LTST-S320KSKT Yellow SMD LED Datasheet - Side Looking - 3.2x2.0x1.1mm - 2.4V Max - 75mW - English Technical Document

1. Product Overview

The LTST-S320KSKT is a surface-mount device (SMD) light-emitting diode (LED) designed for applications requiring a side-emitting light source. It utilizes an Ultra Bright Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor chip to produce yellow light. The device features a water-clear lens and a tin-plated lead frame, packaged in a standard EIA-compliant housing. It is supplied on 8mm tape wound onto 7-inch diameter reels, making it fully compatible with high-speed automated pick-and-place assembly equipment and standard infrared (IR) reflow soldering processes.

1.1 Core Features and Advantages

• High Brightness: The AlInGaP chip technology delivers high luminous intensity, with typical values ranging from 45.0 to 180.0 millicandelas (mcd) at a forward current of 20mA.
• Side-Viewing Design: The package is engineered to emit light from the side, which is ideal for backlighting indicators, edge-lit panels, and status displays where lateral illumination is required.
• Compatibility: The device is I.C. compatible and designed for use with automatic placement systems, streamlining the manufacturing process.
• Environmental Compliance: The product is compliant with RoHS (Restriction of Hazardous Substances) directives and is classified as a Green Product.
• Reflow Solderable: It is rated for infrared reflow soldering processes with a peak temperature of 260°C for 10 seconds, suitable for lead-free (Pb-free) assembly lines.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

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

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED can dissipate as heat without degrading performance or causing failure.
• Peak Forward Current (I_F(PEAK)): 80 mA. This is the maximum allowable pulsed current, specified at a 1/10 duty cycle with a 0.1ms pulse width. It should not be exceeded even momentarily.
• DC Forward Current (I_F): 30 mA. This is the maximum continuous forward current recommended for reliable long-term operation.
• Reverse Voltage (V_R): 5 V. Applying a reverse voltage exceeding this value can cause immediate and catastrophic failure of the LED junction.
• Operating Temperature Range (T_opr): -30°C to +85°C. The ambient temperature range within which the LED is designed to function correctly.
• Storage Temperature Range (T_stg): -40°C to +85°C. The temperature range for storing the device when not in operation.

2.2 Electrical & Optical Characteristics

These parameters are measured at an ambient temperature (T_a) of 25°C and define the typical performance of the device.

• Luminous Intensity (I_V): Min. 45.0 mcd, Typ. (see binning), Max. 180.0 mcd @ I_F=20mA. Measured using a sensor filtered to match the CIE photopic (human eye) response curve.
• Viewing Angle (2θ_1/2): 130 degrees. This is the full angle at which the luminous intensity drops to half of its peak (on-axis) value. A wide viewing angle like this is characteristic of side-emitting packages.
• Peak Emission Wavelength (λ_P): 588 nm. The specific wavelength at which the LED emits the most optical power.
• Dominant Wavelength (λ_d): 587.0 - 594.5 nm @ I_F=20mA. This is the single wavelength perceived by the human eye that defines the color (yellow). It is derived from the CIE chromaticity diagram.
• Spectral Line Half-Width (Δλ): 15 nm. This indicates the spectral purity; a smaller value means a more monochromatic light source.
• Forward Voltage (V_F): Min. 1.80 V, Typ. (see binning), Max. 2.40 V @ I_F=20mA. The voltage drop across the LED when operating.
• Reverse Current (I_R): Max. 10 μA @ V_R=5V. A small leakage current that flows when the device is reverse-biased within its maximum rating.

3. Binning System Explanation

To ensure color and brightness consistency in production, LEDs are sorted into bins based on key parameters. The LTST-S320KSKT uses a three-dimensional binning system.

3.1 Forward Voltage Binning

Units: Volts (V) @ 20mA. Tolerance per bin: ±0.1V.

- Bin F2: 1.80V (Min) to 2.10V (Max)

- Bin F3: 2.10V (Min) to 2.40V (Max)

3.2 Luminous Intensity Binning

Units: Millicandelas (mcd) @ 20mA. Tolerance per bin: ±15%.

- Bin P: 45.0 mcd (Min) to 71.0 mcd (Max)

- Bin Q: 71.0 mcd (Min) to 112.0 mcd (Max)

- Bin R: 112.0 mcd (Min) to 180.0 mcd (Max)

3.3 Dominant Wavelength Binning

Units: Nanometers (nm) @ 20mA. Tolerance per bin: ±1nm.

