LTW-326ZDSKR-5A LED Data Sheet - Dual Color (White/Red) - Side-View - SMD Package - Technical Documentation

1. Product Overview

LTW-326ZDSKR-5A is a dual-color, side-view surface-mount device (SMD) LED. Its primary design application is for LCD backlighting, which requires a compact right-angle light source. The device integrates two distinct semiconductor chips within a single package: an InGaN chip for white light emission and an AlInGaP chip for red light emission. This dual-chip configuration allows for color mixing or independent control of the two colors from a single component, saving PCB space and simplifying assembly in space-constrained designs such as ultra-thin displays.

The core advantages of this LED include: ultra-high luminous intensity output for both chips, compatibility with standard automated pick-and-place equipment, and suitability for lead-free infrared (IR) reflow soldering processes. It is supplied on 8mm carrier tape wound onto 7-inch diameter reels, facilitating high-volume production. The product is also explicitly compliant with the RoHS directive, making it an environmentally friendly product.

2. Detailed Technical Specifications

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 as follows:

• Power Dissipation:White LED chip: 35 mW, Red LED chip: 48 mW. This defines the maximum power that 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:Both chips are 5 V. Applying a reverse bias higher than this value may cause junction breakdown.
• Temperature range:Operating temperature: -20°C to +80°C. Storage temperature: -40°C to +85°C.
• ESD sensitivity:Human Body Model (HBM) threshold is 2000V. Anti-static discharge measures must be taken during handling.
• Soldering:Can withstand infrared reflow soldering with a peak temperature of 260°C for 10 seconds.

2.2 Electro-Optical Characteristics

Measurement conditions are Ta=25°C, forward current (IF)=5mA, unless otherwise specified.

• Luminous intensity (Iv):A key performance indicator. White light: minimum 28.0 mcd, typical value -, maximum 112.0 mcd. Red light: minimum 7.1 mcd, typical value -, maximum 45.0 mcd. The actual Iv of each unit is binned and categorized (see Section 3).
• Viewing Angle (2θ1/2):Both colors are 130 degrees, indicating a wide viewing angle cone typical of side-emitting lenses used for backlight light guides.
• 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 originates from the different bandgap energies of InGaN and AlInGaP materials. This must be considered when designing drive circuits, especially in common-anode or common-cathode configurations.
• Peak Emission Wavelength (λP):Red LED chip: 639 nm (typical).
• Dominant wavelength (λd):Red LED chip: 630 nm (typical). This is the single wavelength perceived by the human eye that defines the color.
• Chromaticity coordinates (x, y):White LED chip: x=0.3, y=0.3 (typical). These CIE 1931 coordinates define the white point color. The applicable tolerance is ±0.01.
• Reverse current (IR):Maximum 100 µA at VR=5V.

3. Grading System Description

LEDs are graded according to performance to ensure consistency in applications. The grading code is marked on the packaging.

3.1 Luminous Intensity (Iv) Binning

White LED Chip:Binning N (28.0-45.0 mcd), P (45.0-71.0 mcd), Q (71.0-112.0 mcd).
Red LED Chip:Binning 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 Red Chip Hue (Color) Binning

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

4. Performance Curve Analysis

The datasheet references typical characteristic curves that are crucial for the design.

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

5. Mechanical and Packaging Information

5.1 Package Dimensions

This LED conforms to the EIA standard package outline for side-view LEDs. Key dimensions include overall height, width, and depth, as well as the position and size of the 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 independent chips, each with its own anode/cathode. The pin assignment is as follows: The cathode of the white InGaN chip is connected to pin C2. The cathode of the red AlInGaP chip is connected to pin C1. The anode may be common or assigned to other pins according to the package drawing. Correct polarity must be observed during PCB layout and assembly.

5.3 Recommended Pad Layout

The datasheet provides recommended land patterns (footprints) for PCB design. Following these patterns ensures good solder joint formation, mechanical stability, and thermal performance during the reflow soldering process. It also indicates the recommended soldering orientation to minimize tombstoning.

6. Soldering and Assembly Guide

6.1 Reflow Soldering Temperature Profile

This LED is compatible with infrared reflow soldering processes. A recommended temperature profile is provided, with one key parameter being a peak temperature of 260°C for a maximum duration of 10 seconds. This profile must be followed to prevent thermal damage to the plastic package and internal bonding wires.

6.2 Cleaning

If cleaning is required after soldering, only specified chemicals should be used. The datasheet recommends immersion in ethanol or isopropanol at room temperature for no more than one minute. Unspecified chemicals may damage the encapsulating resin or lens.

