Dual Color SMD LED LTST-S326KFKGKT Datasheet - Orange/Green - 20mA - 75mW - English Technical Document

1. Product Overview

This document details the specifications for a high-brightness, dual-color, side-looking Surface Mount Device (SMD) Light Emitting Diode (LED). The device incorporates two distinct semiconductor chips within a single package: one emitting orange light and the other emitting green light. It is designed for applications requiring compact, reliable, and efficient indicator or backlighting solutions where space is at a premium and side emission is necessary.

The core advantages of this product include its compliance with RoHS (Restriction of Hazardous Substances) directives, making it suitable for environmentally conscious designs. It features an ultra-bright AlInGaP (Aluminium Indium Gallium Phosphide) material system for both colors, which is known for high efficiency and good color purity. The package is finished with tin plating for excellent solderability. It is fully compatible with standard automated pick-and-place assembly equipment and infrared (IR) reflow soldering processes, facilitating high-volume manufacturing.

The target market encompasses a wide range of consumer electronics, industrial control panels, automotive interior lighting, instrumentation, and communication devices where dual-status indication (e.g., power on/standby, charge status, network activity) or compact side illumination is required.

2. In-Depth Technical Parameter Analysis

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. For both the orange and green chips:

• Power Dissipation (Pd): 75 mW. This is the maximum total power (current * forward voltage) that can be dissipated as heat. Exceeding this limit risks overheating and catastrophic failure.
• Peak Forward Current (I_FP): 80 mA. This is the maximum allowable current under pulsed conditions, specified at a 1/10 duty cycle and 0.1ms pulse width. It is significantly higher than the DC rating, allowing 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 operating condition for testing luminous intensity is 20 mA.
• Reverse Voltage (V_R): 5 V. Applying a reverse bias voltage higher than this can break down the LED's PN junction.
• Operating Temperature Range: -30°C to +85°C. The device is guaranteed to function within this ambient temperature range.
• Storage Temperature Range: -40°C to +85°C.
• Infrared Soldering Condition: Withstands 260°C peak temperature for 10 seconds, which is a standard requirement for lead-free (Pb-free) solder reflow processes.

2.2 Electrical & Optical Characteristics

These parameters are measured at a standard ambient temperature (Ta) of 25°C and a forward current (I_F) of 20 mA, unless otherwise noted. They define the typical performance of the device.

• Luminous Intensity (I_V): A key measure of brightness.
  • Orange: Typical value is 160 mcd (millicandela), with a minimum of 71 mcd.
  • Green: Typical value is 50 mcd, with a minimum of 18 mcd.
  The orange chip is significantly brighter than the green under the same drive current, which is characteristic of AlInGaP technology in the orange/red spectrum.
• Viewing Angle (2θ_1/2): 130 degrees (typical for both colors). This wide viewing angle is a defining feature of a side-looking LED, providing a broad emission pattern suitable for applications where the LED is viewed from the side.
• Peak Emission Wavelength (λ_P): The wavelength at which the emitted light intensity is highest.
  • Orange: 610 nm (typical).
  • Green: 574 nm (typical).
• Dominant Wavelength (λ_d): The single wavelength that best represents the perceived color of the light, derived from the CIE chromaticity diagram.
  • Orange: 601 nm (typical).
  • Green: 570 nm (typical).
• Spectral Line Half-Width (Δλ): The bandwidth of the emitted spectrum at half its maximum intensity. Typical values are 15 nm for orange and 17 nm for green, indicating relatively pure, saturated colors.
• Forward Voltage (V_F): The voltage drop across the LED when operating at the specified current.
  • Both Colors: Typical value is 2.0 V, with a maximum of 2.4 V at 20 mA. This relatively low V_F is compatible with low-voltage logic circuits (e.g., 3.3V or 5V systems).
• Reverse Current (I_R): Maximum of 10 μA at a reverse voltage of 5V, indicating good junction quality.

Important Notes: Luminous intensity is measured using a filter that mimics the human eye's photopic response. The viewing angle (θ_1/2) is the off-axis angle where intensity drops to half its on-axis value. The device is sensitive to Electrostatic Discharge (ESD); proper handling with grounded equipment is mandatory.

3. Binning System Explanation

To ensure consistency in production, LEDs are sorted into performance bins based on measured luminous intensity. This allows designers to select parts that meet specific brightness requirements.

3.1 Orange LED Intensity Bins

Binned at I_F = 20 mA. Tolerance within each bin is ±15%.

• Bin Q: 71.0 – 112.0 mcd
• Bin R: 112.0 – 180.0 mcd
• Bin S: 180.0 – 280.0 mcd

3.2 Green LED Intensity Bins

Binned at I_F = 20 mA. Tolerance within each bin is ±15%.

• 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

This binning structure shows a wider range of available brightness levels for the green LED compared to the orange. Designers must specify the required bin code(s) when ordering to guarantee the luminous intensity range for their application.

4. Performance Curve Analysis

The datasheet references typical performance curves (shown on page 6). While the exact graphs are not reproduced in text, their implications are critical for design.