- Bin J: 587.0 nm (Min) to 589.5 nm (Max)

- Bin K: 589.5 nm (Min) to 592.0 nm (Max)

- Bin L: 592.0 nm (Min) to 594.5 nm (Max)

The full part number, including bin codes (e.g., LTST-S320KSKT), specifies the exact performance characteristics of the device. Designers should select the appropriate bin to meet their application's requirements for brightness and color consistency.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (pages 6-9), the following analysis is based on the provided tabular data and standard LED behavior.

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

The forward voltage (V_F) has a typical range of 1.80V to 2.40V at 20mA. Like all diodes, the I-V relationship is exponential. Operating the LED significantly below 20mA will result in a lower V_F, while driving it at the maximum DC current of 30mA will increase V_F and power dissipation. A current-limiting resistor or constant-current driver is essential for stable operation.

4.2 Luminous Intensity vs. Forward Current

Luminous intensity is approximately proportional to the forward current within the operating range. However, efficiency may drop at very high currents due to increased junction temperature. The binning system ensures predictable brightness at the standard test condition of 20mA.

4.3 Temperature Dependence

The performance of AlInGaP LEDs is affected by temperature. As the junction temperature increases, the forward voltage typically decreases slightly, while the luminous output decreases. The specified operating temperature range of -30°C to +85°C ensures reliable function, but designs should manage thermal dissipation to maintain optimal brightness and longevity, especially when operating near the maximum current or in high ambient temperatures.

5. Mechanical & Package Information

5.1 Package Dimensions

The device conforms to a standard EIA package outline. Key dimensions (in millimeters) include the body size and lead spacing, which are critical for PCB footprint design. The side-looking design means the primary light-emitting surface is on the longer side of the package.

5.2 Suggested Soldering Pad Layout and Polarity

The datasheet provides a recommended land pattern (solder pad design) for the PCB. Adhering to this pattern ensures proper solder joint formation and mechanical stability during reflow. The device has a polarity marking (typically a cathode indicator on the package). Correct orientation is crucial, as applying reverse voltage can destroy the LED.

6. Soldering & Assembly Guidelines

6.1 Infrared Reflow Soldering Profile

A suggested reflow profile for Pb-free processes is provided. Key parameters include:

- Pre-heat: 150-200°C for a maximum of 120 seconds to gradually heat the board and activate flux.

- Peak Temperature: Maximum of 260°C.

- Time Above Liquidus: The device should be exposed to the peak temperature for a maximum of 10 seconds. Reflow should be performed a maximum of two times.

6.2 Hand Soldering

If hand soldering is necessary:

- Iron Temperature: Maximum 300°C.

- Soldering Time: Maximum 3 seconds per lead.

- Frequency: Should be performed only once to minimize thermal stress.

6.3 Cleaning

If cleaning after soldering is required, only specified solvents should be used. The datasheet recommends immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Unspecified chemicals may damage the plastic package or lens.

6.4 Storage and Handling

• ESD Precautions: LEDs are sensitive to electrostatic discharge (ESD). Use wrist straps, anti-static mats, and properly grounded equipment during handling.
• Moisture Sensitivity: While the sealed reel provides protection, devices removed from packaging should be used promptly. If storage is needed, they should be kept in a dry environment (<60% RH, <30°C). For extended storage outside the original packaging, a sealed container with desiccant or a nitrogen desiccator is recommended. Devices stored for over a week may require baking (e.g., 60°C for 20 hours) before soldering to prevent \"popcorning\" during reflow.

7. Packaging and Ordering

The standard packaging is 8mm carrier tape on 7-inch (178mm) diameter reels.

- Quantity per Reel: 3000 pieces.

- Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.

- Tape Specifications: Compliant with ANSI/EIA-481. Empty pockets are sealed with cover tape. The maximum allowable number of consecutive missing components is two.

8. Application Suggestions and Design Considerations

8.1 Typical Application Scenarios

• Consumer Electronics: Side-illumination for button backlighting, power indicators, or status lights in appliances, audio equipment, and remote controls.
• Instrumentation: Panel indicators and backlights for meters, industrial controls, and medical devices (subject to appropriate reliability validation).
• Automotive Interior Lighting: Low-power status indicators, though qualification to automotive-grade standards would be necessary.
• Decorative Lighting: Edge-lighting for acrylic panels or signs.

