LTD-2601JS LED Display Datasheet - 0.28-inch Digit Height - AlInGaP Yellow - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTD-2601JS is a dual-digit, seven-segment alphanumeric display module designed for applications requiring clear, bright numeric readouts. Its primary function is to visually represent numbers and some limited characters through individually addressable segments. The core technology utilizes AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material, specifically engineered to emit light in the yellow wavelength spectrum. This material choice offers advantages in efficiency and color purity compared to older technologies. The device features a gray faceplate with white segment markings, providing high contrast for optimal legibility under various lighting conditions. It is categorized as a common anode configuration, which is a standard design simplifying multiplexing in multi-digit applications.

1.1 Core Advantages and Target Market

The display boasts several key advantages that define its market position. Its 0.28-inch (7 mm) digit height offers a compact yet readable format, suitable for panel meters, instrumentation, consumer appliances, and industrial control interfaces where space is at a premium. The use of AlInGaP technology delivers high luminous intensity and excellent character appearance, ensuring visibility even in brightly lit environments. A wide viewing angle is another critical feature, allowing the display to be read accurately from various positions, which is essential for panel-mounted equipment. The device is also categorized for luminous intensity, meaning units are binned for consistent brightness, and it is offered in a lead-free package compliant with RoHS (Restriction of Hazardous Substances) directives, making it suitable for global markets with strict environmental regulations. The target market includes designers of test and measurement equipment, point-of-sale terminals, automotive dashboards (secondary displays), and household appliances requiring reliable, low-maintenance numeric indicators.

2. In-Depth Technical Parameter Analysis

A thorough understanding of the electrical and optical parameters is crucial for proper circuit design and ensuring long-term reliability.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. They are not for continuous operation.

• Power Dissipation per Segment: 70 mW. This is the maximum power that can be safely dissipated as heat by a single LED segment. Exceeding this limit risks thermal degradation of the semiconductor junction.
• Peak Forward Current per Segment: 60 mA. This is the maximum instantaneous current pulse a segment can handle, typically relevant for multiplexing schemes with high duty-cycle pulses.
• Continuous Forward Current per Segment: 25 mA at 25°C. This is the recommended maximum current for steady-state (DC) operation. A derating factor of 0.28 mA/°C is specified, meaning the maximum allowable continuous current decreases as ambient temperature (Ta) rises above 25°C to prevent overheating.
• Reverse Voltage per Segment: 5 V. Applying a reverse bias voltage higher than this can cause breakdown and damage the LED.
• Operating & Storage Temperature Range: -35°C to +105°C. The device is rated for operation and storage within this broad temperature range, suitable for most industrial and consumer environments.

2.2 Electrical & Optical Characteristics (at Ta=25°C)

These are the typical performance parameters under specified test conditions.

• Average Luminous Intensity (Iv): 200 (Min), 600 (Typ) µcd at a forward current (If) of 1 mA. This parameter, measured with a filter simulating the human eye response (CIE curve), quantifies the perceived brightness. The wide range indicates a binning system is used.
• Peak Emission Wavelength (λp): 588 nm (Typ) at If=20mA. This is the wavelength at which the optical power output is maximum, defining the yellow color.
• Spectral Line Half-Width (Δλ): 15 nm (Typ). This indicates the spectral purity; a narrower width means a more saturated, pure yellow color.
• Dominant Wavelength (λd): 587 nm (Typ). This is the single wavelength perceived by the human eye to match the LED's color, closely related to the peak wavelength.
• Forward Voltage per Segment (Vf): 2.05 (Min), 2.6 (Typ) V at If=20mA. This is the voltage drop across the LED when conducting. It is crucial for designing the current-limiting circuitry.
• Reverse Current per Segment (Ir): 100 µA (Max) at Vr=5V. This is the small leakage current when the LED is reverse-biased at its maximum rating.
• Luminous Intensity Matching Ratio: 2:1 (Max). This specifies the maximum allowable brightness variation between segments within the same digit or between digits, ensuring uniform appearance.
• Cross Talk: ≤2.5%. This parameter measures the unintended illumination of an adjacent segment when a neighboring segment is energized, caused by internal optical reflection or electrical leakage.

3. Binning System Explanation

The datasheet explicitly states the device is \"Categorized for Luminous Intensity.\" This implies a binning or sorting process post-manufacturing.

• Luminous Intensity Binning: The Iv specification shows a minimum of 200 µcd and a typical value of 600 µcd at 1mA. Units are tested and sorted into different intensity bins (e.g., high-brightness, standard-brightness). Designers can select a specific bin for applications requiring consistent brightness across multiple displays or production runs.
• Wavelength/Color Binning: While not explicitly detailed with multiple bins, the tight specifications for peak (588 nm) and dominant (587 nm) wavelength indicate tight process control. For critical color-matching applications, further wavelength sorting might be available as a custom option.
• Forward Voltage Binning: The Vf range (2.05V to 2.6V) suggests some natural variation. For designs sensitive to power supply voltage or aiming for precise current matching in multiplexed arrays, selecting LEDs from a tight Vf bin can be important.