6.3 Storage and Operation

• ESD Precautions:This device is sensitive to electrostatic discharge (2000V HBM). Please use an anti-static wrist strap, grounded workbench, and conductive containers.
• Moisture Sensitivity:As a plastic SMD package, it has moisture sensitivity. If the original sealed moisture barrier bag with desiccant is unopened, the storage conditions should be ≤30°C/≤90%RH, with a shelf life of one year. Once opened, the LEDs should be stored at ≤30°C/≤60%RH and used within one week. For long-term storage after opening, please use a sealed container with desiccant or a nitrogen dry box. Components stored outside the bag for more than one week require baking (approximately 60°C, for over 20 hours) before reflow soldering to prevent the "popcorn" effect.

7. Packaging and Ordering

Standard packaging is 8mm embossed carrier tape, sealed with cover tape, wound on a 7-inch (178mm) diameter reel. Each full reel contains 3000 pieces. For remaining quantities, the minimum packaging quantity is 500 pieces. Packaging complies with ANSI/EIA 481-1 specification. Carrier tape and reel dimensions are provided for automatic feeder setup.

8. Application Recommendations

8.1 Typical Application Scenarios

The primary application is LCD backlighting for consumer electronics, industrial displays, and automotive interior displays, where an ultra-thin form factor is crucial. The dual-color function enables dynamic backlighting (e.g., white light for normal operation, red light for night mode or warnings) or the creation of other colors through color mixing.

8.2 Design Considerations

• Current Drive:Use a constant current driver, not constant voltage, to ensure stable light output and lifespan. Adhere to the absolute maximum DC current ratings (10mA for white light, 20mA for red light).
• Thermal Management:Although power consumption is low, heat is still generated. Ensure sufficient PCB copper foil area or thermal vias under the pad to conduct heat, especially when driving at higher currents or in high ambient temperatures. This helps maintain luminous efficiency and service life.
• Optical Design:The 130-degree side-emitting design is intended for coupling into the Light Guide Plate (LGP). The light entry point and dot pattern design of the LGP are crucial for achieving uniform backlight illumination.
• Circuit Design:When designing the drive circuit, the different forward voltages of the two chips must be considered, especially if a common current-limiting resistor is used for both.

9. Technical Comparison and Differentiation

Compared to monochromatic side-emitting LEDs, its main advantage lies in saving space and simplifying assembly for dual-color applications. Using AlInGaP to produce red light offers higher efficiency and more saturated color compared to older technologies like GaAsP. The InGaN-based white light chip provides high brightness. Combining both within a single package represents a system-level optimization for cost-sensitive, high-volume backlight units.

10. Frequently Asked Questions (FAQ)

Q: Can I drive both 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 simultaneously at maximum current (10mA + 20mA = total 30mA) and typical VF (3.0V + 2.0V = 5.0V) would result in 150mW of electrical input. This exceeds their respective power dissipation ratings (35mW and 48mW) and is likely to cause device overheating. Derating or pulsed operation is required.

Q: How to interpret the Iv bin code on the packaging bag?
A: There will be a code on the packaging bag indicating the specific Iv bin of the internal LED (e.g., "Q" for white light, "L" for red light). You must cross-reference this letter with the Iv specification table in the datasheet to understand the guaranteed minimum/maximum luminous intensity range for that batch.

Q: The peak wavelength of the red LED chip is 639nm, but the dominant wavelength is 630nm. Why is there a 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 on the CIE diagram from the white point (illuminant) through the measured (x,y) coordinates of the LED until it intersects the spectral locus. λd is the single wavelength color perceived by the human eye and may differ from λP, especially when the spectrum is not perfectly symmetrical.

11. Practical Design Case Studies

Scenario:Design status indicator/backlight for portable medical device display. The indicator needs to show white for "Power On/Operating" and red for "Low Battery/Warning". Space is extremely limited.
Implementation Plan:Place an LTW-326ZDSKR-5A LED at the edge of a small-sized LCD. Use a simple microcontroller with two GPIO pins to control two independent current-limiting circuits (e.g., using transistors). One circuit drives the white light chip, and the other drives the red light chip. The 130-degree side-emitting light effectively couples into the display's light guide plate. Compared to using two separate LEDs, this design saves space and simplifies the optical alignment process during assembly.

12. Introduction to Technical Principles

InGaN White LED:Typically, a blue-emitting InGaN semiconductor chip is coated with a yellow phosphor (e.g., YAG:Ce). Part of the blue light is converted to yellow light by the phosphor. The remaining blue light mixes with the converted yellow light, which is perceived by the human eye as white light. The exact color temperature (cool white, warm white) is adjusted via the phosphor composition.

AlInGaP Red Light LED:This material system has a direct bandgap and 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, surpassing the older GaAsP technology.

13. Industry Trends and Development

The trend for backlight LEDs continues towards higher efficiency (more lumens per watt) and higher Color Rendering Index (CRI) to achieve better image quality, especially in professional monitors and TVs. For side-view types, the driving factor is thinner packaging to enable slimmer display designs. Chip Scale Package (CSP) and Mini/Micro LED technologies are also in continuous development, promising smaller form factors, higher density, and local dimming capabilities for advanced backlight units. In mid-range applications, dual-color schemes remain relevant for cost-effective segmented color control.