practice to enhance long-term reliability and reduce thermal stress. The luminous intensity will be proportionally lower, as specified by the LED's performance curves.

Q: How do I interpret the bin codes when ordering?

A> You would specify the full part number LTST-S270TGKT followed by additional codes for Voltage (e.g., D8), Intensity (e.g., S), and Wavelength (e.g., AQ) bins if you require specific performance tiers. Consult the manufacturer's ordering guide for the exact format.

11. Practical Use Case

Scenario: Designing a status indicator for a portable medical device.

The device requires a green "power on/ready" indicator. Space is extremely limited on the vertical edge of the main PCB. A side-looking LED like the LTST-S270TGKT is chosen because it can be mounted on the main board, and its light is emitted horizontally into a thin light guide that channels it to a small window on the device casing. The designer selects bins D8 for voltage (3.0-3.2V) and S for intensity (180-280 mcd) to ensure adequate brightness with good power efficiency. The dominant wavelength bin AQ (525-530 nm) is specified to guarantee a consistent, recognizable green color. The design includes a 100-ohm current-limiting resistor to drive the LED at approximately 18mA from a 5V regulated supply, providing a safety margin below the 20mA maximum. The PCB layout includes thermal relief pads and follows the suggested soldering pad layout to ensure reliable assembly during the lead-free reflow process.

12. Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light when an electric current passes through them. This phenomenon is called electroluminescence. In the LTST-S270TGKT, the active region is made of Indium Gallium Nitride (InGaN). When a forward voltage is applied, electrons from the n-type semiconductor and holes from the p-type semiconductor are injected into the active region. There, they recombine, releasing energy in the form of photons (light). The specific wavelength (color) of the light is determined by the bandgap energy of the InGaN material, which is engineered to be around 2.34 eV, corresponding to green light (~530 nm). The side-looking package incorporates a molded epoxy lens that is shaped to extract and direct the generated light from the side of the chip, maximizing useful optical output for its intended applications.

13. Development Trends

The trend in SMD LEDs like this one is towards ever-higher luminous efficacy (more light output per watt of electrical input), driven by improvements in chip design, epitaxial growth, and package efficiency. There is also a strong focus on improved color consistency and tighter binning tolerances to meet the demands of display and lighting applications. Miniaturization continues, but alongside it, there is development in packages that offer better thermal management to sustain performance at higher drive currents. Furthermore, compatibility with increasingly demanding assembly processes, such as higher-temperature reflow profiles for lead-free solders and double-sided reflow, remains a key design criterion. The integration of LEDs with onboard control circuitry (like constant current drivers) into more complex modules is another growing trend.