SMD LED LTST-C281TGKT-2A Datasheet - Dimensions 1.6x0.8x0.35mm - Voltage 2.5-3.1V - Green Color - English Technical Document

1. Product Overview

The LTST-C281TGKT-2A is a surface-mount device (SMD) LED lamp designed for modern, space-constrained electronic applications. It belongs to a family of miniature LEDs optimized for automated printed circuit board (PCB) assembly processes. The primary market for this component includes portable and compact electronics where board real estate is at a premium.

The core advantage of this LED is its exceptionally thin profile of only 0.35 mm, making it suitable for applications like ultra-slim displays, keypad backlighting, and status indicators in handheld devices. It utilizes an InGaN (Indium Gallium Nitride) semiconductor chip, which is known for producing high-brightness green light efficiently. The device is fully compliant with the Restriction of Hazardous Substances (RoHS) directive, ensuring it meets international environmental standards. It is packaged on 8mm tape wound onto 7-inch diameter reels, conforming to EIA standards, which facilitates high-speed, automated pick-and-place manufacturing.

1.1 Target Applications

This LED is versatile and finds use in a broad spectrum of electronic equipment. Key application areas include:

• Telecommunication Equipment: Status indicators and backlighting in cordless phones, cellular phones, and networking hardware.
• Office Automation: Backlighting for keyboards and keypads in notebook computers and other peripherals.
• Consumer Electronics & Home Appliances: Power indicators, function status lights, and display backlighting.
• Industrial Equipment: Panel indicators and signal luminaries in control systems.
• Micro-Displays & Symbol Luminary: Used in compact information displays and icon illumination.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed and should be avoided in reliable design.

• Power Dissipation (Pd): 76 mW. This is the maximum amount of power the LED package can dissipate as heat without degrading performance or reliability. Exceeding this limit risks overheating the semiconductor junction.
• Peak Forward Current (I_FP): 100 mA. This is the maximum allowable instantaneous forward current, typically specified under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). It is significantly higher than the continuous current rating to account for transient conditions but must not be used for DC operation.
• DC Forward Current (I_F): 20 mA. This is the recommended maximum continuous forward current for reliable long-term operation. Designing the drive circuit to operate at or below this current is critical for lifespan.
• Operating Temperature Range (T_opr): -20°C to +80°C. The ambient temperature range within which the LED will function according to its specifications. Performance outside this range is not characterized.
• Storage Temperature Range (T_stg): -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 maximum thermal profile the LED can withstand during reflow soldering, crucial for Pb-free assembly processes.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters measured at a standard ambient temperature of 25°C. They define the expected behavior of the device under normal operating conditions.

• Luminous Intensity (I_V): 35.5 - 90 mcd (millicandela) at I_F = 2mA. This is a measure of the perceived brightness of the LED as seen by the human eye. The wide range indicates a binning system is used (see Section 3). The test condition uses a sensor filtered to match the CIE photopic eye-response curve.
• Viewing Angle (2θ_1/2): 130 degrees. This is the full angle at which the luminous intensity drops to half of its value measured on-axis (0°). A wide viewing angle like this indicates a Lambertian or near-Lambertian emission pattern, suitable for area illumination rather than focused beams.
• Peak Emission Wavelength (λ_P): 525 nm. This is the wavelength at which the spectral power distribution of the emitted light is at its maximum. It is a physical property of the InGaN chip.
• Dominant Wavelength (λ_d): 520.0 - 535.0 nm at I_F = 2mA. This is derived from the CIE chromaticity diagram and represents the single wavelength that best describes the perceived color (green) of the LED. It is the key parameter for color consistency.
• Spectral Line Half-Width (Δλ): 25 nm. This is the width of the emission spectrum at half of its maximum power. A narrower half-width indicates a more spectrally pure, saturated color.
• Forward Voltage (V_F): 2.5 - 3.1 V at I_F = 2mA. The voltage drop across the LED when operating at the specified current. This range necessitates careful design of the current-limiting circuitry.
• Reverse Current (I_R): 10 μA (max) at V_R = 5V. LEDs are not designed for reverse bias operation. This parameter indicates a small leakage current if reverse voltage is accidentally applied. The datasheet explicitly cautions that the device is not designed for reverse operation.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into bins based on key parameters. This allows designers to select parts that meet specific requirements for color, brightness, and forward voltage.

3.1 Forward Voltage (V_F) Rank

Bins are defined in 0.1V steps from 2.5V to 3.1V at a test current of 2mA. For example, Bin Code '10' includes LEDs with V_F between 2.5V and 2.6V, while '13' includes those between 3.0V and 3.1V. A tolerance of ±0.1V is applied to each bin. Selecting LEDs from a tight V_F bin can help ensure uniform brightness when multiple LEDs are driven in parallel.