4. Performance Curve Analysis

While the provided PDF excerpt mentions \"TYPICAL ELECTRICAL / OPTICAL CHARACTERISTIC CURVES,\" the specific graphs are not included in the text. Based on standard LED behavior, these curves would typically include:

• Current vs. Voltage (I-V) Curve: This graph would show the exponential relationship between forward current (If) and forward voltage (Vf). It is essential for determining the required drive voltage for a desired current and for designing constant-current drivers.
• Luminous Intensity vs. Forward Current (L-I Curve): This plot shows how light output increases with current. It is generally linear at lower currents but may saturate at higher currents due to thermal and efficiency droop. This curve helps optimize the drive current for the desired brightness and efficiency.
• Luminous Intensity vs. Ambient Temperature: This curve illustrates how light output decreases as the junction temperature rises. Understanding this derating is critical for applications operating in high-temperature environments.
• Spectral Distribution Curve: A plot of relative optical power versus wavelength, showing the peak at ~588 nm and the spectral half-width of ~15 nm, confirming the yellow color characteristics.

5. Mechanical & Package Information

5.1 Package Dimensions and Tolerances

The display conforms to a standard through-hole DIP (Dual In-line Package) format. Key dimensional notes from the datasheet include: all dimensions are in millimeters with a general tolerance of ±0.25 mm unless specified otherwise. The pin tip shift tolerance is ±0.4 mm, which is important for PCB hole placement. Specific quality controls are noted: foreign material on a segment must be ≤10 mils, ink contamination on the surface ≤20 mils, bending must be ≤1/100, and bubbles within the segment material must be ≤10 mils.

5.2 Pin Connection and Internal Circuit

The device has 10 pins in a single row. The internal circuit diagram shows it is a common anode type with two separate common anode pins (Pin 6 for Digit 2, Pin 9 for Digit 1). Each segment (A, B, C, D, E, F, G, and Decimal Point) has its own dedicated cathode pin. This configuration is standard for multiplexing: by sequentially enabling one common anode (digit) at a time and driving the appropriate cathode pins for that digit's segments, multiple digits can be controlled with a reduced number of I/O pins.

6. Soldering and Assembly Guidelines

The datasheet provides specific soldering conditions to prevent thermal damage during PCB assembly: \"Soldering Conditions: 1/16 inch below seating plane for 3 seconds at 260°C.\" This refers to wave soldering. The iron tip should be positioned 1.6mm (1/16\") below the plastic body of the display, and the contact time should not exceed 3 seconds at a maximum temperature of 260°C. This prevents the plastic housing from melting or the internal wire bonds from being damaged by excessive heat. For reflow soldering, the profile must not exceed the maximum temperature rating derived from the storage temperature (+105°C) plus a safety margin, though a specific reflow profile is not provided. Components should be stored in their original moisture-barrier bags in a controlled environment to prevent moisture absorption, which can cause \"popcorning\" during reflow.

7. Application Suggestions

7.1 Typical Application Circuits

The most common drive method is multiplexing. A microcontroller would use two I/O pins as digit selectors (sinking current for the common anodes via transistors) and 8 I/O pins (or a shift register) to sink current for the segment cathodes. A current-limiting resistor is required in series with each segment cathode or each common anode. The resistor value is calculated using R = (Vcc - Vf\_led) / I\_desired. Given Vf is typically 2.6V at 20mA, with a 5V supply, R = (5 - 2.6) / 0.02 = 120 Ohms. For multiplexed operation, the instantaneous current per segment can be higher (e.g., 20mA) but the average current, considering duty cycle, must stay within the continuous rating.

7.2 Design Considerations

• Current Limiting: Always use series resistors or constant-current drivers. Never connect an LED directly to a voltage source.
• Multiplexing Frequency: Use a refresh rate high enough to avoid visible flicker (typically >60 Hz per digit). The persistence of vision integrates the light.
• Viewing Angle: Position the display so the primary viewing direction is within the specified wide viewing angle for best contrast.
• ESD Protection: Although not explicitly stated, LEDs are sensitive to electrostatic discharge. Handle with ESD precautions during assembly.
• Heat Dissipation: In high-brightness or high-ambient-temperature applications, ensure the PCB layout allows for some heat dissipation from the LED package, especially if driving near the maximum continuous current.

