LTST-S326KGKFKT Dual Color SMD LED Datasheet - Side Looking - Green/Orange - 20mA - English Technical Document

1. Product Overview

The LTST-S326KGKFKT is a dual-color, side-looking Surface Mount Device (SMD) LED. It integrates two distinct AlInGaP semiconductor chips within a single package: one emitting green light and the other emitting orange light. This configuration allows for bi-color indication or signaling from a single compact component. The device is designed for compatibility with automated assembly processes and modern lead-free (Pb-free) soldering techniques.

1.1 Core Features and Advantages

The primary advantages of this LED stem from its material technology and package design. The use of AlInGaP (Aluminum Indium Gallium Phosphide) chips provides high luminous efficiency, resulting in bright output. The side-looking lens design directs light laterally, making it ideal for applications where the LED is mounted perpendicular to the viewing surface, such as in edge-lit panels or status indicators on the side of a device. Key features include compliance with RoHS (Restriction of Hazardous Substances) directives, tin-plated leads for improved solderability, and packaging on 8mm tape reels for efficient automated pick-and-place assembly.

1.2 Target Applications and Market

This component is targeted at the general electronics market. Its typical applications include status indicators, backlighting for buttons or symbols, and bi-color signal lights in consumer electronics, office equipment, communication devices, and household appliances. The side-emitting characteristic is particularly valuable in space-constrained designs where front-facing LEDs are not feasible.

2. Technical Specifications and Objective Interpretation

This section provides a detailed breakdown of the device's operational limits and performance characteristics under standard conditions (Ta=25°C).

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. They are not intended for normal operation.

• Power Dissipation (Pd): 72 mW per chip. This is the maximum amount of power that can be continuously dissipated as heat. Exceeding this limit risks overheating and accelerated degradation.
• Peak Forward Current (I_FP): 80 mA, permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). This allows for brief periods of high-intensity flashing.
• Continuous Forward Current (I_F): 30 mA DC. This is the recommended maximum current for continuous operation to ensure long-term reliability.
• Reverse Voltage (V_R): 5 V. Applying a reverse voltage higher than this can cause junction breakdown.
• Operating & Storage Temperature: -30°C to +85°C and -40°C to +85°C, respectively. The device can withstand non-operational storage at slightly lower temperatures.
• Soldering Temperature: Withstands infrared reflow soldering at 260°C peak temperature for up to 10 seconds, which aligns with common Pb-free assembly profiles.

2.2 Electro-Optical Characteristics

These parameters define the device's performance at the typical operating point of 20 mA forward current.

• Luminous Intensity (I_V): The green chip has a typical intensity of 35.0 mcd (millicandela), with a minimum of 18.0 mcd. The orange chip is brighter, with a typical intensity of 90.0 mcd and a minimum of 28.0 mcd. Intensity is measured using a filter that mimics the human eye's photopic response (CIE curve).
• Viewing Angle (2θ_1/2): 130 degrees (typical). This wide angle indicates a broad, diffuse emission pattern suitable for side illumination.
• Wavelength:
  • Peak Wavelength (λ_P): 574 nm (green, typical) and 611 nm (orange, typical). This is the wavelength at which the spectral output is strongest.
  • Dominant Wavelength (λ_d): 571 nm (green, typical) and 605 nm (orange, typical). This is the single wavelength perceived by the human eye, derived from the CIE chromaticity diagram, and best defines the color.
  • Spectral Bandwidth (Δλ): 15 nm (green) and 17 nm (orange, typical). This indicates the spectral purity; narrower bandwidths result in more saturated colors.
• Forward Voltage (V_F): 2.0 V typical, 2.4 V maximum at 20 mA. This low voltage makes it compatible with common 3.3V and 5V logic circuits, often without needing a current-limiting resistor for low-current indication.
• Reverse Current (I_R): 10 μA maximum at 5 V reverse bias. A low reverse current is desirable.

3. Binning System Explanation

To ensure consistent color and brightness in production, LEDs are sorted into performance bins. The LTST-S326KGKFKT uses a luminous intensity binning system.

3.1 Luminous Intensity Binning

The luminous output at 20 mA is categorized into bins identified by a letter code. Each bin has a minimum and maximum intensity value, with a +/-15% tolerance allowed within each bin.