3.2 Luminous Intensity (I_V) Rank

Bins are defined for luminous intensity measured at 2mA. Codes range from 'N2' (35.5-45 mcd) to 'Q1' (71-90 mcd). A tolerance of ±15% is applied to each bin. This binning is crucial for applications requiring consistent perceived brightness across multiple indicators or backlighting zones.

3.3 Hue (Dominant Wavelength) Rank

This binning ensures color consistency. The dominant wavelength is binned in 5nm steps: 'AP' (520.0-525.0 nm), 'AQ' (525.0-530.0 nm), and 'AR' (530.0-535.0 nm). A tight tolerance of ±1 nm is maintained per bin. For applications where 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 characteristic curves which are essential for understanding device behavior under varying conditions. While the specific graphs are not reproduced in text, their implications are analyzed below.

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

This curve shows the exponential relationship between current and voltage for a semiconductor diode. For the LED, it will demonstrate the turn-on voltage (around 2.5-3.1V) and how V_F increases with I_F. The curve is vital for designing an appropriate current-limiting driver, as LEDs are current-driven devices. A small change in voltage can lead to a large change in current, potentially exceeding maximum ratings.

4.2 Luminous Intensity vs. Forward Current

This graph typically shows that luminous intensity increases approximately linearly with forward current in the normal operating range (e.g., up to 20mA). However, efficiency (lumens per watt) may peak at a current lower than the maximum rating. Operating above this peak efficiency point generates more heat for diminishing returns in light output, reducing overall reliability.

4.3 Spectral Distribution

The spectrum graph would show a single peak centered around 525 nm with a characteristic width (Δλ) of about 25 nm. This confirms the monochromatic green emission from the InGaN chip. The shape and width of the spectrum influence the color purity and how the LED light mixes with other colors.

5. Mechanical & Package Information

5.1 Package Dimensions

The LED has a compact SMD footprint. Key dimensions (all in millimeters, tolerance ±0.1mm unless noted) include a body size of approximately 1.6mm in length and 0.8mm in width. The most notable feature is its height of only 0.35mm, qualifying it as \"super thin.\" The package features a water-clear lens, which does not diffuse the light, allowing the native chip emission pattern (130° viewing angle) to be preserved.

5.2 Recommended PCB Attachment Pad

The datasheet provides a land pattern design for the PCB. This pattern is critical for ensuring proper solder joint formation during reflow, providing good electrical connection, mechanical strength, and thermal dissipation. Following the recommended pad layout helps prevent tombstoning (one end lifting) and ensures consistent alignment.

5.3 Polarity Identification

SMD LEDs have an anode (+) and cathode (-). The datasheet diagram typically indicates polarity, often by marking the cathode side of the package or showing the internal chip orientation. Correct polarity is mandatory for operation.

6. Soldering & Assembly Guidelines

6.1 IR Reflow Soldering Conditions

For Pb-free solder processes, a specific thermal profile is recommended. The peak temperature should not exceed 260°C, and the time above 260°C should be limited to a maximum of 10 seconds. A pre-heat stage (e.g., 150-200°C) is necessary to gradually heat the assembly and activate the solder paste flux. The profile should be characterized for the specific PCB assembly, as board thickness, component density, and oven type affect the result. The datasheet references compliance with JEDEC standards for reflow profiling.

6.2 Hand Soldering

If hand soldering is necessary, it should be done with extreme care. The recommended maximum soldering iron tip temperature is 300°C, and the contact time should be limited to 3 seconds per joint. Excessive heat can damage the LED's epoxy package and the internal wire bonds.

6.3 Cleaning

Only specified cleaning agents should be used. Recommended solvents are ethyl alcohol or isopropyl alcohol at normal temperature, with immersion time limited to less than one minute. Harsh or unspecified chemicals can craze, cloud, or damage the LED lens and package material.

6.4 Storage & Handling

• ESD Precautions: LEDs are sensitive to electrostatic discharge (ESD). Handling should be done with wrist straps, anti-static gloves, and on properly grounded workstations.
• Moisture Sensitivity: The package is moisture-sensitive. Unopened reels should be stored at ≤30°C and ≤90% RH. Once the original moisture-proof bag is opened, the LEDs are rated at Moisture Sensitivity Level (MSL) 2a, meaning they must be soldered within 672 hours (28 days) of exposure to factory ambient conditions (≤30°C/60% RH). For longer storage after opening, they should be kept in a sealed container with desiccant. If the exposure time exceeds 672 hours, a bake-out at 60°C for at least 20 hours is required before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied on embossed carrier tape with a protective cover tape. The tape width is 8mm, wound onto a standard 7-inch (178mm) diameter reel. 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, ensuring compatibility with automated assembly equipment.

