SMD LED LTST-008EGSW Specification - White Diffused Lens - Multi-Chip (Red, Green, Yellow) - English Technical Document

1. Product Overview

The LTST-008EGSW is a surface-mount device (SMD) LED featuring a white diffused lens and housing three distinct LED chips within a single EIA standard package. This component is engineered for automated printed circuit board (PCB) assembly processes, making it suitable for high-volume manufacturing. Its compact form factor addresses the needs of space-constrained applications across various electronic sectors.

1.1 Core Advantages

• Multi-Color Source: Integrates red (AlInGaP), green (InGaN), and yellow (AlInGaP) chips, allowing for flexible color indication or mixing within a single component footprint.
• Process Compatibility: Designed for compatibility with automated pick-and-place equipment and infrared (IR) reflow soldering processes, supporting efficient PCB assembly.
• Environmental Compliance: The product meets RoHS (Restriction of Hazardous Substances) directives.
• Standardized Packaging: Supplied in tape-and-reel format (12mm tape on 7-inch reels), facilitating automated handling.

1.2 Target Markets and Applications

This LED is targeted at a broad range of consumer, industrial, and communication electronics. Primary application areas include status indicators, signal and symbol illumination, and front panel backlighting in devices such as telecommunication equipment, office automation systems, home appliances, and various industrial control units.

2. In-Depth Technical Parameter Analysis

The following section provides a detailed, objective interpretation of the key electrical, optical, and thermal parameters specified for the LTST-008EGSW.

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. They are specified at an ambient temperature (Ta) of 25°C.

• Power Dissipation (Pd): Red/Yellow: 78 mW; Green: 64 mW. This parameter indicates the maximum power the LED can dissipate as heat. Exceeding this value risks thermal degradation.
• Forward Current: DC Forward Current: Red/Yellow: 30 mA; Green: 20 mA. The Peak Forward Current (1/10 duty cycle) is 80 mA for all colors. Designers must ensure operating currents remain at or below the DC rating for reliable long-term operation.
• Temperature Range: Operating: -40°C to +85°C; Storage: -40°C to +100°C. These ranges define the environmental conditions the device can withstand during use and non-operational periods.

2.2 Electro-Optical Characteristics

These are the typical performance parameters measured under specific test conditions (Ta=25°C).

• Luminous Intensity (Iv) & Flux (Φv): Measured at different forward currents (Red/Yellow: 20mA, Green: 5mA). The values are binned (see Section 3). For example, the minimum luminous intensity for Red and Green is 280 mcd, and for Yellow is 112 mcd. The viewing angle (2θ1/2) is a wide 120 degrees, typical for a diffused lens, providing a broad emission pattern.
• Spectral Characteristics:
  • Peak Wavelength (λP): Red: 632 nm, Green: 518 nm, Yellow: 591 nm.
  • Dominant Wavelength (λd): The single wavelength defining the perceived color. Ranges are specified and binned (e.g., Red: 617-630 nm).
  • Spectral Line Half-Width (Δλ): Green has the broadest spectral width at 30 nm, compared to 15 nm for Red and Yellow, which is characteristic of the InGaN material system.
• Forward Voltage (Vf): The voltage drop across the LED at the specified test current. Ranges are: Red: 1.7-2.6V, Green: 2.4-3.2V, Yellow: 1.8-2.6V. This is a critical parameter for driver circuit design.
• Reverse Current (Ir): Maximum 10 μA at VR=5V. The datasheet explicitly notes the device is not designed for reverse operation; this test is for quality assurance only.

3. Binning System Explanation

The LTST-008EGSW employs a binning system to categorize units based on key optical parameters, ensuring consistency in application performance.

3.1 Luminous Intensity (IV) Binning

LEDs are sorted into bins based on their luminous flux and intensity output. Each bin has a minimum and maximum value with a tolerance of +/-11% within the bin.

• Red & Green: Use bins F, G, H (e.g., Bin F: 280-450 mcd, Bin H: 710-1120 mcd).
• Yellow: Uses bins D, E, F (e.g., Bin D: 112-180 mcd, Bin F: 280-450 mcd).

