SMD LED LTST-N682VSQEWT Datasheet - White Diffused Lens - Dual AlInGaP Yellow/Red - 20mA - English Technical Document

1. Product Overview

The LTST-N682VSQEWT is a surface-mount device (SMD) light-emitting diode (LED) designed for automated printed circuit board (PCB) assembly. It is characterized by its compact size, making it suitable for space-constrained applications. The device features a white diffused lens that houses two independent semiconductor chips: one emitting yellow light and the other emitting red light, both based on Aluminum Indium Gallium Phosphide (AlInGaP) technology. This dual-chip configuration allows for multiple indication states from a single package.

1.1 Features

• Compliant with RoHS (Restriction of Hazardous Substances) directives.
• Packaged in 8mm tape on 7-inch diameter reels for automated pick-and-place equipment.
• Standard EIA (Electronic Industries Alliance) package outline.
• Integrated circuit (IC) compatible drive levels.
• Fully compatible with infrared (IR) reflow soldering processes.
• Preconditioned to JEDEC (Joint Electron Device Engineering Council) Moisture Sensitivity Level 3.

1.2 Target Applications

This LED is intended for a broad range of consumer and industrial electronics where reliable status indication or backlighting is required. Typical application areas include:

• Telecommunication equipment (e.g., cordless phones, cellular phones).
• Office automation devices (e.g., notebook computers, network systems).
• Home appliances and indoor signboards.
• General status indicators, signal luminaries, and front panel backlighting.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

The following limits must not be exceeded under any operating conditions, as doing so may cause permanent damage to the device. Ratings are specified at an ambient temperature (Ta) of 25°C.

• Power Dissipation (Pd): 75 mW per chip (Yellow and Red). This parameter defines the maximum power the LED can dissipate as heat.
• Peak Forward Current (I_FP): 100 mA for Yellow, 80 mA for Red. This is the maximum allowable pulsed current, typically defined at a 1/10 duty cycle and 0.1ms pulse width, used for brief, high-intensity flashes.
• DC Forward Current (I_F): 30 mA for both colors. This is the maximum continuous current recommended for normal operation.
• Operating Temperature Range: -40°C to +85°C. The device is guaranteed to function within this ambient temperature range.
• Storage Temperature Range: -40°C to +100°C. The device can be stored without applied power within these limits.

2.2 Electro-Optical Characteristics

These parameters are measured at Ta=25°C and a forward current (I_F) of 20 mA, which is the standard test condition.

• Luminous Intensity (I_V): A measure of the perceived power of light. For the Yellow chip, the minimum is 710 mcd, typical is unspecified, and maximum is 1800 mcd. For the Red chip, the minimum is 560 mcd, typical is unspecified, and maximum is 1400 mcd. The wide viewing angle (2θ_1/2 = 120° typical) results in a diffuse, wide-area illumination rather than a narrow beam.
• Peak Emission Wavelength (λ_P): The wavelength at which the optical output power is maximum. Typical values are 590 nm (Yellow) and 630 nm (Red).
• Dominant Wavelength (λ_d): The single wavelength that defines the perceived color. The Yellow chip ranges from 585 nm to 595 nm. The Red chip ranges from 617 nm to 627 nm. Tolerance is ±1 nm.
• Spectral Line Half-Width (Δλ): The bandwidth of the emitted spectrum at half the maximum intensity. Typical value is 20 nm for both colors, indicating relatively pure spectral colors.
• Forward Voltage (V_F): The voltage drop across the LED when driven at 20 mA. It ranges from 1.7 V (min) to 2.5 V (max) for both chips. Tolerance is ±0.1 V.
• Reverse Current (I_R): Maximum 10 µA at a reverse voltage (V_R) of 5V. This parameter is for infrared test purposes only; the device is not designed for operation under reverse bias.

3. Binning System Explanation

To ensure consistency in production, LEDs are sorted into performance bins. The LTST-N682VSQEWT uses a two-dimensional binning system based on luminous intensity and dominant wavelength.

