LTST-C150KRKT SMD LED Datasheet - 3.2x1.6x1.1mm - 2.4V - 62.5mW - Red - English Technical Documentation

1. Product Overview

The LTST-C150KRKT is a high-performance, surface-mount LED designed for applications requiring reliable and bright red indication. Utilizing an advanced AlInGaP (Aluminum Indium Gallium Phosphide) chip technology, this component delivers superior luminous intensity and color purity compared to traditional LED materials. Its compact EIA standard package makes it compatible with automated pick-and-place assembly lines and standard infrared reflow soldering processes, streamlining high-volume manufacturing.

Key advantages of this LED include its RoHS compliance, ensuring it meets environmental regulations, and its robust construction suitable for a wide operating temperature range. The device is supplied on 8mm tape mounted on 7-inch reels, facilitating efficient handling and placement in automated production environments.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the stress limits beyond which permanent damage to the device may occur. For the LTST-C150KRKT, the maximum continuous forward current (DC) is specified at 25 mA. Under pulsed operation with a 1/10 duty cycle and a 0.1ms pulse width, the peak forward current can reach 50 mA. The maximum power dissipation is 62.5 mW, a critical parameter for thermal management in the application design. The device can withstand a reverse voltage of up to 5 V. The operating and storage temperature ranges are -30°C to +85°C and -40°C to +85°C, respectively, indicating good reliability across various environmental conditions.

2.2 Electro-Optical Characteristics

The core performance of the LED is defined under standard test conditions at an ambient temperature (Ta) of 25°C and a forward current (IF) of 20 mA.

• Luminous Intensity (Iv): The typical luminous intensity is 54.0 mcd (millicandela), with a minimum specified value of 18.0 mcd. This parameter is measured using a sensor and filter combination that approximates the CIE photopic eye-response curve, ensuring the value correlates with human visual perception.
• Viewing Angle (2θ1/2): The device features a wide viewing angle of 130 degrees. This is defined as the full angle at which the luminous intensity drops to half of its value measured on the central axis (0°).
• Wavelength Characteristics: The peak emission wavelength (λP) is typically 639 nm. The dominant wavelength (λd), which defines the perceived color, ranges from 624 nm to 638 nm. The spectral line half-width (Δλ) is typically 20 nm, describing the spectral purity of the emitted red light.
• Electrical Parameters: The forward voltage (VF) typically measures 2.4 V, with a maximum of 2.4 V at 20 mA. The reverse current (IR) is a maximum of 10 μA when a reverse voltage (VR) of 5 V is applied.

3. Binning System Explanation

To ensure color and brightness consistency in production, LEDs are sorted into bins. The LTST-C150KRKT uses a binning system primarily for luminous intensity.

The luminous intensity is categorized into several bins (M, N, P, Q, R), each with a defined minimum and maximum intensity range measured at 20 mA. For example, bin 'M' covers 18.0 to 28.0 mcd, while bin 'R' covers 112.0 to 180.0 mcd. A tolerance of +/-15% is applied to each intensity bin. Designers should specify the required bin code when ordering to guarantee the desired brightness level for their application, which is crucial for achieving uniform appearance in multi-LED arrays or displays.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Figure 1 for peak emission, Figure 5 for viewing angle), their typical behavior can be described based on semiconductor physics and standard LED characteristics.

• Forward Current vs. Forward Voltage (I-V Curve): The relationship is exponential. A small increase in forward voltage beyond the turn-on threshold (around 1.8-2.0V for AlInGaP) causes a large increase in forward current. This is why current-limiting resistors or constant-current drivers are essential.
• Luminous Intensity vs. Forward Current: Luminous intensity is approximately proportional to the forward current in the normal operating range. However, at very high currents, efficiency drops due to increased heat.
• Temperature Dependence: The forward voltage typically decreases with increasing junction temperature (negative temperature coefficient). Conversely, luminous intensity generally decreases as temperature rises. The datasheet's specified parameters at 25°C should be derated for operation at higher ambient temperatures.

5. Mechanical and Package Information

The LED comes in a standard surface-mount package. Key dimensional notes include that all measurements are in millimeters, with a general tolerance of ±0.10 mm unless otherwise specified. The datasheet provides detailed package dimension drawings, including the body size (approximately 3.2mm x 1.6mm x 1.1mm), lead spacing, and lens geometry. A "Water Clear" lens is used, which does not diffuse the light, resulting in a more focused beam pattern compared to diffused lenses. The polarity is indicated by the cathode mark on the package. Recommended solder pad dimensions are also provided to ensure a reliable mechanical and electrical connection during PCB assembly.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Profile

The component is compatible with infrared (IR) reflow soldering processes suitable for lead-free (Pb-free) solder. A suggested profile is provided, compliant with JEDEC standards. Key parameters include a pre-heat zone from 150°C to 200°C, a maximum peak temperature of 260°C, and a time above 260°C not exceeding 10 seconds. The total number of reflow cycles should be limited to a maximum of two. Adherence to the solder paste manufacturer's specifications is also critical.

