SMD LED LTST-N682TWVSET Datasheet - Dual Color Yellow/White - 30mA - 102mW - English Technical Document

1. Product Overview

This document details the specifications for the LTST-N682TWVSET, a Surface-Mount Device (SMD) Light Emitting Diode (LED). This component integrates two distinct LED chips within a single package: one emitting yellow light and the other emitting white light. It is designed for automated printed circuit board (PCB) assembly processes, making it suitable for high-volume manufacturing. The compact form factor addresses the needs of space-constrained applications across various electronic sectors.

1.1 Core Features and Advantages

• Dual-Color Source: Combines a Yellow AlInGaP chip and a White LED chip in one package, enabling multi-status indication or color mixing in a minimal footprint.
• Automation Compatibility: Packaged on 8mm tape wound onto 7-inch diameter reels, conforming to EIA standards for compatibility with high-speed automatic pick-and-place equipment.
• Robust Manufacturing: Compatible with infrared (IR) reflow soldering processes, which is the standard for modern PCB assembly. The device is preconditioned to JEDEC Level 3 moisture sensitivity standards, enhancing reliability during soldering.
• Environmental Compliance: The product meets RoHS (Restriction of Hazardous Substances) directives.
• Electrical Interface: Designed to be I.C. (Integrated Circuit) compatible, allowing for straightforward driving from typical logic-level outputs or driver circuits.

1.2 Target Applications and Markets

The LTST-N682TWVSET is engineered for a broad spectrum of electronic equipment where reliable, compact status indication is required. Its primary application domains include:

• Telecommunications: Status indicators on routers, modems, and network switches.
• Consumer Electronics & Office Automation: Power, battery, or function status lights in notebook computers, printers, and peripherals.
• Home Appliances & Industrial Equipment: Operational mode indicators on control panels.
• Indoor Signage & Front Panels: Backlighting for symbols or providing multi-color status luminaires.

2. Package Dimensions and Mechanical Information

The physical outline of the LTST-N682TWVSET package is defined by industry-standard SMD form factors to ensure mechanical compatibility. Key dimensional notes specify that all measurements are in millimeters, with a general tolerance of ±0.2 mm unless otherwise stated. The component features a clear lens.

2.1 Pin Assignment and Polarity

The device has four electrical terminals. The pin assignment is as follows:

• Pins 1 and 2: These are the anode and cathode for the Yellow AlInGaP LED chip.
• Pins 3 and 4: These are the anode and cathode for the White LED chip.

It is crucial to consult the detailed package drawing (implied in the datasheet) for the exact physical location of Pin 1, typically marked by a dot or a chamfered corner on the package, to ensure correct orientation during assembly.

3. Ratings and Characteristics

Operating the device within its specified limits is essential for reliability and performance.

3.1 Absolute Maximum Ratings

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

Parameter	White Chip	Yellow Chip	Unit
Power Dissipation	102	78	mW
Peak Forward Current (1/10 Duty Cycle, 0.1ms Pulse)	100	100	mA
DC Forward Current	30	30	mA
Operating Temperature Range	-40°C to +85°C
Storage Temperature Range	-40°C to +100°C

3.2 Electrical and Optical Characteristics

These are the typical performance parameters measured at Ta=25°C and a standard test current (IF) of 20mA, unless noted otherwise.

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Parameter	Symbol	White Chip	Yellow Chip	Unit	Condition / Notes
Luminous Intensity	Iv	Min: 1600, Max: 3200	Min: 710, Max: 1800	mcd	IF=20mA. Measured with CIE eye-response filter.
Viewing Angle (Half Intensity)	2θ1/2	120 (Typical)		deg	Angle where intensity drops to 50% of on-axis value.
Dominant Wavelength	λd	-	585 - 595	nm	Defines perceived color (Yellow).
Peak Emission Wavelength	λP	-	590 (Typical)	nm	Wavelength at peak of spectral output.
Spectral Line Half-Width	Δλ	-	20 (Typical)	nm	Bandwidth of emitted spectrum.
Forward Voltage	VF	2.6 - 3.4	1.7 - 2.6	V	IF=20mA. Tolerance is ±0.1V.
Reverse Current	IR	10 (Max)		μA	VR=5V. Device is not for reverse operation.

