LTST-S326KSTGKT-5A SMD LED Datasheet - Dual Color (Yellow/Green) - 5mA - 130° Viewing Angle - English Technical Document

1. Product Overview

The LTST-S326KSTGKT-5A is a compact, surface-mount dual-color LED designed for modern electronic applications requiring reliable indicator lighting in a minimal footprint. This device integrates two distinct semiconductor chips within a single package: one AlInGaP chip for yellow emission and one InGaN chip for green emission. This configuration allows for two-color indication from a single component, saving valuable PCB real estate. The LED is housed in a standard EIA-compliant package with a water-clear lens, ensuring high light output and a wide viewing angle. It is specifically engineered for compatibility with automated pick-and-place assembly systems and standard infrared (IR) reflow soldering processes, making it suitable for high-volume manufacturing environments.

The core advantages of this LED include its compliance with RoHS directives, the use of ultra-bright chip technology for high luminous intensity, and its design for robustness in automated assembly lines. Its primary target markets span telecommunications equipment, office automation devices, home appliances, industrial control panels, and various consumer electronics where status indication or backlighting is required.

2. Technical Specifications Deep Dive

2.1 Absolute Maximum Ratings

Operating the device beyond these limits may cause permanent damage.

• Power Dissipation: Yellow: 62.5 mW, Green: 76 mW
• Peak Forward Current (1/10 Duty Cycle, 0.1ms Pulse): Yellow: 60 mA, Green: 100 mA
• Continuous DC Forward Current (I_F): Yellow: 25 mA, Green: 20 mA
• Operating Temperature Range (T_a): -20°C to +80°C
• Storage Temperature Range: -30°C to +100°C
• Infrared Soldering Condition: 260°C peak temperature for a maximum of 10 seconds.

2.2 Electrical & Optical Characteristics (at T_a=25°C, I_F=5mA)

These are the typical performance parameters under standard test conditions.

• Luminous Intensity (I_V):
  • Yellow: Minimum 7.1 mcd, Typical -, Maximum 71.0 mcd
  • Green: Minimum 28.0 mcd, Typical -, Maximum 280.0 mcd
  • Measured using a sensor/filter approximating the CIE photopic eye-response curve.
• Viewing Angle (2θ_1/2): 130 degrees (typical for both colors). This is the full angle at which intensity is half the on-axis value.
• Peak Wavelength (λ_P): Yellow: 591 nm (typ), Green: 530 nm (typ).
• Dominant Wavelength (λ_d):
  • Yellow: Min 582.0 nm, Max 596.0 nm
  • Green: Min 520.0 nm, Max 540.0 nm
• Spectral Bandwidth (Δλ): Yellow: 15 nm (typ), Green: 35 nm (typ).
• Forward Voltage (V_F):
  • Yellow: Typical 2.0 V, Maximum 2.3 V
  • Green: Typical 2.8 V, Maximum 3.2 V
• Reverse Current (I_R): Maximum 10 µA for both colors at V_R=5V. Note: The device is not designed for reverse operation; this parameter is for test purposes only.

3. Binning System Explanation

The product is sorted into bins based on luminous intensity to ensure color and brightness consistency within an application. The tolerance for each bin is +/-15%.

3.1 Luminous Intensity Bins

For Yellow Color (I_F=5mA):

• Bin K: 7.1 – 11.2 mcd
• Bin L: 11.2 – 18.0 mcd
• Bin M: 18.0 – 28.0 mcd
• Bin N: 28.0 – 45.0 mcd
• Bin P: 45.0 – 71.0 mcd

For Green Color (I_F=5mA):

• 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
• Bin S: 180.0 – 280.0 mcd

The part number LTST-S326KSTGKT-5A indicates specific bin selections for the yellow (K) and green (S) chips. Designers should specify the required bins for their application to guarantee visual uniformity, especially when multiple LEDs are used adjacent to each other.

4. Performance Curve Analysis

While the PDF references typical curves, their characteristics can be inferred from the provided data:

• I-V (Current-Voltage) Curve: The forward voltage (V_F) specifications suggest a characteristic exponential relationship. The yellow chip, with a lower typical V_F (2.0V), will have a slightly different curve shape compared to the green chip (typical V_F 2.8V). Proper current limiting is essential, as the V_F has a negative temperature coefficient.
• Luminous Intensity vs. Current: Intensity (I_V) is approximately proportional to forward current (I_F) within the rated operating range. However, efficiency may drop at very high currents due to thermal effects.
• Temperature Characteristics: Luminous output for both AlInGaP (yellow) and InGaN (green) LEDs typically decreases with increasing junction temperature. The operating temperature range of -20°C to +80°C defines the ambient conditions under which the specified performance is guaranteed.
• Spectral Distribution: The peak and dominant wavelengths, along with the spectral bandwidth (Δλ), define the color purity. The green chip's wider Δλ (35 nm) compared to the yellow chip (15 nm) is typical for InGaN-based green LEDs.