This allows designers to select a brightness grade suitable for their application's requirements.

3.2 Dominant Wavelength (WD) Binning

LEDs are also binned by the precise shade of their color (dominant wavelength), with a tolerance of +/-1 nm per bin.

• Red: Single bin K (617.0 - 630.0 nm).
• Green: Bins P (520.0-530.0 nm) and Q (530.0-540.0 nm).
• Yellow: Bins H (584.5-589.5 nm) and J (589.5-594.5 nm).

This ensures color consistency, which is vital for applications where precise color matching is needed, such as in multi-LED displays or status indicators.

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet (e.g., Fig.1, Fig.5), typical curves for such LEDs would include:

• I-V (Current-Voltage) Curve: Shows the nonlinear relationship between forward current and forward voltage for each chip color. The curve typically has a threshold voltage (where current begins to rise significantly) specific to the semiconductor material (lowest for Red/Yellow AlInGaP, higher for Green InGaN).
• Luminous Intensity vs. Forward Current (I-Iv Curve): Demonstrates how light output increases with current, typically in a near-linear relationship within the recommended operating range before efficiency drops at very high currents due to thermal effects.
• Temperature Dependence: Luminous intensity generally decreases as junction temperature increases. The exact coefficient varies by material, with InGaN (Green) often showing different thermal behavior compared to AlInGaP (Red/Yellow).

5. Mechanical and Package Information

5.1 Package Dimensions and Pin Assignment

The device conforms to an EIA standard SMD package outline. All dimensions are in millimeters with a typical tolerance of ±0.1 mm. The pin assignment for the multi-chip configuration is clearly defined: Pins (1,2) and 3 for the Red chip, pins 4 and 5 for the Green chip, and pins 6 and (7,8) for the Yellow chip. This information is critical for correct PCB layout and electrical connection.

5.2 Recommended PCB Attachment Pad

A land pattern design is provided to ensure proper soldering and mechanical stability. Adhering to this recommended footprint is essential for achieving reliable solder joints during reflow and for managing heat dissipation from the LED.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Profile

A suggested reflow profile for lead-free (Pb-free) solder processes is provided, referencing the J-STD-020B standard. Key parameters include a pre-heat zone (typically 150-200°C), a defined time above liquidus, and a peak temperature not exceeding 260°C. Following this profile is crucial to prevent thermal shock and damage to the LED package or internal die bonds.

6.2 Storage and Handling

The LEDs are moisture-sensitive. When the sealed moisture-proof bag (with desiccant) is unopened, they should be stored at ≤30°C and ≤70% RH and used within one year. Once the bag is opened, the exposure time at factory conditions (≤30°C / ≤60% RH) should not exceed 168 hours before reflow soldering. If exposure exceeds this limit, a baking procedure (e.g., 60°C for 48 hours) is recommended to remove absorbed moisture and prevent \"popcorning\" during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only specified solvents like ethyl alcohol or isopropyl alcohol should be used at normal temperature for less than one minute. Unspecified chemicals may damage the plastic lens or package.

7. Packaging and Ordering Information

The standard packaging is 12mm wide embossed carrier tape on 7-inch (178mm) diameter reels. Each reel contains 4000 pieces. The tape is sealed with a cover tape. Packaging follows EIA-481-1-B specifications. A minimum order quantity of 500 pieces is specified for remainder quantities.

8. Application Recommendations and Design Considerations

8.1 Typical Application Circuits

Each color chip must be driven independently with a current-limiting resistor in series. The resistor value (R) is calculated using the formula: R = (Vsupply - Vf_LED) / If, where Vf_LED is the forward voltage of the specific chip at the desired operating current (If). Using the maximum Vf from the datasheet in this calculation ensures the current does not exceed the limit even with part-to-part variation.

8.2 Thermal Management

Although power dissipation is low, proper thermal design on the PCB is important for maintaining LED performance and longevity, especially when operating near maximum ratings. The recommended PCB pad design aids in heat transfer. Ensuring adequate copper area around the pads and possible thermal vias to other layers can help manage junction temperature.

