LTST-S220KSKT Yellow SMD LED Datasheet - EIA Package - Voltage 2.4V - Power 75mW - English Technical Document

1. Product Overview

The LTST-S220KSKT is a surface-mount device (SMD) light-emitting diode (LED) designed for modern electronic assembly processes. It belongs to a family of side-looking chip LEDs, meaning its primary light emission is directed parallel to the mounting plane of the printed circuit board (PCB). This orientation is particularly useful for applications requiring edge-lighting or status indicators viewable from the side of a device. The LED utilizes an Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor material, which is known for producing high-efficiency light in the yellow to red spectrum. The device is encapsulated in a water-clear lens, which does not diffuse the light, resulting in a more focused and intense beam suitable for indicator purposes.

The core advantages of this component include its compliance with RoHS (Restriction of Hazardous Substances) directives, making it suitable for global markets with strict environmental regulations. It features tin-plated leads for improved solderability and corrosion resistance. The package is standardized according to EIA (Electronic Industries Alliance) specifications, ensuring compatibility with a wide range of automatic pick-and-place equipment used in high-volume manufacturing. Furthermore, it is designed to withstand infrared (IR) reflow soldering processes, which is the standard for assembling lead-free (Pb-free) solder joints in surface-mount technology.

The target market for this LED includes consumer electronics, industrial control panels, automotive interior lighting, instrumentation, and any application requiring a reliable, bright, yellow status indicator that can be integrated using automated assembly lines.

2. Technical Parameters Deep Objective Interpretation

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. The absolute maximum ratings are specified at an ambient temperature (Ta) of 25°C.

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED package can dissipate as heat without degrading its performance or lifespan. Exceeding this limit risks thermal damage.
• Peak Forward Current (IFP): 80 mA. This is the maximum allowable instantaneous forward current, typically specified under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) to prevent excessive junction temperature rise.
• DC Forward Current (IF): 30 mA. This is the maximum continuous forward current recommended for reliable long-term operation. The typical operating condition for testing optical characteristics is 20 mA.
• Reverse Voltage (VR): 5 V. Applying a reverse voltage higher than this can cause breakdown and irreversible damage to the LED's PN junction.
• Operating Temperature Range: -30°C to +85°C. The LED is designed to function within this ambient temperature range.
• Storage Temperature Range: -40°C to +85°C. The device can be stored without operation within this wider temperature range.
• Infrared Soldering Condition: 260°C for 10 seconds. This defines the peak temperature and time tolerance for the reflow soldering process, critical for Pb-free assembly.

2.2 Electro-Optical Characteristics

These parameters are measured under standard test conditions (Ta=25°C, IF=20mA) and define the device's performance.

• Luminous Intensity (Iv): 18.0 - 54.0 mcd (Typical). This measures the perceived brightness of the LED as seen by the human eye (photopic vision). The wide range indicates a binning system is used (see Section 3). Intensity is measured with a filter simulating the CIE eye-response curve.
• Viewing Angle (2θ1/2): 130 degrees (Typical). This is the full angle at which the luminous intensity drops to half of its value at the central axis (0°). A 130° angle indicates a relatively wide viewing pattern.
• Peak Emission Wavelength (λP): 591 nm (Typical). This is the wavelength at which the spectral power output of the LED is maximum. It falls within the yellow region of the visible spectrum.
• Dominant Wavelength (λd): 589 nm (Typical). This is derived from the CIE chromaticity diagram and represents the single wavelength that best describes the perceived color of the light. It is very close to the peak wavelength for this device.
• Spectral Line Half-Width (Δλ): 20 nm (Typical). This is the width of the emission spectrum at half of its maximum power. A value of 20 nm indicates a moderately pure yellow color.
• Forward Voltage (VF): 2.0 V (Min), 2.4 V (Typ), (Max unspecified at 20mA). This is the voltage drop across the LED when operating at the specified current. It is crucial for designing the current-limiting circuitry.
• Reverse Current (IR): 10 μA (Max) at VR=5V. This is the small leakage current that flows when the specified reverse voltage is applied.

Note on ESD: The datasheet cautions that static electricity and surges can damage the LED. Proper electrostatic discharge (ESD) precautions, such as using grounded wrist straps, anti-static gloves, and ensuring all equipment is grounded, are strongly recommended during handling.

3. Binning System Explanation

To ensure consistency in brightness across production batches, LEDs are sorted into bins based on their measured luminous intensity at the standard test current (20mA). The LTST-S220KSKT uses the following bin code list:

• Bin M: 18.0 - 28.0 mcd
• Bin N: 28.0 - 45.0 mcd
• Bin P: 45.0 - 71.0 mcd
• Bin Q: 71.0 - 112.0 mcd
• Bin R: 112.0 - 180.0 mcd

The tolerance on each intensity bin is +/- 15%. This means an LED labeled as Bin N could have an actual intensity between approximately 23.8 mcd and 51.75 mcd. Designers must account for this variation when specifying brightness requirements for their application. The datasheet does not indicate separate bins for wavelength or forward voltage for this specific part number, suggesting tighter control or single-bin specification for those parameters.

