SMD LED LTST-T180KGKT Datasheet - 120° Viewing Angle - 1.7-2.5V - 30mA - AlInGaP Green - English Technical Document

1. Product Overview

This document details the specifications for a compact, surface-mount LED designed for automated assembly processes. The device utilizes AlInGaP (Aluminum Indium Gallium Phosphide) technology to produce green light, offering a balance of performance and efficiency suitable for modern electronic applications.

1.1 Features and Core Advantages

The LED is engineered for reliability and ease of integration. Key features include compliance with RoHS environmental standards, packaging on 8mm tape within 7-inch reels for automated pick-and-place systems, and compatibility with infrared reflow soldering processes. Its design is I.C. compatible and meets EIA standard package dimensions, ensuring broad applicability.

1.2 Target Market and Applications

This component is targeted at space-constrained and high-volume electronic assemblies. Primary application areas encompass telecommunications equipment, office automation devices, home appliances, and industrial control systems. It is commonly used for status indication, signal and symbol illumination, and front panel backlighting.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

Operating limits are defined at an ambient temperature (Ta) of 25°C. The maximum power dissipation is 75mW. The device can handle a peak forward current of 80mA under pulsed conditions (1/10 duty cycle, 0.1ms pulse width), while the continuous DC forward current rating is 30mA. The operational and storage temperature range is specified from -40°C to +100°C.

2.2 Thermal Characteristics

The maximum allowable junction temperature (Tj) is 115°C. The typical thermal resistance from the junction to the ambient environment (Rθj-a) is 140°C/W. This parameter is crucial for thermal management design, indicating how effectively heat is transferred away from the semiconductor junction.

2.3 Electrical and Optical Characteristics

Measured at Ta=25°C and a test current (IF) of 20mA, the luminous intensity (Iv) ranges from a minimum of 56.0 mcd to a maximum of 180.0 mcd. The viewing angle (2θ1/2), defined as the full angle at which intensity drops to half its axial value, is a wide 120 degrees. The dominant wavelength (λd) spans from 566 nm to 578 nm, defining the green color. The forward voltage (VF) typically falls between 1.7V and 2.5V at the 20mA drive current. The reverse current (IR) is limited to a maximum of 10 µA at a reverse voltage (VR) of 5V, noting that the device is not intended for reverse bias operation.

3. Bin Rank System Explanation

The product is sorted into bins based on key performance parameters to ensure consistency for the end-user.

3.1 Luminous Intensity (IV) Binning

LEDs are categorized into specific bins according to their measured luminous intensity at 20mA. The bin codes (P2, Q1, Q2, R1, R2) define minimum and maximum intensity ranges, from 56.0-71.0 mcd (P2) up to 140.0-180.0 mcd (R2). A tolerance of +/-11% applies within each intensity bin.

3.2 Dominant Wavelength (WD) Binning

Similarly, the dominant wavelength is binned to control color consistency. Bin codes C, D, E, and F correspond to wavelength ranges: C (566-569 nm), D (569-572 nm), E (572-575 nm), and F (575-578 nm). The tolerance for each wavelength bin is +/- 1 nm.

4. Performance Curve Analysis

Typical performance curves provide insight into device behavior under varying conditions. These include the relationship between forward current and luminous intensity (I-V curve), the effect of ambient temperature on light output, and the spectral power distribution showing the concentration of emitted light around the peak wavelength. Analyzing these curves helps designers optimize drive conditions and understand performance trade-offs.

5. Mechanical and Package Information

5.1 Package Dimensions

The device conforms to a standard SMD footprint. All critical dimensions, including length, width, height, and pad spacing, are provided in millimeters with a general tolerance of ±0.2 mm unless otherwise specified. The lens is clear.

5.2 Recommended PCB Attachment Pad Layout

A land pattern design is recommended for reliable soldering, particularly for infrared or vapor phase reflow processes. This layout ensures proper solder fillet formation and mechanical stability.

5.3 Polarity Identification

The cathode is typically indicated by a marking on the package body or a specific pad geometry (e.g., a notch or a chamfered corner on the footprint). Correct polarity orientation is essential for circuit function.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Profile

A suggested reflow profile compliant with J-STD-020B for lead-free processes is provided. Key parameters include a preheat zone, a defined time above liquidus, and a peak temperature not exceeding 260°C. The total time within 5°C of the peak temperature should be limited. Adherence to the solder paste manufacturer's specifications is also critical.

