SMD LED LTST-008UGVEWT Specification - White Diffused Lens - Dual Color (Green/Red) - 20mA - English Technical Document

1. Product Overview

The LTST-008UGVEWT is a surface-mount device (SMD) LED designed for automated printed circuit board (PCB) assembly. It features a compact form factor suitable for space-constrained applications. This component integrates two distinct light-emitting chips within a single package: one producing green light using InGaN (Indium Gallium Nitride) technology and another producing red light using AlInGaP (Aluminum Indium Gallium Phosphide) technology. The external lens is white and diffused, which helps in achieving a wider, more uniform viewing angle compared to clear lenses. This LED is engineered for compatibility with standard infrared (IR) reflow soldering processes, making it ideal for high-volume manufacturing.

1.1 Features

• Compliant with RoHS (Restriction of Hazardous Substances) directives.
• Packaged on 12mm tape wound onto 7-inch diameter reels for automated pick-and-place equipment.
• Standard EIA (Electronic Industries Alliance) package outline.
• Input compatible with standard integrated circuit (IC) logic levels.
• Designed for use with automatic component placement systems.
• Withstands infrared reflow soldering profiles.
• Preconditioned to accelerate to JEDEC (Joint Electron Device Engineering Council) moisture sensitivity Level 3.

1.2 Target Applications

This LED is versatile and finds use in a broad spectrum of electronic equipment where status indication, backlighting, or decorative lighting is required. Primary application areas include:

• Telecommunication Equipment: Status indicators on routers, modems, and handsets.
• Office Automation: Backlighting for keys on keyboards or indicators on printers and scanners.
• Home Appliances: Power, mode, or function indicators on consumer electronics.
• Industrial Equipment: Panel indicators for machinery and control systems.
• Signage & Indoor Display: Low-level illumination for signs or as elements in low-resolution indoor display panels.

2. Technical Parameters: In-Depth Objective Interpretation

The performance of the LTST-008UGVEWT LED is defined by a set of electrical and optical characteristics measured under standard conditions (Ta=25°C). Understanding these parameters is crucial for proper circuit design and achieving expected performance.

2.1 Absolute Maximum Ratings

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

• Power Dissipation (Pd): Green: 102 mW, Red: 78 mW. This is the maximum power the LED can dissipate as heat.
• Peak Forward Current (I_FP): 100 mA for both colors. This is the maximum instantaneous current, permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width).
• DC Forward Current (I_F): 30 mA for both colors. This is the maximum continuous current for reliable operation.
• Operating Temperature Range: -40°C to +85°C. The ambient temperature range for normal operation.
• Storage Temperature Range: -40°C to +100°C. The temperature range for non-operational storage.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters when the device is operated within its recommended conditions (I_F = 20mA).

• Luminous Intensity (Φ_v): A measure of perceived light output. Green: Min 5.00 lm, Max 11.00 lm. Red: Min 2.00 lm, Max 4.75 lm. Measured with a sensor filtered to match the human eye response (CIE curve).
• Viewing Angle (2θ_1/2): Typically 130 degrees. This is the full angle at which the light intensity drops to half of its value at the center (0 degrees). The diffused lens contributes to this wide angle.
• Peak Emission Wavelength (λ_P): The wavelength at which the spectral output is strongest. Green: ~524 nm. Red: ~631 nm.
• Dominant Wavelength (λ_d): The single wavelength perceived by the human eye that defines the color. Green: 520-530 nm. Red: 617-630 nm.
• Spectral Line Half-Width (Δλ): The bandwidth of the emitted light. Green: ~33 nm. Red: ~20 nm. Indicates the color purity.
• Forward Voltage (V_F): The voltage drop across the LED at 20mA. Green: 2.4V to 3.4V. Red: 1.8V to 2.6V. Tolerance is ±0.1V.
• Reverse Current (I_R): Maximum 10 µA at a reverse voltage (V_R) of 5V. This device is not designed for reverse bias operation; this parameter is for test purposes only.

3. Binning System Explanation

To ensure consistency in production, LEDs are sorted into performance bins. The LTST-008UGVEWT uses two primary binning criteria.

3.1 Luminous Intensity (IV) Rank

LEDs are grouped based on their measured light output at 20mA. Each bin has an 11% tolerance.

Green Chip:

G1: 5.00 - 6.50 lm

G2: 6.50 - 8.45 lm

G3: 8.45 - 11.00 lm

Red Chip:

R1: 2.00 - 2.70 lm

R2: 2.70 - 3.65 lm

R3: 3.65 - 4.75 lm

3.2 Dominant Wavelength (WD) Rank

For the green chip only, LEDs are binned by their dominant wavelength to control color consistency. Tolerance is ±1 nm.

