SMD LED LTST-108KGKT Datasheet - 3.2x2.8x1.9mm - 2.4V Max - 72mW - Water Clear AlInGaP Green - English Technical Document

1. Product Overview

This document provides the complete technical specifications for the LTST-108KGKT, a surface-mount device (SMD) light-emitting diode (LED). This component belongs to a family of LEDs designed for automated printed circuit board (PCB) assembly and applications where space is a critical constraint. Its miniature size and standardized package make it suitable for integration into a wide array of modern electronic equipment.

1.1 Core Advantages and Target Market

The primary advantages of this LED include its compliance with RoHS (Restriction of Hazardous Substances) directives, packaging in 8mm tape on 7-inch reels for automated pick-and-place machines, and compatibility with infrared (IR) reflow soldering processes. It is designed to be I.C. (Integrated Circuit) compatible. These features make it an ideal choice for high-volume manufacturing. The target applications span telecommunications, office automation, home appliances, and industrial equipment. It is commonly used as a status indicator, for signal and symbol luminaires, and for front panel backlighting.

2. Technical Parameters: In-Depth Objective Interpretation

This section details the absolute limits and operational characteristics of the LED under standard test conditions (Ta=25°C). Understanding these parameters is crucial for reliable circuit design.

2.1 Absolute Maximum Ratings

The device must not be operated beyond these limits, as doing so may cause permanent damage. The maximum continuous DC forward current (IF) is 30 mA. The maximum power dissipation is 72 mW. A peak forward current of 80 mA is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The operating temperature range is from -40°C to +85°C, and the storage temperature range extends from -40°C to +100°C.

2.2 Electro-Optical Characteristics

These parameters define the device's performance under typical operating conditions (IF=20mA, Ta=25°C). The luminous intensity (Iv) has a typical value, with a minimum of 71 mcd and a maximum of 224 mcd depending on the bin rank. The viewing angle (2θ1/2) is 110 degrees, indicating a wide beam pattern. The dominant wavelength (λd) ranges from 564.5 nm to 576.5 nm, defining its green color. The forward voltage (VF) ranges from 1.8V to 2.4V. The reverse current (IR) is specified at a maximum of 10 μA when a reverse voltage (VR) of 5V is applied; note that the device is not designed for reverse operation.

3. Bin Ranking System Explanation

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

3.1 Forward Voltage (VF) Rank

LEDs are categorized into three voltage bins: D2 (1.8V - 2.0V), D3 (2.0V - 2.2V), and D4 (2.2V - 2.4V). The tolerance on each bin is ±0.10V. Selecting from the same bin helps maintain consistent voltage drops across multiple LEDs in a series circuit.

3.2 Luminous Intensity (IV) Rank

The brightness is sorted into five bins: Q1 (71.0-90.0 mcd), Q2 (90.0-112.0 mcd), R1 (112.0-140.0 mcd), R2 (140.0-180.0 mcd), and S1 (180.0-224.0 mcd). The tolerance on each intensity bin is ±11%. This ranking is critical for applications requiring uniform brightness across an array of indicators.

3.3 Dominant Wavelength (WD) Rank

The color (wavelength) is sorted into four bins: B (564.5-567.5 nm), C (567.5-570.5 nm), D (570.5-573.5 nm), and E (573.5-576.5 nm). The tolerance for each wavelength bin is ±1 nm. This precise sorting ensures minimal color variation in applications where specific hue matching is important.

4. Performance Curve Analysis

Graphical representations of device characteristics provide deeper insight into performance under varying conditions, which is essential for robust design.

4.1 Typical Characteristics Curves

The datasheet includes typical curves showing the relationship between forward current and luminous intensity, forward voltage versus forward current, and the spectral distribution of the emitted light. These curves help designers predict behavior outside the standard test point (20mA). For instance, the luminous intensity typically increases with current but may saturate at higher levels. The forward voltage has a positive temperature coefficient, meaning it decreases slightly as the junction temperature rises.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED is housed in a standard SMD package. Key dimensions include a body size of approximately 3.2mm x 2.8mm, with a height of 1.9mm. All dimensions have a tolerance of ±0.2mm unless otherwise noted. The lens color is water clear, and the light source color is AlInGaP green.

5.2 Recommended PCB Attachment Pad Layout

A diagram is provided showing the recommended copper pad pattern on the PCB for infrared or vapor phase reflow soldering. Adhering to this layout ensures proper solder joint formation, good thermal management, and mechanical stability.

5.3 Polarity Identification

The cathode is typically indicated by a marking on the package or a notch in the body. Correct polarity orientation is essential for the device to function.

6. Soldering and Assembly Guidelines

Proper handling and soldering are critical to maintaining device reliability and performance.

6.1 IR Reflow Soldering Profile

A suggested reflow profile for lead-free processes is provided, compliant with J-STD-020B. Key parameters include a pre-heat temperature of 150-200°C for up to 120 seconds maximum, a peak temperature not exceeding 260°C, and a time above liquidus (TAL) of 10 seconds maximum. The profile should be characterized for the specific PCB assembly.

