SMD LED LTST-T180TGKT Datasheet - 120 Degree Viewing Angle - Water Clear Lens - Green InGaN - 20mA - 3.2V Typ - English Technical Document

1. Product Overview

The LTST-T180TGKT is a surface-mount device (SMD) light-emitting diode (LED) designed for automated printed circuit board (PCB) assembly. Its miniature size makes it suitable for space-constrained applications across a wide range of consumer and industrial electronics.

1.1 Core Advantages and Target Market

This LED offers several key advantages for modern electronics manufacturing. It is fully compliant with RoHS (Restriction of Hazardous Substances) directives, ensuring environmental safety. The component is supplied in industry-standard 8mm tape on 7-inch reels, making it compatible with high-speed automated pick-and-place equipment. Its design is compatible with infrared (IR) reflow soldering processes, which is the standard for high-volume PCB assembly. The device is also I.C. (Integrated Circuit) compatible, simplifying drive circuit design. Primary target markets include telecommunications equipment (cordless and cellular phones), office automation devices (notebook computers, network systems), home appliances, and indoor signage applications where reliable status indication or symbol illumination is required.

2. In-Depth Technical Parameter Analysis

This section provides a detailed breakdown of the electrical, optical, and thermal characteristics that define the performance boundaries and operating conditions of the LED.

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed. The maximum power dissipation is 76 mW. The peak forward current, when driven with a 1/10 duty cycle and a 0.1ms pulse width, must not exceed 80 mA. The continuous DC forward current rating is 20 mA. The device can be operated and stored within a temperature range of -40°C to +100°C.

2.2 Thermal Characteristics

Thermal management is crucial for LED longevity and performance stability. The maximum allowable junction temperature (Tj) is 115°C. The typical thermal resistance from the junction to the ambient environment (Rθja) is 175°C/W. This parameter indicates how effectively heat can be dissipated from the semiconductor junction to the surrounding air; a lower value is better. Proper PCB layout with adequate thermal relief is essential to maintain the junction temperature within safe limits, especially when operating at the maximum forward current.

2.3 Electrical and Optical Characteristics

These are the typical performance parameters measured at an ambient temperature (Ta) of 25°C. The luminous intensity (Iv) ranges from a minimum of 710 mcd to a maximum of 1540 mcd at a forward current (IF) of 20 mA. The viewing angle (2θ1/2), defined as the full angle at which intensity drops to half its axial value, is 120 degrees, providing a very wide field of illumination. The peak emission wavelength (λP) is 523 nm, placing it in the green region of the visible spectrum. The dominant wavelength (λd), which defines the perceived color, ranges from 515 nm to 530 nm at 20mA. The spectral line half-width (Δλ) is typically 25 nm. The forward voltage (VF) at 20mA ranges from 2.8V to 3.8V. The reverse current (IR) is a maximum of 10 μA when a reverse voltage (VR) of 5V is applied; it is critical to note that the device is not designed for reverse operation and this test condition is for informational purposes only.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. This allows designers to select components that meet specific voltage, brightness, and color requirements for their application.

3.1 Forward Voltage (VF) Binning

LEDs are categorized into bins based on their forward voltage drop at 20mA. The bin codes are D7 (2.8V-3.0V), D8 (3.0V-3.2V), D9 (3.2V-3.4V), D10 (3.4V-3.6V), and D11 (3.6V-3.8V). The tolerance within each bin is ±0.1V. Selecting LEDs from a tighter voltage bin can help ensure uniform brightness when multiple LEDs are connected in parallel.

3.2 Luminous Intensity (IV) Binning

Brightness is sorted into three bins: V1 (710-910 mcd), V2 (910-1185 mcd), and W1 (1185-1540 mcd). The tolerance on each intensity bin is ±11%. This binning is crucial for applications requiring consistent visual output across multiple indicators.

3.3 Dominant Wavelength (Wd) Binning

The color (dominant wavelength) is binned as follows: AP (515-520 nm), AQ (520-525 nm), and AR (525-530 nm). The tolerance for each bin is ±1 nm. This ensures a consistent shade of green across all units in a production run, which is important for aesthetic and signaling purposes.

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet, the typical curves for this type of LED would illustrate key relationships. The forward current vs. forward voltage (I-V) curve shows the exponential relationship characteristic of a diode. The relative luminous intensity vs. forward current curve typically shows a near-linear increase in brightness with current up to a point, after which efficiency may drop. The relative luminous intensity vs. ambient temperature curve is critical, as LED output generally decreases with increasing junction temperature. The spectral distribution curve would show a peak at or near 523 nm with a characteristic shape defined by the 25 nm half-width. Understanding these curves is essential for designing robust drive circuits and thermal management systems to achieve consistent performance over the product's lifetime and across the specified operating temperature range.

5. Mechanical and Packaging Information

5.1 Package Dimensions and Polarity

The LED comes in a standard SMD package. The lens color is water clear, and the light source is an InGaN (Indium Gallium Nitride) chip producing green light. All dimensions are provided in millimeters with a standard tolerance of ±0.2 mm unless otherwise noted. The cathode is typically identified by a visual marker on the package, such as a notch or a green dot, which must be aligned with the corresponding marking on the PCB footprint.

5.2 Recommended PCB Attachment Pad

A land pattern diagram is provided for infrared or vapor phase reflow soldering. Adhering to this recommended footprint is vital for achieving proper solder joint formation, ensuring good electrical connection, and providing adequate mechanical strength. The pad design also influences the thermal path for heat dissipation from the LED junction to the PCB.

