SMD LED LTST-M140TBKT Datasheet - Size 3.2x2.8x1.9mm - Voltage 2.8-3.8V - Power 80mW - Blue Color - English Technical Documentation

1. Product Overview

The LTST-M140TBKT is a surface-mount device (SMD) light-emitting diode (LED) designed for modern, space-constrained electronic applications. Its miniature footprint and standardized EIA package make it ideal for automated pick-and-place assembly lines, significantly improving production efficiency. The device is constructed using InGaN (Indium Gallium Nitride) technology, which is responsible for its efficient blue light emission. The primary lens is water-clear, allowing for the true color of the light source to be projected without tinting.

The core advantages of this LED include its RoHS compliance, ensuring it meets international environmental standards, and its full compatibility with lead-free (Pb-free) infrared (IR) reflow soldering processes. This makes it suitable for high-volume manufacturing. Its design targets a broad market, including but not limited to telecommunications equipment (such as status indicators on routers and modems), office automation devices (printers, scanners), home appliances, industrial control panels, and indoor signage where reliable, long-lasting indicator lighting is required.

2. Technical Parameters Deep Objective Interpretation

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the LED may occur. Operating the device continuously at or near these limits is not recommended. The absolute maximum ratings at an ambient temperature (Ta) of 25°C are as follows:

• Power Dissipation (Pd): 80 mW. This is the maximum amount of power the LED package can dissipate as heat without degrading performance or lifespan.
• Peak Forward Current (I_F(PEAK)): 100 mA. This current is permissible only under pulsed conditions, specifically at a 1/10 duty cycle with a pulse width of 0.1ms. It is used for brief, high-intensity flashes.
• Continuous Forward Current (I_F): 20 mA. This is the recommended maximum current for continuous DC operation, ensuring optimal performance and longevity.
• Operating Temperature Range: -40°C to +85°C. The LED is designed to function correctly within this wide temperature span, suitable for various environmental conditions.
• Storage Temperature Range: -40°C to +100°C. The device can be stored safely within this range when not in operation.

2.2 Electro-Optical Characteristics

These parameters are measured under standard test conditions (Ta=25°C, I_F=20mA) and define the LED's performance.

• Luminous Flux (Φ_v): 0.42 to 1.35 Lm. This is the total perceived power of light emitted by the LED. The wide range is due to the binning system (see Section 3).
• Luminous Intensity (I_v): 140 to 450 mcd (millicandela). This measures the light output in a specific direction (typically the central axis). The intensity is for reference, with the luminous flux being the primary photometric quantity.
• Viewing Angle (2θ_1/2): 120 degrees (typical). This is the full angle at which the luminous intensity is half of the intensity at the center (0°). A 120-degree angle indicates a very wide viewing pattern, making it excellent for applications where the LED needs to be visible from a broad range of positions.
• Peak Wavelength (λ_P): 468 nm (typical). This is the wavelength at which the spectral emission is strongest.
• Dominant Wavelength (λ_d): 465 to 475 nm. This is the single wavelength that best represents the perceived color of the light (blue). The tolerance is ±1 nm within its bin.
• Spectral Line Half-Width (Δλ): 25 nm (typical). This indicates the spectral purity; a smaller value means a more monochromatic light. 25nm is standard for a blue InGaN LED.
• Forward Voltage (V_F): 2.8 to 3.8 V at 20mA. The voltage drop across the LED when operating. It is crucial for designing the current-limiting circuit.
• Reverse Current (I_R): 10 μA (max) at V_R=5V. The LED is not designed for reverse bias operation; this parameter is for IR test purposes only. Applying reverse voltage in circuit design must be avoided.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. The LTST-M140TBKT uses a three-dimensional binning system.

3.1 Forward Voltage (V_F) Rank

LEDs are binned based on their forward voltage drop at 20mA. This helps in designing stable driver circuits, especially when multiple LEDs are connected in series. The bins are: D7 (2.8-3.0V), D8 (3.0-3.2V), D9 (3.2-3.4V), D10 (3.4-3.6V), D11 (3.6-3.8V). Tolerance for each bin is ±0.1V.

3.2 Luminous Flux/Intensity Rank

This binning categorizes LEDs by their total light output. It ensures a uniform brightness level in an array. The bins are: C2 (0.42-0.54 Lm / 140-180 mcd), D1 (0.54-0.67 Lm / 180-224 mcd), D2 (0.67-0.84 Lm / 224-280 mcd), E1 (0.84-1.07 Lm / 280-355 mcd), E2 (1.07-1.35 Lm / 355-450 mcd). Luminous Intensity is provided for reference with a tolerance of ±11% per bin.

3.3 Hue (Dominant Wavelength) Rank

This binning ensures color consistency. The dominant wavelength bins are: AC (465.0-470.0 nm) and AD (470.0-475.0 nm). The tolerance is ±1 nm within the bin. This tight control is vital for applications where precise color matching is required, such as in multi-color indicator clusters or backlighting.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet, their implications are critical for design.

• Relative Luminous Intensity vs. Forward Current: This curve shows that light output increases with current but not linearly. Above the recommended 20mA, efficiency typically drops, and heat generation rises significantly.
• Forward Voltage vs. Forward Current: This exponential curve is fundamental for selecting the correct current-limiting resistor or designing a constant-current driver. The V_F value is not fixed but varies with current and temperature.
• Relative Luminous Intensity vs. Ambient Temperature: As temperature increases, the luminous output of an LED generally decreases. Understanding this derating is essential for applications operating at high ambient temperatures to ensure sufficient brightness.
• Spectral Distribution: The graph shows the emission peak around 468nm with a characteristic shape and half-width, confirming the blue color specification.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED conforms to a standard SMD package outline. Key dimensions include a typical length of 3.2mm, width of 2.8mm, and height of 1.9mm. All dimensions have a tolerance of ±0.2mm unless otherwise specified. The cathode is typically identified by a marking on the package or a chamfered corner.

