SMD LED LTST-E142TGKEKT Datasheet - Package 2.0x1.25x0.8mm - Voltage 2.8-3.8V/1.7-2.5V - Power 76mW/75mW - Green/Red - English Technical Document

1. Product Overview

This document details the specifications for a surface-mount LED component designed for automated printed circuit board assembly. The device is particularly suited for space-constrained applications across a broad spectrum of electronic equipment. Its miniature size and compatibility with modern manufacturing processes make it a versatile choice for indicator and backlighting functions.

1.1 Core Advantages and Target Market

The primary advantages of this component include its compliance with RoHS directives, packaging in industry-standard 8mm tape on 7-inch reels for automated placement, and full compatibility with infrared reflow soldering processes. It is preconditioned to JEDEC Level 3 moisture sensitivity standards, ensuring reliability during assembly.

The target applications are diverse, spanning telecommunications, office automation, home appliances, and industrial equipment. Specific uses include status indicators, signal and symbol luminaires, and front panel backlighting, where reliable, compact illumination is required.

2. Technical Parameters: In-Depth Objective Interpretation

This section provides a detailed breakdown of the device's electrical, optical, and thermal characteristics. All parameters are specified at an ambient temperature (Ta) of 25°C unless otherwise noted.

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation under or at these conditions is not guaranteed.

• Power Dissipation (Pd): 76 mW (Green), 75 mW (Red). This is the maximum power the LED can dissipate continuously.
• Peak Forward Current (I_F(PEAK)): 80 mA for both colors. This is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width).
• DC Forward Current (I_F): 20 mA (Green), 30 mA (Red). This is the recommended maximum continuous forward current for reliable operation.
• Temperature Range: Operating and storage temperature range is -40°C to +100°C.

2.2 Thermal Characteristics

Understanding thermal performance is critical for reliability and longevity.

• Maximum Junction Temperature (T_j): 115°C for both colors. The semiconductor junction must not exceed this temperature.
• Thermal Resistance, Junction-to-Ambient (R_θJA): Typical values are 145 °C/W (Green) and 155 °C/W (Red). This parameter indicates how effectively heat is transferred from the LED junction to the surrounding air. A lower value signifies better heat dissipation.

2.3 Electrical and Optical Characteristics

These are the typical performance parameters under standard test conditions (I_F = 20mA).

• Luminous Intensity (I_V): Green: 710-1540 mcd (min-max). Red: 140-420 mcd (min-max). Measured with a filter approximating the CIE photopic eye response.
• Viewing Angle (2θ_1/2): Typically 120 degrees for the Green LED. This is the full angle at which luminous intensity drops to half its axial value.
• Peak Emission Wavelength (λ_P): Typical 523 nm (Green), 630 nm (Red).
• Dominant Wavelength (λ_d): Green: 515-530 nm. Red: 619-629 nm. This defines the perceived color with a tolerance of ±1 nm.
• Spectral Line Half-Width (Δλ): Typical 25 nm (Green), 15 nm (Red). Indicates the spectral purity of the emitted light.
• Forward Voltage (V_F): Green: 2.8-3.8 V. Red: 1.7-2.5 V. Tolerance is ±0.1V. This is the voltage drop across the LED when driven at 20mA.
• Reverse Current (I_R): Maximum 10 µA at V_R = 5V. The device is not designed for reverse operation; this parameter is for infrared test reference only.

3. Binning System Explanation

The devices are sorted into bins based on key optical parameters to ensure color and brightness consistency within a production batch.

3.1 Luminous Intensity (I_V) Binning

LEDs are categorized by their measured luminous intensity at 20mA.

Green LED Bins:

• V1: 710 - 910 mcd
• V2: 910 - 1185 mcd
• W1: 1185 - 1540 mcd

Tolerance within each bin is ±11%.

Red LED Bins:

• R2: 140 - 185 mcd
• S1: 185 - 240 mcd
• S2: 240 - 315 mcd
• T1: 315 - 420 mcd

Tolerance within each bin is ±11%.

3.2 Dominant Wavelength (λ_d) Binning

For the Green LED, devices are also binned by dominant wavelength to control color consistency.

