LTL-2550G Green LED Light Bar Datasheet - Rectangular Source - Voltage 2.1-2.6V - Power 70mW per Segment - English Technical Document

1. Product Overview

The LTL-2550G is a solid-state light source designed as a rectangular light bar. It is engineered for applications requiring a large, bright, and uniform emitting area. The device utilizes green LED chips, which are fabricated using GaP epi on GaP substrate or AlInGaP on a non-transparent GaAs substrate technology, and features a white bar housing. This product falls under the category of universal rectangular bar LEDs and is categorized for luminous intensity to ensure consistent performance across units.

1.1 Core Features and Advantages

• Rectangular Light Bar Form Factor: Provides a distinctive, elongated light emission pattern suitable for backlighting, indicators, and signage where a linear light source is preferred over a point source.
• Large, Bright, Uniform Emitting Area: Engineered to deliver high luminance across the entire surface of the bar, minimizing hotspots and ensuring even illumination.
• Low Power Requirement: Operates efficiently, making it suitable for battery-powered or energy-conscious applications.
• High Brightness & High Contrast: The green chips offer significant luminous intensity, ensuring good visibility even in well-lit ambient conditions.
• Solid-State Reliability: Benefits from the inherent longevity and ruggedness of LED technology, with no filaments or glass to break.
• Categorized for Luminous Intensity: Units are binned (categorized) based on their light output, allowing designers to select parts for consistent brightness in multi-unit assemblies.
• Lead-Free Package (RoHS Compliant): Manufactured in accordance with environmental regulations restricting hazardous substances.

1.2 Target Market and Applications

This device is intended for use in ordinary electronic equipment. Typical applications include, but are not limited to: status indicators on office equipment (printers, copiers), backlighting for switches and panels, decorative lighting, and various consumer electronics where a bright, reliable indicator is needed. It is designed for applications where exceptional reliability is not the primary safety concern (e.g., non-critical indicators). For applications where failure could jeopardize life or health (aviation, medical devices), specific consultation is required.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Electrical and Optical Characteristics

All parameters are specified at an ambient temperature (Ta) of 25°C.

• Average Luminous Intensity (Iv): Ranges from 3500 µcd (minimum) to 8000 µcd (typical) when driven at a forward current (IF) of 10mA. This is a measure of the light output as perceived by the human eye, measured with a sensor filtered to the CIE photopic response curve.
• Peak Emission Wavelength (λp): Typically 565 nm at IF=20mA. This is the wavelength at which the spectral power distribution is at its maximum.
• Spectral Line Half-Width (Δλ): Typically 30 nm at IF=20mA. This parameter indicates the spectral purity or bandwidth of the emitted light; a smaller value indicates a more monochromatic source.
• Dominant Wavelength (λd): Typically 569 nm at IF=20mA. This is the single-wavelength perception of the color by the human eye, which may differ slightly from the peak wavelength.
• Forward Voltage per Segment (VF): Ranges from 2.1V (typical) to 2.6V (maximum) at IF=20mA. Circuit design must account for this range to ensure the intended drive current is delivered to all segments.
• Reverse Current per Segment (IR): Maximum of 100 µA at a reverse voltage (VR) of 5V. It is critical to note that this reverse voltage condition is for test purposes only and the device should not be operated under continuous reverse bias.
• Luminous Intensity Matching Ratio (Iv-m): Maximum ratio of 2:1 between segments at IF=10mA. This specifies the maximum allowable variation in brightness between different segments of the same device.

2.2 Absolute Maximum Ratings

Stresses beyond these limits may cause permanent damage to the device.

• Power Dissipation per Segment: 70 mW.
• Peak Forward Current per Segment: 60 mA (pulsed, 1/10 duty cycle, 0.1ms pulse width).
• Continuous Forward Current per Segment: 25 mA at 25°C. This rating derates linearly at 0.33 mA/°C as temperature increases above 25°C.
• Operating Temperature Range: -35°C to +85°C.
• Storage Temperature Range: -35°C to +85°C.
• Solder Temperature: Maximum 260°C for a maximum of 3 seconds, measured 1.6mm below the seating plane of the component.

3. Binning System Explanation

The datasheet indicates that the LTL-2550G is categorized for luminous intensity. This implies a binning system is in place, although specific bin codes are not provided in this excerpt. Typically, such categorization involves:

• Luminous Intensity Binning: Devices are sorted into groups (bins) based on their measured light output at a standard test current (e.g., 10mA or 20mA). This allows designers to select parts with closely matched brightness for applications using multiple units, preventing visible unevenness.
• Wavelength/Dominant Wavelength Binning: While not explicitly stated for this model, it is common for colored LEDs to also be binned by dominant or peak wavelength to ensure consistent color hue across a production batch or assembly.
• Forward Voltage Binning: Less common for indicator-type LEDs but sometimes performed to group devices with similar Vf for simplified current-limiting circuit design.
• Design Implication: The datasheet explicitly recommends choosing LEDs from the same bin when assembling two or more displays in one set to avoid hue unevenness problems.

