LTST-S326KSTGKT-5A Dual Color SMD LED Datasheet - Yellow/Green Bicolor - 5mA - 130° Viewing Angle - Simplified Chinese Technical Documentation

1. Product Overview

LTST-S326KSTGKT-5A is a compact surface-mount bicolor LED designed for modern electronic applications requiring reliable indicator illumination in a small footprint. The device integrates two distinct semiconductor chips within a single package: an AlInGaP chip for emitting yellow light and an InGaN chip for emitting green light. This configuration allows a single component to achieve bicolor indication, thereby saving valuable PCB space. The LED employs an EIA-compliant package with a transparent lens, ensuring high luminous output and a wide viewing angle. It is specifically designed to be compatible with automated pick-and-place assembly systems and standard infrared reflow soldering processes, making it suitable for high-volume production environments.

The core advantages of this LED include RoHS compliance, the use of ultra-high-brightness chip technology for high luminous intensity, and a design optimized for robustness on automated assembly lines. Its primary target markets encompass telecommunications equipment, office automation devices, home appliances, industrial control panels, and various consumer electronics requiring status indication or backlighting.

2. Detailed Technical Specifications

2.1 Absolute Maximum Ratings

Operating the device beyond these limits may cause permanent damage.

• Power Consumption: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 Welding Conditions:Peak temperature 260°C, maximum 10 seconds.

2.2 Electrical and Optical Characteristics (at T_a=25°C, I_F(under the condition of =5mA)

These are typical performance parameters under standard test conditions.

• Luminous intensity (I_V):
  • Yellow: Min. 7.1 mcd, Typ. -, Max. 71.0 mcd
  • Green: Minimum 28.0 mcd, Typical -, Maximum 280.0 mcd
  • Measured using a sensor/filter approximating the CIE photopic response curve.
• Perspective (2θ_1/2):130 degrees (typical value for two colors). This is the full angle at which the light intensity drops to half of the axial value.
• Peak wavelength (λ_P):Yellow: 591 nm (typical value), Green: 530 nm (typical value).
• 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 value 2.0 V, maximum value 2.3 V
  • Green: typical value 2.8 V, maximum value 3.2 V
• Reverse current (I_R):In V_R=5V, the maximum current for both colors is 10 µA. Note: This device is not designed for reverse operation; this parameter is for test purposes only.

3. Binning System Description

Products are binned according to luminous intensity to ensure color and brightness consistency within applications. The tolerance for each bin is +/-15%.

3.1 Luminous Intensity Binning

For yellow (I_F=5mA):

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

For green (I_F=5mA):

• N grade: 28.0 – 45.0 mcd
• P grade: 45.0 – 71.0 mcd
• Q bin: 71.0 – 112.0 mcd
• R bin: 112.0 – 180.0 mcd
• S bin: 180.0 – 280.0 mcd

Model LTST-S326KSTGKT-5A indicates a specific bin selection for the yellow (K) and green (S) chips. Designers should specify the required bin for their application to ensure visual uniformity, especially when multiple LEDs are used adjacent to each other.

4. Performance Curve Analysis

Although typical curves are referenced in the PDF, their characteristics can be inferred from the provided data:

• I-V (Current-Voltage) curve:Forward Voltage (V_F) specification indicates the presence of a typical exponential relationship. A yellow chip with a lower typical V_F(2.0V) will have a slightly different curve shape compared to a green chip (typical V_F2.8V). Since V_Fhas a negative temperature coefficient, proper current limiting is crucial.
• Luminous Intensity vs. Current:Within the rated operating range, the intensity (I_V) is approximately proportional to the forward current (I_F). However, at extremely high currents, efficiency may decrease due to thermal effects.
• Temperature Characteristics:The light output of AlInGaP (yellow) and InGaN (green) LEDs typically decreases as the junction temperature increases. The operating temperature range of -20°C to +80°C defines the environmental conditions under which specified performance is guaranteed.
• Spectral Distribution:Peak wavelength and dominant wavelength, along with spectral bandwidth (Δλ), collectively define color purity. The wider Δλ (35 nm) of green chips compared to yellow chips (15 nm) is a typical characteristic of InGaN-based green LEDs.

5. Mechanical and Packaging Information

5.1 Package Dimensions

This LED conforms to the standard EIA surface-mount package outline. Unless otherwise specified, all dimensions are in millimeters with a standard tolerance of ±0.1 mm. The package features a low-profile design, making it suitable for space-constrained applications.

