SMD LED LTST-C191TGKT-2A Datasheet - Water Clear Lens - InGaN Green - 0.55mm Height - 10mA DC - 38mW - English Technical Document

1. Product Overview

This document details the specifications for a miniature, surface-mount LED lamp designed for automated printed circuit board assembly and applications where space is a critical constraint. The device is an extra-thin, ultra-bright LED utilizing an InGaN (Indium Gallium Nitride) semiconductor die to produce green light. Its compact form factor and compatibility with modern manufacturing processes make it a versatile component for a wide array of electronic equipment.

1.1 Core Advantages and Target Market

The primary advantages of this LED include its exceptionally low profile of 0.55mm, which allows for integration into ultra-slim devices. It delivers high luminous intensity from its InGaN chip. The component is fully compliant with RoHS (Restriction of Hazardous Substances) directives. It is packaged on 8mm tape wound onto 7-inch reels, conforming to EIA standards, making it fully compatible with high-speed automated pick-and-place equipment. Furthermore, it is designed to withstand infrared (IR) reflow soldering processes, which is standard for surface-mount technology (SMT) assembly lines.

The target applications are broad, encompassing telecommunications equipment, office automation devices, home appliances, and industrial equipment. Specific use cases include backlighting for keypads and keyboards, status indication lights, micro-displays, and various signal or symbol luminary applications.

2. In-Depth Technical Parameter Analysis

This section provides a detailed, objective interpretation of the electrical, optical, and thermal characteristics defined in the datasheet. Understanding these parameters is crucial for reliable circuit design and ensuring long-term performance.

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): 38 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 and accelerated degradation.
• DC Forward Current (IF): 10 mA. The maximum continuous forward current that can be applied.
• Peak Forward Current: 40 mA. This is permissible only under pulsed conditions with a 1/10 duty cycle and a pulse width of 0.1ms. It allows for brief moments of higher brightness without thermal damage.
• Operating Temperature Range: -20°C to +80°C. The ambient temperature range within which the LED is specified to operate correctly.
• Storage Temperature Range: -30°C to +100°C. The temperature range for storing the device when not powered.
• Infrared Soldering Condition: 260°C for 10 seconds. This defines the peak temperature and time profile the LED can withstand during reflow soldering, critical for Pb-free assembly processes.

2.2 Electro-Optical Characteristics at Ta=25°C

These are the typical performance parameters measured under standard test conditions. Designers should use these values for circuit calculations.

• Luminous Intensity (Iv): Ranges from 11.2 mcd (minimum) to 112.0 mcd (maximum) at a forward current (IF) of 2 mA. The wide range is managed through a binning system (see Section 3). This parameter measures the perceived brightness by the human eye.
• Viewing Angle (2θ1/2): 130 degrees. This is the full angle at which the luminous intensity drops to half of its value measured on-axis. A 130-degree angle indicates a wide viewing pattern, suitable for applications where light needs to be seen from various angles.
• Peak Emission Wavelength (λP): 530 nm. This is the wavelength at which the spectral output of the LED is strongest.
• Dominant Wavelength (λd): 525.0 nm to 545.0 nm (at IF=2mA). This is the single wavelength perceived by the human eye that defines the color (green). It is derived from the CIE chromaticity diagram and differs from the peak wavelength.
• Spectral Line Half-Width (Δλ): 35 nm. This indicates the spectral purity or bandwidth of the emitted light, measured as the width at half the maximum intensity.
• Forward Voltage (VF): 2.30 V to 3.30 V (at IF=2 mA). The voltage drop across the LED when conducting current. This range is also subject to binning.
• Reverse Current (IR): 10 μA (maximum) at a Reverse Voltage (VR) of 5V. The device is not designed for reverse operation; this test is for quality verification only. Applying reverse voltage in circuit must be avoided, typically by ensuring correct polarity or using protection circuitry.

2.3 Thermal Considerations

While not explicitly graphed, thermal management is inferred from the power dissipation rating and operating temperature range. The low 38mW Pd rating emphasizes that this is a low-power device. However, in high-density layouts or enclosed spaces, ensuring adequate thermal relief via the PCB pads is recommended to maintain junction temperature within safe limits, preserving luminous output and lifespan.

3. Binning System Explanation

To ensure consistent color and brightness in production, LEDs are sorted into bins based on key parameters. This allows designers to select a specific performance grade for their application.

3.1 Forward Voltage (Vf) Binning

LEDs are categorized by their forward voltage drop at 2 mA. Bins range from D4 (2.30V - 2.50V) to D8 (3.10V - 3.30V), with a tolerance of ±0.1V per bin. Selecting a tight Vf bin can help ensure uniform brightness when multiple LEDs are driven in parallel from a constant voltage source.

