LTST-S327TBKFKT Dual-Color SMD LED Datasheet - Blue & Orange - 20mA/25mA - 76mW/62.5mW - English Technical Document

1. Product Overview

The LTST-S327TBKFKT is a compact, surface-mount dual-color LED designed for modern electronic applications requiring space efficiency and automated assembly. This device integrates two distinct semiconductor chips within a single package: an InGaN (Indium Gallium Nitride) chip for blue emission and an AlInGaP (Aluminum Indium Gallium Phosphide) chip for orange emission. This configuration allows for two-color indication from a single component footprint, simplifying PCB design and reducing part count.

The primary market for this LED includes portable and handheld devices, telecommunications equipment, computer peripherals, and various consumer electronics where status indication, backlighting, or symbolic illumination is required. Its compatibility with high-volume, automated pick-and-place machines and standard infrared (IR) reflow soldering processes makes it ideal for cost-effective manufacturing.

1.1 Core Features and Advantages

• Dual-Color Integration: Combines blue and orange light sources in one EIA-standard package, enabling versatile signaling and display functions.
• High-Brightness Chips: Utilizes advanced InGaN and AlInGaP semiconductor technology to deliver high luminous intensity with typical values of 45 mcd (Blue) and 90 mcd (Orange) at 20mA.
• Manufacturing Readiness: Supplied on 8mm tape mounted on 7-inch reels, facilitating automated assembly. The package is designed to be compatible with infrared reflow soldering profiles, including lead-free (Pb-free) processes.
• Environmental Compliance: The product is compliant with the Restriction of Hazardous Substances (RoHS) directive.
• Wide Viewing Angle: Features a typical viewing angle (2θ1/2) of 130 degrees for both colors, providing broad visibility.

1.2 Target Applications

This LED is suited for a broad range of applications where reliable, compact indicator lighting is needed. Key application areas include:

• Status Indicators: Power, connectivity, battery, or mode indicators in phones, routers, and network equipment.
• Keyboard/Keypad Backlighting: Providing illumination for keys in low-light conditions.
• Consumer and Office Electronics: Indicators in appliances, printers, and audio-visual equipment.
• Industrial Control Panels: Signal lights for machinery status or alerts.

2. In-Depth Technical Parameter Analysis

A detailed examination of the electrical and optical specifications is crucial for proper circuit design and performance prediction.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation at or beyond these limits is not advised.

• Power Dissipation (Pd): Blue: 76 mW, Orange: 62.5 mW. This is the maximum power the LED can dissipate as heat at an ambient temperature (Ta) of 25°C.
• Forward Current: Continuous DC forward current (IF) is rated at 20 mA for the Blue chip and 25 mA for the Orange chip. A higher Peak Forward Current of 100 mA (Blue) and 60 mA (Orange) is permissible under pulsed conditions (1/10 duty cycle, 0.1ms pulse width).
• Temperature Ranges: Operating: -20°C to +80°C. Storage: -30°C to +100°C.
• Soldering Limit: The device can withstand infrared reflow soldering with a peak temperature of 260°C for a maximum of 10 seconds.

2.2 Electrical & Optical Characteristics (Ta=25°C)

These are the typical performance parameters under standard test conditions.

• Luminous Intensity (Iv): Measured in millicandelas (mcd) at IF=20mA. The Blue chip has a range from 28.0 mcd (Min) to 180.0 mcd (Max), with a typical value of 45.0 mcd. The Orange chip ranges from 45.0 mcd to 180.0 mcd, with a typical value of 90.0 mcd.
• Forward Voltage (Vf): At IF=20mA, Vf for Blue is between 2.8V (Min) and 3.8V (Max). For Orange, it is between 1.6V (Min) and 2.4V (Max). Designers must ensure the driving circuit can provide adequate voltage.
• Wavelength: The Peak Emission Wavelength (λp) is typically 468 nm for Blue and 611 nm for Orange. The Dominant Wavelength (λd), which defines the perceived color, is typically 470 nm for Blue and 605 nm for Orange.
• Spectral Width: The Spectral Line Half-Width (Δλ) is typically 25 nm for Blue and 17 nm for Orange, indicating the spectral purity of the emitted light.
• Reverse Current (Ir): Maximum of 10 µA at a Reverse Voltage (Vr) of 5V. The device is not designed for operation under reverse bias.

3. Binning System Explanation

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

3.1 Luminous Intensity Binning

The bin code defines a minimum and maximum luminous intensity range. A tolerance of +/-15% applies within each bin.