Green LED Wavelength Bins:

• AP: 515 - 520 nm
• AQ: 520 - 525 nm
• AR: 525 - 530 nm

Tolerance for each wavelength bin is ±1 nm.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Figure 1 for spectral distribution, Figure 5 for viewing angle), their typical interpretations are crucial for design.

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

The relationship is exponential. For the Green LED, V_F typically ranges from ~2.8V to 3.8V at 20mA. For the Red LED, V_F is lower, ranging from ~1.7V to 2.5V at 20mA. Designers must use appropriate current-limiting resistors or drivers based on the supply voltage and the specific V_F of the LED bin used.

4.2 Luminous Intensity vs. Forward Current

Luminous intensity generally increases with forward current but not linearly. Operating above the recommended DC forward current (20mA/30mA) can lead to accelerated lumen depreciation, color shift, and reduced lifetime due to excessive heat and current density.

4.3 Temperature Characteristics

LED performance is temperature-dependent. Typically, forward voltage (V_F) decreases with increasing junction temperature. More critically, luminous intensity decreases as temperature rises. Effective thermal management (via PCB layout, copper area, etc.) is essential to maintain stable light output and longevity, especially when operating near maximum ratings.

5. Mechanical and Package Information

5.1 Package Dimensions

The device conforms to an EIA standard package outline. Key dimensions (in millimeters, tolerance ±0.2mm unless noted) define its footprint: length, width, and height. The specific pin assignment is: Pins 2 and 3 are for the Green LED chip (InGaN), and Pins 1 and 4 are for the Red LED chip (AlInGaP). The lens is clear.

5.2 Recommended PCB Attachment Pad Layout

A land pattern design is provided to ensure proper soldering and mechanical stability. Adhering to this recommended footprint facilitates good solder joint formation during reflow, prevents tombstoning, and aids in heat dissipation from the LED package to the PCB.

5.3 Polarity Identification

Correct orientation is vital. The datasheet specifies the pin assignment (Green: pins 2,3; Red: pins 1,4). The PCB silkscreen and footprint should clearly indicate the cathode/anode or pin 1 location to prevent assembly errors.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Parameters

The component is compatible with lead-free (Pb-free) IR reflow processes. A suggested profile compliant with J-STD-020B is referenced. Key parameters include:

• Pre-heat: 150-200°C maximum.
• Time above liquidus: 120 seconds maximum.
• Peak Temperature: 260°C maximum.
• Time at peak: 10 seconds maximum (maximum of two reflow cycles).

Profiles must be characterized for the specific PCB assembly.

6.2 Hand Soldering (Soldering Iron)

If hand soldering is necessary, extreme care is required:

• Iron Temperature: 300°C maximum.
• Soldering Time: 3 seconds maximum per joint.
• Limit: One soldering cycle only to prevent thermal damage.

6.3 Storage Conditions

Moisture sensitivity is a critical factor (JEDEC Level 3).

• Sealed Bag: Store at ≤30°C and ≤70% RH. Use within one year of bag seal date.
• After Bag Opening: Store at ≤30°C and ≤60% RH. It is recommended to complete IR reflow within 168 hours (7 days).
• Extended Storage (Opened): Store in a sealed container with desiccant or in a nitrogen desiccator.
• Rebaking: If exposed for more than 168 hours, bake at approximately 60°C for at least 48 hours before soldering.

6.4 Cleaning

If post-assembly cleaning is required, use only specified solvents. Immerse the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Do not use unspecified chemicals.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The component is supplied in embossed carrier tape for automated pick-and-place machines.

• Tape Width: 8 mm.
• Reel Diameter: 7 inches (178 mm).
• Quantity per Reel: 4000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Packing Standard: Complies with ANSI/EIA-481 specifications. Empty pockets are sealed with cover tape.

8. Application Suggestions

8.1 Typical Application Circuits

The LED requires a current-limiting mechanism. The simplest method is a series resistor. The resistor value (R_s) is calculated as: R_s = (V_supply - V_F) / I_F. Use the maximum V_F from the datasheet for a conservative design to ensure I_F does not exceed limits even with component tolerances. For the dual-color device, independent current control for each color channel is necessary for mixed-color or alternating operation.