3.2 Luminous Intensity (Iv) Binning

This binning controls the brightness output. Bins range from L (11.2 - 18.0 mcd) to Q (71.0 - 112.0 mcd), measured at 2 mA, with a ±15% tolerance per bin. Applications requiring specific brightness levels, such as indicators with defined luminosity classes, will specify an Iv bin.

3.3 Hue (Dominant Wavelength) Binning

This ensures color consistency. The dominant wavelength bins for this green LED are: AQ (525.0 - 530.0 nm), AR (530.0 - 535.0 nm), AS (535.0 - 540.0 nm), and AT (540.0 - 545.0 nm), with a ±1nm tolerance. For applications where precise color matching is critical (e.g., multi-color displays or traffic signals), specifying a narrow hue bin is essential.

4. Performance Curve Analysis

The datasheet references typical performance curves. While the specific graphs are not reproduced in the provided text, their standard interpretations are crucial for design.

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

This curve shows the non-linear relationship between the current flowing through the LED and the voltage across it. It is exponential in nature. The typical VF value given (e.g., ~2.8V at 2mA) is a point on this curve. Designers use this curve to determine the necessary current-limiting resistor value for a given supply voltage. Driving the LED with a constant current source is generally preferred over a constant voltage with a series resistor, as it provides more stable brightness and better tolerance to Vf variations.

4.2 Luminous Intensity vs. Forward Current

This graph typically shows that luminous intensity increases with forward current, but not linearly. At higher currents, efficiency may drop due to increased heat generation. The rated DC current of 10mA represents a point where a good balance of brightness and reliability is achieved. Operating near the absolute maximum current will reduce lifetime.

4.3 Spectral Distribution

The spectral output graph would show intensity versus wavelength, centering around the 530nm peak with the 35nm half-width. This information is vital for applications sensitive to specific wavelengths, such as optical sensors or color-filtered systems.

4.4 Temperature Dependence

While not explicitly detailed, LED performance is temperature-sensitive. Typically, forward voltage decreases with increasing temperature (negative temperature coefficient), while luminous output also decreases. For precision applications, these effects must be considered, especially if the LED operates in a varying thermal environment.

5. Mechanical and Package Information

5.1 Package Dimensions and Polarity

The LED has an extra-thin profile with a height of 0.55mm. The package dimensions are provided in the datasheet with a standard tolerance of ±0.1mm. The lens is water clear. The cathode is typically identified by a marking on the package, such as a notch, green dot, or cut corner. Correct polarity identification is mandatory during assembly to prevent reverse bias damage.

5.2 Recommended PCB Pad Design

A land pattern (footprint) recommendation is provided to ensure reliable soldering and mechanical stability. Adhering to this design is critical for achieving proper solder fillets, managing thermal dissipation, and preventing tombstoning (where one end of the component lifts during reflow). The pad design also aids in aligning the component during automated placement.

6. Soldering, Assembly, and Handling Guide

6.1 Soldering Process Guidelines

The LED is compatible with infrared reflow soldering. A suggested profile for Pb-free processes is provided, with key parameters:

• Pre-heat: 150-200°C.
• Pre-heat Time: Maximum 120 seconds to gradually heat the board and components.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus (at peak): Maximum 10 seconds. The profile should comply with JEDEC standards to ensure reliability.

Hand soldering with an iron is possible but must be controlled: temperature ≤300°C and time ≤3 seconds for a single operation only. Excessive heat from a soldering iron can easily damage the LED or its epoxy lens.

6.2 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. The datasheet recommends immersion in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Unspecified or aggressive chemicals can damage the package material or optical lens.

6.3 Storage and Moisture Sensitivity

The LEDs are moisture-sensitive. When the 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 original packaging is opened, the storage ambient should not exceed 30°C / 60% RH. Components removed from their original packaging should undergo IR reflow within 672 hours (28 days, MSL2a level). If stored longer outside the original bag, they must be baked at approximately 60°C for at least 20 hours before soldering to remove absorbed moisture and prevent "popcorning" (package cracking due to vapor pressure during reflow).

6.4 Electrostatic Discharge (ESD) Precautions

This LED is susceptible to damage from electrostatic discharge (ESD) and electrical surges. It is recommended to handle the device using a grounded wrist strap or anti-static gloves. All handling equipment, workstations, and machinery must be properly grounded to prevent static buildup.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied in embossed carrier tape with a protective cover tape, wound onto 7-inch (178mm) diameter reels. Standard reel quantity is 5,000 pieces. The tape width is 8mm. The packaging conforms to ANSI/EIA-481 specifications. There are guidelines for minimum packing quantities for remainders and the maximum number of consecutive missing components in the tape.