• Green 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).
• Orange Chip Bins: N (28.0-45.0 mcd), P (45.0-71.0 mcd), Q (71.0-112.0 mcd), R (112.0-180.0 mcd).

This system allows designers to select a bin that meets their specific brightness requirements. For example, an application requiring uniform panel brightness would specify a tight bin like P or Q to minimize variation between units.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (pages 6-7), their implications are standard for LED technology.

4.1 Current vs. Luminous Intensity (I_V Curve)

The light output of an LED is approximately proportional to the forward current over a range. Operating above the recommended 20 mA will increase brightness but also increase power dissipation (heat) and potentially reduce operational lifespan. The pulsed peak current rating (80mA) allows for short, bright flashes without thermal buildup.

4.2 Temperature Dependence

LED performance is temperature-sensitive. Typically, the forward voltage (V_F) decreases slightly with increasing temperature. More significantly, luminous intensity generally decreases as the junction temperature rises. Proper thermal management in the PCB design (e.g., adequate copper area for heat sinking) is crucial for maintaining consistent brightness, especially in high-ambient-temperature environments or at higher drive currents.

4.3 Spectral Distribution

The referenced spectral curves would show the emission profile of each chip. The peak and dominant wavelengths are specified, and the curves would illustrate the spectral bandwidth (Δλ). The orange AlInGaP chip typically has a broader spectral width than the green, which is reflected in the 17 nm vs. 15 nm specification.

5. Mechanical and Package Information

5.1 Physical Dimensions and Polarity

The device conforms to an EIA standard SMD package outline. The pin assignment is clearly defined: Cathode 1 (C1) is for the orange chip, and Cathode 2 (C2) is for the green chip. The common anode is not explicitly labeled in the snippet but is standard for this type of dual-color, common-anode LED. The side-looking lens is a key mechanical feature.

5.2 Recommended PCB Land Pattern

The datasheet provides suggested soldering pad dimensions and orientation. Following these recommendations is critical for achieving reliable solder joints, preventing tombstoning (one end lifting), and ensuring proper alignment for the side light emission. The suggested soldering direction is provided to optimize the reflow process.

6. Assembly, Soldering, and Handling Guidelines

6.1 Reflow Soldering Profile

A detailed suggested infrared reflow profile is provided for Pb-free processes. Key parameters include a pre-heat zone (150-200°C), a controlled ramp to a peak temperature of 260°C maximum, and a time above liquidus (TAL) that ensures proper solder joint formation without thermal damage to the LED package. The profile is based on JEDEC standards to ensure reliability.

6.2 Manual Soldering

If manual soldering with an iron is necessary, the temperature must not exceed 300°C, and contact time should be limited to 3 seconds maximum for a single soldering event. Excessive heat or time can damage the internal wire bonds or the epoxy lens.

6.3 Cleaning

Only specified cleaning agents should be used. Recommended solvents are ethyl alcohol or isopropyl alcohol at room temperature, with immersion time limited to less than one minute. Harsh or unspecified chemicals can craze, cloud, or damage the LED lens.

6.4 Storage and Moisture Sensitivity

The LEDs are moisture-sensitive. Unopened, factory-sealed reels with desiccant have a shelf life of one year when stored at ≤30°C and ≤90% RH. Once the moisture-proof bag is opened, the components should be stored at ≤30°C and ≤60% RH and ideally used within one week. For longer storage outside the original packaging, they must be kept in a dry, sealed environment (e.g., with desiccant or in nitrogen) and may require a baking cycle (e.g., 60°C for 20 hours) before soldering to prevent \"popcorning\" damage during reflow.

6.5 ESD (Electrostatic Discharge) Precautions

LEDs are susceptible to damage from electrostatic discharge. Proper ESD controls must be in place during handling: use grounded wrist straps, anti-static mats, and ensure all equipment is properly grounded.

7. Packaging and Ordering

7.1 Tape and Reel Specifications

The product is supplied standard on 8mm wide embossed carrier tape wound onto 7-inch (178mm) diameter reels. Each full reel contains 3000 pieces. The tape and reel specifications comply with ANSI/EIA-481 standards to ensure compatibility with automated equipment. A minimum order quantity of 500 pieces applies for partial reels (remainders). The packaging ensures component orientation and protects the devices during shipping and handling.

