LTW-S225DSKS-PH SMD LED Datasheet - Side Looking Dual Color (White/Yellow) - Package Dimensions - Voltage 2.5-3.7V/1.6-2.4V - Power 72/62.5mW - English Technical Document

1. Product Overview

This document provides the complete technical specifications for the LTW-S225DSKS-PH, a side-looking dual-color Surface Mount Device (SMD) LED. This component integrates two distinct light-emitting chips within a single, compact package designed for automated assembly processes. The primary application focus is on space-constrained electronic devices requiring reliable status indication or backlighting functionality.

1.1 Core Features and Target Market

The LTW-S225DSKS-PH is engineered with several key features that make it suitable for modern electronics manufacturing. It is compliant with RoHS (Restriction of Hazardous Substances) directives, ensuring environmental regulatory adherence. The device utilizes a tin-plated lead frame for improved solderability. It incorporates ultra-bright semiconductor chips: one based on InGaN technology for white light emission and another based on AlInGaP technology for yellow light emission.

The package is supplied in a standard 8mm tape format on 7-inch diameter reels, conforming to EIA (Electronic Industries Alliance) standards, which facilitates compatibility with high-speed automated pick-and-place equipment commonly used in volume production. The device is also designed to be compatible with infrared (IR) reflow soldering processes, which is the standard for lead-free (Pb-free) PCB assembly.

Its primary target applications span across telecommunications equipment (such as cellular and cordless phones), office automation devices (like notebook computers), network systems, various home appliances, and indoor signage or display applications. Specific uses include keypad or keyboard backlighting, status indicators for power, connectivity, or system state, micro-displays, and general signal or symbol illumination.

2. Technical Parameters: In-Depth Objective Interpretation

The performance of the LTW-S225DSKS-PH is defined by a comprehensive set of electrical, optical, and thermal parameters measured under standard conditions (Ta=25°C unless otherwise specified). Understanding these parameters is critical for proper circuit design and reliable operation.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed and should be avoided for reliable long-term performance.

• Power Dissipation (Pd): 72 mW for the white chip, 62.5 mW for the yellow chip. This is the maximum amount of power the LED can dissipate as heat.
• Peak Forward Current (I_FP): 100 mA for white, 60 mA for yellow. This is the maximum instantaneous current allowed under pulsed conditions (1/10 duty cycle, 0.1ms pulse width).
• DC Forward Current (I_F): 20 mA for white, 25 mA for yellow. This is the maximum continuous forward current recommended for normal operation.
• Operating Temperature Range: -20°C to +80°C. The ambient temperature range within which the LED is designed to function.
• Storage Temperature Range: -30°C to +85°C. The temperature range for storing the device when not powered.
• Infrared Soldering Condition: Withstands 260°C for 10 seconds, which is a typical profile for lead-free reflow soldering.

2.2 Electrical and Optical Characteristics

These are the typical performance parameters measured at the standard test current of I_F = 20mA.

• Luminous Intensity (I_V): For the white LED, the intensity ranges from a minimum of 112.0 mcd to a maximum of 450.0 mcd. For the yellow LED, the range is from 45.0 mcd to 180.0 mcd. The actual value for a specific unit depends on its bin rank (see Section 4). The measurement uses a sensor filtered to approximate the CIE photopic eye-response curve.
• Viewing Angle (2θ_1/2): Typically 130 degrees for both colors. This is the full angle at which the luminous intensity is half of the intensity measured on the central axis (0°). A wide viewing angle like this is characteristic of side-looking LEDs.
• Dominant Wavelength (λ_d): Applies to the yellow LED only, ranging from 584.0 nm to 596.0 nm. This is the single wavelength perceived by the human eye that defines the color.
• Peak Emission Wavelength (λ_P): Typically 591.0 nm for the yellow LED, representing the peak in its spectral power distribution.
• Chromaticity Coordinates (x, y): For the white LED, typical coordinates are x=0.31, y=0.31, placing it in the "cool white" region of the CIE 1931 chromaticity diagram. The yellow LED's color is defined by its dominant wavelength bin.
• Spectral Line Half-Width (Δλ): Typically 15 nm for the yellow LED, indicating the spectral purity or bandwidth of the emitted light.
• Forward Voltage (V_F): For the white LED: Min 2.5V, Max 3.7V. For the yellow LED: Min 1.6V, Max 2.4V. This is the voltage drop across the LED when driven at 20mA. The difference in V_F between the two colors is significant and must be accounted for in circuit design, especially if they are to be driven from a common current source.
• Reverse Current (I_R): Maximum 10.0 μA for both colors at a reverse voltage (V_R) of 5V. Important Note: The datasheet explicitly states that the reverse voltage condition is applied for infrared (IR) testing only, and the device is not designed for reverse operation. Applying reverse bias in an application circuit is not recommended.

