SMD LED Green Diffused Lens LTST-E681UGWT Datasheet - Package Dimensions - 3.8V Forward Voltage - 30mA - 114mW Power Dissipation - English Technical Document

1. Product Overview

This document provides the complete technical specifications for a surface-mount device (SMD) light-emitting diode (LED). The component features a diffused lens designed to provide a wide, uniform light distribution, making it suitable for applications requiring even illumination rather than a focused beam. The light source utilizes an Indium Gallium Nitride (InGaN) semiconductor material, which is engineered to emit light in the green wavelength spectrum. The product is designed for compatibility with modern electronic assembly processes.

1.1 Core Advantages and Target Market

The primary advantages of this LED include its compliance with environmental regulations, its packaging format suitable for automated high-volume manufacturing, and its compatibility with standard infrared reflow soldering processes. These features make it an ideal choice for consumer electronics, general indicator lights, backlighting for panels and displays, and various other applications within office equipment, communication devices, and household appliances where reliable, consistent green illumination is required.

2. In-Depth Technical Parameter Analysis

The performance of the LED is defined under standard ambient temperature conditions (25°C). Understanding these parameters is critical for proper circuit design and achieving expected performance.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed and should be avoided for reliable long-term performance.

• Power Dissipation (Pd): 114 mW. This is the maximum amount of power the device can safely dissipate as heat.
• Peak Forward Current (I_FP): 100 mA. This is the maximum instantaneous forward current, permissible only under pulsed conditions (1/10 duty cycle, 1ms pulse width).
• DC Forward Current (I_F): 30 mA. This is the maximum continuous forward current for steady-state operation.
• Operating Temperature Range (T_opr): -40°C to +85°C. The ambient temperature range over which the device is designed to function.
• Storage Temperature Range (T_stg): -40°C to +100°C. The temperature range for storing the device when not in operation.

2.2 Electrical and Optical Characteristics

These are the typical performance parameters measured at the recommended operating point (I_F = 30mA, T_a=25°C).

• Luminous Intensity (I_V): 1120 - 2800 mcd (millicandela). This specifies the perceived brightness of the LED as measured by a sensor filtered to match the human eye's photopic response. The wide range indicates a binning system is used (see Section 3).
• Viewing Angle (2θ_1/2): 120 degrees. This is the full angle at which the luminous intensity drops to half of its value measured on-axis. A 120-degree angle confirms the diffused lens provides a very wide viewing pattern.
• Peak Emission Wavelength (λ_P): 518 nm. This is the wavelength at which the spectral power output of the LED is at its maximum.
• Dominant Wavelength (λ_d): 520 - 535 nm. Derived from the CIE chromaticity diagram, this is the single wavelength that best describes the perceived color of the light. It is the key parameter for color specification.
• Spectral Line Half-Width (Δλ): 35 nm. This indicates the spectral bandwidth, or the range of wavelengths emitted. A value of 35nm is typical for a green InGaN LED.
• Forward Voltage (V_F): 3.3V (Typ.), 3.8V (Max.) at 30mA. This is the voltage drop across the LED when operating at the specified current. It is crucial for calculating the necessary current-limiting resistor value.
• Reverse Current (I_R): 10 μA (Max.) at V_R = 5V. The device is not designed for reverse bias operation; this parameter simply specifies the leakage current under a small reverse voltage.

3. Bin Code System Explanation

Due to inherent variations in semiconductor manufacturing, LEDs are sorted into performance bins after production. This ensures consistency within a specific batch. Three key parameters are binned.

3.1 Forward Voltage Binning

Bins D7 through D11 categorize LEDs based on their forward voltage drop at 30mA. For example, bin D9 contains LEDs with a V_F between 3.2V and 3.4V. A tolerance of ±0.1V is applied to each bin limit. Selecting LEDs from the same voltage bin is important for applications where multiple LEDs are connected in parallel to ensure uniform current sharing.

3.2 Luminous Intensity Binning

Bins W1, W2, X1, and X2 categorize the brightness output. For instance, bin X2 contains the brightest LEDs with an intensity between 2240 and 2800 mcd. A tolerance of ±11% applies to each bin's range. This binning allows designers to select a brightness grade suitable for their application, ensuring visual consistency.

3.3 Dominant Wavelength Binning

Bins AP, AQ, and AR sort the LEDs by their precise shade of green, defined by the dominant wavelength. Bin AP covers 520.0-525.0 nm (a slightly bluer green), while bin AR covers 530.0-535.0 nm (a yellower green). The tolerance is ±1nm. This is critical for color-critical applications where a specific hue is required.

4. Mechanical and Package Information

4.1 Package Dimensions

The LED conforms to a standard EIA package footprint. All critical dimensions for PCB pad design and component placement are provided in the datasheet drawings, including body length, width, height, and lead spacing. Tolerances are typically ±0.2mm unless otherwise specified. The diffused lens is integrated into the package body.

4.2 Polarity Identification and Pad Design

The component is polarized. The cathode is typically identified by a visual marker on the package, such as a notch, a green dot, or a cut corner on the lens. The recommended PCB attachment pad layout is provided to ensure proper solder joint formation and mechanical stability during and after the reflow soldering process. The pad design accounts for thermal relief and solder wicking.

5. Soldering and Assembly Guidelines

5.1 Reflow Soldering Parameters

The device is compatible with infrared (IR) reflow soldering processes, including lead-free soldering. A recommended profile is suggested, aligned with the J-STD-020B standard. Key parameters include:

• Pre-heat Temperature: 150-200°C.
• Pre-heat Time: Maximum 120 seconds.
• Peak Body Temperature: Maximum 260°C.
• Time Above Liquidus: Recommended duration as per the solder paste specification.