5.2 Recommended PCB Attachment Pad Layout

A land pattern diagram is provided to ensure proper solder joint formation during reflow. Following this recommendation prevents issues like tombstoning (one end lifting) or insufficient solder. The pad design accounts for thermal mass and promotes reliable soldering.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Profile

The datasheet provides a detailed temperature profile compliant with J-STD-020B for lead-free processes. Key parameters include: a pre-heat zone (150-200°C, max 120 sec), a peak temperature not exceeding 260°C, and a time above liquidus (TAL) appropriate for the solder paste used. Adhering to this profile is critical to prevent thermal damage to the LED's epoxy lens and internal die bonds.

6.2 Storage and Handling

The LEDs are moisture-sensitive (MSL Level 3). In their sealed moisture-proof bag with desiccant, they have a shelf life of one year when stored at ≤30°C and ≤70% RH. Once the bag is opened, components must be used within 168 hours (1 week) under conditions of ≤30°C and ≤60% RH. If this exposure time is exceeded, a bake-out at approximately 60°C for at least 48 hours is required before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only alcohol-based solvents like isopropyl alcohol (IPA) or ethyl alcohol should be used. The LED should be immersed at normal temperature for less than one minute. Harsh or unspecified chemicals can damage the package material and optical properties.

7. Packaging and Ordering Information

The standard packaging is in 12mm wide embossed carrier tape on 7-inch (178mm) diameter reels. Each reel contains 3000 pieces. The tape and reel specifications comply with ANSI/EIA 481. For smaller quantities, a minimum packing of 500 pieces is available. The tape is sealed with a cover tape to protect components during shipping and handling.

8. Application Suggestions

8.1 Typical Application Scenarios

• Status Indicators: Power, network activity, battery charging, and system readiness in consumer electronics, telecom gear, and industrial equipment.
• Front Panel Backlighting: Illuminating buttons, switches, or symbols on control panels and appliances.
• Signal and Symbol Luminary: Used in indoor signage or equipment where a clear blue signal is needed.

8.2 Design Considerations

• Current Limiting: Always use a series resistor or constant-current driver to set the forward current to 20mA or less for continuous operation. Calculate the resistor value using R = (V_supply - V_F) / I_F, using the maximum V_F from the bin to ensure current does not exceed limits even with a low V_F LED.
• Thermal Management: Although power dissipation is low, ensure adequate PCB copper area or thermal vias if operating at high ambient temperatures or maximum current to maintain junction temperature within safe limits.
• ESD Protection: LEDs are sensitive to electrostatic discharge. Implement standard ESD handling precautions during assembly.

9. Technical Comparison and Differentiation

Compared to generic blue SMD LEDs, the LTST-M140TBKT offers distinct advantages: a standardized and well-documented binning system for predictable performance, a wide 120-degree viewing angle for excellent off-axis visibility, and guaranteed compatibility with lead-free IR reflow processes, which is essential for modern, RoHS-compliant manufacturing. Its detailed and conservative maximum ratings and application notes provide a higher degree of design reliability.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED with 3.3V without a resistor?
A: No. The forward voltage ranges from 2.8V to 3.8V. Connecting a 3.3V source directly could overcurrent an LED with a low V_F (e.g., 2.9V), potentially destroying it. A current-limiting circuit is always required.

Q: Why is the luminous intensity given as a range and \"for reference\"?
A: Luminous flux (lumens) is the total light output, while intensity (candela) is light in a specific direction. For a wide-angle LED, total flux is a more meaningful metric. The intensity is provided as a helpful reference but varies greatly with viewing angle.

Q: What does \"I.C. compatible\" mean in the features?
A> It means the LED's electrical characteristics (like forward voltage and current requirements) are suitable for direct interfacing with standard integrated circuit (IC) outputs, such as microcontroller GPIO pins, typically through a simple transistor or resistor.

11. Practical Design and Usage Case

Case: Designing a Multi-LED Status Bar: Imagine designing a status bar with 5 blue LEDs for a network switch. To ensure uniform brightness, specify LEDs from the same luminous flux bin (e.g., all from E1). To simplify the driver circuit, specify LEDs from a tight forward voltage bin (e.g., all D9). Connect them in parallel, each with its own current-limiting resistor calculated using the maximum V_F from the bin. This approach compensates for natural V_F variations and prevents current hogging, leading to consistent light output across all indicators.

12. Principle Introduction

This LED operates on the principle of electroluminescence in a semiconductor. The active region is made of InGaN. When a forward voltage is applied, electrons and holes are injected into the active region. When they recombine, energy is released in the form of photons (light). The specific composition of the InGaN alloy determines the bandgap energy, which directly corresponds to the wavelength (color) of the emitted light—in this case, blue. The water-clear epoxy lens encapsulates the semiconductor die, provides mechanical protection, and shapes the light output into the desired 120-degree viewing pattern.

13. Development Trends

The general trend in SMD LEDs like this one is towards higher efficiency (more lumens per watt), which reduces power consumption and heat generation for the same light output. There is also a continuous drive for improved color consistency and tighter binning tolerances to meet the demands of high-end display and lighting applications. Furthermore, packaging technology is evolving to allow for even smaller form factors while maintaining or improving thermal performance and reliability. The compatibility with automated assembly and lead-free processes, as seen in this device, remains a fundamental industry standard.