2.3 Thermal Considerations

The power dissipation ratings (72mW/62.5mW) are directly related to thermal management. Exceeding these limits increases junction temperature, which can lead to accelerated lumen depreciation (light output decrease over time), a shift in chromaticity coordinates, and ultimately, device failure. The operating temperature range of -20°C to +80°C defines the ambient conditions. Designers must ensure that the combined effects of ambient temperature and self-heating from power dissipation keep the LED's junction temperature within safe limits.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into "bins" based on key performance parameters. The LTW-S225DSKS-PH uses a multi-dimensional binning system.

3.1 Luminous Intensity (I_V) Binning

LEDs are categorized based on their measured light output at 20mA.

White LED Bins:

• Bin R: 112.0 – 180.0 mcd
• Bin S: 180.0 – 280.0 mcd
• Bin T: 280.0 – 450.0 mcd

Tolerance within each bin is +/- 15%.

Yellow LED Bins:

• Bin P: 45.0 – 71.0 mcd
• Bin Q: 71.0 – 112.0 mcd
• Bin R: 112.0 – 180.0 mcd

Tolerance within each bin is +/- 15%.

3.2 Hue / Chromaticity Binning

For the white LED, color consistency is managed through chromaticity coordinate (x, y) bins defined by specific quadrilaterals on the CIE 1931 diagram (e.g., S1-1, S1-2, S2-1, etc.). The tolerance for each hue bin is +/- 0.01 in both x and y coordinates. For the yellow LED, a simpler dominant wavelength binning is used:

• Bin H: 584.0 – 590.0 nm
• Bin J: 590.0 – 596.0 nm

Tolerance for each wavelength bin is +/- 1 nm.

This binning system allows designers to select parts that meet specific brightness and color consistency requirements for their application, which is crucial for applications like multi-LED backlighting or status arrays where uniformity is important.

4. Performance Curve Analysis

While the specific graphs are not fully detailed in the provided text, typical curves for such LEDs would include the following, all measured at 25°C ambient unless noted:

4.1 Current vs. Voltage (I-V) Curve

This graph shows the relationship between forward current (I_F) and forward voltage (V_F). It is non-linear, characteristic of a diode. The curve for the AlInGaP (yellow) chip would typically have a lower knee voltage (~1.8V) compared to the InGaN (white) chip (~3.0V). This curve is essential for designing the current-limiting circuitry, whether using a simple resistor or a constant-current driver.

4.2 Relative Luminous Intensity vs. Forward Current

This plot illustrates how light output increases with drive current. It is generally linear over a range but will saturate at higher currents due to efficiency droop and thermal effects. Operating near or above the absolute maximum DC current (20/25mA) is not advised, as it reduces efficiency and lifespan.

4.3 Relative Luminous Intensity vs. Ambient Temperature

LED light output decreases as the junction temperature increases. This curve quantifies that relationship. For AlInGaP LEDs (yellow), the decrease is typically more pronounced than for InGaN LEDs (white). This is a critical consideration for applications with high ambient temperatures or poor thermal management on the PCB.

4.4 Spectral Distribution

For the yellow AlInGaP LED, this would show a relatively narrow peak centered around 591 nm. For the white InGaN LED, the spectrum would be much broader, consisting of a blue InGaN chip emission combined with light from a phosphor layer, resulting in a continuous spectrum across visible wavelengths.