5. Mechanical & Package Information

5.1 Package Dimensions

The LED conforms to a standard EIA surface-mount package outline. All dimensions are in millimeters with a standard tolerance of ±0.1 mm unless otherwise specified. The package features a low-profile design suitable for space-constrained applications.

5.2 Pin Assignment & Polarity

The device has two anodes (one for each chip) and a common cathode. The pin assignment is as follows:

• Cathode 1 (C1): Connected to the Green InGaN chip.
• Cathode 2 (C2): Connected to the Yellow AlInGaP chip.

Correct polarity must be observed during PCB layout and assembly. The recommended PCB attachment pad layout is provided to ensure proper soldering and mechanical stability.

6. Soldering & Assembly Guide

6.1 Reflow Soldering Parameters (Pb-Free Process)

The device is compatible with infrared reflow soldering. A suggested profile compliant with JEDEC standards is:

• 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 Cycles: Maximum two times.

Note: The actual profile must be characterized for the specific PCB design, solder paste, and oven used.

6.2 Hand Soldering

If hand soldering is necessary:

• Iron Temperature: Maximum 300°C
• Soldering Time: Maximum 3 seconds per pad
• Number of Cycles: One time only.

6.3 Storage & Handling

• ESD Precautions: The device is sensitive to electrostatic discharge (ESD). Use wrist straps, anti-static mats, and properly grounded equipment during handling.
• Moisture Sensitivity: As a surface-mount device, it is moisture-sensitive.
  • Sealed Bag: Store at ≤30°C and ≤60% RH. Use within one year of bag opening.
  • After Bag Opening: For components out of the original bag for more than one week, a bake at 60°C for at least 20 hours is recommended before reflow to prevent "popcorning."
• Cleaning: Use only approved alcohol-based solvents like isopropyl alcohol (IPA) or ethyl alcohol. Immersion should be for less than one minute at room temperature. Avoid unspecified chemicals.

7. Packaging & Ordering Information

The standard packaging for automated assembly is:

• Tape: 8mm wide embossed carrier tape.
• Reel: 7-inch (178mm) diameter reel.
• Quantity per Reel: 3000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• The packaging follows ANSI/EIA-481 specifications. Empty pockets are sealed with cover tape, and a maximum of two consecutive missing components is allowed.

8. Application Recommendations

8.1 Typical Application Scenarios

• Status Indicators: Power-on, standby, mode, battery charge, or network activity indicators in routers, modems, base stations, and telecom equipment.
• Keypad/Keyboard Backlighting: Providing dual-color feedback (e.g., green for active, yellow for warning) in industrial panels, medical devices, or consumer electronics.
• Panel Indicators: On control panels for home appliances (ovens, washing machines) and office automation equipment (printers, scanners).
• Symbolic Luminaires: Small signage or icon illumination.

8.2 Design Considerations

• Current Limiting: Always use a series current-limiting resistor for each color channel. Calculate the resistor value based on the supply voltage (V_CC), the desired forward current (I_F), and the LED's forward voltage (V_F). Use the maximum V_F from the datasheet for a robust design: R = (V_CC - V_{F_max}) / I_F.
• Thermal Management: While power dissipation is low, ensure adequate PCB copper area or thermal vias if operating at high ambient temperatures or near maximum current to maintain performance and longevity.
• Optical Design: The 130-degree viewing angle provides wide visibility. For directed light, external lenses or light guides may be necessary.
• Driving Circuitry: The LED is logic-level compatible and can be driven directly from microcontroller GPIO pins (with a current-limiting resistor) or through transistor/MOSFET switches for higher current control.

9. Technical Comparison & Differentiation

The LTST-S326KSTGKT-5A offers specific advantages in its category:

• Dual Color in One Package: Eliminates the need for two separate SMD LEDs, saving PCB space, reducing placement time/cost, and simplifying bill of materials (BOM).
• High Brightness: The use of ultra-bright AlInGaP and InGaN chips provides high luminous intensity, making it suitable for applications requiring good visibility even in well-lit conditions.
• Standardized Package: The EIA-standard footprint ensures compatibility with a vast array of existing PCB layouts, pick-and-place nozzles, and feeder systems.
• Robust Process Compatibility: Designed explicitly for IR reflow and automated assembly, ensuring high yield and reliability in mass production.

