LTD-5721AJF LED Display Datasheet - 0.56-inch Digit Height - AlInGaP Yellow Orange - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTD-5721AJF 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 alphanumeric characters using individually addressable LED segments. The core technology utilizes Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor material deposited on a non-transparent Gallium Arsenide (GaAs) substrate to produce its characteristic yellow-orange light emission. This device features a gray faceplate with white segment markings, which enhances contrast and readability when the segments are illuminated or unlit. The display is categorized based on luminous intensity, ensuring consistency in brightness levels for applications where uniform appearance across multiple units is critical.

1.1 Core Advantages and Target Market

The display offers several key benefits that make it suitable for a range of industrial and consumer applications. Its high brightness and excellent contrast ratio ensure legibility even in brightly lit environments. The wide viewing angle allows the displayed information to be read from various positions without significant loss of clarity. As a solid-state device, it offers high reliability, long operational life, and resistance to shock and vibration compared to mechanical or older display technologies like vacuum fluorescent displays (VFDs). The low power requirement makes it energy-efficient. These features make the LTD-5721AJF ideal for target markets including test and measurement equipment, industrial control panels, point-of-sale terminals, automotive dashboard instrumentation, and various consumer electronics where reliable numeric display is needed.

2. Technical Parameter Deep-Dive

This section provides an objective analysis of the key electrical and optical parameters specified in the datasheet, explaining their significance for design engineers.

2.1 Absolute Maximum Ratings

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

• Power Dissipation per Segment: 70 mW. This is the maximum allowable power that can be dissipated as heat by a single LED segment under any condition. Exceeding this can lead to overheating and accelerated degradation of the LED chip.
• Peak Forward Current per Segment: 60 mA (at 1/10 duty cycle, 0.1 ms pulse width). This rating is for brief, pulsed operation, often used in multiplexing schemes to achieve higher perceived brightness without exceeding the average current limit.
• Continuous Forward Current per Segment: 25 mA (derated linearly from 25°C at 0.33 mA/°C). This is the maximum DC current recommended for continuous operation at 25°C. The derating factor indicates that the safe operating current must be reduced as the ambient temperature (Ta) increases to prevent thermal runaway.
• Reverse Voltage per Segment: 5 V. Applying a reverse bias voltage higher than this can cause breakdown and failure of the LED junction.
• Operating & Storage Temperature Range: -35°C to +85°C. The device is rated to function and be stored within this temperature range.
• Solder Temperature: 260°C for 3 seconds, measured 1/16 inch below the seating plane. This defines the reflow soldering profile conditions to avoid damaging the package or internal bonds.

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

These are the typical performance parameters under specified test conditions.

• Average Luminous Intensity (I_V): 320 - 900 µcd (Typical 900 µcd) at I_F=1mA. This measures the light output power as perceived by the human eye. The range indicates a binning process; designers must account for the minimum value (320 µcd) to ensure sufficient brightness in their application.
• Peak Emission Wavelength (λ_p): 611 nm (Typical) at I_F=20mA. This is the wavelength at which the spectral power distribution of the emitted light is maximum. It defines the perceived color (yellow-orange).
• Spectral Line Half-Width (Δλ): 17 nm (Typical) at I_F=20mA. This parameter indicates the spectral purity or bandwidth of the emitted light. A smaller value means a more monochromatic (pure color) output.
• Dominant Wavelength (λ_d): 605 nm (Typical) at I_F=20mA. This is the single wavelength that best matches the perceived color of the LED by the human eye, often used for color specification.
• Forward Voltage per Segment (V_F): 2.05 - 2.6 V (Typical 2.6V) at I_F=20mA. This is the voltage drop across the LED when operating. It is crucial for designing the current-limiting circuitry. The maximum value (2.6V) should be used for worst-case design to ensure sufficient drive voltage.
• Reverse Current per Segment (I_R): 100 µA (Max) at V_R=5V. This is the small leakage current that flows when the LED is reverse-biased within its maximum rating.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 (Max). This specifies the maximum allowable ratio between the brightest and dimmest segment within a single device or between devices from the same bin. A ratio of 2:1 means the dimmest segment can be no less than half as bright as the brightest, ensuring visual uniformity.

3. Binning System Explanation

The datasheet indicates the device is \"categorized for luminous intensity.\" This refers to a binning or sorting process performed during manufacturing.