8. Application Design Considerations

8.1 Circuit Design

A current-limiting resistor is almost always required in series with each LED chip to set the forward current. The resistor value can be calculated using Ohm's Law: R = (V_supply - V_F) / I_F. Using the typical V_F of 2.0V and a desired I_F of 20mA from a 5V supply: R = (5V - 2.0V) / 0.020A = 150 Ω. A slightly higher value (e.g., 180 Ω) can be used to increase margin and slightly reduce current/power. For multiplexing or driving from a microcontroller GPIO pin, ensure the pin's current sourcing/sinking capability is not exceeded.

8.2 Thermal Management

While the power dissipation is low (72mW max per chip), continuous operation at maximum ratings in a high ambient temperature can lead to junction temperatures exceeding specifications. Providing adequate copper area on the PCB around the LED pads helps dissipate heat. Avoid placing the LED near other significant heat sources.

8.3 Optical Integration

The 130-degree side emission must be considered in the mechanical design. Light guides, diffusers, or reflective cavities may be needed to direct or shape the light output for the intended visual effect. The chosen intensity bin will directly impact the final brightness.

9. Technical Comparison and Differentiation

The key differentiators of this component are its dual-color capability in a side-looking package. Compared to single-color LEDs, it saves board space and simplifies assembly for bi-color indication. Compared to top-emitting LEDs, it solves a specific mechanical layout challenge. The use of AlInGaP technology offers higher efficiency and better temperature stability than older technologies like GaAsP for these colors, resulting in brighter and more consistent output.

10. Frequently Asked Questions (FAQ)

10.1 Can I drive both colors simultaneously?

Yes, but you must consider the total power dissipation. The combined power of both chips at their maximum continuous current (30mA each at ~2.0V) would be approximately 120mW, which exceeds the individual chip rating of 72mW. The combined heat in the shared package must be managed. For reliable long-term operation, it is advisable to drive both chips at a lower current (e.g., 15-20mA each) if they are to be on simultaneously for extended periods.

10.2 What is the difference between peak and dominant wavelength?

Peak wavelength (λ_P) is the physical measurement of the highest point on the spectral output curve. Dominant wavelength (λ_d) is a calculated value based on how the human eye perceives the color mixture from the LED; it is the single wavelength that best matches the perceived hue. For LEDs with a relatively narrow spectrum, they are often close, but λ_d is more relevant for color specification.

10.3 Why is a baking process required before soldering?

SMD components absorb moisture from the air. During the rapid heating of reflow soldering, this trapped moisture can vaporize explosively, causing internal delamination, cracks, or \"popcorning.\" Baking removes this absorbed moisture, making the components safe for the high-temperature reflow process.

11. Practical Application Example

Scenario: Dual-Status Indicator on a Network Router. A router uses a single cutout on its side panel for status indication. The LTST-S326KGKFKT is mounted on the PCB directly behind this cutout. The microcontroller drives the LEDs: Solid green indicates normal operation and network connection. Flashing orange indicates data activity. Solid orange indicates a system error or boot-up sequence. This design uses one component footprint to provide three clear visual states, leveraging the side emission to be visible from the front of the device, saving space and simplifying the front panel design compared to using two separate top-emitting LEDs.

12. Technology Principle Introduction

An LED is a semiconductor diode. 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 color of the light is determined by the bandgap energy of the semiconductor material. AlInGaP (Aluminum Indium Gallium Phosphide) is a compound semiconductor whose bandgap can be tuned by varying the ratios of its constituents. For the LTST-S326KGKFKT, one chip is engineered with a bandgap corresponding to green light (~571 nm), and another with a bandgap corresponding to orange light (~605 nm). The side-looking package incorporates a molded epoxy lens that shapes the emitted light into a wide, lateral pattern.

13. Technology Trends

The general trend in LED technology for indicator applications continues toward higher efficiency (more light output per unit of electrical power), which allows for lower operating currents and reduced system power consumption. There is also a drive for miniaturization while maintaining or improving optical performance. Furthermore, integration is a key trend, such as incorporating current-limiting resistors or driver ICs within the LED package itself to simplify circuit design. While this specific datasheet represents a mature product, newer offerings in the market may feature these advancements, offering designers even smaller, more efficient, and easier-to-use solutions for status indication and panel lighting.