3.1 Luminous Intensity (I_V) Binning

For Yellow Chip:

Bin Code U: 710 mcd to 965 mcd

Bin Code V: 965 mcd to 1315 mcd

Bin Code W: 1315 mcd to 1800 mcd

Tolerance on each bin is ±11%.

For Red Chip:

Bin Code T: 560 mcd to 760 mcd

Bin Code U: 760 mcd to 1030 mcd

Bin Code V: 1030 mcd to 1400 mcd

Tolerance on each bin is ±11%.

3.2 Dominant Wavelength (W_d) Binning

For Yellow Chip Only:

Bin Code J: 585 nm to 590 nm

Bin Code K: 590 nm to 595 nm

Tolerance on each bin is ±1 nm.

4. Performance Curve Analysis

The datasheet references typical characteristic curves which illustrate the relationship between key parameters. While the specific graphs are not reproduced in text, their implications are analyzed below.

• I-V (Current-Voltage) Curve: This curve would show the exponential relationship between forward voltage (V_F) and forward current (I_F). The typical V_F range of 1.7-2.5V at 20mA indicates the driving voltage requirement for circuit design.
• Luminous Intensity vs. Forward Current: This curve typically shows that light output increases approximately linearly with current up to the maximum rated current. Operating above 20mA will yield higher brightness but also increases power dissipation and junction temperature.
• Luminous Intensity vs. Ambient Temperature: For AlInGaP LEDs, luminous intensity generally decreases as ambient temperature increases. Designers must account for this derating in high-temperature environments to ensure sufficient brightness.
• Spectral Distribution: The graphs would show the relative optical power output across wavelengths, centered around the peak emission wavelength (λ_P) with a typical half-width of 20 nm.

5. Mechanical and Package Information

5.1 Package Dimensions and Pin Assignment

The device conforms to a standard SMD package outline. All dimensions are in millimeters with a general tolerance of ±0.2 mm unless otherwise noted. The pin assignment is as follows: Pins 1 and 2 are for the Yellow AlInGaP chip, and Pins 3 and 4 are for the Red AlInGaP chip. The white diffused lens provides a uniform, wide-angle light emission.

5.2 Recommended PCB Attachment Pad Layout

A land pattern (footprint) diagram is provided for infrared or vapor phase reflow soldering. Adhering to this recommended pad geometry is crucial for achieving proper solder joint formation, self-alignment during reflow, and long-term mechanical reliability.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Profile

A suggested reflow profile compliant with J-STD-020B for lead-free processes is provided. Key parameters include:

• Pre-heat Temperature: 150°C to 200°C.
• Pre-heat Time: Maximum 120 seconds.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus: Maximum 10 seconds (maximum two reflow cycles allowed).

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, use a soldering iron with a temperature not exceeding 300°C, and limit the soldering time to a maximum of 3 seconds per joint. Only one hand-soldering cycle is permitted.

6.3 Cleaning

If cleaning after soldering is required, only use specified solvents. Immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute is acceptable. Unspecified chemicals may damage the package material.

6.4 Storage and Handling

• Sealed Package: Store at ≤ 30°C and ≤ 70% Relative Humidity (RH). The shelf life is one year when stored in the original moisture-proof bag with desiccant.
• Opened Package: For components removed from their original packaging, the storage ambient should not exceed 30°C and 60% RH. It is recommended to complete IR reflow within 168 hours (7 days) of exposure. For longer storage, use a sealed container with desiccant or a nitrogen desiccator. Components exposed for more than 168 hours should be baked at approximately 60°C for at least 48 hours before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied in embossed carrier tape with a width of 8 mm, wound onto 7-inch (178 mm) diameter reels. Each reel contains 2000 pieces. The tape uses a top cover to seal empty pockets. Packaging conforms to ANSI/EIA-481 specifications. The minimum order quantity for remainder lots is 500 pieces.