8.2 Design Considerations and Precautions

• Current Driving: Always drive with a constant current or use a series resistor. Never connect directly to a voltage source.
• Thermal Management: Maximize copper area connected to the LED pads on the PCB to act as a heat sink, especially for high-brightness bins or continuous operation.
• ESD Protection: Although not explicitly stated as sensitive, handling with ESD precautions is good practice for all semiconductor devices.
• Reverse Voltage: The device is not designed for reverse bias operation. Ensure correct polarity in the circuit.
• Application Scope: The component is intended for standard electronic equipment. For applications requiring exceptional reliability (e.g., aviation, medical, safety systems), specific qualification and consultation are necessary.

9. Technical Comparison and Differentiation

This dual-color SMD LED offers a compact, single-package solution for applications requiring two distinct indicator colors (Green and Red), saving PCB space compared to using two separate single-color LEDs. The use of InGaN for green and AlInGaP for red provides efficient, saturated colors. Its compatibility with high-volume, automated IR reflow assembly differentiates it from LEDs requiring manual or wave soldering. The detailed binning structure allows designers to select consistency levels appropriate for their cost and performance targets.

10. Frequently Asked Questions (Based on Technical Parameters)

10.1 Can I drive the Green and Red LEDs simultaneously at their full current?

No, not from the same pins. The Green and Red chips are electrically separate, connected to different pin pairs (2,3 for Green; 1,4 for Red). They must be driven by independent current sources or with separate series resistors. The total power dissipation for the package must not be exceeded, which would require considering the combined heat from both chips if operated concurrently.

10.2 Why is the forward voltage different for Green and Red?

The forward voltage is a fundamental property of the semiconductor material's bandgap. Green light from InGaN has a higher photon energy (shorter wavelength) than red light from AlInGaP, which correlates with a larger semiconductor bandgap. A larger bandgap typically results in a higher forward voltage, explaining the Green LED's higher V_F range (2.8-3.8V) compared to the Red LED (1.7-2.5V).

10.3 What does "Preconditioning to JEDEC Level 3" mean?

It means the component has been classified as Moisture Sensitivity Level (MSL) 3 per JEDEC standards. This indicates the device can be exposed to factory floor conditions (≤30°C/60% RH) for up to 168 hours (7 days) after the moisture-protective bag is opened without requiring a bake prior to reflow soldering. Exceeding this floor life requires the baking procedure outlined in the storage section.

10.4 How do I interpret the luminous intensity bin codes (V1, W1, R2, T1, etc.)?

These are arbitrary labels assigned to specific ranges of measured luminous output. For example, a Green LED from bin "W1" will have an intensity between 1185 and 1540 mcd when driven at 20mA. Ordering a specific bin code ensures you receive LEDs with brightness within that defined range, promoting consistency in your product's appearance.

11. Practical Design and Usage Case

Scenario: Dual-Status Indicator for a Network Router
A designer needs a single component to show "Power/Activity" (Green) and "Fault/Alert" (Red) on a router's front panel. Using the LTST-E142TGKEKT saves space. The microcontroller GPIO pins drive each color via separate current-limiting resistors. The Green LED (driven from pin 2, with pin 3 to ground) indicates normal operation with a steady or blinking light. The Red LED (driven from pin 1, with pin 4 to ground) illuminates upon a system error. The 120-degree viewing angle ensures visibility from a wide range. The designer selects a mid-range intensity bin (e.g., V2 for Green, S1 for Red) for adequate brightness without excessive power consumption. The PCB layout follows the recommended pad design and includes a generous thermal relief connected to a ground plane.

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, electrons from the n-type material recombine with holes from the p-type material in the active region. This recombination releases energy in the form of photons (light). The specific wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor materials used. In this component, Indium Gallium Nitride (InGaN) is used for the green emitter, and Aluminum Indium Gallium Phosphide (AlInGaP) is used for the red emitter, each chosen for their efficiency and color characteristics in their respective spectral regions.

13. Technology Trends

The field of SMD LEDs continues to evolve towards higher efficiency (more lumens per watt), improved color rendering, and greater miniaturization. There is a trend for integrating multiple color chips (RGB, RGBW) into a single package for tunable white or full-color applications. Furthermore, advancements in packaging materials and thermal management techniques are pushing the boundaries of power density and reliability, allowing SMD LEDs to be used in increasingly demanding applications, including automotive lighting and specialized industrial indicators. The drive for sustainability also emphasizes materials and processes with lower environmental impact.