8. Application Notes and Design Considerations

8.1 Typical Application Circuits

The most common drive method is a series current-limiting resistor. The resistor value (R) is calculated as: R = (V_supply - VF_LED) / I_desired. For example, with a 5V supply, a typical VF of 2.8V, and a desired current of 5mA: R = (5 - 2.8) / 0.005 = 440 Ohms. A 470 Ohm standard resistor would be suitable. For better brightness stability over temperature and supply voltage variations, a simple constant current source using a transistor or a dedicated LED driver IC is recommended, especially for multiple LEDs or critical brightness applications.

8.2 Design Considerations

• Current Driving: Always drive with a controlled current, not a fixed voltage directly. Use the Absolute Maximum Ratings as limits, not targets.
• Thermal Management: Ensure the PCB layout provides adequate copper area for the LED pads to act as a heat sink, especially if operating near maximum current.
• Optical Design: The wide 130-degree viewing angle provides good off-axis visibility. For focused light, external lenses or light guides may be required.
• Reverse Voltage Protection: If there is any possibility of reverse voltage being applied (e.g., in AC circuits or with inductive loads), a protection diode in parallel with the LED (cathode to anode) is necessary.

8.3 Application Limitations

The datasheet includes a caution that these LEDs are intended for ordinary electronic equipment. For applications requiring exceptional reliability where failure could jeopardize life or health (aviation, medical devices, critical safety systems), consultation with the manufacturer is required prior to design-in. This is a standard disclaimer for commercial-grade components.

9. Technical Comparison and Differentiation

Compared to older technology like AlGaInP (Aluminum Gallium Indium Phosphide) based green LEDs, this InGaN-based green LED typically offers higher luminous efficiency and better performance stability. The 0.55mm height is a key differentiator in the market, enabling designs that are thinner than those using standard 0.6mm or 0.8mm height LEDs. Its compatibility with standard IR reflow and tape-and-reel packaging aligns it with mainstream, cost-effective SMT assembly, unlike some niche LEDs that may require special handling.

10. Frequently Asked Questions (FAQs)

10.1 What is the difference between Peak Wavelength and Dominant Wavelength?

Peak Wavelength (λP) is the physical wavelength where the LED emits the most optical power. Dominant Wavelength (λd) is a calculated value based on human color perception (CIE chart) that best represents the color we see. For a monochromatic green LED, they are often close but not identical.

10.2 Can I drive this LED at 20mA for higher brightness?

No. The Absolute Maximum Rating for DC forward current is 10 mA. Operating at 20mA would exceed this rating, leading to excessive heat, rapid luminous decay, and potential catastrophic failure. For higher brightness, select an LED from the higher Iv bins (e.g., Q bin) or choose a product rated for a higher current.

10.3 Why is binning important?

Manufacturing variations cause differences in Vf, Iv, and color between individual LEDs. Binning sorts them into groups with tightly controlled parameters. For a product using multiple LEDs (like a backlight array), using LEDs from the same bin ensures uniform brightness and color, which is critical for aesthetic and functional quality.

10.4 How do I interpret the "Infrared Soldering Condition" rating?

This means the LED can survive a reflow solder profile where the component's body temperature reaches a peak of 260°C for up to 10 seconds. This is a standard requirement for Pb-free (lead-free) solder pastes, which have higher melting points than traditional tin-lead solder.

11. Practical Design and Usage Examples

11.1 Mobile Device Keypad Backlighting

In a mobile phone keypad, multiple LEDs are often placed under a light guide panel. Using LEDs from the same Iv and Hue bin (e.g., N bin for intensity, AR bin for color) ensures every key is evenly lit with the same color tone. The 0.55mm height is crucial here to fit within the ultra-thin chassis. They would be driven in parallel with individual series resistors or by a dedicated backlight driver IC that provides constant current.

11.2 Status Indicator on a Network Router

A single LED can be used to indicate power, network activity, or error status. The wide 130-degree viewing angle allows the status to be seen from almost any direction in a room. A simple circuit with a microcontroller GPIO pin, a series resistor (e.g., 330 Ohms for 5mA from a 3.3V supply), and the LED is sufficient. The software can control blinking patterns.

12. Operating Principle Introduction

This LED is a semiconductor photonic device. It is based on an InGaN heterostructure. When a forward voltage is applied, electrons and holes are injected into the active region of the semiconductor die. They recombine, releasing energy in the form of photons (light). The specific composition of the InGaN alloy determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, green. The water-clear epoxy lens encapsulates the chip, provides mechanical protection, and shapes the light output pattern.

13. Technology Trends

The development of InGaN materials was a breakthrough for achieving high-efficiency green and blue LEDs, enabling white LEDs (via phosphor conversion) and full-color displays. Current trends in SMD LEDs continue towards higher efficacy (more light output per watt), lower thermal resistance for better power handling, and even smaller package sizes. There is also a focus on improving color rendering and consistency for lighting applications. The drive for miniaturization in consumer electronics pushes packages to thinner heights and smaller footprints, as exemplified by this 0.55mm component.