8. Application Suggestions and Design Considerations

8.1 Typical Application Circuits

Each chip (Yellow and Red) is driven independently. A simple series current-limiting resistor is the most common drive circuit. The resistor value (R_limit) can be calculated using Ohm's Law: R_limit = (V_supply - V_F) / I_F. Use the maximum V_F from the datasheet (2.5V) for a conservative design to ensure the current does not exceed the desired level (e.g., 20mA) even with part-to-part variation. For example, with a 5V supply: R_limit = (5V - 2.5V) / 0.020A = 125 Ω. A standard 120 Ω or 150 Ω resistor would be suitable.

8.2 Thermal Management

Although power dissipation is low (75 mW max per chip), maintaining the junction temperature within limits is vital for longevity and stable light output. Ensure adequate PCB copper area around the solder pads to act as a heat sink, especially if operating at high ambient temperatures or near the maximum current.

8.3 Optical Design

The white diffused lens and 120° viewing angle make this LED ideal for applications requiring wide, even illumination without hotspots, such as front panel indicators or backlighting for symbols. For more focused light, external lenses or light guides may be necessary.

9. Technical Comparison and Differentiation

The primary differentiating factors of this component are its dual-chip-in-one-package design and white diffused lens. Compared to using two separate single-color LEDs, this design saves PCB space, simplifies assembly (one placement operation instead of two), and can provide a more compact indicator. The AlInGaP technology offers high efficiency and good color purity for yellow and red wavelengths. The wide viewing angle is a key advantage over clear-lens LEDs for area lighting applications.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive both the yellow and red chips simultaneously at 20mA each?

A: Yes, but you must consider the total power dissipation. Simultaneous operation at 20mA (V_F~2.1V typical) results in about 42 mW per chip, totaling 84 mW. This exceeds the absolute maximum power dissipation rating of 75 mW per chip. It is not recommended to drive both at absolute maximum current continuously. Derating the current or using pulsed operation is advised for dual simultaneous operation.

Q: What is the difference between peak wavelength and dominant wavelength?

A: Peak wavelength (λ_P) is the physical wavelength where the emission spectrum is strongest. Dominant wavelength (λ_d) is a calculated value from the CIE chromaticity diagram that corresponds to the perceived color (hue) of the light. For monochromatic LEDs like these, they are typically very close.

Q: How do I interpret the bin codes when ordering?

A: The specific bin codes (e.g., W for high-intensity yellow, K for specific yellow wavelength) may be part of the full ordering code. Consult the manufacturer for available combinations. Selecting a tighter bin (e.g., a specific I_V and W_d bin) ensures greater consistency in brightness and color across all units in your production run.

11. Practical Use Case Example

Scenario: Dual-State Status Indicator in a Network Router.

The LTST-N682VSQEWT can be used as a single LED to indicate two distinct operational states of a router.

Design: The microcontroller unit (MCU) has two GPIO pins. One pin drives the Yellow chip via a current-limiting resistor to indicate \"Power On / Standby\" mode. The other pin drives the Red chip via another resistor to indicate \"Data Activity / Fault\" mode. The white diffused lens blends the light, providing a uniform, aesthetically pleasing indicator that can show Yellow (standby), Red (fault), or a potential mix if both are briefly pulsed (e.g., during startup sequence). This design reduces front-panel clutter compared to using two separate LEDs.

12. Operating Principle Introduction

Light emission in the AlInGaP chips is based on electroluminescence in a semiconductor p-n junction. When a forward voltage is applied, electrons from the n-type region and holes from the p-type region are injected into the active region where they recombine. The energy released during this recombination is emitted as photons (light). The specific wavelength (color) of the light is determined by the bandgap energy of the AlInGaP semiconductor material, which is engineered during the crystal growth process to produce yellow (~590 nm) and red (~630 nm) light.

13. Technology Trends

AlInGaP technology is mature and offers high efficiency for amber, yellow, and red wavelengths. Current trends in indicator LEDs focus on increasing luminous efficacy (more light output per electrical watt), improving color consistency through advanced binning, and developing packages that withstand higher temperature reflow profiles required for lead-free soldering. There is also a drive towards miniaturization while maintaining or increasing optical performance, and integrating more features (like multiple colors or built-in ICs for control) into single packages.