LTST-S326TBKFKT-5A SMD LED Datasheet - Side Looking Dual Color (Blue/Orange) - EIA Package - English Technical Document

1. Product Overview

The LTST-S326TBKFKT-5A is a compact, side-looking, dual-color Surface Mount Device (SMD) LED lamp. It is engineered for automated printed circuit board (PCB) assembly and is ideal for applications where space is a critical constraint. The device incorporates 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 independent status indicators or backlighting colors from one component footprint.

The primary market for this LED includes a wide array of consumer and industrial electronics. Its miniature size and compatibility with high-volume assembly processes make it suitable for portable devices, communication equipment, computing hardware, and various indicator applications.

1.1 Core Features and Advantages

• Dual Color in One Package: Integrates blue and orange light sources, saving PCB space and simplifying design for multi-status indication.
• High Brightness: Utilizes Ultra Bright InGaN and AlInGaP chip technology for good luminous intensity.
• Industry-Standard Package: Complies with EIA (Electronic Industries Alliance) standards, ensuring compatibility with automated pick-and-place machinery.
• RoHS Compliance: Manufactured to meet Restriction of Hazardous Substances directives.
• Reflow Solder Compatible: Designed to withstand infrared (IR) reflow soldering processes, crucial for modern PCB assembly.
• Tin-Plated Leads: Enhances solderability and long-term reliability of the electrical connection.

1.2 Target Applications

• Backlighting for keypads, keyboards, and micro-displays.
• Status and power indicators in telecommunications and network equipment.
• Signal and symbol illumination in home appliances and office automation devices.
• Industrial equipment status panels.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

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

• 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. Exceeding this can lead to overheating and reduced lifespan.
• DC Forward Current (IF): Blue: 20 mA, Orange: 25 mA. The maximum continuous current that can be applied. A current-limiting resistor is mandatory in series with the LED in any practical circuit.
• Peak Forward Current: Blue: 100 mA, Orange: 60 mA (at 1/10 duty cycle, 0.1ms pulse width). This rating is relevant for pulsed operation, such as in multiplexed displays.
• Temperature Range: Operating: -20°C to +80°C; Storage: -30°C to +100°C. The device's performance is characterized within the operating range.
• Soldering Condition: Withstands 260°C for 10 seconds, which aligns with common lead-free (Pb-free) reflow profiles.

2.2 Electro-Optical Characteristics

Measured at Ta=25°C and a standard test current (IF) of 5 mA, these parameters define the typical performance.

• Luminous Intensity (Iv): A key measure of perceived brightness. For the Blue chip, it ranges from 11.2 mcd (min) to 45.0 mcd (max). For the Orange chip, it ranges from 18.0 mcd to 112.0 mcd. The orange chip typically exhibits higher luminous efficacy.
• Viewing Angle (2θ1/2): 130 degrees (typical for both colors). This wide viewing angle is characteristic of side-looking LEDs, providing a broad emission pattern suitable for edge-lit or indicator applications.
• Forward Voltage (VF): Blue: 2.6V to 3.4V; Orange: 1.6V to 2.4V (at IF=5mA). The forward voltage is a critical parameter for circuit design, as it determines the voltage drop across the LED and the value of the required series resistor. The blue LED requires a higher drive voltage due to its wider bandgap semiconductor material.
• Peak Wavelength (λP) & Dominant Wavelength (λd): Blue: λP ~468 nm, λd 463-477 nm. Orange: λP ~611 nm, λd 598-612 nm. The dominant wavelength defines the perceived color. The spectral half-width (Δλ) is 25 nm for blue and 17 nm for orange, indicating the color purity.
• Reverse Current (IR): Max 10 μA at VR=5V. LEDs are not designed for reverse bias operation; this parameter is for test purposes only. Applying reverse voltage can damage the device.

3. Binning System Explanation

To ensure consistency in production, LEDs are sorted (binned) based on key optical parameters. The LTST-S326TBKFKT-5A uses a binning system for Luminous Intensity.

3.1 Luminous Intensity Binning

The luminous output is categorized into bins with a +/-15% tolerance within each bin.

• Blue Chip Bins: L (11.2-18.0 mcd), M (18.0-28.0 mcd), N (28.0-45.0 mcd).
• Orange Chip Bins: M (18.0-28.0 mcd), N (28.0-45.0 mcd), P (45.0-71.0 mcd), Q (71.0-112.0 mcd).

This binning allows designers to select parts with a guaranteed minimum brightness for their application, ensuring visual consistency in end products. The specific bin for a given production lot is typically indicated in the ordering code or on packaging labels.

