LTW-326ZDSKR-5A LED Datasheet - Dual Color (White/Red) - Side View - SMD Package - English Technical Document

1. Product Overview

The LTW-326ZDSKR-5A is a dual-color, side-viewing Surface Mount Device (SMD) LED. Its primary design purpose is for LCD backlighting applications, where a compact, right-angle light source is required. The device integrates two distinct semiconductor chips within a single package: an InGaN (Indium Gallium Nitride) chip for white light emission and an AlInGaP (Aluminum Indium Gallium Phosphide) chip for red light emission. This dual-chip configuration allows for color mixing or independent control of two colors from one component, saving board space and simplifying assembly in space-constrained designs like thin displays.

The core advantages of this LED include its ultra-bright output from both chips, compatibility with standard automated pick-and-place equipment, and its qualification for lead-free, infrared (IR) reflow soldering processes. It is packaged on 8mm tape wound onto 7-inch diameter reels, facilitating high-volume manufacturing. The product is also specified as meeting RoHS (Restriction of Hazardous Substances) directives, classifying it as a green product.

2. Technical Specifications Deep Dive

2.1 Absolute Maximum Ratings

Operating the device beyond these limits may cause permanent damage. Key ratings at an ambient temperature (Ta) of 25°C are:

• Power Dissipation: White Chip: 35 mW, Red Chip: 48 mW. This defines the maximum power the LED can dissipate as heat under continuous operation.
• Forward Current: DC Forward Current: White: 10 mA, Red: 20 mA. Peak Forward Current (1/10 duty cycle, 0.1ms pulse): White: 50 mA, Red: 40 mA. Exceeding the DC current will overstress the semiconductor junction.
• Reverse Voltage: 5 V for both chips. Applying a reverse bias voltage higher than this can cause junction breakdown.
• Temperature Range: Operating: -20°C to +80°C. Storage: -40°C to +85°C.
• ESD Sensitivity: Human Body Model (HBM) threshold is 2000V. Precautions against electrostatic discharge are necessary during handling.
• Soldering: Withstands infrared reflow soldering at 260°C peak temperature for 10 seconds.

2.2 Electro-Optical Characteristics

Measured at Ta=25°C with a forward current (IF) of 5mA, unless stated otherwise.

• Luminous Intensity (Iv): A key performance metric. White: Min 28.0 mcd, Typ -, Max 112.0 mcd. Red: Min 7.1 mcd, Typ -, Max 45.0 mcd. The actual Iv for each unit is classified into bins (see Section 3).
• Viewing Angle (2θ1/2): 130 degrees for both colors, indicating a wide viewing cone typical for side-emitting lenses used in backlighting waveguides.
• Forward Voltage (VF): White: Min 2.7V, Typ 3.0V, Max 3.7V. Red: Min 1.70V, Typ 2.00V, Max 2.40V. The difference in VF is due to the different bandgap energies of the InGaN and AlInGaP materials. This must be considered when designing driving circuits, especially for common-anode or common-cathode configurations.
• Peak Emission Wavelength (λP): For the red chip: 639 nm (typical).
• Dominant Wavelength (λd): For the red chip: 630 nm (typical). This is the single wavelength perceived by the human eye that defines the color.
• Chromaticity Coordinates (x, y): For the white chip: x=0.3, y=0.3 (typical). These CIE 1931 coordinates define the white point color. A tolerance of ±0.01 applies.
• Reverse Current (IR): Max 100 µA at VR=5V.

3. Binning System Explanation

The LEDs are sorted into performance bins to ensure consistency in application. The bin code is marked on the packaging.

3.1 Luminous Intensity (Iv) Binning

White Chip: Bins N (28.0-45.0 mcd), P (45.0-71.0 mcd), Q (71.0-112.0 mcd).
Red Chip: Bins K (7.1-11.2 mcd), L (11.2-18.0 mcd), M (18.0-28.0 mcd), N (28.0-45.0 mcd).
A tolerance of ±15% applies within each bin.

