SMD LED LTST-E142KGKEKT Datasheet - Package 2.0x1.25x0.8mm - Voltage 1.7-2.5V - Power 75mW - Green/Red Dual Color - English Technical Document

1. Product Overview

This document details the specifications for the LTST-E142KGKEKT, a surface-mount device (SMD) light-emitting diode (LED). This component integrates two distinct LED chips within a single, compact package: one emitting green light and the other emitting red light. The primary design objective is to provide a reliable, space-efficient solution for status indication, backlighting, and symbolic illumination in modern electronic assemblies.

1.1 Core Advantages and Target Market

The device is engineered for automated assembly processes, featuring compatibility with infrared reflow soldering and standard pick-and-place equipment. Its miniature footprint makes it suitable for applications where board space is at a premium. Key target markets include telecommunications infrastructure (e.g., network switches, routers), consumer electronics (notebooks, mobile devices), office automation equipment, home appliances, and industrial control panels. Its primary function is to serve as a visual status or signal indicator.

2. Technical Parameters: In-Depth Objective Interpretation

The following sections provide a detailed breakdown of the device's operational limits and performance characteristics under standard test conditions (Ta=25°C).

2.1 Absolute Maximum Ratings

These values define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed. For both the green and red chips: the maximum continuous DC forward current is 30 mA; the peak forward current (under pulsed conditions: 1/10 duty cycle, 0.1ms pulse width) is 80 mA; and the maximum power dissipation is 75 mW. The device is rated for an operating and storage temperature range of -40°C to +100°C.

2.2 Thermal Characteristics

Thermal management is critical for LED longevity and performance stability. The maximum allowable junction temperature (Tj) for both chips is 115°C. The typical thermal resistance from the junction to the ambient environment (Rθja) is 155 °C/W. This parameter indicates how effectively the package can dissipate heat; a lower value is preferable. Exceeding the maximum junction temperature will accelerate lumen depreciation and can lead to catastrophic failure.

2.3 Electro-Optical Characteristics

These parameters are measured at a standard test current of 20 mA. The luminous intensity (Iv) for the green chip ranges from a minimum of 56 mcd to a maximum of 180 mcd. For the red chip, the range is from 140 mcd to 420 mcd. The viewing angle (2θ1/2), defined as the full angle at which intensity drops to half its axial value, is typically 120 degrees, indicating a wide viewing pattern.

The dominant wavelength (λd), which defines the perceived color, is specified for the green chip between 564 nm and 576 nm, and for the red chip between 616 nm and 626 nm. The forward voltage (Vf) for both colors ranges from 1.7 V to 2.5 V at 20 mA. The reverse current (Ir) is specified at a maximum of 10 µA when a reverse voltage (Vr) of 5V is applied. It is crucial to note that the device is not designed for operation under reverse bias; this test condition is for informational purposes only.

3. Binning System Explanation

To ensure consistency in production, LEDs are sorted into performance bins. This allows designers to select components that meet specific brightness and color requirements.

3.1 Luminous Intensity (Iv) Binning

The green LED chips are categorized into five intensity bins: P2 (56-71 mcd), Q1 (71-90 mcd), Q2 (90-112 mcd), R1 (112-140 mcd), and R2 (140-180 mcd). The red LED chips are categorized into four bins: P (140-185 mcd), Q (185-240 mcd), R (240-315 mcd), and S (315-420 mcd). A tolerance of ±11% is applied within each bin.

3.2 Dominant Wavelength (WD) Binning

For the green LED, dominant wavelength bins are defined as G1 (564-568 nm), G2 (568-572 nm), and G3 (572-576 nm). The tolerance for each wavelength bin is ±1 nm. Binning information for the red LED's dominant wavelength is not explicitly detailed in the provided extract but follows a similar principle of tight wavelength control.

4. Performance Curve Analysis

While specific graphical data is referenced in the document (e.g., Figure 1 for spectral output, Figure 5 for viewing angle), the typical characteristics can be inferred from the tabulated data. The relationship between forward current (If) and forward voltage (Vf) is non-linear, typical of a diode. The luminous intensity is directly proportional to the forward current up to the maximum rated limits. Performance will degrade as the junction temperature increases; therefore, the thermal design of the application is paramount to maintaining specified light output and color point over the device's lifetime.

5. Mechanical and Package Information

5.1 Package Dimensions and Pin Assignment

The device conforms to an industry-standard SMD package outline. Key dimensions include a body size of approximately 2.0 mm in length and 1.25 mm in width, with a typical height of 0.8 mm. Tolerances are ±0.2 mm unless otherwise noted. The pin assignment is critical for correct operation: Pins 2 and 3 are assigned to the green AlInGaP chip, while Pins 1 and 4 are assigned to the red AlInGaP chip. The lens is clear.

5.2 Recommended PCB Attachment Pad Layout

A recommended land pattern (footprint) for the printed circuit board is provided to ensure reliable soldering and proper mechanical alignment. Adhering to this design minimizes tombstoning and ensures optimal thermal transfer from the LED package to the PCB.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Conditions

The device is compatible with lead-free (Pb-free) solder processes. A suggested infrared (IR) reflow profile is provided, compliant with the J-STD-020B standard. Key parameters include a pre-heat temperature of 150-200°C, a peak body temperature not exceeding 260°C, and a time above liquidus (TAL) tailored to the specific board assembly. The total soldering time at peak temperature should be limited to a maximum of 10 seconds, and reflow should be performed a maximum of two times.