4. Performance Curve Analysis

While the PDF references typical curves, they are not provided in the excerpt. Based on standard LED behavior, the following analyses are inferred from the given parameters.

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

The I-V relationship is exponential. For the blue LED, the turn-on voltage is higher (~2.6V) compared to the orange LED (~1.6V). The curve will show a sharp increase in current once the forward voltage exceeds this threshold. Proper current regulation (via a series resistor or constant current driver) is essential to prevent thermal runaway, as the forward voltage decreases with increasing temperature, which can lead to a destructive increase in current if driven by a voltage source.

4.2 Luminous Intensity vs. Forward Current

Luminous intensity is approximately proportional to the forward current up to a point. Operating above the recommended DC current (20/25 mA) will increase brightness but at the cost of higher power dissipation, reduced efficiency, and accelerated lumen depreciation (light output decline over time).

4.3 Temperature Dependence

LED performance is temperature-sensitive. As the junction temperature increases: Luminous intensity generally decreases, the forward voltage (VF) decreases slightly, and the dominant wavelength may shift (typically longer for InGaN). The specified operating temperature range of -20°C to +80°C defines the ambient conditions under which the published characteristics are valid. Adequate thermal management on the PCB is important for maintaining performance and longevity.

5. Mechanical and Package Information

5.1 Package Dimensions and Pin Assignment

The device conforms to an EIA standard SMD package outline. Key dimensions include body size and lead spacing. All dimensions have a tolerance of ±0.1 mm unless otherwise specified. The pin assignment is critical for correct orientation: Pin C1 is assigned to the Orange (AlInGaP) chip anode, and Pin C2 is assigned to the Blue (InGaN) chip anode. The cathode is common. The package is "water clear," meaning the lens is transparent, allowing the true chip color to be visible.

5.2 Recommended PCB Pad Design and Polarity

A recommended land pattern (footprint) is provided to ensure reliable soldering and proper alignment. The design typically includes thermal reliefs and solder mask definitions. Polarity must be strictly observed during placement. The marking on the device body (often a dot or a cut corner) indicates the cathode (common) side. Incorrect polarity will prevent the LED from illuminating and applying reverse voltage may damage it.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Parameters

For lead-free (Pb-free) solder processes, a suggested reflow profile is provided. Key parameters include: Pre-heat zone (150-200°C), pre-heat time (max 120 seconds), peak temperature (max 260°C), and time above liquidus (at peak temperature, max 10 seconds). The device can withstand a maximum of two reflow cycles under these conditions. Adherence to this profile is crucial to prevent thermal shock, delamination, or damage to the LED chip and epoxy lens.

6.2 Hand Soldering

If hand soldering is necessary, it should be performed with caution. The soldering iron tip temperature should not exceed 300°C, and the soldering time per lead should be limited to a maximum of 3 seconds. Only one soldering cycle is recommended for hand soldering to minimize thermal stress.

6.3 Storage and Handling Conditions

Storage (Sealed Package): Store at ≤30°C and ≤90% Relative Humidity (RH). The shelf life is one year when stored in the original moisture-proof bag with desiccant.
Storage (Opened Package): For components removed from their sealed packaging, the ambient should not exceed 30°C / 60% RH. Components should be used within one week (MSL Level 3). For longer storage outside the original bag, they must be stored in a sealed container with desiccant or in a nitrogen environment. If stored for more than one week, a bake-out at 60°C for at least 20 hours is required before soldering to remove absorbed moisture and prevent "popcorning" during reflow.
ESD Precautions: LEDs are sensitive to electrostatic discharge (ESD). Handling should be performed on grounded workstations using wrist straps or anti-static gloves to prevent latent or catastrophic failure.

6.4 Cleaning

If cleaning after soldering is required, only specified solvents should be used. 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 plastic package material, leading to discoloration or cracking.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied packaged in 8mm wide embossed carrier tape on 7-inch (178 mm) diameter reels. This is the standard packaging for automated assembly equipment. Each reel contains 3000 pieces. The tape has a cover tape to protect components during shipping and handling. The packaging conforms to ANSI/EIA-481 specifications.

7.2 Minimum Order Quantity and Reel Details

The standard full reel quantity is 3000 pieces. For quantities less than a full reel, a minimum packing quantity of 500 pieces applies for remainder parts. The packaging specification allows for a maximum of two consecutive missing components in the tape.