The profile emphasizes a controlled ramp-up and cool-down to minimize thermal shock.

5.2 Hand Soldering Notes

If hand soldering is necessary, extreme care must be taken:

• Soldering Iron Temperature: Maximum 300°C.
• Contact Time: Maximum 3 seconds per lead.
• Frequency: Soldering should be performed only once to avoid damaging the package or the internal die bond.

5.3 Storage and Handling Conditions

The LEDs are moisture-sensitive. Specific storage conditions are mandated to prevent "popcorning" (package cracking) during reflow due to absorbed moisture.

• Sealed Package: Store at ≤30°C and ≤70% Relative Humidity (RH). Use within one year.
• Opened Package: Store at ≤30°C and ≤60% RH. If exposed to ambient air for more than 168 hours, a bake-out at approximately 60°C for at least 48 hours is required before soldering to drive off moisture.
• For extended storage after opening, use a sealed container with desiccant or a nitrogen-purged desiccator.

5.4 Cleaning

If post-solder cleaning is required, only specified solvents should be used. Immersing the LED in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute is acceptable. Unspecified chemical cleaners may damage the plastic package or lens.

6. Packaging and Ordering Information

6.1 Tape and Reel Specifications

The components are supplied in a format compatible with automated pick-and-place machines.

• Tape Width: 8 mm.
• Reel Diameter: 7 inches (178 mm).
• Quantity per Reel: 2000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• The packaging follows ANSI/EIA-481 specifications. Empty pockets in the carrier tape are sealed with a top cover tape to protect components.

7. Application Notes and Design Considerations

7.1 Drive Circuit Design

An LED is a current-operated device. Its light output is primarily a function of forward current (I_F), not voltage. Therefore, driving it with a constant voltage source is not recommended as it can lead to thermal runaway and destruction. The standard and most reliable method is to use a series current-limiting resistor when powered from a voltage source (e.g., V_CC = 5V or 3.3V). The resistor value (R_S) is calculated using Ohm's Law: R_S = (V_CC - V_F) / I_F. For multiple LEDs, it is strongly advised to use a separate resistor for each LED connected in parallel to ensure uniform current distribution and brightness, as the forward voltage (V_F) can vary slightly even within a bin.

7.2 Thermal Management

While the power dissipation is relatively low (114mW max), proper thermal design extends LED lifespan and maintains stable optical output. Ensure the PCB pad design provides adequate thermal relief to dissipate heat into the board. Operating the LED at or near its maximum current rating (30mA) or in high ambient temperatures (approaching +85°C) will reduce its luminous output and potentially shorten its lifetime. Derating the operating current is a common practice for high-reliability applications.

7.3 Optical Integration

The 120-degree viewing angle of the diffused lens provides a wide, soft light pattern. This makes it suitable for applications where the LED itself is meant to be directly viewed as an indicator or where even backlighting of a small area or icon is needed. For applications requiring more focused light, secondary optics (like a separate lens) would be required. The diffused lens also helps to minimize the appearance of the bright die point, creating a more uniform emitting surface.

8. Technical Comparison and Differentiation

Compared to LEDs with clear lenses, this diffused lens variant trades off peak axial intensity (candela) for a much wider and more uniform viewing angle. This is a functional choice, not a performance deficiency. Compared to older technologies like Gallium Phosphide (GaP) green LEDs, the InGaN-based device offers significantly higher luminous efficiency (brighter light output for the same current) and a more saturated, pure green color. Its compatibility with lead-free, high-temperature reflow soldering differentiates it from older through-hole LEDs or devices requiring manual soldering, aligning it with modern, automated SMT assembly lines.

9. Frequently Asked Questions (FAQ)

9.1 What resistor should I use with a 5V supply?

Using the typical V_F of 3.3V and desired I_F of 20mA (for a longer life), the calculation is: R = (5V - 3.3V) / 0.020A = 85 Ohms. The nearest standard value is 82 Ohms or 100 Ohms. Recalculate the actual current with the chosen resistor and the max/min V_F from the bin to ensure it stays within safe limits.

9.2 Can I drive this LED with a 3.3V microcontroller pin?

It is possible but challenging. The typical V_F (3.3V) is equal to the supply, leaving no voltage headroom for a series resistor at the desired operating current. The LED may light dimly or not at all, especially if the V_F is at the higher end of the range (up to 3.8V). A dedicated LED driver circuit or a boost converter is recommended for efficient operation from a 3.3V rail.

9.3 Why is the storage condition so strict?

The plastic epoxy package can absorb moisture from the air. During the rapid heating of reflow soldering, this trapped moisture can vaporize instantly, creating high internal pressure. This can cause the package to crack ("popcorn effect") or delaminate, leading to immediate failure or reduced long-term reliability. The storage and baking procedures prevent moisture absorption.

10. Operational Principle

Light emission in this LED is based on electroluminescence in a semiconductor InGaN p-n junction. When a forward voltage exceeding the junction's built-in potential is applied, electrons from the n-type region and holes from the p-type region are injected into the active region. When these charge carriers recombine, energy is released in the form of photons (light). The specific composition of the Indium Gallium Nitride (InGaN) alloy in the active region determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, green. The diffused lens is made of an epoxy resin containing scattering particles that randomize the direction of the emitted light, broadening the viewing angle.

11. Industry Trends

The LED industry continues to focus on increasing luminous efficacy (lumens per watt), improving color rendering, and reducing cost. For indicator-type SMD LEDs, trends include further miniaturization (smaller package sizes like 0402 and 0201), higher reliability for automotive and industrial applications, and the development of more consistent and tighter performance bins to aid designers in achieving uniform visual results. The drive towards higher levels of automation in assembly also pushes for more robust packaging that can withstand increasingly demanding reflow profiles.