3.2 Hue (Color) Binning for Red Chip

The red LEDs are binned based on their chromaticity coordinates (x, y) on the CIE 1931 diagram. Six bins are defined (S1 through S6), each representing a small quadrilateral area on the color chart. The coordinates for each vertex of these bins are provided in the datasheet. A tolerance of ±0.01 applies to the (x, y) coordinates within each bin. This ensures tight color consistency for the red emission across different production lots.

4. Performance Curve Analysis

The datasheet references typical characteristic curves which are essential for design.

• IV Curve (Current vs. Voltage): Shows the exponential relationship between forward voltage and current for both the white and red chips. The different turn-on voltages are clearly visible.
• Luminous Intensity vs. Forward Current: Illustrates how light output increases with current. It is typically linear within the recommended operating range but will saturate at higher currents.
• Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as junction temperature increases. This is critical for thermal management in the final application.
• Spectral Distribution: For the red chip, the curve would show a narrow peak around 639nm, characteristic of AlInGaP technology. For the white chip (typically a blue die with phosphor), the spectrum would be broad, covering the visible range.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED conforms to an EIA standard package outline for side-view LEDs. Critical dimensions include the overall height, width, and depth, as well as the placement and size of the solder pads. All dimensions are in millimeters with a standard tolerance of ±0.10mm unless otherwise specified. The lens is designed for side emission.

5.2 Pin Assignment and Polarity

The device has two anodes/cathodes for the independent chips. The pin assignment is: Cathode for the White InGaN chip is connected to Pin C2. Cathode for the Red AlInGaP chip is connected to Pin C1. The anodes are likely common or assigned to other pins as per the package drawing. Correct polarity must be observed during PCB layout and assembly.

5.3 Suggested Solder Pad Layout

The datasheet provides a recommended land pattern (footprint) for PCB design. Adhering to this pattern ensures proper solder joint formation, mechanical stability, and thermal performance during reflow. A suggested soldering direction is also indicated to minimize potential tombstoning.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Profile

The LED is compatible with infrared reflow processes. A suggested profile is provided, with a critical parameter being a peak temperature of 260°C for a maximum of 10 seconds. This profile must be followed to prevent thermal damage to the plastic package and the internal wire bonds.

6.2 Cleaning

If cleaning is required after soldering, only specified chemicals should be used. The datasheet recommends immersion in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Unspecified chemicals may damage the package resin or lens.

6.3 Storage and Handling

• ESD Precautions: The device is sensitive to electrostatic discharge (2000V HBM). Use wrist straps, grounded workstations, and conductive containers.
• Moisture Sensitivity: As a plastic SMD package, it is moisture-sensitive. If the original sealed moisture-proof bag with desiccant is unopened, storage should be at ≤30°C/≤90%RH, with a shelf life of one year. Once opened, LEDs should be stored at ≤30°C/≤60%RH and used within one week. For longer storage out of the original bag, use a sealed container with desiccant or a nitrogen desiccator. Components stored out of bag for >1 week require baking (approx. 60°C for >20 hours) before reflow to prevent popcorning.

7. Packaging and Ordering

The standard packaging is 8mm embossed carrier tape sealed with cover tape, wound onto 7-inch (178mm) diameter reels. Each full reel contains 3000 pieces. A minimum packing quantity of 500 pieces is available for remainders. The packaging complies with ANSI/EIA 481-1 specifications. The tape and reel dimensions are provided for automated feeder setup.

8. Application Suggestions

8.1 Typical Application Scenarios

The primary application is LCD backlighting for consumer electronics, industrial displays, and automotive interior displays where a thin profile is essential. The dual-color capability allows for dynamic backlighting (e.g., white for normal operation, red for night mode or warnings) or creation of other colors by mixing.