8. Application Design Suggestions

8.1 Circuit Design Considerations

• Current Limiting: Always use a series resistor to limit the forward current to the desired value (e.g., 5 mA for testing, up to the maximum DC rating for full brightness). Calculate the resistor value using Ohm's Law: R = (Vcc - VF) / IF, where Vcc is the supply voltage, VF is the LED forward voltage (use max value for a safe design), and IF is the desired current.
• Power Supply: Ensure a stable DC power supply. Ripple or voltage spikes can affect brightness and longevity.
• Parallel Connection: Avoid connecting LEDs directly in parallel without individual current-limiting resistors, as slight variations in VF can cause current hogging, where one LED draws most of the current.

8.2 Thermal Management

While SMD LEDs are small, power dissipation (up to 76 mW) generates heat. Ensure the PCB has adequate copper area (thermal pads) connected to the LED's cathode/anode pads to act as a heat sink. Avoid placing the LED near other heat-generating components.

8.3 Optical Integration

The side-looking nature of this LED makes it ideal for applications where light needs to be directed parallel to the PCB surface, such as into a light guide for edge-lit panels or for illuminating symbols on a front panel. Consider the 130-degree viewing angle when designing light pipes or diffusers to ensure uniform illumination.

9. Technical Comparison and Differentiation

The primary differentiation of the LTST-S326TBKFKT-5A lies in its dual-color, side-looking configuration within a standard SMD package. Compared to using two separate single-color LEDs, it offers a 50% reduction in required PCB footprint. The use of InGaN for blue and AlInGaP for orange provides a good combination of brightness and color saturation. The wide viewing angle is a specific advantage over top-view LEDs for lateral illumination tasks. Its compatibility with standard IR reflow and tape-and-reel packaging aligns it with high-volume, cost-effective manufacturing processes.

10. Frequently Asked Questions (Based on Technical Parameters)

10.1 Can I drive both colors simultaneously?

No, the two chips share a common cathode but have independent anodes (C1 for Orange, C2 for Blue). They must be driven by separate current sources (e.g., two GPIO pins from a microcontroller, each with its own series resistor). Driving them simultaneously with a single source connected to both anodes is not possible with this pin configuration.

10.2 Why is the forward voltage different for the two colors?

The forward voltage is a fundamental property of the semiconductor material's bandgap energy. Blue light has higher photon energy, which requires a semiconductor with a wider bandgap (InGaN). A wider bandgap correlates with a higher forward voltage. Orange light from AlInGaP has a lower photon energy and thus a lower forward voltage.

10.3 What does \"Water Clear\" lens mean?

A \"Water Clear\" or transparent lens does not diffuse the light. It allows the true, saturated color of the LED chip to be seen. This is in contrast to a \"diffused\" or \"milky\" lens, which scatters the light, creating a wider, softer emission pattern but often with a slight reduction in perceived color saturation and axial intensity.

10.4 How do I interpret the bin code for my order?

The bin code (e.g., \"N\" for blue, \"Q\" for orange) specifies the guaranteed range of luminous intensity for that production batch. You should specify the required bin(s) when ordering to ensure brightness consistency across all units in your product. If not specified, you may receive parts from any available bin within the product's range.

11. Practical Design and Usage Case

Scenario: Dual-Status Indicator for a Network Router. A designer needs two status indicators (Power and Network Activity) but has limited space on the front panel. They use one LTST-S326TBKFKT-5A. The Orange chip (C1) is connected to a constant 5mA current source to indicate \"Power On\" (steady). The Blue chip (C2) is connected to a microcontroller GPIO pin programmed to blink at 1Hz to indicate \"Network Activity\". A single component footprint provides two distinct visual signals. The side-looking emission is coupled into a small, custom-molded light guide that directs the light to the front panel labels.

12. Operating Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light through electroluminescence. When a forward voltage is applied across the p-n junction, electrons from the n-type material recombine with holes from the p-type material. This recombination releases energy in the form of photons (light). The color (wavelength) of the emitted light is determined by the energy bandgap of the semiconductor material. InGaN materials are used for shorter wavelengths (blue, green, white), while AlInGaP materials are used for longer wavelengths (red, orange, yellow). The side-looking package incorporates a reflective cavity and a molded epoxy lens to shape and direct the light output laterally from the chip.

13. Technology Trends

The trend in SMD LEDs for indicators and backlighting continues towards higher efficiency (more lumens per watt), smaller package sizes, and increased integration. Dual- and multi-color packages in ultra-miniature footprints (e.g., 0402, 0201 metric) are becoming more common. There is also a focus on improving color consistency and tightening binning tolerances. Furthermore, the drive for higher reliability and performance in harsh environments pushes advancements in package materials and chip technology. The principles of efficient current drive, thermal management, and ESD protection remain foundational to all LED applications.