Key Measurement Notes:

• Luminous intensity measurement follows the CIE standard photopic eye-response curve.
• The dominant wavelength is derived from CIE chromaticity coordinates.
• The reverse voltage test is for informational/quality purposes only; the LED should not be operated in reverse bias in an application.

4. Binning System Explanation

To ensure color and brightness consistency in production, LEDs are sorted into performance bins. The LTST-N682TWVSET uses separate binning for the white and yellow chips.

4.1 Luminous Intensity (Iv) Binning

White Chip: Binned into two groups based on minimum luminous intensity at 20mA.

• W1: 1600 mcd to 2265 mcd.
• W2: 2265 mcd to 3200 mcd.

Yellow Chip: Binned into three groups.

• U: 710 mcd to 965 mcd.
• V: 965 mcd to 1315 mcd.
• W: 1315 mcd to 1800 mcd.

Tolerance within each intensity bin is ±11%.

4.2 Wavelength (WD) Binning for Yellow Chip

The dominant wavelength of the yellow chip is binned to control hue.

• J: 585 nm to 590 nm.
• K: 590 nm to 595 nm.

Tolerance within each wavelength bin is ±1 nm.

4.3 Chromaticity (CIE) Binning for White Chip

The white LED's color point is defined by its CIE 1931 (x, y) chromaticity coordinates. The datasheet provides a table with multiple bin codes (A1, A2, A3, B1, B2, B3, C1, C2, C3), each representing a quadrilateral region on the chromaticity diagram defined by four (x,y) coordinate points. This allows for precise selection of white color temperature and tint. The tolerance for the (x, y) coordinates within a bin is ±0.01.

5. Performance Curve Analysis

The datasheet references typical performance curves which graphically represent key relationships. Analyzing these is critical for design.

5.1 Forward Current vs. Forward Voltage (I-V Curve)

This curve shows the exponential relationship between the current flowing through the LED and the voltage drop across it. The Yellow AlInGaP chip will have a lower forward voltage (V_F) for a given current compared to the White chip, as indicated in the electrical characteristics table. Designers use this curve to select appropriate current-limiting resistors or constant-current driver settings to achieve desired brightness while staying within power limits.

5.2 Luminous Intensity vs. Forward Current

This plot demonstrates how light output increases with drive current. It is generally linear over a range but will saturate at higher currents. Operating at the recommended 20mA DC ensures optimal efficiency and longevity. The 100mA peak pulsed current rating allows for brief, high-intensity flashes without damage.

5.3 Spectral Distribution

For the yellow chip, a spectral distribution curve would show a relatively narrow peak around 590nm (typical), with a half-width of about 20nm, confirming its monochromatic yellow output. The white LED's spectrum would be much broader, typically a blue LED chip combined with a phosphor to produce a wide emission across the visible spectrum.

6. Assembly and Application Guidelines

6.1 Soldering Process

The device is designed for lead-free (Pb-free) solder processes. The recommended IR reflow profile should comply with J-STD-020B. Key parameters include:

• Pre-heat: Ramp-up to 150-200°C.
• Pre-heat Time: Maximum of 120 seconds.
• Peak Temperature: Should not exceed 260°C.
• Time Above Liquidus: Should be limited, with total soldering time at peak temperature not exceeding 10 seconds, and reflow should be performed a maximum of two times.

For hand soldering with an iron, the tip temperature should not exceed 300°C, and contact time should be limited to 3 seconds, for one time only.

6.2 Recommended PCB Pad Layout

The datasheet includes a suggested land pattern (footprint) for the PCB. Using this recommended design ensures proper solder joint formation, mechanical stability, and heat dissipation during and after soldering. Adherence to this pattern is critical for successful automated assembly and reliability.