6.2 Storage Conditions

Unopened packages should be stored at ≤30°C and ≤70% Relative Humidity (RH) and used within one year. Once the moisture-proof bag is opened, the LEDs should be stored at ≤30°C and ≤60% RH. It is recommended to complete the IR reflow process within 168 hours (7 days) of exposure to ambient air. For longer storage outside the original bag, use a sealed container with desiccant. If exposed for more than 168 hours, a bake at 60°C for at least 48 hours is required before soldering.

6.3 Cleaning

If cleaning is necessary after soldering, only use specified solvents such as ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Unspecified chemicals may damage the package.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied on 8mm wide embossed carrier tape wound onto 7-inch (178mm) diameter reels. Each reel contains 4000 pieces. The tape pockets are sealed with a top cover tape. Packaging follows ANSI/EIA 481 specifications.

7.2 Minimum Order Quantity

The standard packing quantity is 4000 pieces per reel. A minimum packing quantity of 500 pieces is available for remainder stock.

8. Application Suggestions

8.1 Typical Application Scenarios

This LED is well-suited for status indication in consumer electronics (phones, laptops, appliances), network equipment, and indoor signage. Its wide viewing angle makes it effective for front panel illumination where visibility from multiple angles is needed.

8.2 Design Considerations

Current Limiting: Always use a series current-limiting resistor or a constant-current driver. The value can be calculated using Ohm's Law: R = (Vsupply - VF) / IF. Ensure the resistor power rating is adequate.
Thermal Management: While the power dissipation is low, ensure adequate PCB copper area or thermal vias if operating at high ambient temperatures or near the maximum current to prevent excessive junction temperature rise.
ESD Protection: Although not explicitly stated as sensitive, standard ESD (Electrostatic Discharge) handling precautions should be observed during assembly.

9. Technical Comparison and Differentiation

Compared to older technology like GaP (Gallium Phosphide) green LEDs, the AlInGaP (Aluminum Indium Gallium Phosphide) material system used in this device typically offers higher luminous efficiency and better color purity (more saturated green). The wide 110-degree viewing angle is a key differentiator from narrower-beam LEDs used for focused illumination, making it ideal for indicator purposes. The compatibility with standard IR reflow processes differentiates it from LEDs that require manual or wave soldering.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: What resistor should I use with a 5V supply?
A: Using the maximum VF of 2.4V and a desired IF of 20mA: R = (5V - 2.4V) / 0.02A = 130 Ohms. A standard 130Ω or 150Ω resistor would be suitable. Always calculate based on the actual VF bin if known.
Q: Can I drive this LED with a 3.3V microcontroller pin?
A: Possibly, but it depends on the VF bin. For a D4 bin LED (VF up to 2.4V), there is sufficient headroom (3.3V - 2.4V = 0.9V). A current-limiting resistor is still mandatory. For a microcontroller pin, ensure the pin can source/sink the required 20mA.
Q: Why is there a reverse current specification if the device is not for reverse operation?
A: The IR test (VR=5V) is a quality and reliability test performed during manufacturing. It verifies the integrity of the LED chip's PN junction. In application, reverse voltage should be avoided as it is not a designed operating condition.

11. Practical Design and Usage Case

Scenario: Designing a multi-LED status bar for a router. Ten LTST-108KGKT LEDs are used to indicate network activity levels. To ensure uniform brightness, LEDs from the same IV bin (e.g., R2) should be selected. They can be connected in parallel, each with its own current-limiting resistor (e.g., 150Ω for a 5V rail). Alternatively, for better current matching, a single constant-current driver IC with multiple channels could be used. The wide 110° viewing angle ensures the lights are visible from across a room. The design must follow the recommended reflow profile and ensure the PCB layout uses the suggested pad geometry for reliable soldering.

12. Operating Principle Introduction

An LED is a semiconductor diode. When a forward voltage is applied across its terminals (anode positive relative to cathode), electrons and holes are injected into the active region of the device. When these charge carriers recombine, energy is released in the form of photons (light). The color of the light is determined by the bandgap energy of the semiconductor material. In this case, the AlInGaP material system has a bandgap that corresponds to green light with a dominant wavelength in the 565-577 nm range. The water-clear lens helps in extracting and shaping the emitted light.

13. Technology Trends (Objective Perspective)

The general trend in indicator LEDs is toward higher efficiency (more light output per unit of electrical power), smaller package sizes for denser integration, and improved color consistency through tighter binning. There is also a move toward broader adoption of lead-free and halogen-free materials to meet environmental regulations. While this specific part uses AlInGaP technology, other green LEDs may use InGaN (Indium Gallium Nitride) materials, which can offer different performance characteristics. The choice of technology involves trade-offs between efficiency, color point, cost, and viewing angle.