For the Blue Chip:

• 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

For the Orange Chip:

• Bin P: 45.0 – 71.0 mcd
• Bin Q: 71.0 – 112.0 mcd
• Bin R: 112.0 – 180.0 mcd
• Bin S: 180.0 – 280.0 mcd

When specifying or ordering, the bin code ensures you receive LEDs with brightness within the desired range. For applications requiring uniform appearance across multiple LEDs, specifying a tight bin (e.g., Bin Q or R) is recommended.

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet, the typical relationships described are critical for understanding device behavior under varying conditions.

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

The I-V relationship is non-linear. For both the Blue (InGaN) and Orange (AlInGaP) chips, the forward voltage increases with current. The Blue chip exhibits a higher turn-on and operating voltage (~3.2V typical) compared to the Orange chip (~2.0V typical). This difference must be accounted for in series or parallel driving configurations.

4.2 Luminous Intensity vs. Forward Current

Luminous intensity is approximately proportional to forward current within the recommended operating range. However, efficiency may drop at very high currents due to increased heat generation. Operating at or below the recommended DC current ensures optimal brightness and longevity.

4.3 Temperature Dependence

LED performance is temperature-sensitive. As the junction temperature increases:

• Luminous Intensity Decreases: Output light drops. The derating is more pronounced at higher ambient temperatures or currents.
• Forward Voltage Decreases: The Vf typically has a negative temperature coefficient.
• Wavelength Shifts: The peak wavelength may shift slightly with temperature, potentially affecting color perception in critical applications.

Proper thermal management on the PCB is essential to maintain stable performance.

5. Mechanical & Package Information

The physical dimensions and construction details are vital for PCB layout and assembly.

5.1 Package Dimensions and Pin Assignment

The device conforms to an industry-standard SMD package outline. Key dimensions include body size and lead spacing. All dimensional tolerances are ±0.1 mm unless otherwise specified. The pin assignment is clearly defined: Pin A1 is the anode for the Blue chip, and Pin A2 is the anode for the Orange chip. The cathodes are common or configured according to the internal package design (refer to the package diagram for the exact common connection point).

5.2 Recommended PCB Land Pattern and Polarity

A recommended solder pad layout is provided to ensure reliable solder joint formation during reflow. The pad design accounts for proper solder fillet formation and component alignment. The polarity marking on the device (typically a dot, notch, or beveled edge) must be aligned with the corresponding marking on the PCB silkscreen to ensure correct electrical connection.

6. Soldering & Assembly Guidelines

Adherence to recommended soldering procedures is critical to prevent damage.

6.1 Infrared Reflow Soldering Profile

For Pb-free assembly processes, a suggested reflow profile is provided. Key parameters include:

• Pre-heat: 150-200°C for up to 120 seconds to gradually heat the board and activate flux.
• Peak Temperature: Maximum of 260°C.
• Time Above Liquidus: The time the component leads are exposed to temperatures above the solder melting point should be controlled, with a maximum of 10 seconds at peak temperature. The device should not be subjected to more than two reflow cycles.

The profile should be developed and validated for the specific PCB assembly, considering board thickness, component density, and solder paste used.

6.2 Manual Soldering (Soldering Iron)

If manual rework is necessary, use a temperature-controlled iron set to a maximum of 300°C. The soldering time at the lead should not exceed 3 seconds per joint. Apply heat to the PCB pad, not directly to the LED body, to minimize thermal stress.

6.3 Cleaning

If post-solder cleaning is required, use only approved solvents. Immersing the LED in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute is acceptable. Harsh or unspecified chemicals can damage the epoxy lens or package.

6.4 Storage and Handling

• ESD Precautions: LEDs are sensitive to electrostatic discharge (ESD). Handle with appropriate ESD controls: use grounded wrist straps, anti-static mats, and properly grounded equipment.
• Moisture Sensitivity: The package has a Moisture Sensitivity Level (MSL) rating. If the original moisture-proof bag is opened, the components should be used within one week (MSL3). For longer storage outside the original bag, bake at approximately 60°C for at least 20 hours before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.
• Storage Conditions: Store in a cool, dry place. For opened packages, the environment should not exceed 30°C and 60% relative humidity.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The product is supplied for automated assembly. Key packaging details include:

• Tape Width: 8 mm.
• Reel Size: 7 inches in diameter.
• Quantity per Reel: 3000 pieces.
• Minimum Order Quantity (MOQ): For quantities less than a full reel, a minimum of 500 pieces is available as remnants.
• Packaging Standard: Conforms to ANSI/EIA-481 specifications. Empty pockets in the tape are covered with a protective top cover.