AP: 520 - 525 nm

AQ: 525 - 530 nm

4. Performance Curve Analysis

The datasheet includes typical characteristic curves which are essential for understanding device behavior under varying conditions.

4.1 Current vs. Voltage (I-V) Curve

This curve shows the relationship between forward voltage (V_F) and forward current (I_F). It is non-linear, typical of a diode. The curve for the green chip (InGaN) will have a higher knee voltage (~2.8V) compared to the red chip (AlInGaP, ~2.0V). Designers use this to calculate the necessary current-limiting resistor value for a given supply voltage.

4.2 Relative Luminous Intensity vs. Forward Current

This graph illustrates how light output increases with current. It is generally linear within the recommended operating range (up to 30mA). Driving the LED beyond this point yields diminishing returns in light output while significantly increasing heat and reducing lifespan.

4.3 Spectral Distribution

These plots show the intensity of light emitted at each wavelength. The green chip's spectrum centers around 524nm with a broader half-width, while the red chip's spectrum is narrower and centered around 631nm. The diffused lens does not alter the spectrum but scatters the light.

5. Mechanical & Package Information

5.1 Package Dimensions

The LED conforms to a standard SMD footprint. All critical dimensions (length, width, height, pad spacing) are provided in millimeters with a standard tolerance of ±0.1mm unless otherwise specified. The pin assignment is clearly defined: Pins (0,1) and 2 are for the green chip, pins 3 and 4 are for the red chip, and pins 5,6,7 are null (no connection).

5.2 Polarity Identification

The package includes a marking or a physical feature (like a chamfered corner or a dot) to identify Pin 1 or the cathode. Correct orientation during assembly is critical to ensure the intended chip is energized.

5.3 Recommended PCB Attachment Pad Layout

A land pattern design is suggested to ensure reliable soldering. This includes the size and shape of the copper pads on the PCB, which should match the LED's terminals to form a good solder fillet and provide mechanical stability.

6. Soldering & Assembly Guidelines

6.1 IR Reflow Soldering Profile

A recommended temperature profile for lead-free (Pb-free) solder processes is provided, compliant with J-STD-020B. Key parameters include:

- Pre-heat: 150-200°C for a maximum of 120 seconds to gradually heat the board and activate flux.

- Peak Temperature: Maximum of 260°C. The time above liquidus (typically 217°C for SnAgCu solder) should be controlled.

- Total Soldering Time: Maximum 10 seconds at peak temperature, with a maximum of two reflow cycles allowed.

6.2 Hand Soldering (Soldering Iron)

If manual rework is necessary, the iron tip temperature should not exceed 300°C, and contact time should be limited to a maximum of 3 seconds per solder joint. Only one rework cycle is recommended to prevent thermal damage to the plastic package and internal wire bonds.

6.3 Storage Conditions

Moisture sensitivity is a critical factor for SMD components.

- Sealed Package: Store at ≤30°C and ≤70% Relative Humidity (RH). Use within one year.

- Opened Package: Store at ≤30°C and ≤60% RH. If exposed to ambient air for more than 168 hours (1 week), the LEDs must be baked at approximately 60°C for at least 48 hours before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

6.4 Cleaning

If post-solder cleaning is required, only alcohol-based solvents like ethyl alcohol or isopropyl alcohol should be used. Immersion should be at normal temperature for less than one minute. Harsh or unspecified chemicals can damage the plastic lens and package.

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied in embossed carrier tape with a protective cover tape. Key dimensions for the tape pockets, reel hub, and flange are specified. The standard reel is 7 inches in diameter and holds 4000 pieces. A minimum order quantity of 500 pieces may apply for remnants.

7.2 Reel Packaging Details

The packaging follows ANSI/EIA-481 specifications. Empty component pockets are sealed. The maximum number of consecutive missing components (\"missing lamps\") on a reel is two, ensuring feed reliability in automated assembly machines.

8. Application Suggestions

8.1 Typical Application Circuits

The LED is a current-driven device. A series current-limiting resistor is mandatory. The resistor value (R_s) is calculated using Ohm's Law: R_s = (V_supply - V_F) / I_F. For a 5V supply and the green LED (V_F ~3.0V) at 20mA, R_s = (5 - 3) / 0.02 = 100 Ω. A slightly higher value (e.g., 120 Ω) is often used for margin and to reduce power consumption.

8.2 Design Considerations

• Thermal Management: Although power dissipation is low, ensuring adequate PCB copper area around the pads helps dissipate heat, especially in high ambient temperature environments or when driven near maximum current.
• Current Control: For precise brightness control or to maximize longevity, consider using a constant current driver instead of a simple resistor, particularly in applications with variable supply voltage.
• Optical Design: The white diffused lens provides a wide, soft light pattern. For applications requiring a more directed beam, secondary optics (like a light pipe or external lens) may be needed.
• ESD Protection: While not explicitly stated as sensitive, implementing basic ESD precautions during handling and design (e.g., series resistors on I/O lines) is good practice for all semiconductor devices.

