SMD LED LTST-S320KRKT Datasheet - Red - 639nm Peak - 20mA - 2.4V - English Technical Document

1. Product Overview

The LTST-S320KRKT is a high-brightness, side-looking Surface Mount Device (SMD) LED designed for modern electronic applications requiring reliable and efficient indicator or backlighting functions. Utilizing an advanced AlInGaP (Aluminum Indium Gallium Phosphide) chip technology, this LED delivers superior luminous intensity and color purity in the red spectrum. Its side-emitting design allows for light to be directed parallel to the mounting surface, making it ideal for edge-lit panels, status indicators on vertical PCBs, or space-constrained applications where top-down lighting is not feasible.

Key advantages of this component include its compliance with RoHS (Restriction of Hazardous Substances) directives, classifying it as a green product. The package features a water-clear lens that maximizes light output and is supplied on industry-standard 8mm tape mounted on 7-inch reels, ensuring compatibility with high-speed automated pick-and-place assembly equipment. The device is also designed to withstand standard infrared (IR) reflow soldering processes, facilitating integration into streamlined surface-mount technology (SMT) production lines.

2. Technical Parameter Deep Dive

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 and should be avoided for reliable performance.

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED package can dissipate as heat without exceeding its maximum junction temperature.
• Peak Forward Current (I_F(PEAK)): 80 mA. This current can be applied only under pulsed conditions, specifically at a 1/10 duty cycle with a pulse width of 0.1ms. It is useful for multiplexing or brief high-intensity flashes.
• Continuous Forward Current (I_F): 30 mA DC. This is the maximum recommended current for continuous operation, ensuring long-term reliability and stable light output.
• Reverse Voltage (V_R): 5 V. Exceeding this voltage in reverse bias can cause immediate and catastrophic failure of the LED junction.
• Operating & Storage Temperature: -30°C to +85°C and -40°C to +85°C, respectively. These ranges ensure the LED's mechanical integrity and performance across various environmental conditions.
• Soldering Condition: Withstands 260°C for 10 seconds, which aligns with typical lead-free (Pb-free) reflow soldering profiles.

2.2 Electro-Optical Characteristics

Measured at a standard ambient temperature (T_a) of 25°C and a forward current (I_F) of 20 mA, these parameters define the core performance of the LED.

• Luminous Intensity (I_V): Ranges from a minimum of 18.0 mcd to a typical value of 54.0 mcd. The actual delivered intensity is binned (see Section 3), providing predictable brightness levels for design.
• Viewing Angle (2θ_1/2): 130 degrees. This wide viewing angle is characteristic of side-looking LEDs with a diffused lens, providing a broad, even illumination pattern suitable for status indicators.
• Peak Wavelength (λ_P): 639 nm. This is the wavelength at which the spectral power output is maximum, defining the perceived hue of the red light.
• 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.
• Spectral Bandwidth (Δλ): 20 nm. This narrow bandwidth indicates high color purity, with most of the emitted light concentrated around the peak wavelength.
• Forward Voltage (V_F): Typically 2.4 V, with a maximum of 2.4 V at 20mA. This parameter is critical for designing the current-limiting circuitry.
• Reverse Current (I_R): Maximum 10 µA at a reverse voltage of 5V, indicating good junction quality.

3. Binning System Explanation

To ensure consistency in brightness across production batches, the LTST-S320KRKT employs a luminous intensity binning system. Each LED is tested and sorted into a specific bin code based on its measured intensity at 20 mA.

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

A tolerance of +/-15% is applied to each intensity bin. Designers should select the appropriate bin based on their application's brightness requirements. For example, high-visibility indicators may require Bin R or Q, while less critical status lights may use Bin M or N. This system allows for predictable performance and simplifies inventory management for manufacturers.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Fig.1, Fig.6), their implications are standard for AlInGaP LEDs. Designers can expect the following general relationships:

• I-V (Current-Voltage) Curve: The forward voltage (V_F) exhibits a logarithmic relationship with current. It remains relatively stable around the typical 2.4V within the recommended operating current range but increases with higher currents and temperature.
• Luminous Intensity vs. Forward Current: Intensity is approximately proportional to forward current up to the maximum rated current. However, efficiency (lumens per watt) typically peaks at a current lower than the absolute maximum and decreases thereafter due to thermal effects.
• Temperature Dependence: The luminous intensity of AlInGaP LEDs has a negative temperature coefficient. As the junction temperature increases, the light output decreases. The forward voltage also decreases slightly with rising temperature. Proper thermal management is crucial for maintaining consistent brightness.
• Spectral Distribution: The emission spectrum is a Gaussian-like curve centered at 639 nm (peak) with a half-width of 20 nm. The dominant wavelength (631 nm) may shift slightly (typically towards longer wavelengths) with increased junction temperature and drive current.