5. Mechanical and Package Information

5.1 Package Dimensions and Pin Assignment

The LTW-S225DSKS-PH is a side-looking SMD package. Key dimensional notes: all dimensions are in millimeters, with a standard tolerance of ±0.1 mm unless otherwise specified. The pin assignment is crucial for correct orientation:

• Pins 1 and 2 are assigned to the AlInGaP Yellow chip.
• Pins 3 and 4 are assigned to the InGaN White chip.

The physical layout ensures the primary light emission is from the side of the package, not the top.

5.2 Recommended PCB Pad Design and Polarity

The datasheet includes a diagram for the recommended solder pad footprint on the printed circuit board. Adhering to this design promotes reliable soldering, proper alignment, and good mechanical strength. The pad pattern also provides the necessary thermal relief and solder volume. Polarity is indicated by the pin numbering; connecting the anode and cathode correctly is essential. Applying reverse voltage can damage the LED.

6. Soldering and Assembly Guidelines

6.1 Infrared Reflow Soldering Process

The device is compatible with infrared (IR) reflow soldering, which is standard for Pb-free assembly. The maximum rated condition is 260°C for 10 seconds. In practice, a standard lead-free reflow profile with a peak temperature between 240°C and 260°C, and time above liquidus (TAL) appropriate for the solder paste, should be used. The suggested profile in the datasheet should be followed to avoid thermal shock or damage to the LED package or internal wire bonds.

6.2 Cleaning

Post-solder cleaning must be performed with care. Only specified chemicals should be used. The datasheet recommends immersion in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute if cleaning is necessary. The use of unspecified or aggressive chemical liquids can damage the LED's epoxy lens or packaging materials, leading to reduced light output or premature failure.

6.3 Storage and Handling

Electrostatic Discharge (ESD) Caution: LEDs are sensitive to static electricity and voltage surges. It is recommended to use a wrist strap or anti-static gloves when handling them. All equipment and workstations must be properly grounded.

Moisture Sensitivity: The LEDs are packaged in a moisture-barrier bag with desiccant. While sealed, they should be stored at 30°C or less and 90% relative humidity (RH) or less, with a recommended shelf life of one year. Once the original packaging is opened, the storage ambient should not exceed 30°C or 60% RH. Components removed from their dry-pack should be subjected to IR reflow soldering within one week (Moisture Sensitivity Level 3, MSL-3). For longer storage outside the original bag, they should be kept in a sealed container with desiccant. If stored open for more than one week, a bake-out at approximately 60°C for at least 20 hours is required before soldering to prevent "popcorning" during reflow.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LTW-S225DSKS-PH is supplied in industry-standard embossed carrier tape, 8mm wide, wound on 7-inch (178mm) diameter reels. Each reel contains 4000 pieces. The tape pockets are sealed with a top cover tape to protect components during shipping and handling. The packaging conforms to ANSI/EIA-481 specifications. For quantities less than a full reel, a minimum packing quantity of 500 pieces is specified for remnants. The tape is designed to allow a maximum of two consecutive missing components (empty pockets).

8. Application Suggestions and Design Considerations

8.1 Typical Application Circuits

Each color chip within the LTW-S225DSKS-PH must be driven independently due to their different forward voltage characteristics. The simplest drive method is using a series current-limiting resistor for each chip. The resistor value is calculated as R = (V_supply - V_F) / I_F, where I_F is the desired drive current (e.g., 20mA) and V_F is the typical or maximum forward voltage from the datasheet, depending on the design margin. For better consistency and stability, especially over temperature or supply voltage variations, a constant current driver circuit is recommended.

8.2 Thermal Management in Design

Although SMD LEDs are small, effective thermal management is vital for performance and longevity. The PCB acts as the primary heat sink. Using the recommended pad design with adequate copper area connected to the thermal pads of the LED helps dissipate heat. For high-power or high-ambient-temperature applications, additional thermal vias under the package or a larger copper pour may be necessary to transfer heat away from the LED junction.

8.3 Optical Design Considerations

As a side-looking LED, the primary light emission is parallel to the PCB surface. This is ideal for edge-lighting light guides, illuminating side-firing indicators, or backlighting keys from the side. Designers should consider the 130-degree viewing angle when designing light pipes, lenses, or diffusers to ensure even illumination and the desired visual effect.