8. Application Design Considerations

8.1 Driving Circuit Design

Always drive LEDs with a constant current source, not a constant voltage, to ensure stable light output and prevent thermal runaway. A simple series resistor can be used for basic applications, calculated as R = (Vsupply - Vf) / If. For the Blue LED at 20mA with a 5V supply and typical Vf of 3.2V: R = (5 - 3.2) / 0.02 = 90 Ohms. For the Orange LED at 20mA with typical Vf of 2.0V: R = (5 - 2.0) / 0.02 = 150 Ohms. Dedicated LED driver ICs offer better efficiency and control for multi-LED or brightness-controlled applications.

8.2 Thermal Management

Although power dissipation is low, ensuring adequate heat sinking through the PCB copper pads is good practice, especially in high ambient temperature environments or when driving near maximum current. This helps maintain luminous intensity and extends operational life.

8.3 Optical Design

The wide 130-degree viewing angle makes this LED suitable for applications requiring broad-area visibility. For focused beams, secondary optics (lenses, light guides) may be required. The water-clear lens provides the true chip color.

9. Technical Comparison and Differentiation

The LTST-S327TBKFKT offers specific advantages in its class:

• Dual-Chip vs. Two Single LEDs: Saves PCB space and assembly cost compared to using two separate single-color LEDs.
• Chip Technology: Uses high-efficiency InGaN and AlInGaP materials, providing good brightness for the current consumption.
• Process Compatibility: Full compatibility with standard SMT assembly lines, including aggressive Pb-free reflow profiles, reduces manufacturing barriers.

10. Frequently Asked Questions (FAQ)

10.1 Can I drive both colors simultaneously at full current?

No. The Absolute Maximum Ratings for power dissipation (76 mW Blue, 62.5 mW Orange) and the thermal design of the package must be considered. Driving both chips at their maximum DC current (20mA Blue, 25mA Orange) simultaneously would generate significant heat. It is advisable to consult derating curves or operate at lower currents if both LEDs are to be on continuously.

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

Peak Wavelength (λp) is the wavelength at which the emission spectrum has its maximum intensity. Dominant Wavelength (λd) is the single wavelength of monochromatic light that would appear to have the same color as the LED's output to the human eye, calculated from the CIE chromaticity diagram. λd is often more relevant for color specification.

10.3 How do I interpret the bin code when ordering?

Specify the desired bin code(s) for each color (e.g., Blue: Bin P, Orange: Bin Q) to ensure you receive LEDs with luminous intensity within the corresponding range. This is crucial for achieving uniform brightness in an array of LEDs.

11. Design and Usage Case Study

Scenario: Dual-Status Indicator for a Wireless Device
A designer needs a single component to indicate both \"Bluetooth Connecting\" (flashing blue) and \"Battery Low\" (steady orange) on a compact wearable device.
Implementation: The LTST-S327TBKFKT is placed on the main PCB. A microcontroller GPIO pin drives the Blue LED anode (A1) through a 100Ω current-limiting resistor. Another GPIO pin drives the Orange LED anode (A2) through a 150Ω resistor. The common cathode is connected to ground. The microcontroller firmware controls the blinking pattern for the blue LED and turns the orange LED on when the battery voltage falls below a threshold. This solution uses minimal board space, requires only two microcontroller pins, and simplifies the bill of materials.

12. Operating Principle

Light Emitting Diodes (LEDs) are semiconductor devices that emit light when an electric current passes through them. This phenomenon, called electroluminescence, occurs when electrons recombine with electron holes within the device, releasing energy in the form of photons. The specific color of the light is determined by the energy band gap of the semiconductor material used. The InGaN chip has a wider band gap, emitting higher-energy photons perceived as blue light. The AlInGaP chip has a narrower band gap, emitting lower-energy photons perceived as orange/red light. The two chips are housed in a single epoxy package with a water-clear lens that does not alter the emitted color.

13. Technology Trends

The development of SMD LEDs like the LTST-S327TBKFKT is driven by several ongoing trends in electronics:

• Miniaturization: Continuous demand for smaller package sizes to enable more compact end products.
• Increased Efficiency: Advancements in semiconductor epitaxy and chip design yield higher luminous efficacy (more light output per watt of electrical input).
• Multi-Chip Integration: Combining more than two colors (e.g., RGB) or integrating control circuitry (e.g., addressable LEDs) within a single package is becoming more common.
• Enhanced Reliability: Improvements in packaging materials and processes lead to longer operational lifetimes and better performance under harsh environmental conditions.
• Broader Spectrum: Research into new materials like perovskites and quantum dots aims to expand the available color range and color rendering quality of LEDs.