9. Technical Comparison & Differentiation

The primary differentiating factors of the LTST-008UGVEWT are its dual-color capability in a single package and its wide-viewing-angle diffused lens. Compared to using two separate single-color LEDs, this design saves PCB space, simplifies assembly (one component instead of two), and can create a blended color effect if both chips are driven simultaneously. The diffused lens offers a more uniform appearance from different viewing angles compared to a clear-lens LED, which often has a more focused \"hot spot.\" The JEDEC Level 3 preconditioning indicates a moderate level of moisture resistance, suitable for most standard assembly floor environments.

10. Frequently Asked Questions (Based on Technical Parameters)

10.1 Can I drive both the green and red chips at the same time?

Yes, electrically they are independent. You would need two separate current-limiting circuits (resistors or drivers), one for the green chip's anode/cathode pair and another for the red chip's pair. Driving them simultaneously at full current (20mA each) would require ensuring the total power dissipation (Pd_Green + Pd_Red) and the local thermal conditions on the PCB are within acceptable limits.

10.2 What is the difference between Peak Wavelength and Dominant Wavelength?

Peak Wavelength (λ_P) is the physical wavelength where the LED emits the most optical power. Dominant Wavelength (λ_d) is a calculated value based on the CIE color chart that corresponds to the perceived color by the human eye. For monochromatic LEDs like these, they are usually close, but λ_d is the more relevant parameter for color specification in applications.

10.3 Why is the maximum DC current (30mA) lower than the peak pulsed current (100mA)?

This is due to thermal limitations. Continuous current generates continuous heat. The 30mA DC rating ensures the junction temperature stays within safe limits for long-term reliability. The 100mA pulsed rating allows for short, high-intensity bursts (like in multiplexed displays or communication) where the average power and heat generation are much lower because the duty cycle is only 10%.

10.4 How do I interpret the bin codes when ordering?

For consistent visual performance in a production run, specify the desired Intensity (IV) and Wavelength (WD) bin codes. For example, ordering \"LTST-008UGVEWT, G2, AP\" would request LEDs with green chip luminous intensity between 6.50-8.45 lm and a dominant wavelength between 520-525 nm. If not specified, you will receive components from standard production bins.

11. Practical Use Case Example

Scenario: Dual-Status Indicator for a Network Device.

A network router designer needs two status LEDs (Power and Internet Connection) but has limited front-panel space. Using the LTST-008UGVEWT, they can design a single LED location that shows:

- Solid Green: Power On, Internet Connected (Green chip only).

- Solid Red: Power On, No Internet (Red chip only).

- Flashing Green: Booting/System Activity.

- Flashing Red: Error Condition.

This is achieved by connecting the green and red anodes to separate GPIO pins of a microcontroller, each with its own series resistor. The microcontroller firmware controls the state and color. The wide 130-degree viewing angle ensures the status is visible from almost any angle in the room.

12. Operating Principle

Light emission in LEDs is based on electroluminescence in a semiconductor material. When a forward voltage is applied across the p-n junction, electrons from the n-type region recombine with holes from the p-type region. This recombination releases energy in the form of photons (light). The specific wavelength (color) of the light is determined by the energy bandgap of the semiconductor material. InGaN has a wider bandgap, producing higher-energy photons perceived as green/blue light. AlInGaP has a narrower bandgap, producing lower-energy photons perceived as red/orange light. The white diffused lens is made of an epoxy or silicone material containing scattering particles that randomize the direction of the emitted light, creating a Lambertian-like emission pattern.

13. Technology Trends

The SMD LED market continues to evolve towards:

1. Higher Efficiency (lm/W): Ongoing improvements in epitaxial growth and chip design yield more light output for the same electrical input, reducing power consumption and thermal load.

2. Improved Color Consistency & Binning: Tighter manufacturing controls and more sophisticated binning strategies (e.g., multi-parameter bins covering intensity, wavelength, and sometimes forward voltage) allow for better color matching in applications requiring multiple LEDs.

3. Miniaturization: Packages continue to shrink (e.g., 0402, 0201 metric sizes) to enable higher-density designs, particularly in portable consumer electronics.

4. Enhanced Reliability: Developments in package materials (mold compounds, leadframes) and die attach technologies improve resistance to thermal cycling, moisture, and other environmental stresses.

5. Integrated Solutions: Growth in LEDs with built-in drivers (constant current ICs), protection components (ESD, surge), or even microcontrollers for \"smart LED\" applications, reducing external component count.