3.1 Luminous Intensity Binning

Due to inherent variations in semiconductor manufacturing, LED chips from the same production batch can have different light outputs. To ensure consistency for customers, LEDs are tested and sorted into groups (bins) based on their measured luminous intensity at a standard test current (e.g., 1mA). The LTD-5721AJF's specified range of 320 to 900 µcd likely represents the spread across multiple bins. A specific order code or suffix in the full part number would typically indicate the purchased bin, guaranteeing the intensity falls within a narrower, predefined range (e.g., 700-900 µcd). Designers must consult the manufacturer's binning documentation or specify the required bin when ordering to guarantee brightness consistency in their product.

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 illustrate the following relationships, which are critical for understanding device performance under non-standard conditions:

• Forward Current (I_F) vs. Forward Voltage (V_F): Shows the exponential I-V characteristic of the diode. Important for determining the necessary drive voltage for a desired current.
• Luminous Intensity (I_V) vs. Forward Current (I_F): Generally shows a near-linear relationship at lower currents, potentially saturating at very high currents due to thermal effects. Essential for brightness control via current modulation or PWM.
• Luminous Intensity (I_V) vs. Ambient Temperature (T_a): Typically shows a decrease in light output as temperature increases. This thermal derating must be considered for applications operating in high-temperature environments.
• Spectral Distribution: A graph plotting relative intensity against wavelength, showing the peak at ~611 nm and the shape defined by the half-width of 17 nm.

5. Mechanical & Package Information

5.1 Package Dimensions

The device features a standard dual-digit seven-segment LED package. The drawing (referenced but not detailed in text) would show the overall length, width, and height of the module, the digit height (0.56 inch / 14.22 mm), the segment dimensions, and the spacing between digits. It would also specify the location and diameter of the mounting holes, if any. Tolerances are typically ±0.25 mm unless otherwise noted on the drawing.

5.2 Pin Connection and Polarity

The LTD-5721AJF has an 18-pin configuration and uses a Common Anode circuit architecture. This means the anodes of all LEDs for each digit are connected together internally to a common pin (Pin 13 for Digit 2, Pin 14 for Digit 1). To illuminate a segment, its corresponding cathode pin must be driven to a low logic level (ground or a current sink) while the common anode for that digit is held at a positive voltage (through a current-limiting resistor). The pinout list provides the specific cathode connection for each segment (A-G and DP) for both digits. Correct identification of pin 1 (often marked by a notch, bevel, or dot on the package) is crucial for proper orientation during assembly.

5.3 Internal Circuit Diagram

The schematic (referenced in the PDF) visually represents the common anode structure. It shows two blocks (one for each digit), each containing seven segment LEDs (A-G) and one decimal point (DP) LED. All anodes within a digit block are tied together to the common anode pin for that digit. The cathodes of each individual segment are brought out to separate pins, allowing independent control.

6. Soldering & Assembly Guidelines

The Absolute Maximum Ratings specify a key soldering parameter: the package can withstand a peak temperature of 260°C for 3 seconds, measured at a point 1/16 inch (approximately 1.6 mm) below the seating plane (typically the PCB surface). This is a standard rating for wave or reflow soldering processes using lead-free (SnAgCu) solder. Designers should ensure their reflow oven profile does not exceed this time-temperature combination to avoid damaging the plastic package, internal wire bonds, or the LED chips themselves. Standard ESD (Electrostatic Discharge) precautions should be observed during handling and assembly. Storage should be within the specified -35°C to +85°C range in a low-humidity environment.

7. Application Suggestions

7.1 Typical Application Circuits

For a common anode display like the LTD-5721AJF, a typical drive circuit involves using a microcontroller or dedicated display driver IC. The common anode pins (13, 14) are connected to a positive supply voltage (e.g., 5V) through individual current-limiting resistors or via transistor switches if multiplexing. The segment cathode pins (1-12, 15-18) are connected to the sink outputs of the driver. The current for each segment must be limited to the Continuous Forward Current rating (25 mA max, typically operated at 10-20 mA for balance of brightness and longevity). The forward voltage drop (max 2.6V) must be subtracted from the supply voltage to calculate the appropriate current-limiting resistor value: R = (V_supply - V_F) / I_F.

7.2 Design Considerations

• Multiplexing: To control two digits with fewer I/O pins, a multiplexing technique is used. The digits are illuminated one at a time in rapid succession (e.g., at 100Hz or higher). The human eye perceives this as both digits being constantly on. This requires driving the common anodes with a switching signal and synchronizing the segment data for each digit. The peak current per segment can be increased during its brief on-time (up to the 60mA peak rating) to compensate for the reduced duty cycle and maintain average brightness.
• Heat Management: While power dissipation is low per segment, the total power for all illuminated segments in a digit can add up. Ensure adequate ventilation if the display is enclosed, especially in high ambient temperatures, to prevent the junction temperature from exceeding safe limits.
• Viewing Angle: The wide viewing angle is an advantage, but the mechanical design of the product enclosure (e.g., depth of the display window, use of filters or lenses) can affect the effective viewing angle for the end-user.