5.2 Pin Assignment and Polarity

This device has two anodes (one per chip) and one common cathode. The pin assignment is as follows:

• Cathode 1 (C1):Connected to the green InGaN chip.
• Cathode 2 (C2):Connect to the yellow AlInGaP chip.

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

6. Welding and Assembly Guide

6.1 Reflow Soldering Parameters (Lead-Free Process)

This device is compatible with infrared reflow soldering. The recommended JEDEC-compliant temperature profile is as follows:

• Preheating temperature:150°C to 200°C
• Preheating time:Longest 120 seconds
• Body peak temperature:Maximum 260°C
• Time above 260°C:Maximum 10 seconds
• Reflow soldering count:Maximum two times.

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

6.2 Manual Soldering

If manual soldering must be performed:

• Soldering iron temperature:Maximum 300°C
• Soldering time:Maximum 3 seconds per pad
• Number of welds:Only once.

6.3 Storage and Handling

• ESD Precautions:This device is sensitive to Electrostatic Discharge (ESD). Use wrist straps, antistatic mats, and properly grounded equipment when handling.
• Humidity Sensitivity:As a surface mount device, it is sensitive to moisture.
  • Sealed Bag:Store at ≤30°C and ≤60% RH. Use within one year after opening the bag.
  • After opening the bag:For components that have been out of their original packaging for more than one week, it is recommended to bake at 60°C for at least 20 hours before reflow soldering to prevent "popcorn" effect.
• Cleaning:Use only approved alcohol-based solvents, such as isopropyl alcohol (IPA) or ethanol. The immersion time at room temperature should be less than one minute. Avoid using unspecified chemicals.

7. Packaging and Ordering Information

The standard packaging for automated assembly is:

• Carrier tape:8mm wide embossed carrier tape.
• Reel:7-inch (178mm) diameter reel.
• Quantity per reel:3000 pieces.
• Minimum Order Quantity (MOQ):Remaining quantity available for order starts from 500 pieces.
• Packaging complies with ANSI/EIA-481 specification. Empty positions are sealed with cover tape, with a maximum of two consecutive missing components allowed.

8. Application Suggestions

8.1 Typical Application Scenarios

• Status Indicator:Power on, standby, mode, battery charging, or network activity indicator lights in routers, modems, base stations, and telecommunications equipment.
• Keyboard/key backlight:Provides dual-color feedback in industrial panels, medical equipment, or consumer electronics (e.g., green for active, yellow for warning).
• Panel Indicator Light:Used on control panels for household appliances (ovens, washing machines) and office automation equipment (printers, scanners).
• Symbol Illumination:Small sign or icon lighting.

8.2 Design Considerations

• Current Limiting:Always use series current-limiting resistors for each color channel. Based on the supply voltage (V_CC), the required forward current (I_F), and the LED's forward voltage (V_F) Calculate the resistance value. For robust design, please use the maximum V_F: R = (V_CC- V_{F_max}) / I_F.
• Thermal Management:Although power consumption is low, when operating at high ambient temperatures or near maximum current, ensure sufficient PCB copper foil area or thermal vias to maintain performance and lifespan.
• Optical Design:The 130-degree viewing angle provides wide visibility. For directional light, external lenses or light guides may be required.
• Drive Circuit:This LED is logic-level compatible and can be driven directly by a microcontroller GPIO pin (with a current-limiting resistor) or controlled for higher current via a transistor/MOSFET switch.

9. Technical Comparison and Differentiation

LTST-S326KSTGKT-5A offers specific advantages within its category:

• Single Package, Dual Color:Eliminates the need for two separate SMD LEDs, saving PCB space, reducing placement time/cost, and simplifying the Bill of Materials (BOM).
• High Brightness:Utilizes ultra-high brightness AlInGaP and InGaN chips to provide high luminous intensity, making it suitable for applications requiring good visibility even under well-lit conditions.
• Standardized Packaging:EIA standard packaging ensures compatibility with a wide range of existing PCB layouts, pick-and-place machine nozzles, and feeder systems.
• Robust Process Compatibility:Designed specifically for infrared reflow soldering and automated assembly, ensuring high yield and reliability in mass production.