6.2 Storage Conditions

For unopened moisture-sensitive packaging (with desiccant), storage should be at ≤ 30°C and ≤ 70% RH, with a recommended use-within period of one year. Once opened, components should be stored at ≤ 30°C and ≤ 60% RH. If exposed beyond 168 hours, a bake-out at approximately 60°C for at least 48 hours is recommended before soldering to prevent moisture-induced damage (popcorning).

6.3 Cleaning

If cleaning is necessary after soldering, only specified solvents like ethyl alcohol or isopropyl alcohol should be used. The LEDs should be immersed 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. Standard reel quantity is 5000 pieces. A minimum packing quantity of 500 pieces applies for remainder lots. The packaging conforms to ANSI/EIA 481 specifications.

7.2 Model Numbering Rule

The part number LTST-T180KGKT encodes specific attributes: likely indicating the series, package type, color (G for Green), and performance bin. The exact decoding may follow an internal scheme.

8. Application Suggestions

8.1 Typical Application Circuits

As a current-driven device, the LED should be driven using a constant current source or a voltage source with a series current-limiting resistor. The resistor value can be calculated using Ohm's Law: R = (Vcc - VF) / IF, where Vcc is the supply voltage, VF is the LED forward voltage (use max value for reliability), and IF is the desired forward current (≤ 30mA DC).

8.2 Design Considerations

Consider thermal management on the PCB, especially when operating at high currents or in elevated ambient temperatures, due to the 140°C/W thermal resistance. Ensure the PCB pad design matches the recommended layout for reliable soldering. Account for the wide 120-degree viewing angle when designing light guides or indicator apertures.

9. Technical Comparison and Differentiation

Compared to older technology like GaP (Gallium Phosphide) green LEDs, AlInGaP offers higher efficiency and brighter output. The 120-degree viewing angle is wider than many “low-profile” LEDs, providing a broader emission pattern suitable for status indicators that need to be visible from various angles. Its 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 is the difference between peak wavelength and dominant wavelength?

A: Peak wavelength (λP) is the single wavelength at which the emission spectrum has its maximum intensity. Dominant wavelength (λd) is the single wavelength of monochromatic light that matches the perceived color of the LED when compared to a reference white light. λd is more relevant for color specification.

Q: Can I drive this LED with a 3.3V supply without a resistor?

A: No. Without a current-limiting resistor, the LED would attempt to draw excessive current, likely exceeding its absolute maximum rating and causing immediate failure. Always use a series resistor or constant-current driver.

Q: What does “Preconditioning: accelerate to JEDEC level 3” mean?

A: It indicates the moisture sensitivity level (MSL) of the package. MSL 3 means the component can be exposed to factory floor conditions (≤ 30°C/60% RH) for up to 168 hours (7 days) before it must be soldered or rebaked.

11. Practical Use Case Examples

Case 1: Network Router Status Panel: Multiple LTST-T180KGKT LEDs can be used to indicate power, internet connectivity, Wi-Fi activity, and port status. Their wide viewing angle ensures visibility from across a room, and their compatibility with reflow soldering allows for cost-effective, automated assembly of the main PCB.

Case 2: Industrial Control HMI: Integrated into a membrane switch or behind a polycarbonate window, this LED provides a clear, green “System Ready” or “Machine On” indication. The defined wavelength binning ensures color consistency across all units on the production line.

12. Principle of Operation Introduction

Light emission in this AlInGaP LED is based on electroluminescence. When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region. Their recombination releases energy in the form of photons (light). The specific composition of the Aluminum, Indium, Gallium, and Phosphide layers in the semiconductor crystal determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, green.

13. Technology Trends

The general trend in SMD LEDs is toward higher luminous efficacy (more light output per electrical watt), improved color consistency through tighter binning, and increased reliability under higher temperature soldering profiles. Package sizes continue to shrink for greater design flexibility, while maintaining or improving optical performance. There is also a strong focus on developing materials and processes that meet evolving environmental regulations beyond RoHS.