6.3 Cleaning

If post-solder cleaning is necessary, only specified solvents should be used. Immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute is acceptable. The use of unspecified or aggressive chemicals can damage the LED package or lens.

7. Storage and Handling Precautions

7.1 Moisture Sensitivity

The LEDs are packaged in a moisture-barrier bag with desiccant to prevent absorption of atmospheric moisture, which can cause "popcorning" (package cracking) during reflow. While sealed, they should be stored at ≤30°C and ≤70% RH and used within one year.

Once the bag is opened, the "floor life" begins. Components should be stored at ≤30°C and ≤60% RH. It is strongly recommended to complete the IR reflow process within 168 hours (7 days) of opening the bag.

If components are exposed beyond 168 hours, they must be "baked" (dehydrated) at approximately 60°C for at least 48 hours before soldering to remove absorbed moisture.

7.2 Application Caution

These LEDs are intended for standard commercial and industrial electronic equipment. For applications requiring exceptional reliability where failure could jeopardize safety (e.g., aviation, medical life-support, transportation control), specific qualification and consultation are necessary prior to design-in.

8. Packaging and Ordering Information

8.1 Tape and Reel Specifications

The components are supplied on embossed carrier tape, 8mm in width, sealed with a cover tape. The tape is wound onto standard 7-inch (178mm) diameter reels. Each full reel contains 2000 pieces. For quantities less than a full reel, a minimum packing quantity of 500 pieces applies. The packaging conforms to EIA-481-1-B specifications.

8.2 Part Number Interpretation

The part number LTST-N682TWVSET follows the manufacturer's internal coding system, where "TWVSET" likely indicates the specific color combination (T=?, W=White, V=?, SET=dual?). For precise ordering, the full part number along with any required bin code selections (e.g., for intensity or color) must be specified.

9. Design Considerations and Typical Application Circuits

9.1 Current Limiting

LEDs are current-driven devices. A simple and common driving method is to use a series resistor. The resistor value (R_s) can be calculated using Ohm's Law: R_s = (V_supply - V_F) / I_F. For example, to drive the Yellow chip at 20mA from a 5V supply, assuming a typical V_F of 2.2V: R_s = (5V - 2.2V) / 0.020A = 140 Ω. A standard 150 Ω resistor would be suitable. The power rating of the resistor should be checked: P = I²R = (0.02)² * 150 = 0.06W, so a 1/8W (0.125W) resistor is sufficient.

9.2 Independent vs. Common Drive

Since the yellow and white chips have separate anodes and cathodes (4 pins total), they can be controlled completely independently. This allows for three visual states: Yellow only, White only, or Both on (which may appear as a blended color depending on intensity). They should not be connected in parallel directly to the same driver due to potential V_F mismatch.

9.3 Thermal Management

While the power dissipation is low (max 102mW for white, 78mW for yellow), proper PCB design aids longevity. Using the recommended solder pad pattern helps conduct heat away from the LED junction into the PCB copper. Operating at or below the recommended DC current and within the specified temperature range ensures the LED maintains its rated lifetime and color stability.

10. Technical Comparison and Differentiation

The primary differentiating factor of the LTST-N682TWVSET is its dual-color, single-package design. Compared to using two separate SMD LEDs, this solution offers significant advantages:

• Space Savings: Reduces the PCB footprint by approximately 50%, crucial for miniaturized designs.
• Assembly Efficiency: Only one component needs to be picked, placed, and soldered instead of two, increasing assembly throughput and reducing potential placement errors.
• Optical Alignment: Both light sources are fixed in a known, consistent spatial relationship within the package, which can be important for light-pipe or lens coupling.
• Performance Matching: Although binned separately, chips from the same production lot may have more consistent thermal characteristics when housed together.

The choice of AlInGaP for the yellow chip provides high luminous efficiency and excellent color purity (narrow spectrum) compared to older technologies like GaAsP.

