SMD LED LTST-S225KGKSKT-NU Datasheet - Dual Color (Green/Yellow) - 25mA - 60mW - English Technical Document

1. Product Overview

This document details the specifications for a dual-color, side-looking SMD (Surface Mount Device) LED. The device integrates two distinct LED chips within a single package: one emitting in the green spectrum and the other in the yellow spectrum. This configuration is designed for applications requiring compact, multi-indication status lights or backlighting in space-constrained electronic assemblies.

The core advantages of this component include its ultra-bright output using AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology, compatibility with automated pick-and-place assembly systems, and suitability for high-volume infrared (IR) reflow soldering processes. It is compliant with RoHS (Restriction of Hazardous Substances) directives.

The target market encompasses a wide range of consumer and industrial electronics, including but not limited to telecommunications equipment (cordless/cellular phones), portable computing devices (notebooks), network hardware, home appliances, and indoor signage or display panels where reliable, dual-color indication is required.

2. Technical Parameters Deep Dive

2.1 Absolute Maximum Ratings

All ratings are specified at an ambient temperature (Ta) of 25°C. Exceeding these limits may cause permanent damage.

• Power Dissipation (Pd): 60 mW per color chip.
• Peak Forward Current (I_FP): 40 mA, permissible under pulsed conditions (1/10 duty cycle, 0.1ms pulse width).
• Continuous Forward Current (I_F): 25 mA DC.
• Operating Temperature Range: -30°C to +85°C.
• Storage Temperature Range: -40°C to +85°C.
• Soldering Temperature: Withstands IR reflow profiles with a peak temperature of 260°C for up to 10 seconds (Pb-free process).

2.2 Electro-Optical Characteristics

Measured at Ta=25°C with I_F = 20mA, unless otherwise stated.

• Luminous Intensity (I_V):
  • Green Chip: Minimum 22.5 mcd, Typical unspecified, Maximum 57.0 mcd.
  • Yellow Chip: Minimum 45.0 mcd, Typical unspecified, Maximum 112.0 mcd.
• Viewing Angle (2θ_1/2): Typically 130 degrees. This is the full angle at which luminous intensity drops to half its axial value, indicating a very wide viewing cone suitable for side-emitting applications.
• Peak Wavelength (λ_P):
  • Green: Typically 573.0 nm.
  • Yellow: Typically 591.0 nm.
• Dominant Wavelength (λ_d): The single wavelength perceived by the human eye.
  • Green: Range from 567.5 nm (Min) to 576.5 nm (Max).
  • Yellow: Range from 585.5 nm (Min) to 591.5 nm (Max).
• Spectral Bandwidth (Δλ): Typically 15.0 nm (Full Width at Half Maximum) for both colors.
• Forward Voltage (V_F):
  • Green & Yellow: Range from 1.7V (Min) to 2.4V (Max) at 20mA.
• Reverse Current (I_R): Maximum 10 μA at a reverse voltage (V_R) of 5V. Note: The device is not designed for operation under reverse bias; this parameter is for test purposes only.

Important Notes: Luminous intensity is measured using a sensor filtered to match the CIE photopic eye response. The device is sensitive to Electrostatic Discharge (ESD); proper ESD handling procedures (wrist straps, grounded equipment) are mandatory.

3. Binning System Explanation

To ensure color and brightness consistency in production, LEDs are sorted into bins. This device uses two binning criteria per color.

3.1 Luminous Intensity (Brightness) Binning

• Green Chip:
  • Bin Code N: 22.5 mcd to 35.5 mcd.
  • Bin Code P: 35.5 mcd to 57.0 mcd.
• Yellow Chip:
  • Bin Code P: 45.0 mcd to 71.0 mcd.
  • Bin Code Q: 71.0 mcd to 112.0 mcd.
• Tolerance within each intensity bin is ±15%.

3.2 Hue (Dominant Wavelength) Binning

• Green Chip:
  • Bin Code C: 567.5 nm to 570.5 nm.
  • Bin Code D: 570.5 nm to 573.5 nm.
  • Bin Code E: 573.5 nm to 576.5 nm.
• Yellow Chip:
  • Bin Code J: 585.5 nm to 588.5 nm.
  • Bin Code K: 588.5 nm to 591.5 nm.
• Tolerance within each wavelength bin is ±1 nm.

