SMD LED LTST-T180UWET Datasheet - 120-Degree Viewing Angle - 2.45-3.25V Forward Voltage - 30mA Current - White Light with Yellow Lens - English Technical Document

1. Product Overview

The LTST-T180UWET is a surface-mount device (SMD) light-emitting diode (LED) designed for automated printed circuit board (PCB) assembly. It features a compact form factor suitable for space-constrained applications. The LED emits white light through a yellow-tinted lens, which can influence the perceived color temperature and diffusion of the output. This component is engineered for high-volume manufacturing processes, including compatibility with infrared (IR) reflow soldering profiles.

1.1 Core Advantages and Target Market

Key features of this LED include compliance with RoHS (Restriction of Hazardous Substances) directives, packaging on 8mm tape within 7-inch reels for automated pick-and-place equipment, and preconditioning to JEDEC Level 3 moisture sensitivity standards. Its primary applications span telecommunications equipment, office automation devices, home appliances, industrial control panels, and indoor signage. It is commonly used for status indication, symbolic illumination, and front-panel backlighting where a reliable, compact light source is required.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

At an ambient temperature (Ta) of 25°C, the device has defined operational limits to ensure reliability and prevent damage. The maximum power dissipation is 97.5 mW. It can handle a peak forward current of 100 mA under pulsed conditions (1/10 duty cycle, 0.1ms pulse width), while the recommended continuous DC forward current is 30 mA. The device is rated for operation and storage within a temperature range of -40°C to +100°C.

2.2 Thermal Characteristics

The maximum allowable junction temperature (Tj) is 125°C. The typical thermal resistance from the junction to the ambient environment (Rθja) is 60°C/W. This parameter is crucial for thermal management design; the power dissipated by the LED will cause the junction temperature to rise above the ambient temperature by 60°C for every watt of power. Proper PCB layout and, if necessary, additional heat sinking must be considered to maintain the junction within safe limits during continuous operation.

2.3 Electrical and Optical Characteristics

Measured at Ta=25°C and a forward current (IF) of 20mA, the key performance parameters are defined. The luminous intensity (Iv) has a typical range from 1500 mcd (millicandela) to 3050 mcd, indicating a bright output. The viewing angle (2θ1/2), defined as the full angle where intensity drops to half of its axial value, is 120 degrees, providing a very wide field of illumination. The forward voltage (VF) ranges from a minimum of 2.45V to a maximum of 3.25V. The reverse current (IR) is specified at a maximum of 10 μA when a reverse voltage (VR) of 5V is applied, noting that the device is not designed for reverse-bias operation.

3. Bin Ranking System Explanation

The LEDs are sorted into bins based on key parameters to ensure consistency in mass production. This allows designers to select parts that meet specific circuit or brightness requirements.

3.1 Forward Voltage (VF) Rank

LEDs are categorized into four voltage bins (D5 to D8), each with a 0.2V range spanning from 2.45V to 3.25V at 20mA. A tolerance of ±0.1V is applied to each bin. This helps in designing power supplies and current-limiting circuits with predictable voltage drops.

3.2 Luminous Intensity (IV) Rank

Three intensity bins are defined: W2 (1500-1800 mcd), X1 (1800-2340 mcd), and X2 (2340-3050 mcd). A tolerance of ±11% applies to each bin. Selecting a higher bin ensures greater light output, which may be necessary for applications requiring higher visibility or to compensate for light diffusion through materials.

3.3 Color Rank

The chromaticity coordinates (x, y) on the CIE 1931 diagram are binned into six primary groups (A1 through F1). Each bin defines a quadrilateral area on the color chart. The tolerance for hue (x, y) within a bin is ±0.01. This binning is critical for applications where color consistency across multiple LEDs is important, such as in backlighting arrays or status indicators where uniform appearance is desired.

4. Performance Curve Analysis

While specific graphical data is referenced in the document (e.g., typical curves), the provided tabular data allows for analysis. The relationship between forward current (IF) and forward voltage (VF) is non-linear and typical of a diode. The 20mA test condition provides the standard operating point. The wide viewing angle of 120 degrees suggests a Lambertian or similar radiation pattern where light is emitted over a broad area rather than a focused beam. The variation of luminous intensity and forward voltage with junction temperature is a critical consideration for design; generally, LED efficiency decreases and forward voltage drops as temperature increases.

5. Mechanical and Packaging Information

5.1 Package Dimensions

The LED conforms to an EIA standard SMD package footprint. All dimensions are provided in millimeters with a standard tolerance of ±0.2mm unless otherwise noted. The specific dimensions for body length, width, height, and lead/pad spacing are defined in the package drawing, which is essential for creating accurate PCB land patterns.

5.2 Polarity Identification and Pad Design

The component includes a recommended PCB attachment pad layout diagram for infrared or vapor phase reflow soldering. This layout ensures proper solder joint formation and mechanical stability. The diagram typically indicates the anode and cathode pads, which must be correctly aligned with the polarity markings on the LED package itself (often a notch, dot, or trimmed lead).

6. Soldering and Assembly Guidelines

6.1 Recommended IR Reflow Profile

A suggested reflow soldering profile for lead-free (Pb-free) processes is provided, referencing the J-STD-020B standard. This profile includes pre-heat, thermal soak, reflow, and cooling stages with specific time and temperature constraints, with a peak temperature not exceeding 260°C. Adherence to this profile is necessary to prevent thermal damage to the LED package or lens.