8.2 Critical Design Considerations

1. Current Limiting: Always use a series resistor or constant-current driver. Calculate the resistor value using R = (V_supply - V_F) / I_F. Use the maximum V_F from the bin to ensure current does not exceed limits even with part-to-part variation.
2. Thermal Management: Ensure the PCB layout provides adequate thermal relief, especially if multiple LEDs are used or if operating at high ambient temperatures. The 75mW power dissipation limit must be respected.
3. Optical Design: The 130-degree viewing angle provides a wide beam. For more directed light, external lenses or light guides may be necessary. The water-clear lens offers minimal light diffusion.
4. Waveform Selection: For applications requiring higher apparent brightness or multiplexing, pulsed operation up to the peak current (80mA, 1/10 duty cycle) can be used, but the average current must not exceed the DC rating.

9. Technical Comparison and Differentiation

The LTST-S320KSKT differentiates itself through its specific combination of attributes:

- Material (AlInGaP): Compared to older GaAsP or GaP technologies, AlInGaP offers significantly higher efficiency and brightness for yellow and amber colors, resulting in lower power consumption for the same light output.

- Package (Side-Looking): Unlike top-emitting LEDs, this package is purpose-built for applications where light needs to be emitted parallel to the PCB surface, saving vertical space and simplifying optical coupling into light guides.

- Tin Plating: The tin-plated leads offer excellent solderability and are compatible with lead-free processes, providing better environmental and reliability characteristics compared to older lead-based platings.

10. Frequently Asked Questions (FAQs)

10.1 What is the difference between Peak Wavelength and Dominant Wavelength?

Peak Wavelength (λ_P): The wavelength at the highest point of the LED's emission spectrum (588 nm). Dominant Wavelength (λ_d): The single wavelength that the human eye would perceive as matching the LED's color (587-594.5 nm), calculated from color coordinates. Dominant wavelength is more relevant for color specification.

10.2 Can I drive this LED at 30mA continuously?

Yes, 30mA is the maximum recommended DC forward current. However, operating at this maximum will generate more heat and may reduce the LED's lifespan compared to operating at a lower current like 20mA. Adequate thermal design is crucial at 30mA.

10.3 How do I interpret the bin code in the part number?

The full part number LTST-S320KSKT includes embedded bin codes for forward voltage (F), intensity (P/Q/R), and dominant wavelength (J/K/L). Consult the bin code tables in sections 3.1-3.3 to understand the specific performance range of the device you are ordering.

10.4 Is a heat sink required?

For a single LED operating at 20mA, a dedicated heat sink is typically not required if the PCB provides a reasonable copper pad for heat spreading. For arrays, high-current operation, or high ambient temperatures, thermal analysis should be performed to ensure the junction temperature remains within safe limits.

11. Practical Application Example

11.1 Designing a Low-Power Status Indicator

Scenario: A product requires a yellow side-emitting status LED powered from a 5V digital logic rail.

Design Steps:

1. Select Operating Point: Choose I_F = 15mA for a good balance of brightness and longevity.

2. Calculate Series Resistor: Use the maximum V_F from the worst-case bin (F3: 2.40V) for a safe design. R = (5V - 2.40V) / 0.015A = 173.3Ω. Select the nearest standard value, 180Ω.

3. Check Power: Power in LED: P_LED = V_F * I_F ≈ 2.4V * 0.015A = 36mW, well below the 75mW maximum. Power in resistor: P_R = (I_F)² * R = (0.015)² * 180 = 40.5mW. Use at least an 0805 size resistor.

4. PCB Layout: Place the LED according to the suggested land pattern. Ensure the cathode (marked) pad is connected to ground or the lower voltage side.

12. Technology Principle Introduction

The LTST-S320KSKT is based on AlInGaP semiconductor technology. When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region where they recombine. In AlInGaP materials, this recombination primarily releases energy in the form of photons (light) in the yellow region of the visible spectrum (around 590 nm). The specific color (dominant wavelength) is determined by the precise atomic composition (bandgap) of the semiconductor layers grown during fabrication. The side-emitting package uses a reflective cavity and a clear epoxy lens to direct the generated light out of the side of the component.

13. Industry Trends and Developments

The general trend in SMD LEDs like this one is towards:

- Higher Efficiency: Ongoing material science improvements aim to produce more lumens per watt (lm/W), reducing energy consumption for the same light output.

- Improved Color Consistency: Tighter binning tolerances and advanced manufacturing processes lead to less variation in color and brightness within a production batch, which is critical for applications using multiple LEDs.

- Miniaturization: While this is a standard package, the industry continues to develop smaller footprints for high-density applications.

- Enhanced Reliability: Improvements in package materials (epoxy, lead frames) and manufacturing processes continue to extend operational lifetime and tolerance to harsh environmental conditions like high temperature and humidity.