8. Technical Comparison and Differentiation

Compared to older red GaAsP (Gallium Arsenide Phosphide) LED displays, the AlInGaP technology in the LTD-2601JS offers significantly higher luminous efficiency, resulting in brighter displays at the same current, or equivalent brightness at lower power. The yellow color (587-588 nm) is in a region of high sensitivity for the human photopic (daylight) vision, making it appear subjectively brighter than red or green LEDs of similar radiant power. Compared to contemporary side-glow or dot-matrix displays, the seven-segment format is simpler to drive and decode, offering lower system cost for pure numeric applications. Its through-hole package provides robust mechanical attachment compared to surface-mount alternatives, which is beneficial in applications subject to vibration.

9. Frequently Asked Questions (Based on Technical Parameters)

• Q: Can I drive this display with a 3.3V microcontroller? A: Yes. The typical Vf is 2.6V, so with a 3.3V supply, there is 0.7V headroom for a current-limiting resistor. The resistor value would be smaller: R = (3.3 - 2.6) / I\_desired. Ensure the desired current is achievable within the microcontroller's pin current sourcing/sinking capabilities.
• Q: What is the purpose of the derating factor for continuous current? A: The derating factor (0.28 mA/°C) accounts for reduced heat dissipation capability at higher ambient temperatures. At 85°C ambient, the maximum allowed continuous current is 25mA - [0.28mA/°C * (85°C-25°C)] = 25mA - 16.8mA = 8.2mA. Operating above this derated current risks exceeding the maximum junction temperature.
• Q: The datasheet mentions a \"Right Hand Decimal.\" What does this mean? A: This indicates the position of the decimal point segment. A \"Right Hand Decimal\" means the decimal point is located to the right of the digit, which is the standard convention for displaying fractional numbers (e.g., \"12.3\").
• Q: Is a heat sink required? A: For typical operation at or below 20mA per segment in a moderate ambient temperature, a dedicated heat sink is not required. The PCB itself acts as a heat spreader. However, for continuous operation at the absolute maximum ratings or in high-temperature environments, thermal management should be considered.

10. Practical Design and Usage Case

Case: Designing a Simple Digital Voltmeter Readout. A designer needs a two-digit display to show voltages from 0.0 to 9.9V for a benchtop power supply. The LTD-2601JS is selected for its readability and simple interface. The microcontroller's ADC reads the voltage, converts it to a decimal number, and looks up the 7-segment codes for the tens digit, units digit, and decimal point. Two NPN transistors are used to switch the common anode pins (Digits 1 & 2) to ground. Eight microcontroller I/O pins, each with a 120-ohm series resistor, are connected to the segment cathodes (A-G and DP). The firmware multiplexes the digits at 100 Hz. The gray face/white segment provides excellent contrast against the black panel of the power supply. The high brightness ensures it is visible in a well-lit lab. The lead-free compliance meets the company's environmental standards for new products.

11. Operating Principle Introduction

The fundamental principle is electroluminescence in a semiconductor P-N junction. The AlInGaP material is a direct bandgap semiconductor. When a forward voltage exceeding the junction's built-in potential (roughly equal to Vf) is applied, electrons from the N-region are injected across the junction into the P-region, and holes from the P-region move into the N-region. These injected minority carriers (electrons in the P-side, holes in the N-side) recombine with the majority carriers. In a direct bandgap material like AlInGaP, a significant portion of these recombinations are radiative, meaning they release energy in the form of photons (light). The specific energy of the photon, and thus its wavelength (color), is determined by the bandgap energy of the semiconductor material, which is engineered by the precise ratios of Aluminum, Indium, Gallium, and Phosphorus. The non-transparent GaAs substrate helps reflect light upward, increasing the forward luminous intensity. Each segment is a separate LED chip, and the combination of segments lit forms the desired numeral or character.

12. Technology Trends and Developments

While through-hole seven-segment displays like the LTD-2601JS remain relevant for prototyping, educational kits, and applications requiring robust mechanical mounting, the broader industry trend is decisively towards surface-mount device (SMD) packages. SMD LEDs offer smaller footprint, lower profile, suitability for automated pick-and-place assembly, and often better thermal performance via direct attachment to the PCB. For displays, integrated driver ICs are becoming more common, combining the LED array with scanning logic and sometimes even serial communication interfaces (like I2C or SPI), drastically reducing the microcontroller I/O and software overhead. In terms of materials, while AlInGaP is excellent for red, orange, and yellow, InGaN (Indium Gallium Nitride) dominates the blue, green, and white LED markets due to its wider bandgap tunability. For future displays, micro-LED and mini-LED technologies promise even higher density, brightness, and efficiency, though these are currently targeted at high-resolution video screens rather than simple segment displays. The enduring principle of the seven-segment format, however, ensures its utility in cost-sensitive, legibility-critical numeric applications for the foreseeable future.