10. Frequently Asked Questions (FAQs)

Q1: Can I drive both the yellow and green LEDs simultaneously at their maximum DC current?
A1: No. The absolute maximum ratings specify individual DC forward currents (Yellow: 25mA, Green: 20mA). Driving both simultaneously at these levels would likely exceed the total package power dissipation rating. For simultaneous operation, derate the currents accordingly based on thermal considerations.

Q2: What is the difference between peak wavelength (λ_P) and dominant wavelength (λ_d)?
A2: Peak wavelength is the single wavelength at which the emission spectrum has its highest intensity. Dominant wavelength is the single wavelength of monochromatic light that would match the perceived color of the LED when combined with a specified white reference. λ_d is more closely related to human color perception.

Q3: Why is the reverse current (I_R) test condition specified if the device is not for reverse operation?
A3: The I_R test is a standard quality and reliability test to check for junction integrity and leakage. It verifies that the LED chip and package do not have significant defects. Applying reverse voltage in an actual circuit is not recommended and can damage the device.

Q4: How critical is the 1-week timeline after opening the moisture barrier bag?
A4: It is a conservative guideline to prevent moisture-induced damage during reflow soldering ("popcorning"). If the exposure time is exceeded, baking the components as specified (60°C for 20+ hours) effectively removes absorbed moisture and restores them to a solderable condition.

11. Practical Design Case Study

Scenario: Designing a dual-status indicator for a wireless router. Green indicates a stable internet connection, and yellow indicates a connection attempt or degraded signal.

Implementation:

1. The LED is placed on the front panel PCB. The common cathode is connected to ground.
2. The green anode (C1) is connected to a microcontroller GPIO pin (e.g., 3.3V) via a current-limiting resistor. R_green = (3.3V - 3.2V_max) / 0.005A = 20Ω (use 22Ω standard value).
3. The yellow anode (C2) is connected to a different GPIO pin via another resistor. R_yellow = (3.3V - 2.3V_max) / 0.005A = 200Ω (use 220Ω standard value).
4. The microcontroller firmware controls the pins: drives the green pin high for a stable link, drives the yellow pin high for searching/degraded, and drives both low for off.
5. The wide 130° viewing angle ensures the indicator is visible from various angles in a typical room.

This design uses a single component to provide two clear visual states, simplifying assembly and saving space compared to using two separate LEDs.

12. Technology Principle Introduction

The LTST-S326KSTGKT-5A is based on solid-state semiconductor light emission. It contains two different semiconductor materials within its package:

• Yellow Emission (AlInGaP): The yellow light is produced by an Aluminum Indium Gallium Phosphide (AlInGaP) chip. When a forward voltage is applied, electrons and holes recombine in the chip's active region, releasing energy in the form of photons. The specific composition of the AlInGaP alloy determines the bandgap energy, which corresponds to the yellow wavelength (~590 nm).
• Green Emission (InGaN): The green light is produced by an Indium Gallium Nitride (InGaN) chip. The operating principle is the same (electroluminescence), but the InGaN material system has a wider bandgap tunability. By adjusting the indium content, the emission wavelength can be varied across the blue, green, and cyan spectrum. Achieving high-efficiency green with InGaN is more challenging than blue, which is reflected in the broader spectral width.

The water-clear epoxy lens encapsulates the chips, providing mechanical protection, shaping the light output beam, and offering environmental sealing.

13. Industry Trends & Developments

The market for SMD LEDs like the LTST-S326KSTGKT-5A continues to evolve driven by several key trends:

• Increased Miniaturization: Demand persists for even smaller package sizes (e.g., 0402, 0201 metric) to enable denser electronics and new form factors like wearable devices.
• Higher Efficiency & Luminance: Ongoing improvements in epitaxial growth and chip design yield LEDs with higher luminous efficacy (more light output per electrical watt), allowing for lower power consumption or brighter indicators at the same current.
• Color Consistency & Advanced Binning: Tighter binning tolerances for wavelength (color) and intensity are becoming standard, especially for applications where multiple LEDs must match perfectly, such as in full-color displays or indicator arrays.
• Integration & Smart Features: The trend extends beyond simple discrete LEDs towards integrated solutions, such as LEDs with built-in current-limiting resistors, driver ICs, or even microcontrollers for addressable RGB LEDs (e.g., WS2812).
• Reliability & Harsh Environment Suitability: Development focuses on improving performance and longevity under higher temperature, humidity, and chemical exposure, expanding applications into automotive, industrial, and outdoor settings.

Devices like the LTST-S326KSTGKT-5A represent a mature, reliable, and cost-effective solution for standard indicator applications, while newer technologies push the boundaries for specialized, high-performance uses.