4. Performance Curve Analysis

While the specific graphs are not detailed in the provided text, typical curves for such an LED would include:

• Relative Luminous Intensity vs. Forward Current (I-V Curve): This curve shows how light output increases with forward current. It is generally linear at lower currents but may saturate at higher currents due to thermal effects and efficiency droop.
• Relative Luminous Intensity vs. Ambient Temperature: This graph illustrates the derating of light output as the ambient (or junction) temperature increases. AlInGaP LEDs typically experience a decrease in output with rising temperature.
• Forward Voltage vs. Forward Current: This shows the exponential relationship characteristic of a diode. The voltage increases with current.
• Forward Voltage vs. Ambient Temperature: The forward voltage typically has a negative temperature coefficient, meaning it decreases slightly as temperature rises.
• Spectral Distribution: A plot of relative radiant power versus wavelength, showing a peak around 591 nm with a width of approximately 20 nm at half maximum.

These curves are essential for understanding the device's behavior under non-standard operating conditions and for thermal management design.

5. Mechanical and Packaging Information

5.1 Package Dimensions

The LED conforms to an EIA standard SMD package outline. All dimensions are provided in millimeters with a typical tolerance of ±0.10 mm unless otherwise noted. The datasheet includes a detailed dimensional drawing showing the length, width, height, lead spacing, and other critical mechanical features necessary for PCB footprint design.

5.2 Pad Design and Polarity

The datasheet provides suggested soldering pad dimensions for the PCB layout. Adhering to these recommendations ensures a reliable solder joint and proper alignment during reflow. The component has a polarity marking, typically a notch or a cathode indicator on the package body. Correct orientation is vital as LEDs only allow current to flow in one direction.

5.3 Tape and Reel Packaging

The LEDs are supplied in industry-standard 8mm tape on 7-inch diameter reels for compatibility with automated assembly equipment. Key packaging notes include:

• Empty component pockets are sealed with a top cover tape.
• Each 7-inch reel contains 4000 pieces.
• The minimum packing quantity for remainder parts is 500 pieces.
• A maximum of two consecutive missing LEDs (empty pockets) is allowed per reel specification.
• Packaging follows ANSI/EIA 481 specifications.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Profile

A suggested infrared (IR) reflow profile is provided for lead-free (Pb-free) soldering processes. The critical parameters are:

• Pre-heat Temperature: 150–200°C
• Pre-heat Time: Maximum 120 seconds
• Peak Temperature: Maximum 260°C
• Time at Peak Temperature: Maximum 10 seconds (and maximum two reflow cycles allowed).

The profile is based on JEDEC standards. The datasheet emphasizes that the optimal profile depends on the specific PCB design, components, solder paste, and oven, so characterization is necessary.

6.2 Hand Soldering

If hand soldering is necessary, the following limits apply:

• Soldering Iron Temperature: Maximum 300°C
• Soldering Time: Maximum 3 seconds (one time only).

6.3 Cleaning

Unspecified chemical cleaners should not be used as they may damage the LED package. If cleaning is required, immersion in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute is recommended.

6.4 Storage Conditions

• Sealed Package: Store at ≤30°C and ≤90% Relative Humidity (RH). The shelf life is one year when stored in the original moisture-proof bag with desiccant.
• Opened Package: Storage ambient should not exceed 30°C or 60% RH. LEDs removed from their original packaging should be IR-reflowed within one week.
• Extended Storage (Opened): For storage beyond one week, place LEDs in a sealed container with desiccant or in a nitrogen desiccator. LEDs stored out of packaging for more than a week should be baked at approximately 60°C for at least 20 hours before soldering to remove moisture absorption and prevent "popcorning" during reflow.

7. Application Suggestions

7.1 Typical Application Scenarios

This side-looking yellow LED is ideal for applications where space is constrained on the top surface of a PCB, or where the indicator needs to be viewed from the edge. Common uses include:

• Status indicators on consumer electronics (routers, set-top boxes, chargers).
• Backlighting for membrane switches or side-lit panels.
• Instrument cluster and dashboard lighting in automotive interiors.
• Industrial equipment status and fault indicators.
• Battery level or charging indicators in portable devices.