4. Performance Curve Analysis

The datasheet references Typical Electrical/Optical Characteristics Curves. While the specific graphs are not provided in the text, standard curves for such a device would typically include:

• Forward Current vs. Forward Voltage (I-V Curve): Shows the exponential relationship, crucial for designing the driving circuit. The curve will illustrate the typical Vf at various currents, including the 20mA test point.
• Luminous Intensity vs. Forward Current (L-I Curve): Depicts how light output increases with drive current. It is generally linear within the operating range but will saturate at higher currents. This curve helps determine the optimal drive current for desired brightness while considering efficiency and lifetime.
• Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as the junction temperature rises. LEDs become less efficient at higher temperatures, so this curve is vital for thermal management and predicting performance in elevated ambient conditions.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the peak at ~565nm and the spectral width (Δλ) of ~30nm.

5. Mechanical and Package Information

5.1 Package Dimensions

The device has a rectangular light bar form factor. All dimensions are provided in millimeters. The general tolerance for dimensions is ±0.25 mm (0.01 inch) unless a specific note states otherwise. The exact dimensional drawing is referenced in the datasheet but not reproduced in this text excerpt.

5.2 Pin Connection and Polarity Identification

The LTL-2550G is a multi-segment device with 8 pins. The pinout is as follows:

• Pin 1: Cathode A
• Pin 2: Anode A
• Pin 3: Cathode B
• Pin 4: Anode B
• Pin 5: Cathode C
• Pin 6: Anode C
• Pin 7: Cathode D
• Pin 8: Anode D

This configuration suggests the light bar may be internally divided into four independently addressable segments (A, B, C, D), allowing for partial illumination or simple animation patterns if driven by a suitable controller.

5.3 Internal Circuit Diagram

The datasheet includes an internal circuit diagram. Based on the pin description, it likely shows four separate LED segments, each with its own anode and cathode connection, arranged in a common configuration but not connected in series or parallel internally. This gives the designer flexibility in driving the segments.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Parameters

The absolute maximum rating specifies a solder temperature of 260°C maximum for a maximum of 3 seconds, measured 1.6mm below the seating plane. This defines the peak temperature and time-at-temperature constraints for a standard reflow soldering profile. A standard lead-free (SnAgCu) reflow profile with a peak temperature between 245°C and 260°C is typically applicable, ensuring the time above liquidus and at peak temperature is controlled.

6.2 Handling and Assembly Cautions

• Avoid using unsuitable tools or assembly methods that apply abnormal force to the display body.
• If a printing/pattern film is applied with pressure-sensitive adhesive, avoid letting the film side make close contact with a front panel/cover, as external force may cause the film to shift.
• Rapid changes in ambient temperature, especially in high humidity, should be avoided as they can cause condensation on the LED.

7. Storage Conditions

Proper storage is critical to prevent oxidation of the pins or solder pads.

• For LED Display (Through-Hole): In original packaging, store at 5°C to 30°C with humidity below 60% RH. Long-term storage of large inventories is discouraged; consume stock promptly.
• For LED SMD Display:
  • In original sealed bag: 5°C to 30°C, humidity below 60% RH.
  • After bag is opened: 5°C to 30°C, humidity below 60% RH, for a maximum of 168 hours (MSL Level 3).
  • If unpacked for more than 168 hours, baking at 60°C for 24 hours before soldering is recommended.
• General: The display should be used within 12 months from the shipping date. Do not expose to environments with high moisture or corrosive gases. Avoid long-term storage.

8. Application Suggestions and Design Considerations

8.1 Typical Application Scenarios

• Status and Indicator Lighting: Ideal for power, activity, or mode indicators on consumer and industrial equipment due to its high brightness and uniform bar shape.
• Backlighting: Can be used to edge-light small panels, labels, or membrane switches.
• Decorative and Architectural Lighting: The linear form factor can be used in accents, outlines, or simple signage.