9. Technical Comparison and Differentiation

The key differentiating factor of the LTW-S225DSKS-PH is its dual-color, side-looking configuration in a single SMD package. This saves PCB space compared to using two separate side-looking LEDs. The use of AlInGaP for yellow offers high efficiency and good color purity, while the InGaN-based white provides a modern cool white source. The combination of a wide 130-degree viewing angle and compatibility with automated assembly and reflow processes makes it a versatile choice for cost-effective, high-volume manufacturing.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive both the white and yellow chips from the same current-limiting resistor?
A: No. Due to the significant difference in forward voltage (V_F ~3.2V for white vs. ~2.0V for yellow at 20mA), connecting them in parallel with a single resistor would result in a severe current imbalance, potentially overdriving one chip and underdriving the other. Each chip requires its own independent current control.

Q: What is the meaning of the luminous intensity bin code (e.g., R, S, T)?
A: The bin code indicates the guaranteed range of light output for that specific LED when driven at the standard test current (20mA). For example, a white LED from Bin T will be brighter (280-450 mcd) than one from Bin R (112-180 mcd). Designers specify the required bin to ensure consistency in their product's brightness.

Q: Is this LED suitable for outdoor applications?
A: The datasheet specifies an operating temperature range of -20°C to +80°C and lists typical indoor applications. For outdoor use, factors like wider temperature extremes, UV exposure degrading the epoxy, and moisture ingress must be evaluated. The device is not specifically rated for harsh environments.

Q: How critical is the one-week reflow deadline after opening the moisture barrier bag?
A: It is very important for reliability. If MSL-3 components absorb too much moisture from the air and are then subjected to the high heat of reflow soldering, the rapid vaporization of the moisture can cause internal delamination or cracking ("popcorning"), leading to immediate or latent failures. Adhere to the baking guidelines if the deadline is exceeded.

11. Practical Application Examples

Example 1: Mobile Device Status Indicator: A single LTW-S225DSKS-PH can provide multiple statuses. The white LED could indicate "power on" or "fully charged," while the yellow LED could indicate "charging" or "low battery." The side emission allows the light to be coupled into a light guide that runs to the edge of the device casing, creating a sleek indicator.

Example 2: Industrial Control Panel Backlighting: An array of these LEDs could be placed along the edge of a membrane switch panel. The white LEDs provide general backlighting for all keys in low-light conditions. The yellow LEDs could be wired to specific function keys (e.g., emergency stop, warning) to provide a distinct, attention-grabbing color when activated, all using the same compact component footprint.

12. Operational Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light through electroluminescence. When a forward voltage is applied across the p-n junction, electrons and holes recombine, releasing energy in the form of photons. The color of the light is determined by the energy bandgap of the semiconductor material.

• AlInGaP (Aluminum Indium Gallium Phosphide): This material system is used for the yellow LED. It has a bandgap that corresponds to light emission in the red, orange, amber, and yellow regions of the spectrum. It is known for its high efficiency in these colors.
• InGaN (Indium Gallium Nitride): This material system is used for the white LED. Typically, a blue-emitting InGaN chip is combined with a phosphor coating. The blue light from the chip excites the phosphor, which then re-emits light across a broader spectrum, resulting in the perception of white light. The specific mix of phosphors determines the white point (e.g., cool white, warm white).

The side-looking package structure uses a reflective cavity and a molded epoxy lens to direct the primary light output sideways from the component body.

13. Technology Trends

The optoelectronics industry continues to advance in several key areas relevant to components like the LTW-S225DSKS-PH. There is a constant drive for increased luminous efficacy (more light output per watt of electrical input), which improves energy efficiency and allows for lower drive currents or brighter outputs. Improved color rendering and a wider range of available white points (CCT - Correlated Color Temperature) are trends, especially for white LEDs. Miniaturization persists, allowing for even smaller package sizes with comparable or better performance. Furthermore, enhanced reliability and longevity under higher temperature and humidity conditions are ongoing development goals, expanding the potential application environments for SMD LEDs. The integration of multiple functions (like multiple colors or even integrated drivers) into single packages also represents a significant trend in component design.