8.2 Design Considerations

• Current Driving: Use constant current drivers, not constant voltage, to ensure stable light output and longevity. Respect the absolute maximum DC current ratings (10mA white, 20mA red).
• Thermal Management: The power dissipation, though low, generates heat. Ensure adequate PCB copper area or thermal vias under the solder pads to conduct heat away, especially if driven at higher currents or in high ambient temperatures. This maintains luminous efficiency and lifespan.
• Optical Design: The 130-degree side emission is designed to couple into a light guide plate (LGP). The design of the LGP's injection point and pattern is crucial for achieving uniform backlight illumination.
• Circuit Design: Account for the different forward voltages of the two chips when designing the drive circuitry, particularly if using a common current-limiting resistor for both.

9. Technical Comparison and Differentiation

Compared to single-color side-view LEDs, the key advantage is space savings and simplified assembly for two-color applications. The use of AlInGaP for red offers higher efficiency and more saturated color compared to older technologies like GaAsP. The InGaN-based white chip provides high brightness. The combination in one package is a system-level optimization for cost-sensitive, high-volume backlight units.

10. Frequently Asked Questions (FAQ)

Q: Can I drive the white and red chips simultaneously at their maximum DC current?
A: You must consider the total power dissipation and thermal load on the package. Driving both at max current (10mA + 20mA = 30mA total) at their typical VF (3.0V + 2.0V = 5.0V) results in 150mW of electrical input. This exceeds the individual power dissipation ratings (35mW & 48mW) and would likely overheat the device. Derating or pulsed operation is necessary.

Q: How do I interpret the Iv bin code on the bag?
A: The bag will have a code indicating the specific Iv bin (e.g., \"Q\" for white, \"L\" for red) for the LEDs inside. You must cross-reference this letter with the Iv Spec. Tables in the datasheet to know the guaranteed min/max luminous intensity range for that batch.

Q: The red chip has a peak wavelength of 639nm but a dominant wavelength of 630nm. Why the difference?
A> The peak wavelength (λP) is the highest point on the spectral power distribution curve. The dominant wavelength (λd) is determined by drawing a line from the white point (illuminant) on the CIE diagram through the measured (x,y) coordinates of the LED to the spectral locus. λd is the single-wavelength color the human eye perceives, which can differ from λP, especially if the spectrum is not perfectly symmetrical.

11. Practical Design Case Study

Scenario: Designing a status indicator/backlight for a portable medical device display. The indicator needs to show white for \"power on/active,\" and red for \"low battery/warning.\" Space is extremely limited.
Implementation: A single LTW-326ZDSKR-5A LED is placed at the edge of a small LCD. A simple microcontroller with two GPIO pins is used to control two independent current-limiting circuits (e.g., using transistors). One circuit drives the white chip, the other drives the red chip. The 130-degree side emission effectively couples into the display's light guide. The design saves space versus using two separate LEDs and simplifies the optical alignment process during assembly.

12. Technology Principle Introduction

InGaN White LED: Typically, a blue-light-emitting InGaN semiconductor chip is coated with a yellow phosphor (e.g., YAG:Ce). Part 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 color temperature (cool white, warm white) is tuned by the phosphor composition.

AlInGaP Red LED: This material system has a direct bandgap that can be tuned across the red, orange, and yellow spectral regions by varying the aluminum and indium ratios. AlInGaP LEDs are known for their high efficiency and excellent color purity (narrow spectral width) in the red-to-amber range, superior to older GaAsP technology.

13. Industry Trends and Developments

The trend in backlighting LEDs continues towards higher efficiency (more lumens per watt) and higher color rendering index (CRI) for better image quality, especially in professional monitors and TVs. For side-view types, the drive is for thinner packages to enable ever-slimmer display designs. There is also ongoing development in chip-scale packaging (CSP) and mini/micro-LED technologies, which promise even smaller form factors, higher density, and local dimming capabilities for advanced backlight units. The dual-color approach remains relevant for cost-effective segmented color control in mid-range applications.