11. Frequently Asked Questions (FAQ) Based on Technical Parameters

Q1: Can I drive the yellow and white LEDs from the same current-limiting resistor?
A1: No. They have different forward voltage characteristics (Yellow: ~1.7-2.6V, White: ~2.6-3.4V). Connecting them in parallel with one resistor would cause an uneven current split, potentially over-driving one chip and under-driving the other. They require separate current-limiting circuits.

Q2: What is the purpose of the peak forward current rating (100mA at 1/10 duty)?
A2: This rating allows for pulsed operation at higher currents for short durations, such as in blinking or strobe applications, to achieve higher instantaneous brightness. The low duty cycle and short pulse width ensure the average power and junction temperature remain within safe limits.

Q3: Why is the storage and baking procedure so specific?
A3: SMD plastic packages can absorb moisture from the air. During the high-temperature reflow soldering process, this trapped moisture rapidly turns to steam, creating high internal pressure that can delaminate the package or crack the die ("popcorning"). The moisture-sensitive labeling and baking procedures are critical industry practices to prevent this failure mode.

Q4: How do I interpret the CIE bin codes for the white LED?
A4: The CIE bin codes (A1, B2, C3, etc.) define a small region on the CIE chromaticity diagram. Designers select a specific bin code to ensure all white LEDs in their product have a consistent color appearance (same white point, avoiding yellowish or bluish tints). For most applications, specifying a bin is necessary for color uniformity.

12. Practical Application Example

Scenario: Dual-Status Indicator for a Network Device
A network router design requires a single indicator to show two states: Power On/Network Activity and System Error.

• Design Choice: Use the LTST-N682TWVSET.
• Implementation:
  1. The White LED is connected to a GPIO pin on the main microcontroller via a 150Ω series resistor to a 3.3V rail. The firmware pulses this LED gently to indicate network activity when the system is operating normally.
  2. The Yellow LED is connected to a different GPIO pin via a 100Ω series resistor (for slightly higher brightness as an alert). The firmware drives this LED in a steady-on or fast-blink pattern only when a system error is detected.
• Outcome: A single, compact component on the PCB provides clear, distinct visual feedback for two operational states, simplifying the front panel design and user interface.

13. Operational 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 across the junction. When these charge carriers recombine, they release energy in the form of photons (light). The color (wavelength) of the emitted light is determined by the bandgap energy of the semiconductor material.

• Yellow Chip (AlInGaP): Uses an Aluminum Indium Gallium Phosphide semiconductor. This material system has a bandgap corresponding to light emission in the yellow/amber/orange/red part of the spectrum. It is known for high efficiency and good temperature stability.
• White Chip: Most commonly, a white LED is a blue LED chip (typically based on InGaN semiconductor) coated with a yellow phosphor. Some of the blue light is converted by the phosphor to yellow light. The mixture of the remaining blue light and the converted yellow light is perceived by the human eye as white. The exact "shade" of white (cool, neutral, warm) is controlled by the phosphor composition and thickness.

14. Technology Trends and Context

The LTST-N682TWVSET represents a mature and optimized product within the SMD LED market. Key ongoing trends in this sector include:

• Increased Integration: Moving beyond dual-color to RGB (Red-Green-Blue) or RGBW (Red-Green-Blue-White) packages in a single SMD footprint, enabling full-color programmability for indicators and micro-displays.
• Higher Efficiency: Continuous improvement in the internal quantum efficiency of semiconductor materials (like AlInGaP and InGaN) and phosphors, leading to higher luminous output (lumens) per unit of electrical input power (watts), reducing energy consumption and thermal load.
• Miniaturization: The drive for smaller devices continues, with chip-scale package (CSP) LEDs that have no traditional plastic package, further reducing size and improving optical design flexibility.
• Improved Color Consistency: Advances in manufacturing and binning processes allow for tighter tolerances on wavelength and chromaticity, giving designers more precise control over the final visual appearance in their products.
• Smart Features: Integration of control circuitry (like constant-current drivers or simple logic) directly into the LED package, creating "intelligent" LED modules that simplify system design.

Devices like the LTST-N682TWVSET remain highly relevant for cost-effective, reliable, and space-efficient status indication where advanced color control or programmability is not required.