LTST-S270KRKT SMD LED Datasheet - AlInGaP Red - 20mA - 2.4V - English Technical Document

1. Product Overview

The LTST-S270KRKT is a high-brightness, side-looking Surface Mount Device (SMD) LED designed for modern electronic applications requiring reliable and efficient indicator lighting. It utilizes an advanced AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor chip, which is known for producing high luminous intensity with excellent color purity in the red spectrum. The device is housed in a standard EIA-compliant package, making it compatible with automated pick-and-place assembly lines and standard infrared (IR) reflow soldering processes, which are critical for high-volume manufacturing. Its side-emitting lens design (water clear) allows the light to be directed parallel to the mounting surface, which is ideal for applications where space is constrained vertically, such as in edge-lit panels, backlighting for membrane switches, or status indicators on slim consumer electronics.

1.1 Core Features and Advantages

• High Brightness AlInGaP Chip: Delivers superior luminous intensity compared to traditional LED materials, ensuring clear visibility.
• Side-Viewing Package: The primary light emission is from the side of the component, perfect for space-saving designs.
• RoHS Compliant & Green Product: Manufactured without hazardous substances like lead, mercury, and cadmium, meeting global environmental regulations.
• Tin-Plated Terminals: Enhances solderability and provides good resistance to oxidation, ensuring reliable solder joints during assembly.
• Automation Friendly: Supplied on 8mm tape mounted on 7-inch reels, fully compatible with high-speed automatic placement equipment.
• Reflow Solderable: Withstands standard IR reflow soldering profiles required for lead-free (Pb-free) assembly processes.

2. Technical Specifications and Objective Interpretation

This section provides a detailed, objective analysis of the key electrical, optical, and thermal parameters defined in the datasheet. Understanding these values is crucial for proper circuit design and ensuring long-term reliability.

2.1 Absolute Maximum Ratings

These ratings represent the stress limits beyond which permanent damage to the device may occur. Operation at or near these limits is not recommended for normal use and will likely shorten the LED's lifespan.

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED package can dissipate as heat. Exceeding this can lead to overheating and catastrophic failure.
• Peak Forward Current (I_FP): 80 mA. This is the maximum instantaneous current allowed under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). It is significantly higher than the DC rating, useful for brief, high-intensity flashes.
• DC Forward Current (I_F): 30 mA. This is the maximum continuous current recommended for reliable long-term operation. The typical test condition for optical specs is 20mA.
• Reverse Voltage (V_R): 5 V. Applying a reverse voltage greater than this can break down the LED's PN junction, causing immediate failure. Proper circuit protection (e.g., a series diode in reverse parallel) is advised in AC or bipolar signal environments.
• Operating & Storage Temperature: -30°C to +85°C / -40°C to +85°C. The device can function and be stored within these ambient temperature ranges. Performance, particularly luminous intensity and forward voltage, will vary with temperature.
• IR Reflow Condition: 260°C peak for 10 seconds. This defines the maximum thermal profile the package can endure during soldering without damage.

2.2 Electro-Optical Characteristics

Measured at an ambient temperature (T_a) of 25°C, these parameters define the LED's performance under normal operating conditions.

• Luminous Intensity (I_V): 18.0 - 54.0 mcd (typical 54.0 mcd) at I_F = 20mA. This is a measure of the perceived brightness of the LED as seen by the human eye. The wide min-max range indicates the need for a binning system (see Section 3).
• Viewing Angle (2θ_1/2): 130 degrees. This is the full angle at which the luminous intensity drops to half of its maximum (on-axis) value. A 130° angle indicates a very wide viewing pattern, typical for side-emitting lenses without a narrow beam.
• Peak Wavelength (λ_P): 639 nm. This is the wavelength at which the optical power output of the LED is at its maximum. It defines the "color" in physical terms.
• Dominant Wavelength (λ_d): 631 nm. Derived from the CIE chromaticity diagram, this is the single wavelength that best represents the color perceived by the human eye. It is the key parameter for color specification.
• Spectral Bandwidth (Δλ): 20 nm. This is the width of the emitted spectrum at half its maximum power (Full Width at Half Maximum - FWHM). A narrower bandwidth indicates a more spectrally pure, saturated color.
• Forward Voltage (V_F): 2.0V - 2.4V (typical 2.4V) at I_F = 20mA. This is the voltage drop across the LED when operating. It is crucial for designing the current-limiting resistor in series with the LED. Designers must use the maximum V_F to ensure the current limit is not exceeded under worst-case conditions.
• Reverse Current (I_R): 10 µA max at V_R = 5V. This is the small leakage current that flows when the LED is reverse-biased within its maximum rating.