5. Mechanical & Package Information

The LED conforms to EIA (Electronic Industries Alliance) standard package dimensions for side-looking SMD LEDs. Key mechanical features include:

• Package Type: Standard side-view SMD package.
• Lens: Water clear, non-diffused (for the KRKT variant), maximizing light output.
• Termination: Tin (Sn) plating on the leads, providing good solderability and compatibility with lead-free processes.
• Polarity Identification: The cathode is typically identified by a marking on the package, such as a notch, dot, or trimmed lead. The datasheet includes a diagram showing the suggested soldering pad layout and orientation to ensure correct placement.
• Tape and Reel: Packaged in 8mm wide embossed carrier tape on 7-inch (178mm) diameter reels. Standard reel quantity is 3000 pieces. This packaging is compliant with ANSI/EIA-481 specifications for automated handling.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profile

A suggested infrared (IR) reflow profile for Pb-free assembly is provided. Key parameters include:

• Preheat: 150-200°C for a maximum of 120 seconds to gradually heat the board and components, minimizing thermal shock.
• Peak Temperature: Maximum of 260°C. The component is rated for 10 seconds at this peak temperature.
• Time Above Liquidus (TAL): The profile should be characterized to ensure proper solder joint formation without overheating the LED. The example profile is based on JEDEC standards.

6.2 Hand Soldering

If hand soldering is necessary, use a temperature-controlled iron set to a maximum of 300°C. Limit the contact time to 3 seconds per lead, and perform this operation only once to prevent damage to the plastic package and the internal wire bonds.

6.3 Storage & Handling

• ESD (Electrostatic Discharge) Sensitivity: LEDs are susceptible to ESD. Use proper anti-static precautions like grounded wrist straps, conductive mats, and ESD-safe packaging during handling.
• Moisture Sensitivity: While the sealed reel provides protection, components removed from their original packaging should be used within one week. For longer storage, keep them in a dry environment (\u003c 30°C, \u003c 60% RH) or in a sealed container with desiccant. If stored unpacked for over a week, a bake-out at 60°C for 20+ hours is recommended before soldering to prevent \"popcorning\" (package cracking due to vaporized moisture during reflow).
• Cleaning: If post-solder cleaning is required, use only specified solvents like isopropyl alcohol (IPA) or ethyl alcohol at room temperature for less than one minute. Avoid aggressive or unspecified chemicals that may damage the epoxy lens or package.

7. Application Suggestions

7.1 Typical Application Scenarios

• Consumer Electronics: Power, battery, or function status indicators on smartphones, tablets, routers, and audio equipment.
• Industrial Controls: Panel-mounted indicators for machine status, fault alarms, or operational modes.
• Automotive Interior: Backlighting for buttons, switches, or minor status displays (subject to specific automotive-grade qualification which this standard part may not have).
• Instrumentation: Indicator lights on test equipment, medical devices (for non-critical functions), and communication hardware.

7.2 Design Considerations

• Current Limiting: Always drive the LED with a constant current source or a current-limiting resistor in series with a voltage source. Calculate the resistor value using R = (V_source - V_F) / I_F. For a 5V supply and a target I_F of 20mA with V_F=2.4V: R = (5 - 2.4) / 0.02 = 130 Ω. Use the nearest standard value (e.g., 120Ω or 150Ω) and check the actual current.
• Thermal Management: Although power dissipation is low, ensure adequate PCB copper area or thermal vias around the solder pads to conduct heat away from the LED junction, especially when operating near maximum current or in high ambient temperatures.
• Optical Design: The side-emitting nature requires the design to incorporate a light guide or a properly positioned viewing window to channel the light to the desired location on the product housing.