8. Technical Comparison & Differentiation

The primary differentiator of the LTD-5721AJF is its use of AlInGaP semiconductor technology for yellow-orange emission. Compared to older technologies like standard Gallium Phosphide (GaP) yellow LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in greater brightness for the same drive current. It also generally provides better color saturation and stability over temperature and lifetime. Compared to displays that use filtered light (e.g., a white LED with a color filter), AlInGaP provides a purer spectral output and higher efficiency, as no light is lost in the filtering process. The gray face/white segment design offers a professional, high-contrast appearance whether powered on or off, which can be preferable to green or red faceplates in certain applications.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the difference between Peak Emission Wavelength and Dominant Wavelength?
A: Peak wavelength is the physical peak of the light spectrum emitted. Dominant wavelength is the single wavelength of monochromatic light that would appear to have the same color to a human observer. They are often close but not identical, especially for LEDs with asymmetric spectral curves. Dominant wavelength is more relevant for color matching.

Q: Can I drive this display with a 3.3V microcontroller without a level shifter?
A: Possibly, but careful calculation is needed. If the microcontroller's I/O pins can sink the required segment current (e.g., 10-20mA), and you use a 3.3V supply for the common anode, the forward voltage drop (max 2.6V) leaves only 0.7V for the current-limiting resistor. This results in a very small resistor value (e.g., 35 ohms for 20mA), which may be impractical and sensitive to variations in V_F. A 5V supply for the anodes is more typical and provides better headroom for stable current control.

Q: What does \"Luminous Intensity Matching Ratio 2:1\" mean for my design?
A: It means that within one display unit, the dimmest segment could be half as bright as the brightest segment. If absolute uniformity is critical (e.g., in medical equipment), you should select devices from a tighter bin or implement software brightness calibration for each segment, which is complex. For many applications, a 2:1 ratio is acceptable and not visually distracting.

10. Practical Use Case Example

Scenario: Designing a simple digital timer/stopwatch.
The LTD-5721AJF is an excellent choice for displaying minutes and seconds (MM:SS). A low-cost microcontroller can be used to manage timekeeping and drive the display. The two digits would be multiplexed. The common anode for the \"minutes\" digit and the \"seconds\" digit would be connected to two separate GPIO pins configured as outputs, switched high (through a transistor for higher current capability) one at a time. The seven segment cathode lines (A-G) would be connected to seven other GPIO pins configured as open-drain or actively driven low, with a series resistor on each line (or a single resistor on the common anode path if brightness uniformity is less critical). The microcontroller software updates the segment pattern for the active digit, then rapidly switches to the other digit. The yellow-orange color is often associated with caution or attention, making it suitable for a timer display. The high brightness ensures it's visible in various lighting conditions.

11. Operating Principle Introduction

The device operates on the principle of electroluminescence in a semiconductor p-n junction. The AlInGaP material system has a direct bandgap corresponding to photon energies in the yellow-orange region of the visible spectrum (~2.0 eV). When a forward bias voltage exceeding the junction's built-in potential is applied (the forward voltage V_F), electrons from the n-type region and holes from the p-type region are injected across the junction. When these charge carriers recombine in the active region of the semiconductor, they release energy in the form of photons (light). The specific alloy composition of Aluminum, Indium, Gallium, and Phosphide determines the bandgap energy and thus the color (wavelength) of the emitted light. The non-transparent GaAs substrate absorbs any light emitted downward, making the device more efficient in the intended viewing direction.

12. Technology Trends

While AlInGaP remains a high-performance technology for red, orange, and yellow LEDs, the broader display technology landscape continues to evolve. For seven-segment numeric displays, trends include: 1) Higher Integration: Modules with built-in driver ICs, controllers, and even communication interfaces (I2C, SPI) are becoming more common, simplifying system design. 2) Alternative Technologies: Organic LED (OLED) segments offer ultra-thin profiles and wide viewing angles, though lifetime and cost can be factors. 3) Miniaturization & Density: While 0.56-inch is a standard size, there is demand for both smaller (for portable devices) and larger, higher-brightness displays. 4) Color Options & RGB: Multi-color or full-color seven-segment displays using RGB LED chips allow for dynamic color changing, though they require more complex drive electronics. The fundamental advantages of LED technology—reliability, efficiency, and solid-state robustness—ensure its continued relevance in numeric display applications for the foreseeable future.