3. Binning System Explanation

Due to inherent variations in semiconductor manufacturing, LEDs are sorted into performance bins. This ensures consistency within a production batch. The LTST-S270KRKT uses a binning system for luminous intensity.

3.1 Luminous Intensity Binning

The LEDs are categorized into bins based on their measured luminous intensity at 20mA. Each bin has a minimum and maximum value, with a tolerance of +/-15% within the bin. This allows designers to select the appropriate brightness level for their application.

• 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

Design Implication: For applications requiring uniform brightness across multiple LEDs (e.g., an array of status lights), it is critical to specify and procure LEDs from the same intensity bin. Mixing bins can lead to visibly uneven lighting.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Fig.1, Fig.6), their typical behavior can be described based on standard LED physics.

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

The relationship is exponential. A small increase in voltage beyond the "turn-on" point (~1.8V for AlInGaP red) causes a large increase in current. This is why a current-limiting circuit (usually a resistor) is mandatory; connecting the LED directly to a voltage source will destroy it.

4.2 Luminous Intensity vs. Forward Current

Luminous intensity is approximately proportional to the forward current up to a point. Operating above the recommended DC current (30mA) will yield diminishing returns in brightness while generating excessive heat, accelerating lumen depreciation.

4.3 Temperature Dependence

As junction temperature increases:

• Forward Voltage (V_F): Decreases slightly. This can lead to a small increase in current if driven by a constant voltage source with a series resistor.
• Luminous Intensity (I_V): Decreases. High temperatures reduce light output efficiency. Proper thermal management (e.g., adequate PCB copper area) is important for maintaining consistent brightness.
• Wavelength (λ_d): Shifts slightly, typically to longer wavelengths (red shift).

5. Mechanical and Packaging Information

5.1 Package Dimensions and Polarity

The datasheet includes detailed mechanical drawings. Key features include the side-looking lens geometry and the anode/cathode pad identification. The cathode is typically marked by a notch, a green stripe on the tape, or a different pad shape. Correct polarity is essential during assembly.

5.2 Recommended Solder Pad Layout

A suggested land pattern (solder pad footprint) is provided to ensure a reliable solder fillet and proper alignment during reflow. Following this recommendation helps prevent tombstoning (component standing up on one end) and ensures good mechanical strength.

5.3 Tape and Reel Specifications

The component is supplied in embossed carrier tape (8mm pitch) on 7-inch reels, compliant with ANSI/EIA-481.

• Pieces per Reel: 4000
• Minimum Order Quantity: 500 pieces for remainder quantities.
• Cover Tape: Seals the pockets to prevent part fallout.
• Missing Lamps: A maximum of two consecutive empty pockets is allowed per specification.

6. Soldering, Assembly, and Handling Guidelines

6.1 IR Reflow Soldering Profile

A suggested reflow profile for Pb-free processes is provided, adhering to JEDEC standards. Key parameters include:

• Preheat: 150-200°C for up to 120 seconds to slowly ramp temperature and activate flux.
• Peak Temperature: Maximum of 260°C.
• Time Above Liquidus (TAL): The profile suggests a peak temperature time of 10 seconds maximum. The total time from ~217°C to peak should be controlled.
• Maximum Cycles: The LED should not be subjected to more than two reflow cycles.

Note: The actual profile must be characterized for the specific PCB design, solder paste, and oven used.

6.2 Hand Soldering

If hand soldering is necessary:

• Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per lead.
• Limit: Only one hand-soldering cycle is permitted.

6.3 Cleaning

Only alcohol-based solvents like isopropyl alcohol (IPA) or ethyl alcohol should be used for cleaning, at normal temperature for less than one minute. Harsh or unspecified chemicals can damage the plastic lens and package.