6.2 Storage and Handling

The LEDs are moisture-sensitive. Unopened, moisture-proof bags with desiccant have a shelf life of one year when stored at ≤30°C and ≤90% RH. Once opened, components should be stored at ≤30°C and ≤60% RH. It is recommended to complete IR reflow within one week after opening. For longer storage outside the original bag, use a sealed container with desiccant or a nitrogen desiccator. Components 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 absorbed moisture and prevent "popcorning" damage during reflow.

6.3 Cleaning

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

6.4 ESD Precautions

LEDs are susceptible to damage from electrostatic discharge (ESD). Proper ESD controls must be implemented during handling and assembly. This includes using grounded wrist straps, anti-static gloves, and ensuring all equipment and work surfaces are properly grounded.

7. Packaging and Ordering Information

The standard packaging is 8mm carrier tape on 7-inch (178mm) diameter reels. Each full reel contains 3000 pieces. A minimum packing quantity of 500 pieces applies for remainder quantities. The packaging follows ANSI/EIA-481 specifications. The tape uses a top cover to seal empty component pockets. The maximum allowed number of consecutive missing components on a reel is two.

8. Application Recommendations

8.1 Typical Application Circuits

LEDs are current-driven devices. To ensure uniform brightness, especially when multiple LEDs are used in parallel, a series current-limiting resistor for each LED is strongly recommended (Circuit Model A). The resistor value (R) can be calculated using Ohm's Law: R = (Vcc - VF) / IF, where Vcc is the supply voltage, VF is the LED forward voltage, and IF is the desired forward current (e.g., 20mA). Driving multiple LEDs in series (Circuit Model B) is another common method that ensures identical current through each LED, promoting brightness uniformity.

8.2 Design Considerations

• Thermal Management: Ensure the PCB design allows for adequate heat dissipation, especially when operating near maximum current or in high ambient temperatures. Excessive heat reduces light output and lifespan.
• Current Control: Always use a constant current source or a current-limiting resistor. Connecting an LED directly to a voltage source will cause excessive current flow and rapid failure.
• Application Scope: This LED is intended for general electronic equipment. For applications requiring exceptional reliability where failure could risk safety (e.g., aviation, medical devices), additional qualification and consultation are necessary.

9. Technical Comparison and Differentiation

The use of AlInGaP technology is a key differentiator. Compared to older technologies like standard GaP (Gallium Phosphide) red LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in much brighter output for the same drive current. It also provides better temperature stability and color consistency. The wide 130-degree viewing angle makes it suitable for applications where visibility from off-axis angles is important. The compatibility with automated assembly and lead-free reflow soldering aligns it with modern, high-volume, environmentally compliant manufacturing practices.

10. Frequently Asked Questions (FAQ)

Q: What is the difference between peak wavelength and dominant wavelength?

A: Peak wavelength (λP) is the single wavelength at which the emission spectrum has its maximum intensity. Dominant wavelength (λd) is derived from the CIE chromaticity diagram and represents the single wavelength of pure spectral light that would be perceived by the human eye as having the same color as the LED. λd is more relevant for color specification.

Q: Can I drive this LED with a 3.3V supply without a resistor?

A: No. With a typical VF of 2.4V, connecting it directly to 3.3V would attempt to drive a very high, uncontrolled current through the LED, exceeding its absolute maximum rating and causing immediate damage. A series resistor is mandatory for voltage source driving.

Q: Why is the storage condition after opening the bag so important?

A: The plastic package 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 bonds—a phenomenon known as "popcorning."

11. Practical Design and Usage Examples

Example 1: Status Indicator on a Consumer Device: A designer needs a bright red power-on indicator. Using a 5V supply rail and targeting 20mA, the series resistor is calculated as R = (5V - 2.4V) / 0.02A = 130 Ohms. A standard 130Ω or 150Ω resistor can be used. The wide viewing angle ensures the indicator is visible from various angles.

Example 2: Backlighting for a Small Symbol: Multiple LTST-C150KRKT LEDs can be arranged in an array behind a translucent panel. To ensure even illumination, LEDs from the same luminous intensity bin (e.g., bin 'P') should be selected. They can be driven in a series-parallel configuration with appropriate current-limiting for each series string.

12. Technology Principle Introduction

AlInGaP is a III-V semiconductor compound. When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region where they recombine. This recombination process releases energy in the form of photons (light). The specific composition of Aluminum, Indium, Gallium, and Phosphide in the crystal lattice determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, in the red spectrum. The "Water Clear" epoxy lens is formulated to have minimal absorption at the emission wavelength, allowing maximum light extraction.

13. Industry Trends and Developments

The general trend in indicator LEDs is toward higher efficiency (more light output per watt of electrical input), improved reliability, and smaller package sizes to enable denser PCB layouts. While AlInGaP remains a dominant technology for high-efficiency red, orange, and yellow LEDs, InGaN (Indium Gallium Nitride) technology has become prevalent for blue, green, and white LEDs. There is also ongoing development in areas like chip-scale packaging (CSP) LEDs, which eliminate the traditional plastic package for even smaller form factors. Furthermore, the drive for sustainability continues to push for RoHS compliance and halogen-free materials across all electronic components.