8.2 Critical Design Considerations

• Drive Circuit: Constant current driving is strongly recommended to ensure consistent luminous intensity and longevity. The circuit must be designed to accommodate the full range of forward voltage (2.1V to 2.6V) to guarantee the target current is delivered.
• Current Limiting: The safe operating current must be chosen considering the maximum ambient temperature, applying the derating factor of 0.33 mA/°C above 25°C.
• Reverse Bias Protection: The driving circuit should incorporate protection (e.g., a diode in parallel) to shield the LEDs from reverse voltages and transient voltage spikes during power cycling. Continuous reverse bias can cause metal migration and failure.
• Thermal Management: Exceeding the recommended operating temperature or drive current will lead to severe light output degradation and/or premature failure. Ensure adequate heat dissipation if operating near maximum ratings.
• Binning for Multi-Unit Assemblies: Always specify and use LEDs from the same luminous intensity and wavelength bin when multiple units are used adjacently to ensure visual uniformity.

9. Technical Comparison and Differentiation

While a direct competitor comparison is not provided in the datasheet, the LTL-2550G's key differentiating features based on its specifications are:

• Form Factor: The rectangular light bar offers a distinct advantage over single-point 3mm or 5mm LEDs for applications requiring a linear illuminated area without using multiple discrete LEDs.
• Segmented Design: The four independent segments provide basic animation capability, which is not available in a single-die LED package.
• High Brightness: With a typical luminous intensity of 8000 µcd at only 10mA, it offers high light output efficiency.
• Categorized Output: The binning for intensity provides an assurance of consistency, which is critical for professional applications.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the difference between peak wavelength (565nm) and dominant wavelength (569nm)?
A: Peak wavelength is the physical peak of the spectral emission. Dominant wavelength is the perceived color point by the human eye, calculated from the full spectrum. They often differ slightly for green LEDs.

Q: Can I drive this LED with a constant voltage source?
A: It is not recommended. The forward voltage varies (2.1V-2.6V). A constant voltage source with a simple series resistor may not regulate current effectively across this range or with temperature changes, leading to inconsistent brightness and potential overcurrent. A constant current driver is preferred.

Q: Why is there a storage time limit (168 hours) after opening the bag for the SMD version?
A: This is due to Moisture Sensitivity Level (MSL 3). The plastic package absorbs moisture from the air. If soldered too quickly after exposure, trapped moisture can vaporize during reflow, causing internal damage (\"popcorning\"). Baking removes this moisture.

Q: What does \"Luminous Intensity Matching Ratio of 2:1\" mean?
A: It means the luminous intensity of the brightest segment should not be more than twice the intensity of the dimmest segment on the same device when measured under the same conditions (IF=10mA). This ensures uniformity across the bar.

11. Practical Use Case Example

Scenario: Designing a multi-status indicator panel for a network router.
The LTL-2550G can be used to indicate different states (Power, Internet, Wi-Fi, Ethernet Activity). Each of the four segments (A, B, C, D) can be assigned to one status. A microcontroller can independently control each segment via its anode/cathode pairs. The high brightness ensures visibility. The designer would:
1. Use a constant current driver IC capable of sourcing four channels at ~10-20mA each.
2. Design the PCB layout according to the mechanical drawing, ensuring correct pin alignment.
3. Specify to the supplier that all LTL-2550G units for this product must be from the same luminous intensity bin to prevent one status light from appearing brighter than another.
4. Follow the storage and soldering guidelines to prevent oxidation and moisture-related defects during assembly.

12. Operating Principle Introduction

The LTL-2550G is based on semiconductor electroluminescence. When a forward voltage exceeding the diode's built-in potential is applied across the anode and cathode of a segment, electrons and holes are injected into the active region of the semiconductor chip (made of GaP or AlInGaP). These charge carriers recombine, releasing energy in the form of photons. The specific composition of the semiconductor materials (the \"bandgap\") determines the wavelength (color) of the emitted light—in this case, green (~565-569 nm). The white bar housing acts as a diffuser and lens, shaping the light into a uniform rectangular beam.

13. Technology Trends and Context

The LTL-2550G represents an application-specific package type within the broader LED industry. Trends influencing such devices include:
Increased Efficiency: Ongoing material science improvements (like the use of AlInGaP mentioned) lead to higher luminous efficacy (more light per watt), allowing for either brighter output at the same current or the same output with lower power consumption and less heat.
Miniaturization & Integration: While this is a discrete component, the trend is towards integrating control logic and multiple LEDs into smarter, surface-mount modules.
Color Quality and Consistency: Advances in epitaxy and binning processes continue to improve the color uniformity and precision from batch to batch, which is critical for multi-unit applications as highlighted in the cautions section.
Reliability Focus: Datasheets increasingly provide detailed lifetime and lumen maintenance data under various conditions, though this specific datasheet focuses on basic ratings and handling.