• Forward Current vs. Forward Voltage (I-V Curve): This curve is non-linear. The forward voltage (V_F) has a negative temperature coefficient; it decreases slightly as the junction temperature increases. Driving the LED with a constant current source, rather than a constant voltage, is essential for stable light output.
• Luminous Intensity vs. Forward Current: Intensity increases approximately linearly with current up to a point, but efficiency may drop at very high currents due to increased heat. Operating at or below the recommended 20-30 mA ensures optimal performance and longevity.
• Luminous Intensity vs. Ambient Temperature: The output of AlInGaP LEDs generally decreases as ambient temperature rises. Designers must account for this derating in high-temperature environments to ensure sufficient brightness.
• Spectral Distribution: The graphs would show the relative intensity across wavelengths, confirming the peak and dominant wavelengths and the spectral half-width, which affects color purity.

5. Mechanical & Package Information

5.1 Package Dimensions and Polarity

The device conforms to an EIA standard SMD package outline. Key dimensional tolerances are ±0.10 mm unless specified otherwise. The lens is water clear. The pin assignment is crucial for correct operation:

• Pin C1: Anode for the Green LED chip.
• Pin C2: Anode for the Orange LED chip.
• The cathodes for both chips are internally connected to a common terminal (typically the third pin or the thermal pad, depending on package). The schematic in the datasheet must be consulted for the exact connection diagram.

5.2 Recommended Solder Pad Layout

The datasheet provides suggested land pattern (footprint) dimensions for the PCB. Adhering to these recommendations is vital for achieving reliable solder joints, proper alignment, and effective heat dissipation during the reflow process. The suggested pattern ensures sufficient solder volume and prevents issues like tombstoning (component standing up on one end). A recommended soldering direction is also indicated to optimize the reflow process.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profile

A detailed suggested IR reflow profile for Pb-free processes is provided (page 3). Key parameters include:

• Pre-heat: 150–200°C for a maximum of 120 seconds to gradually heat the board and activate the flux.
• Peak Temperature: Maximum of 260°C.
• Time Above Liquidus: The time within the critical temperature zone (typically ~217°C for Pb-free solder) must be controlled to ensure proper solder joint formation without overheating the LED. The profile is based on JEDEC standards.
• Limit: The device can withstand this reflow process a maximum of two times.

Note: The optimal profile depends on the specific PCB design, solder paste, and oven. The provided profile serves as a starting point that must be characterized and adjusted for the actual production setup.

6.2 Hand Soldering

If hand soldering is necessary, extreme care must be taken:

• Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per joint.
• Limit: Hand soldering should be performed only once to minimize thermal stress.

6.3 Cleaning

Only specified cleaning agents should be used. Unspecified chemicals may damage the epoxy lens or package. If cleaning is required post-soldering, immersion in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute is acceptable.

6.4 Storage and Handling

• Moisture Sensitivity: The LEDs are packaged in moisture-barrier bags with desiccant. Once the original sealed bag is opened, the components are exposed to ambient humidity.
• Floor Life: It is recommended to complete IR reflow soldering within one week of opening the moisture-proof bag.
• Extended Storage: For storage beyond one week outside the original bag, components should be kept in a sealed container with desiccant or in a nitrogen desiccator.
• Baking: Components stored out of their original packaging for more than a week should be baked at approximately 60°C for at least 20 hours before assembly to remove absorbed moisture and prevent "popcorning" (package cracking) during reflow.

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The device is supplied for automated assembly, packaged in 8mm wide embossed carrier tape on 7-inch (178mm) diameter reels.

• Quantity per Reel: 3000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Cover Tape: Empty component pockets are sealed with a top cover tape.
• Missing Components: The maximum allowed number of consecutive missing LEDs in the tape is two.
• Standard: Packaging conforms to ANSI/EIA-481 specifications.

7.2 Part Number Structure

The part number LTST-S326KFKGKT encodes specific attributes. While the full corporate decoding may not be public, typical structures include series code (LTST), package size/type (S326), color/lens (KFKGKT for dual-color water clear), and potentially bin codes. The exact bin code for intensity must be confirmed or specified at the time of order.

8. Application Notes & Design Considerations

8.1 Typical Application Scenarios

• Dual-State Indicators: Power (Green) / Fault (Orange); Charge Complete (Green) / Charging (Orange); Network Link/Activity.
• Side-Illumination: Backlighting for membrane switches, edge-lit panels, or light guides where the LED is mounted perpendicular to the viewing surface.
• Consumer Electronics: Status indicators on routers, printers, audio equipment, and gaming consoles.
• Industrial Controls: Panel indicators for machine status, alarm conditions, or mode selection.