6.4 Electrostatic Discharge (ESD) Precautions

LEDs are sensitive to ESD. Handling precautions are mandatory:

• Use grounded wrist straps or anti-static gloves.
• Ensure all workstations, equipment, and tools are properly grounded.
• Store and transport components in ESD-safe packaging.

6.5 Storage Conditions

• Sealed Bag (Moisture Barrier Bag - MBB): Store at ≤30°C and ≤90% RH. Shelf life is one year from the bag seal date when stored with desiccant.
• Opened Bag or Loose Parts: Store at ≤30°C and ≤60% RH. It is recommended to complete IR reflow within one week of opening. For longer storage, place parts in a sealed container with desiccant or in a nitrogen desiccator. Parts stored out of the MBB for over one week should be baked at 60°C for at least 20 hours before soldering to remove absorbed moisture and prevent "popcorning" during reflow.

7. Application Notes and Design Considerations

7.1 Typical Application Scenarios

• Status Indicators: Power, connectivity, or mode indicators in consumer electronics, appliances, and industrial control panels.
• Backlighting: Edge-lighting for membrane switches, keypads, or small graphic displays.
• Automotive Interior Lighting: Non-critical indicator lights (subject to temperature and vibration validation).
• Portable Devices: Battery level or notification LEDs in smartphones, tablets, and wearables (utilizing the side-emitting feature).

7.2 Circuit Design

The most common drive circuit is a voltage source (V_CC) in series with a current-limiting resistor (R_S). The resistor value is calculated using Ohm's Law:
R_S = (V_CC - V_F) / I_F
Where V_F is the LED forward voltage and I_F is the desired forward current (e.g., 20mA). Always use the maximum V_F from the datasheet (2.4V) for this calculation to guarantee the current does not exceed the design target under worst-case conditions. For example, with a 5V supply:
R_S = (5V - 2.4V) / 0.020A = 130 Ω. A standard 130Ω or 150Ω resistor would be suitable.

7.3 Thermal Management

While the power dissipation is low, continuous operation at high ambient temperatures or at the maximum DC current can raise the junction temperature. To maintain performance and longevity:

• Use sufficient copper area on the PCB connected to the LED's thermal pads (if any) or adjacent ground plane to act as a heat sink.
• Avoid placing the LED near other heat-generating components.
• Consider derating the operating current (e.g., use 15mA instead of 20mA) in high-temperature environments.

7.4 Application Limitations and Warnings

The datasheet explicitly states that these LEDs are intended for ordinary electronic equipment (office, communication, household). They are not qualified for safety-critical applications where failure could jeopardize life or health, such as:

• Aviation and aerospace systems
• Transportation and traffic control equipment
• Medical and life-support devices
• Critical safety systems

For such applications, components with appropriate reliability certifications must be sourced.

8. Frequently Asked Questions (FAQ)

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

Peak Wavelength (λ_P): The physical wavelength where the LED emits the most optical power. It's measured directly from the spectrum.
Dominant Wavelength (λ_d): The perceived color. It's calculated from the CIE color chart to find the single wavelength that matches the LED's color point as seen by the human eye. For monochromatic LEDs like this red one, they are close but not identical. λ_d is the more relevant parameter for color specification.

8.2 Can I drive this LED with a 3.3V supply?

Yes. Using the formula R_S = (3.3V - 2.4V) / 0.020A = 45 Ω. A 47Ω standard resistor would work. Ensure the supply can deliver the required current.

8.3 Why is the storage humidity requirement so strict after opening the bag?

SMD packages can absorb moisture from the air. During the high-temperature reflow soldering process, this trapped moisture can vaporize rapidly, creating internal pressure that can crack the package or delaminate internal layers—a phenomenon known as "popcorning" or "moisture-induced stress." The baking process (60°C for 20+ hours) safely drives out this absorbed moisture.

8.4 How do I interpret the bin code (e.g., P) on an order?

The bin code (M, N, P, Q, R) specifies the guaranteed range of luminous intensity for the LEDs in that batch. When placing an order, you can specify the required bin code to ensure you receive LEDs with brightness in your desired range. If not specified, the supplier may ship from any available bin.