7.2 Design Considerations

• Current Drive: LEDs are current-operated devices. To ensure uniform brightness, especially when multiple LEDs are connected in parallel, a current-limiting mechanism is essential. This is typically achieved using a series resistor or a constant current driver circuit. The resistor value can be calculated using the formula: R = (Vcc - VF) / IF, where Vcc is the supply voltage, VF is the LED forward voltage (use max or typ value for safety), and IF is the desired forward current (e.g., 20mA).
• Thermal Management: While the power dissipation is low, maintaining the junction temperature within limits is crucial for longevity and stable light output. Ensure adequate PCB copper area or thermal vias if operating at high ambient temperatures or near maximum current.
• ESD Protection: Incorporate ESD protection diodes on sensitive signal lines connected to the LED, or ensure the driving circuit has inherent protection, particularly if the LED is user-accessible.
• Optical Design: The water-clear lens produces a focused beam. If a diffused or wider illumination pattern is needed, external diffusers or light guides must be considered in the mechanical design.

8. Technical Comparison and Differentiation

Compared to other yellow indicator LEDs, the key differentiators of the LTST-S220KSKT are:

• Side-Viewing Package: Unlike top-emitting LEDs, this form factor saves vertical space and enables unique lighting geometries, which is a distinct mechanical advantage.
• AlInGaP Technology: Offers higher efficiency and better temperature stability compared to older Yellow Gallium Phosphide (GaP) based LEDs, resulting in brighter and more consistent output.
• Full Process Compatibility: Its design for tape-and-reel packaging, automatic placement, and IR reflow soldering makes it a preferred choice for cost-effective, high-volume, automated manufacturing.
• RoHS Compliance: Meets modern environmental standards, which is a mandatory requirement for many markets.

9. Frequently Asked Questions (Based on Technical Parameters)

Q1: What resistor do I need for a 5V supply?
A: Using the typical forward voltage (VF) of 2.4V and a target current (IF) of 20mA, the series resistor value is R = (5V - 2.4V) / 0.02A = 130 Ohms. A standard 130Ω or 150Ω resistor would be suitable. Always verify actual brightness and consider using the maximum VF for a more conservative design.

Q2: Can I drive this LED with a 3.3V microcontroller pin?
A: Yes, but the available voltage headroom is small. VF_min is 2.0V, VF_typ is 2.4V. At 3.3V, the resistor calculation becomes R = (3.3V - 2.4V) / 0.02A = 45 Ohms. This is feasible, but variations in VF and supply voltage may cause significant current changes. A constant-current driver or careful characterization is advised for critical applications.

Q3: Why is the viewing angle so wide (130°)?
A> The side-looking package and the water-clear lens design are optimized to emit light over a broad hemisphere. This is beneficial for indicators that need to be visible from various angles without requiring a diffused lens.

Q4: How do I interpret the bin code (e.g., N) on an order?
A: The bin code specifies the guaranteed range of luminous intensity. Ordering Bin N ensures you receive LEDs with intensity between 28.0 and 45.0 mcd at 20mA. For applications requiring minimum brightness, specify the appropriate bin or consult with the supplier for availability.

10. Practical Use Case

Scenario: Designing a Status Indicator for a Network Router
A designer needs a power/activity indicator visible from the front of a slim router. The PCB is mounted vertically, so a side-looking LED is perfect. They place the LTST-S220KSKT at the edge of the PCB, facing a light guide that channels the light to a small window on the router's fascia. They drive it from the 3.3V system rail using a 47Ω series resistor, resulting in a current of approximately 19mA ((3.3V-2.4V)/47Ω). They select Bin P LEDs to ensure sufficient brightness is visible through the light guide. The design utilizes the automated pick-and-place and reflow process specified in the datasheet, ensuring reliable and fast assembly.

11. Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light when an electric current passes through them. This phenomenon is called electroluminescence. In the LTST-S220KSKT, the active region is made of Aluminum Indium Gallium Phosphide (AlInGaP). When a forward voltage is applied, electrons from the n-type semiconductor and holes from the p-type semiconductor are injected into the active region. When an electron recombines with a hole, it falls from a higher energy state to a lower one, releasing energy in the form of a photon (light particle). The specific composition of the AlInGaP alloy determines the bandgap energy, which in turn dictates the wavelength (color) of the emitted light—in this case, yellow (~589-591 nm). The side-looking package incorporates a reflective cavity and a molded epoxy lens to direct the generated light laterally out of the package.

12. Development Trends

The trend in SMD indicator LEDs like this one continues towards several key areas:

• Increased Efficiency: Ongoing material science improvements aim to produce more lumens per watt (efficacy), reducing power consumption for the same brightness.
• Miniaturization: Package sizes continue to shrink (e.g., from 0603 to 0402 metric sizes) while maintaining or improving optical performance, enabling denser PCB designs.
• Higher Reliability and Stability: Improvements in packaging materials and die attach technologies enhance lifespan and color stability over time and temperature.
• Broader Color Gamut and Consistency: Tighter binning tolerances for wavelength and intensity are becoming standard, providing designers with more predictable performance.
• Integration: There is a growing trend towards integrating multiple LEDs (e.g., RGB), control ICs, and even passive components into single, smarter modular packages.

Components like the LTST-S220KSKT represent a mature, highly optimized solution within this evolving landscape, balancing performance, cost, and manufacturability.