10. Frequently Asked Questions

Q1: Can I drive both the yellow and green LEDs at their maximum DC current simultaneously?
A1: No. The absolute maximum ratings specify the respective DC forward currents (yellow: 25mA, green: 20mA). Driving both at these levels simultaneously may exceed the total power dissipation rating of the package. For simultaneous operation, the current should be reduced 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 wavelength of monochromatic light that matches the perceived color of the LED when mixed with a specified white reference light. λ_dYana da alaƙa da fahimtar launi na ɗan adam.

Q3: Idan na'urar ba a yi amfani da ita don aikin baya ba, me ya sa aka tsara sharuɗɗan gwajin kwararar baya (I_R)?
A3: Gwajin I_Rgwaji ne na inganci da amintacce na ƙa'ida, wanda ake amfani da shi don duba cikakkiyar haɗin kai da ɓarkewar wutar lantarki. Yana tabbatar da cewa guntuwar LED da kunshewar ba su da babban lahani. Ba a ba da shawarar amfani da ƙarfin lantarki na baya a cikin da'irar ainihi ba, yana iya lalata na'urar.

Q4: How critical is the one-week time limit after opening the moisture barrier bag?
A4: This is a conservative guideline designed to prevent damage during the reflow soldering process due to moisture ("popcorn" effect). If the exposure time is exceeded, baking the components under specified conditions (60°C, for more than 20 hours) can effectively remove the absorbed moisture and restore them to a solderable condition.

11. Practical Design Case Analysis

Scene:Design a dual-state indicator light for a wireless router. Green indicates a stable internet connection, yellow indicates connection attempts or signal degradation.

Implementation:

1. Place the LED on the front panel PCB. Connect the common cathode to ground.
2. Connect the green anode (C1) to a microcontroller GPIO pin (e.g., 3.3V) through a current-limiting resistor. R_green = (3.3V - 3.2V_max) / 0.005A = 20Ω (use 22Ω standard value).
3. Connect the yellow anode (C2) to another GPIO pin through another resistor. R_yellow = (3.3V - 2.3V_max) / 0.005A = 200Ω (use 220Ω standard value).
4. Microcontroller firmware control pins: drive the green pin high when the connection is stable, drive the yellow pin high during search/degradation, and drive both pins low when off.
5. The wide 130° viewing angle ensures the indicator light is visible from all angles in a typical room.

Compared to using two separate LEDs, this design utilizes a single component to provide two distinct visual states, simplifying assembly and saving space.

12. Technical Principle Introduction

LTST-S326KSTGKT-5A is based on the principle of solid-state semiconductor light emission. Its package contains two different semiconductor materials:

• Yellow luminescence (AlInGaP):Yellow light is generated by an aluminum indium gallium phosphide (AlInGaP) chip. When a forward voltage is applied, electrons and holes recombine in the active region of the chip, releasing energy in the form of photons. The specific composition of the AlInGaP alloy determines the bandgap energy, which corresponds to the yellow wavelength (approximately 590 nm).
• Green luminescence (InGaN):Green light is generated by an indium gallium nitride (InGaN) chip. The working principle is the same (electroluminescence), but the InGaN material system offers a wider bandgap tunability. By adjusting the indium content, the emission wavelength can vary across the blue, green, and cyan spectral ranges. Achieving high-efficiency green light with InGaN is more challenging than with blue light, which is reflected in its broader spectral width.

The chip is encapsulated with a transparent epoxy resin lens, providing mechanical protection, shaping the light output beam, and offering environmental sealing.

13. Industry Trends and Development

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

• Increased Miniaturization:The demand for smaller package sizes (e.g., 0402, 0201 metric) persists to enable denser electronics and new form factors like wearable devices.
• Higher Efficiency and Brightness:Continuous improvements in epitaxial growth and chip design have produced LEDs with higher luminous efficacy (more light output per watt of electrical power), allowing for lower power consumption or brighter indicator lights at the same current.
• Color Consistency and Advanced Binning:Tighter binning tolerances for wavelength (color) and intensity are becoming standard, especially in applications where multiple LEDs must match perfectly, such as full-color displays or indicator arrays.
• Integration and Intelligent Features:The trend is expanding from simple discrete LEDs to integrated solutions, such as LEDs with built-in current-limiting resistors, driver ICs, or even microcontrollers, for addressable RGB LEDs (e.g., WS2812).
• Reliability and Harsh Environment Suitability:Development focuses on enhancing performance and lifespan under higher temperatures, humidity, and chemical exposure, extending applications to automotive, industrial, and outdoor environments.

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