5.3 Tape and Reel Packaging

The components are supplied on 8mm wide embossed carrier tape wound onto 7-inch (178mm) diameter reels. Each reel contains 5000 pieces. For quantities less than a full reel, a minimum packing quantity of 500 pieces applies. The packaging conforms to ANSI/EIA-481 specifications. The tape pockets are sealed with a top cover tape to protect the components from moisture and contamination during storage and handling.

6. Soldering and Assembly Guidelines

6.1 Storage Conditions

Proper storage is critical to prevent moisture absorption, which can cause \"popcorning\" or cracking during reflow soldering. In the original sealed moisture-proof bag with desiccant, LEDs should be stored at ≤30°C and ≤70% Relative Humidity (RH) and used within one year. Once the bag is opened, the storage environment must not exceed 30°C and 60% RH. Components exposed to ambient conditions for more than 168 hours (7 days) should be baked at approximately 60°C for at least 48 hours before soldering to remove absorbed moisture.

6.2 Soldering Recommendations

The LED is compatible with lead-free (Pb-free) infrared reflow soldering processes. A suggested profile compliant with J-STD-020B is provided. Key parameters include a pre-heat zone of 150-200°C for a maximum of 120 seconds, and a peak package body temperature not exceeding 260°C for a maximum of 10 seconds. Reflow should be limited to a maximum of two 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 for a single operation only. It is emphasized that the optimal profile depends on the specific PCB design, solder paste, and oven, so process characterization is necessary.

6.3 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. Immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute is acceptable. The use of unspecified chemical cleaners can damage the LED package material.

7. Application Notes and Design Considerations

7.1 Drive Method

An LED is a current-operated device. Its brightness is primarily a function of forward current (IF), not voltage. Therefore, it should always be driven using a constant current source or a current-limiting resistor in series with a voltage source. Driving with a simple voltage source is not recommended as it can lead to thermal runaway and device failure. The series resistor value can be calculated using Ohm's Law: R = (V_supply - VF_LED) / IF, where VF_LED is the typical or maximum forward voltage from the datasheet to ensure the current does not exceed the maximum rating under worst-case conditions.

7.2 Thermal Management in Design

Given the thermal resistance of 175°C/W, effective heat sinking is necessary for reliable operation, especially at high ambient temperatures or maximum current. The PCB itself acts as the primary heat sink. Using a larger copper pad area connected to ground or power planes through thermal vias can significantly improve heat dissipation, lower the junction temperature, and thereby increase luminous output and operational lifespan.

7.3 Application Limitations

This LED is intended for use in ordinary electronic equipment. It is not designed or qualified for applications where exceptional reliability is required, particularly in safety-critical systems such as aviation, transportation, medical life-support, or safety devices where failure could jeopardize life or health. For such applications, consultation with the manufacturer for specifically qualified components is mandatory.

8. Typical Application Scenarios and Case Studies

Scenario 1: Front Panel Status Indicator: In a network router or industrial control panel, multiple LTST-T180TGKT LEDs can be used to indicate power status, network activity, or system faults. The 120-degree viewing angle ensures the indicator is visible from a wide range of perspectives. By selecting LEDs from the same intensity bin (e.g., V2), a uniform brightness can be achieved across all indicators.

Scenario 2: Backlighting for Membrane Switch Panels: The water clear lens and wide viewing angle make this LED suitable for edge-lighting thin acrylic or polycarbonate light guides used behind symbols on control panels for appliances or medical devices. The green color provides clear, low-glare illumination.

Scenario 3: Symbol Luminary in Low-Light Environments: The LED can be used to illuminate exit signs, control labels, or instrumentation in environments where ambient light is low. Its relatively high luminous intensity (up to 1540 mcd) ensures good visibility.

9. Frequently Asked Questions (FAQ)

Q: Can I drive this LED directly from a 5V microcontroller pin?
A: No. A microcontroller pin typically cannot source 20mA continuously, and more importantly, connecting 5V directly would destroy the LED due to excessive current. You must use a current-limiting resistor or a transistor driver circuit.

Q: Why is there such a wide range in forward voltage (2.8V to 3.8V)?
A> This is due to normal variations in semiconductor manufacturing. The binning system allows you to select parts with a tighter voltage range for your design to ensure consistent behavior, especially when connecting LEDs in parallel.

Q: What happens if I exceed the maximum junction temperature of 115°C?
A: Operating above Tj(max) will accelerate the degradation of the LED, leading to a rapid decrease in luminous output (lumen depreciation) and a significantly shortened operational lifespan. In extreme cases, it can cause immediate catastrophic failure.

Q: Is this LED suitable for outdoor use?
A: The datasheet does not specify ingress protection (IP) rating or qualification for outdoor environmental conditions (UV exposure, moisture, thermal cycling). It is primarily designed for indoor applications. For outdoor use, a specifically designed and qualified LED package would be required.

10. Operating Principle and Technology Trends

10.1 Basic Operating Principle

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, energy is released in the form of photons (light). The color of the light is determined by the energy bandgap of the semiconductor material. The LTST-T180TGKT uses an InGaN (Indium Gallium Nitride) chip, which is the standard material system for producing green, blue, and white LEDs.

10.2 Industry Trends

The general trend in SMD LEDs is towards higher efficiency (more lumens per watt), higher power density in smaller packages, and improved color consistency and rendering. There is also a strong focus on reliability and longevity, driven by applications in automotive lighting and general illumination. Furthermore, integration with intelligent drivers and sensors for smart lighting systems is an emerging area. While this particular component is a standard indicator LED, the underlying InGaN technology continues to evolve, pushing the boundaries of performance in all LED categories.