Designers should specify the required bin codes when ordering to guarantee the desired visual performance in their application.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Fig.1 for spectral measurement, Fig.5 for viewing angle), the following typical behaviors can be inferred from the provided data:

• I-V (Current-Voltage) Characteristic: The forward voltage (V_F) range of 1.7V to 2.4V at 20mA is characteristic of AlInGaP technology. V_F will have a negative temperature coefficient, decreasing slightly as junction temperature rises.
• Luminous Intensity vs. Current: Light output is approximately proportional to forward current within the specified operating range. Driving the LED above 20mA will increase brightness but also power dissipation and junction temperature, potentially affecting longevity and wavelength.
• Temperature Dependence: Like all LEDs, luminous intensity decreases as junction temperature increases. The AlInGaP material system is generally more temperature-stable than some alternatives, but thermal management is still important for maintaining consistent brightness.
• Spectral Distribution: The 15 nm typical spectral bandwidth indicates a relatively pure, saturated color output for both green and yellow chips, which is beneficial for clear color differentiation.

5. Mechanical & Package Information

5.1 Device Dimensions and Pinout

The LED conforms to a standard EIA package footprint. Key dimensional tolerances are ±0.1 mm unless otherwise noted.

• Pin Assignment:
  • Pins 1 and 2 are assigned to the Yellow AlInGaP chip.
  • Pins 3 and 4 are assigned to the Green AlInGaP chip.
• Lens: Water Clear, allowing the true chip color to be visible.

5.2 Recommended PCB Land Pattern

The datasheet includes a recommended solder pad layout to ensure proper mechanical alignment and solder joint formation during reflow. Adhering to this pattern is critical for achieving reliable electrical connection and optimal heat dissipation from the LED package to the circuit board.

5.3 Polarity Identification

As a diode, each chip within the package is polarity-sensitive. The pin assignment table must be consulted to correctly connect the anode and cathode for each color. Incorrect polarity will prevent the LED from illuminating and applying reverse voltage beyond 5V may damage the device.

6. Soldering & Assembly Guide

6.1 Reflow Soldering Parameters (Pb-Free)

• Pre-heat Temperature: 150°C to 200°C.
• Pre-heat Time: Maximum 120 seconds.
• Peak Body Temperature: Maximum 260°C.
• Time Above 260°C: Maximum 10 seconds.
• Number of Reflow Passes: Maximum two times.

Note: Actual temperature profiles must be characterized for the specific PCB design, solder paste, and oven used.

6.2 Hand Soldering (If Necessary)

• Iron Temperature: Maximum 300°C.
• Contact Time: Maximum 3 seconds per joint.
• Number of Soldering Attempts: One time only. Excessive heat can damage the plastic package and the semiconductor die.

6.3 Cleaning

If cleaning is required after soldering, only use specified solvents to avoid damaging the package material. Acceptable methods include immersion in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute.

6.4 Storage and Handling

• ESD Sensitivity: Device is sensitive to Electrostatic Discharge. Use appropriate ESD controls.
• Moisture Sensitivity Level (MSL): MSL 3. Once the original moisture-barrier bag is opened, the components must be subjected to IR reflow within one week under ambient conditions not exceeding 30°C/60% RH.
• Long-term Storage (Opened Bag): For storage beyond one week, store in a sealed container with desiccant or in a nitrogen atmosphere. Components stored out of bag for more than a week require baking at approximately 60°C for at least 20 hours before soldering.

7. Packaging & Ordering

The device is supplied in a tape-and-reel format compatible with automated assembly equipment.

• Tape Width: 8 mm.
• Reel Diameter: 7 inches.
• Quantity per Reel: 4000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Packaging Standard: Conforms to ANSI/EIA-481 specifications. Empty pockets in the tape are sealed with cover tape.

The full part number LTST-S225KGKSKT-NU should be used for ordering, along with any specific bin code requirements for luminous intensity and dominant wavelength.

8. Application Recommendations

8.1 Typical Application Scenarios

• Status Indicators: Dual-color capability allows for multiple states (e.g., Green=On/Ready, Yellow=Standby/Warning, Both=Special Mode).
• Keypad/Keyboard Backlighting: The side-looking emission profile is ideal for edge-lighting thin panels or membranes.
• Consumer Electronics: Power, connectivity, or function status lights in phones, routers, appliances.
• Industrial Panel Indicators: Equipment status, fault conditions.
• Symbolic Illumination: Lighting small icons or symbols on control panels.

8.2 Design Considerations

• Current Limiting: Always use a series current-limiting resistor (or constant-current driver) for each color chip. Calculate resistor value based on supply voltage (V_cc), desired forward current (I_F, max 25mA DC), and the LED's forward voltage (V_F). Use the maximum V_F from the datasheet for a conservative design. Formula: R = (V_cc - V_F) / I_F.
• Thermal Management: Although power dissipation is low, ensuring a good thermal path from the LED pads to the PCB copper helps maintain stable light output and long-term reliability, especially in high ambient temperatures or when driven at maximum current.
• Optical Design: The 130-degree viewing angle provides wide visibility. Consider light pipes or diffusers if a specific beam pattern or softened appearance is needed.