8. Application Suggestions & Design Considerations

8.1 Typical Application Circuits

The LED must be driven with a constant current source or through a current-limiting resistor connected in series with a voltage supply. The resistor value (R) can be calculated using Ohm's Law: R = (V_supply - V_F) / I_F. It is critical to use the maximum V_F from the bin or datasheet to ensure the current does not exceed the limit even with worst-case component tolerances. For example, with a 5V supply, a V_F of 3.1V, and a desired I_F of 20mA: R = (5 - 3.1) / 0.02 = 95 Ohms. A standard 100 Ohm resistor would be a safe choice, resulting in a slightly lower current.

8.2 Thermal Management

Although power dissipation is low (76 mW max), proper thermal design extends lifespan. Ensure the recommended PCB pad is used, as it acts as a heat sink. Avoid placing the LED near other heat-generating components. Operating at lower currents (e.g., 10mA instead of 20mA) significantly reduces internal heating and can dramatically increase operational lifetime.

8.3 Optical Design

The 130-degree viewing angle provides wide, even illumination. For applications requiring a more focused beam, external secondary optics (lenses) would be necessary. The water-clear lens offers the highest possible light output but may cause a visible bright chip image (\"hot spot\"). If diffuse, uniform illumination is needed, consider using LEDs with a diffused lens or adding a light guide/diffuser film in the application.

9. Technical Comparison & Differentiation

The primary differentiating factor of the LTST-C281TGKT-2A is its ultra-thin 0.35mm height. Compared to standard SMD LEDs like 0603 (0.8mm height) or even 0402 (0.6mm height) packages, this device enables designs with stricter Z-height constraints. The use of an InGaN chip provides higher brightness and efficiency compared to older technologies like AlGaInP for green light in a similar package size. Its compatibility with standard IR reflow processes and tape-and-reel packaging makes it a drop-in replacement for many existing designs seeking miniaturization or performance upgrades.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED at 20mA continuously?
A: Yes, 20mA is the maximum recommended DC forward current. For maximum reliability and longevity, consider operating at a lower current, such as 10-15mA.

Q: Why is there such a wide range in Luminous Intensity (35.5 to 90 mcd)?
A: This reflects the binning process. You must specify the desired IV bin code (N2, P1, P2, Q1) when ordering to get LEDs within a specific brightness range.

Q: How do I ensure consistent color across multiple LEDs in my product?
A: Specify a tight Hue Bin code (e.g., AQ only) when ordering. This ensures all LEDs have a dominant wavelength within a 5nm range, resulting in visually consistent green color.

Q: My reflow oven profile peaks at 250°C. Is this acceptable?
A: Yes, a peak temperature of 250°C is below the maximum rating of 260°C and is generally acceptable, provided other aspects of the profile (time above liquidus, ramp rates) are controlled.

11. Practical Use Case Example

Scenario: Backlighting a Membrane Keypad for a Medical Device.
The device requires thin, reliable green backlighting for its keys. The LTST-C281TGKT-2A is chosen for its 0.35mm height, which fits within the layered construction of the membrane switch. LEDs from the \"Q1\" intensity bin and \"AQ\" hue bin are selected to ensure bright, uniform, and consistent green illumination across all keys. They are placed on a flexible PCB and driven via a constant-current driver IC at 15mA each to balance brightness with long-term reliability. The assembly undergoes a carefully profiled IR reflow process, and the LEDs are stored in a dry cabinet before use to comply with MSL requirements.

12. Operating Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light through electroluminescence. When a forward voltage is applied across the p-n junction of the semiconductor material (InGaN in this case), electrons and holes recombine in the active region. This recombination process releases energy in the form of photons (light particles). The wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material. InGaN is commonly used to produce light in the blue, green, and cyan regions of the spectrum. The specific doping and structure of the chip are engineered to achieve high efficiency and the desired green color at 525 nm.

13. Technology Trends

The trend in SMD LEDs for consumer electronics continues toward further miniaturization, increased efficiency (lumens per watt), and higher reliability. The move to ultra-thin packages like the 0.35mm profile discussed here enables ever-slimmer end products. There is also a focus on improving color consistency and expanding color gamuts for display applications. Furthermore, integration of driver circuitry or multiple LED chips within a single package (e.g., RGB LEDs) is a growing trend to simplify system design. The underlying semiconductor technology, particularly for green LEDs, is an area of active research to close the \"green gap\" and achieve efficiencies comparable to blue and red LEDs.