8.3 Optical Design

The white diffused lens provides a wide, Lambertian-like emission pattern (120-degree viewing angle). This is ideal for applications requiring wide-angle visibility. For more focused light, secondary optics would be required. Designers should consider the different luminous intensities of the three colors when aiming for uniform apparent brightness or specific color mixing ratios.

9. Technical Comparison and Differentiation

The primary differentiation of the LTST-008EGSW lies in its integration of three distinct LED chips (Red, Green, Yellow) in a single, standard SMD package with a white diffused lens. This contrasts with:

• Single-Color SMD LEDs: Offers only one color per device.
• RGB LEDs: Integrate Red, Green, and Blue chips for full-color mixing. The RGY combination here is tailored for specific indicator color needs (e.g., traffic signal simulations, specific status codes) and may offer higher efficiency in the yellow region compared to an RGB LED creating yellow from red+green.
• Clear Lens vs. Diffused Lens: The diffused lens sacrifices some forward intensity for a much wider and more uniform viewing angle, which is often preferable for front-panel indicators.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive all three chips simultaneously at their maximum DC current?
A: No. The Absolute Maximum Ratings for power dissipation (78 mW for Red/Yellow, 64 mW for Green) must be respected. Simultaneously driving all chips at max current could exceed the total package power dissipation limit, leading to overheating. A detailed thermal analysis is required for such operation.

Q: Why is the test current different for the Green chip (5mA) compared to Red/Yellow (20mA)?
A> This is common practice because InGaN-based green LEDs typically have higher luminous efficacy (more light output per unit of current) at lower currents compared to AlInGaP-based LEDs. Specifying at 5mA likely provides a comparable brightness level for binning purposes and reflects a common operating point.

Q: What is the difference between Peak Wavelength and Dominant Wavelength?
A: Peak Wavelength (λP) is the wavelength at the highest point in the LED's spectral power distribution curve. Dominant Wavelength (λd) is derived from the color coordinates on the CIE chromaticity diagram and represents the single wavelength of a pure monochromatic light that would match the perceived color of the LED. λd is more relevant for color specification.

11. Practical Application Example

Scenario: Multi-State System Status Indicator
A network router uses a single LTST-008EGSW to indicate multiple operational states:
- Red (Solid): Boot-up/Error state (driven at 15mA).
- Green (Blinking): Data activity (driven at 5mA, pulsed).
- Yellow (Solid): Standby/Idle mode (driven at 15mA).
- Red+Green (appearing Orange): Warning state (both driven at lower currents to mix color).
This design consolidates what would require three separate LED placements into one, saving PCB space and simplifying the front panel design, while the wide viewing angle ensures visibility from various angles.

12. Operating Principle

Light emission in LEDs is based on electroluminescence in a semiconductor p-n junction. When a forward voltage is applied, electrons and holes are injected into the active region where they recombine, releasing energy in the form of photons (light). The specific wavelength (color) of the light is determined by the bandgap energy of the semiconductor material used:
- AlInGaP (Aluminum Indium Gallium Phosphide): Used for the Red and Yellow chips, capable of producing high-efficiency light in the red to yellow-orange spectrum.
- InGaN (Indium Gallium Nitride): Used for the Green chip, this material system is capable of producing light across the blue to green spectrum. The white diffused lens scatters the light from the individual chips, creating a uniform, blended appearance from the outside.

13. Technology Trends

The development of multi-chip SMD LEDs like the LTST-008EGSW aligns with several ongoing trends in optoelectronics:
- Miniaturization and Integration: Combining multiple functions (colors) into a single package saves board space, reduces component count, and simplifies assembly.
- Enhanced Efficiency: Continuous improvements in materials like InGaN and AlInGaP lead to higher luminous efficacy (more lumens per watt), allowing for brighter output at lower currents or reduced power consumption.
- Advanced Packaging: Improvements in package design and materials improve thermal performance, allowing for higher power densities and more reliable operation in harsh environments. The use of materials resistant to high-temperature reflow is standard.
- Application-Specific Solutions: The move towards components like this RGY LED indicates a trend towards providing optimized solutions for specific application needs rather than just generic single-color devices.