8. Technical Comparison & Differentiation

The LTST-S320KRKT differentiates itself in the market through several key features:

• Chip Technology: The use of AlInGaP, compared to older GaAsP or standard GaP, provides significantly higher luminous efficiency and better temperature stability, resulting in brighter and more consistent red light.
• Side-Looking Package: Offers a design alternative to top-emitting LEDs, solving specific layout challenges where light needs to travel parallel to the PCB.
• High Brightness Binning: Availability of bins up to 180 mcd (Bin R) allows for applications requiring very high visibility.
• Robust Process Compatibility: Explicit compatibility with IR reflow and automatic placement streamlines manufacturing, reducing assembly cost and complexity compared to through-hole alternatives.

9. Frequently Asked Questions (FAQ)

Q: Can I drive this LED directly from a microcontroller GPIO pin?
A: It depends on the GPIO's current sourcing capability. Many MCU pins can source only 10-25mA. At 20mA, you are likely at or above the limit. It is safer to use the GPIO to control a transistor (e.g., a MOSFET) that switches the higher LED current.

Q: Why is there a difference between Peak Wavelength (639nm) and Dominant Wavelength (631nm)?
A: The peak wavelength is the physical maximum of the emission spectrum. The dominant wavelength is a calculated value based on human color perception (CIE chart). The human eye's sensitivity (photopic response) causes this shift, making the \"apparent\" color correspond to 631nm.

Q: What happens if I operate the LED at 30mA continuously?
A: While this is the maximum DC rating, operating at the absolute maximum will generate more heat, reduce luminous efficiency over time, and potentially shorten the LED's lifespan. For optimal reliability, derating to 15-20mA is recommended for most applications.

Q: How do I interpret the bin code when ordering?
A: Specify the required luminous intensity bin code (e.g., \"P\") in your purchase order to ensure you receive LEDs with brightness in the 45-71 mcd range. This guarantees consistency in your product's appearance.

10. Design-in Case Study

Scenario: Designing a status indicator for a compact IoT sensor module. The PCB is densely populated, and the indicator must be visible from the side of the enclosed unit.

Implementation: The LTST-S320KRKT is selected for its side-emitting property. It is placed at the edge of the PCB. A 120Ω current-limiting resistor is connected in series to a 3.3V rail, resulting in an approximate forward current of (3.3V - 2.4V)/120Ω = 7.5mA. This provides sufficient brightness for indoor use while minimizing power consumption, a critical factor for battery-powered IoT devices. The LED's wide viewing angle ensures visibility even if the user's viewpoint is not perfectly aligned. The component is placed using standard SMT assembly, and the IR reflow profile is adjusted to stay within the 260°C for 10s limit, ensuring a reliable solder joint without thermal damage.

11. Technology Principle Introduction

The LTST-S320KRKT is based on AlInGaP semiconductor technology. This material is a compound semiconductor from the III-V group. When a forward voltage is applied across the p-n junction, electrons from the n-type region and holes from the p-type region are injected into the active region. Here, they recombine, releasing energy in the form of photons (light). The specific composition of Aluminum, Indium, Gallium, and Phosphide in the active layer determines the bandgap energy of the semiconductor, which directly dictates the wavelength (color) of the emitted light. For this red LED, the bandgap is engineered to produce photons with energy corresponding to approximately 639 nm. The water-clear epoxy lens encapsulates the chip, providing mechanical protection, shaping the light output pattern (130-degree viewing angle), and enhancing light extraction from the semiconductor material.

12. Industry Trends

The trend in indicator LEDs like the LTST-S320KRKT continues towards higher efficiency, smaller packages, and greater integration. While AlInGaP remains the dominant technology for high-efficiency red and amber LEDs, InGaN (Indium Gallium Nitride) technology has advanced to cover the full visible spectrum with high efficiency, including green, blue, and white. Future developments may see further miniaturization of side-looking packages and increased adoption of chip-scale packaging (CSP) LEDs, which eliminate the traditional plastic package for even smaller footprint and potentially better thermal performance. Additionally, there is a growing emphasis on precise color tuning and tighter binning to meet the demands of applications like full-color indicator arrays and sophisticated human-machine interfaces where consistent color and brightness are paramount.