6.2 Storage and Handling

The LEDs are moisture-sensitive. When stored in their original sealed moisture-proof bag with desiccant, they should be kept at ≤30°C and ≤70% RH and used within one year. Once the bag is opened, the "floor life" is 168 hours (7 days) at conditions not exceeding 30°C and 60% RH (JEDEC Level 3). If exposed beyond this period, a bake-out at approximately 60°C for at least 48 hours is required before soldering to prevent popcorn cracking during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only specified alcohol-based solvents such as ethyl alcohol or isopropyl alcohol should be used. The LEDs should be immersed at normal temperature for less than one minute. Unspecified chemical cleaners may damage the package epoxy or lens.

7. Packaging and Ordering Information

The devices are supplied packaged for automated assembly. They are mounted on 8mm wide carrier tape and wound onto 7-inch (178 mm) diameter reels. Each full reel contains 4000 pieces. The tape is sealed with a cover tape to protect the components. The packaging conforms to ANSI/EIA-481 specifications.

8. Application Suggestions

8.1 Typical Application Scenarios

This dual-color LED is ideal for applications requiring multi-state indication. For example, it can show green for "power on/ready," red for "fault/standby," or both for a specific mode. Common uses include status indicators on network equipment, power supplies, and consumer electronics; backlighting for front panel legends or buttons; and low-level signal luminaires.

8.2 Design Considerations

Current Limiting: An external current-limiting resistor is mandatory for each LED chip to prevent exceeding the maximum forward current. The resistor value is calculated based on the supply voltage (Vs), the LED's forward voltage (Vf) at the desired current, and the target current (If): R = (Vs - Vf) / If. Always use the maximum Vf from the datasheet for a conservative design.
Thermal Design: Ensure adequate PCB copper area (thermal relief) connected to the LED pads to help dissipate heat, especially if operating near maximum ratings.
ESD Protection: While not explicitly stated, standard ESD handling precautions should be observed during assembly.

9. Technical Comparison and Differentiation

The key differentiator of this component is the integration of two distinct monochromatic LED chips (AlInGaP for both colors) in one miniature SMD package. AlInGaP technology offers high luminous efficiency and good color saturation for red and amber/green hues compared to older technologies. The 120-degree viewing angle provides a wide emission pattern suitable for front-panel applications. The dual-chip design saves board space and simplifies assembly compared to using two separate single-color LEDs.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive the green and red LEDs simultaneously at their full 20mA each?
A: Yes, but you must consider the total power dissipation. At 20mA, if we assume a typical Vf of 2.1V for each, the total power would be (2.1V * 0.02A)*2 = 84 mW. This exceeds the absolute maximum power dissipation of 75 mW per chip (but note, the rating is per chip, not for the package sum; the thermal coupling must be considered). It is safer to derate the current or use pulsed operation to stay within thermal limits.

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength (λp) is the wavelength at the highest point in the LED's spectral power distribution curve. Dominant wavelength (λd) is derived from the CIE chromaticity diagram and represents the single wavelength of a monochromatic light that would appear to have the same color as the LED. λd is more relevant for perceived color.

Q: Why is the reverse current specification important if I shouldn't operate it in reverse?
A: The reverse current test (typically at 5V) is a quality and leakage test. A high reverse current can indicate potential defects in the semiconductor junction.

11. Practical Design and Usage Case

Scenario: Designing a dual-status indicator for a 5V USB-powered device. The green LED should indicate "active," and the red LED should indicate "charging/error."
Design Steps:
1. Current Selection: Choose a drive current of 15 mA for good brightness while maintaining a safety margin below the 30 mA maximum.
2. Resistor Calculation for Green LED: Using a typical Vf_green of 2.1V and Vs=5V. R_green = (5V - 2.1V) / 0.015A ≈ 193 Ω. Use the nearest standard value, e.g., 200 Ω.
3. Resistor Calculation for Red LED: Using a typical Vf_red of 2.0V. R_red = (5V - 2.0V) / 0.015A = 200 Ω.
4. PCB Layout: Place the LED and its current-limiting resistors close together. Use the recommended pad layout from the datasheet. Include a modest copper pour connected to the cathode pads for heat sinking.
5. Software Control: Use microcontroller GPIO pins to independently control the anode of each LED (with the resistors in series).

12. Operating Principle Introduction

Light-emitting diodes are semiconductor p-n junction devices. When a forward voltage is applied, electrons from the n-type region recombine with holes from the p-type region within the active layer. This recombination process releases energy in the form of photons (light). The specific wavelength (color) of the emitted light is determined by the energy bandgap of the semiconductor material used. The LTST-E142KGKEKT uses Aluminum Indium Gallium Phosphide (AlInGaP) for both its red and green-emitting chips, a material system known for high efficiency in the red to yellow-green spectrum. The clear epoxy package acts as a lens, shaping the light output beam.

13. Technology Trends

The general trend in SMD indicator LEDs continues toward higher luminous efficacy (more light output per electrical watt), smaller package sizes for increased density, and improved color consistency through tighter binning. There is also a focus on enhancing reliability under higher temperature reflow profiles required for lead-free soldering. The integration of multiple chips or even different colored chips in a single package, as seen in this device, addresses the need for multifunctional indicators in compact designs. The underlying material science research aims to develop more efficient and stable semiconductor compounds across the visible spectrum.