8.2 Critical Design Considerations

1. Current Limiting: NEVER connect an LED directly to a voltage source. Always use a series current-limiting resistor or, preferably, a constant current driver. Calculate the resistor value using R = (V_supply - V_F) / I_F. Use the maximum V_F from the datasheet (2.4V) for a robust design.
2. Thermal Management: While power dissipation is low, PCB layout should provide adequate copper area around the solder pads to act as a heat sink, especially if operating near maximum current or in high ambient temperatures.
3. ESD Protection: Implement ESD protection on signal lines driving the LED in sensitive environments. Follow strict ESD protocols during handling and assembly.
4. Optical Design: The 130-degree viewing angle provides wide dispersion. For applications requiring a more focused beam, an external lens or light pipe may be necessary.
5. Independent Control: The two LEDs have separate anodes. This allows them to be controlled independently by two microcontroller GPIO pins (with appropriate drivers/resistors) or multiplexed.

9. Technical Comparison & Differentiation

Compared to single-color SMD LEDs, this dual-color device offers significant space savings on the PCB by combining two functions in one package footprint. Versus older through-hole bi-color LEDs, the SMD format enables automated assembly, higher board density, and better reliability.

Key differentiators of this specific part include the use of AlInGaP technology for both colors, which typically offers higher efficiency and better temperature stability compared to some other material systems for orange/red, paired with a compatible green. The side-looking form factor is a distinct advantage over top-emitting LEDs for edge-lighting applications. The wide 130-degree viewing angle and RoHS compliance are standard expectations for modern components.

10. Frequently Asked Questions (FAQs)

Q1: Can I drive both LED chips simultaneously at their maximum DC current (30mA each)?

A1: Technically yes, but you must consider the total power dissipation. At 30mA and a typical V_F of 2.0V, each chip dissipates 60mW, for a total of 120mW. This exceeds the absolute maximum power dissipation rating of 75mW per chip and the combined thermal load may cause overheating. It is safer to operate each chip at or below 20mA for continuous use.

Q2: How do I identify the correct pin (C1 vs C2) on the physical component?

A2: The datasheet package drawing will show a polarity marker, such as a dot, notch, or chamfered corner on the package. This marker corresponds to a specific pin (e.g., Pin 1). You must cross-reference this marker with the pin assignment table (C1=Green, C2=Orange) in the datasheet. Always verify with the supplier's documentation.

Q3: Why is the binning tolerance ±15%? Can I get tighter bins?

A3: ±15% is a common industry tolerance for luminous intensity bins in standard indicator LEDs. It accounts for normal process variations. Tighter bins (e.g., ±5%) may be available as a special order or for higher-grade components, but they typically come at a higher cost. For most indicator applications, ±15% is acceptable.

Q4: My reflow oven profile differs from the suggestion. Is this a problem?

A4: The suggested profile is a guideline. It is essential that your actual profile does not exceed the absolute maximum ratings (260°C for 10 sec). You should characterize your process to ensure the LED's peak temperature and time above liquidus are within safe limits. Profile verification through thermalcouples is recommended.

11. Practical Design Case Study

Scenario: Designing a status indicator for a portable device with a single side-view window. The indicator must show Green for "Normal Operation" and Orange for "Low Battery".

Implementation:

1. Component Selection: The LTST-S326KFKGKT is ideal due to its side emission, fitting perfectly next to the edge of the window, and its dual-color capability in one package.
2. Schematic: Connect Pin C1 (Green) and Pin C2 (Orange) to two separate GPIO pins of the device's microcontroller via current-limiting resistors. Calculate resistor values for a drive current of 15mA (conservative for battery life) using a supply voltage of 3.3V: R = (3.3V - 2.4V) / 0.015A = 60 Ohms. Use the next standard value, 62 Ohms.
3. PCB Layout: Place the LED as close as possible to the edge of the board adjacent to the indicator window. Follow the recommended solder pad dimensions from the datasheet. Add a small copper pour connected to the thermal pad (cathode) for heat dissipation.
4. Firmware: The microcontroller code simply sets the corresponding GPIO pin high to illuminate the Green or Orange LED based on the system status.

This solution minimizes board space, simplifies assembly, and provides a clear, reliable dual-status indication.

12. Technology Principle Introduction

This LED is based on semiconductor electroluminescence. The core of each chip is a PN junction made from AlInGaP (Aluminium Indium Gallium Phosphide) semiconductor materials. When a forward voltage is applied, electrons from the N-type region and holes from the P-type region are injected across the junction. When these charge carriers recombine, they release energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy of the semiconductor, which directly dictates the wavelength (color) of the emitted light. The orange chip has a smaller bandgap than the green chip. The light generated at the junction escapes through a dome-shaped epoxy lens, which also protects the semiconductor die and wire bonds. The side-looking package incorporates a reflector cup that directs the primary emission laterally.

13. Industry Trends & Developments

The trend in SMD indicator LEDs continues toward higher efficiency (more light output per unit of electrical power), which reduces energy consumption and heat generation. There is also a drive for miniaturization, with packages becoming ever smaller while maintaining or improving optical performance. The integration of multiple colors or even RGB capabilities into a single miniature package is common. Furthermore, advancements in packaging materials aim to improve reliability under higher temperature reflow profiles and harsher environmental conditions. The adoption of more robust and consistent binning systems helps designers achieve tighter color and brightness uniformity in their products. The underlying semiconductor materials, like AlInGaP, are continually refined to improve internal quantum efficiency and color stability over temperature and lifetime.