9. Technical Comparison & Differentiation

This dual-color LED offers specific advantages in its class:

• vs. Two Discrete LEDs: Saves significant PCB space and reduces component count, simplifying assembly and bill of materials (BOM).
• AlInGaP Technology: Provides higher luminous efficiency and better temperature stability compared to older technologies like standard GaP (Gallium Phosphide) for green/yellow colors, resulting in brighter and more consistent output.
• Side-View Package: The primary emission direction is parallel to the PCB, which is optimal for applications where light needs to be directed across a surface (e.g., edge-lighting) rather than perpendicularly away from it.
• Tin Plating: Offers good solderability and is compatible with lead-free (Pb-free) soldering processes.

10. Frequently Asked Questions (FAQs)

Q1: Can I drive both the green and yellow chips simultaneously at 25mA each?
A1: Yes, but you must consider the total power dissipation on the package. With both chips at 25mA and a typical V_F of ~2.0V, each dissipates ~50mW, totaling ~100mW. This exceeds the absolute maximum rating of 60mW per chip. For continuous simultaneous operation, you should derate the current for each chip to keep individual and combined power dissipation within safe limits.

Q2: What is the difference between Peak Wavelength and Dominant Wavelength?
A2: Peak Wavelength (λ_P) is the wavelength at the highest point of the LED's spectral output curve. Dominant Wavelength (λ_d) is the single wavelength of monochromatic light that would appear to have the same color to the human eye. λ_d is more relevant for color specification in visual applications.

Q3: How do I interpret the bin codes when ordering?
A3: You need to specify two bin codes per color: one for Luminous Intensity (e.g., P for Green) and one for Dominant Wavelength (e.g., D for Green). This ensures you receive LEDs with brightness and color within your desired, narrow ranges. Consult the bin code lists in Section 3 of this document.

Q4: Is a heat sink required?
A4: For most applications operating at or below 20mA per chip in typical ambient conditions, the PCB copper itself is sufficient for heat dissipation. For high-ambient-temperature environments or continuous operation at the maximum 25mA, enhancing the thermal relief on the PCB (using larger copper pads or thermal vias) is recommended.

11. Practical Design Case Study

Scenario: Designing a dual-status indicator for a network router. Green indicates "Internet Connected," Yellow indicates "Data Transmitting," and both off indicates "No Connection."

Implementation:

1. Circuit Design: Use two GPIO pins from the router's microcontroller. Each pin drives one color chip through a separate current-limiting resistor. Calculate resistor value for a 3.3V supply, target I_F=15mA (for longevity and lower heat), and using max V_F=2.4V: R = (3.3V - 2.4V) / 0.015A = 60 Ohms. Use the nearest standard value (e.g., 62 Ohms).
2. PCB Layout: Place the LED near the edge of the board. Follow the recommended land pattern from the datasheet. Connect the cathode pads (likely pins 2 and 4) to the microcontroller GPIOs via the resistors, and connect the anode pads (likely pins 1 and 3) to the 3.3V rail. Include a small copper pour around the pads for slight thermal improvement.
3. Software: Control the GPIOs to turn Green/Yellow/Both on/off as needed.
4. Optical: A small, clear light pipe can be used to guide the light from the side-emitting LED to a front-panel label.

This approach provides a reliable, compact, and easily manufacturable solution.

12. Technology Principle Introduction

This LED utilizes AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material grown on a substrate. When a forward voltage is applied across the p-n junction, electrons and holes recombine, releasing energy in the form of photons (light). The specific ratio of aluminum, indium, and gallium in the crystal lattice determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—green (~573 nm) and yellow (~591 nm) in this device.

The "side-looking" design is achieved by mounting the LED chip on a vertical surface within the package or using a reflector/optic to direct the primary light output sideways. The water-clear lens minimizes light absorption, allowing the true chip color and brightness to be perceived.

13. Industry Trends

The market for SMD LEDs continues to evolve towards:

• Higher Efficiency: Ongoing improvements in epitaxial growth and chip design yield more lumens per watt, reducing power consumption for a given brightness.
• Miniaturization: Packages are becoming smaller while maintaining or increasing light output, enabling denser and more discreet indicator placement.
• Improved Color Consistency: Tighter binning tolerances and advanced manufacturing processes ensure less variation in color and brightness between individual LEDs, which is critical for applications using multiple units.
• Enhanced Reliability: Improvements in package materials (mold compounds, lead frames) and manufacturing processes lead to longer operational lifetimes and better performance under harsh environmental conditions (temperature, humidity).
• Integration: The trend of combining multiple functions (like this dual-color chip) or integrating control electronics (e.g., driver ICs) within the LED package continues to simplify end-product design.

This dual-color SMD LED represents a mature and optimized component within these broader trends, offering a reliable solution for modern electronic design needs.