6.2 Storage Conditions

The LEDs are moisture-sensitive. When sealed in their original moisture-proof bag with desiccant, they should be stored at ≤30°C and ≤70% RH and used within one year. Once the bag is opened, the storage environment must not exceed 30°C and 60% RH. Components exposed beyond 168 hours require baking at approximately 60°C for at least 48 hours before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

6.3 Cleaning

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

7. Packaging and Ordering Information

The standard packaging is 8mm tape on 7-inch diameter reels, with 5000 pieces per reel. A minimum order quantity of 500 pieces is available for remnants. The tape and reel specifications comply with ANSI/EIA 481 standards. The packaging includes a top cover tape to seal empty pockets, and there is a limit on the number of consecutive missing components.

8. Application Recommendations

8.1 Typical Application Scenarios

This LED is ideal for status indicators in consumer electronics (phones, laptops, appliances), backlighting for buttons or panels in network equipment and industrial controls, and low-level illumination in indoor signs. Its wide viewing angle makes it suitable for applications where the light needs to be visible from various angles.

8.2 Design Considerations

1. Current Limiting: Always use a series resistor or constant current driver to limit the forward current to 30mA DC or less. The circuit design must account for the forward voltage bin to ensure proper current regulation.
2. Thermal Management: Consider the 60°C/W thermal resistance. For continuous operation at high currents, ensure the PCB can dissipate heat effectively to keep the junction temperature below 125°C.
3. Optical Design: The yellow lens will affect the output color. For pure white light requirements, verify the chromaticity bin. The wide viewing angle may require diffusers or light guides to shape the beam for specific applications.
4. ESD Precautions: While not explicitly stated for this model, standard ESD handling precautions for LEDs are recommended during assembly.

9. Technical Comparison and Differentiation

Compared to generic SMD LEDs, this component offers specific binning for voltage, intensity, and color, providing greater consistency for production runs. The 120-degree viewing angle is notably wider than many standard LEDs (which may be 60-90 degrees), offering broader illumination. Its compatibility with JEDEC Level 3 preconditioning and standard IR reflow profiles indicates robustness for standard surface-mount assembly lines. The explicit thermal resistance rating provides a concrete parameter for thermal design, which is often omitted in simpler datasheets.

10. Frequently Asked Questions Based on Technical Parameters

Q: What resistor value should I use with a 5V supply?
A: Using Ohm's Law (R = (Vsupply - Vf) / If) and the worst-case Vf (max 3.25V at 20mA), the minimum resistor is (5 - 3.25) / 0.02 = 87.5 ohms. Use a standard value like 100 ohms or slightly higher to ensure current does not exceed 20mA for a typical LED.

Q: Can I drive this LED with a PWM signal for dimming?
A: Yes, pulsed operation is acceptable. The absolute maximum rating allows for 100mA peak current at a 1/10 duty cycle with a 0.1ms pulse width. For PWM dimming, ensure the average current over time does not exceed the 30mA DC rating, and the instantaneous current during the \"on\" pulse respects the peak rating.

Q: How does temperature affect brightness?
A: Luminous output of LEDs generally decreases as junction temperature increases. For precise brightness control over temperature, feedback or compensation may be necessary. The thermal resistance value helps calculate the expected junction temperature rise for a given operating condition.

11. Practical Design and Usage Case

Case: Front Panel Status Indicator Array
In a network router, ten LTST-T180UWET LEDs are used to indicate link status for different ports. Design steps include: 1) Selecting LEDs from the same intensity bin (e.g., X1) and color bin to ensure uniform brightness and hue across the panel. 2) Designing a PCB with the recommended pad layout. 3) Using a 3.3V rail and calculating a current-limiting resistor for ~18mA per LED (e.g., (3.3V - 2.85V_typ) / 0.018A = 25 ohms). 4) Ensuring the PCB copper area around the pads is sufficient to act as a heat sink, especially if all LEDs are on continuously. 5) Following the specified reflow profile during assembly. 6) Performing a visual inspection post-assembly to check for proper soldering and alignment.

12. Principle Introduction

Light-emitting diodes are semiconductor devices that emit light when an electric current passes through them. This phenomenon, called electroluminescence, occurs when electrons recombine with electron holes within the device, releasing energy in the form of photons. The color of the light is determined by the energy band gap of the semiconductor material. White LEDs are typically created by using a blue or ultraviolet LED chip coated with a phosphor material that converts some of the emitted light to longer wavelengths (yellow, red), resulting in a mixture perceived as white light. The yellow lens on this particular model may further modify the spectral output or diffuse the light.

13. Development Trends

The general trend in SMD LED technology continues toward higher luminous efficacy (more light output per watt of electrical input), improved color rendering index (CRI) for white LEDs, and smaller package sizes enabling higher density layouts. There is also a focus on enhanced reliability under higher temperature operating conditions and more precise binning for color and flux to meet the demands of applications like high-resolution displays and automotive lighting. The drive for energy efficiency across all electronic devices further pushes the adoption of LEDs with optimal performance characteristics.