LTD-5721AKF LED Display Datasheet - 0.56 Inch Digit Height - AlInGaP Yellow Orange - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTD-5721AKF is a high-performance, two-digit numeric LED display module designed for applications requiring clear, bright, and reliable numerical readouts. Its primary function is to provide visual numeric data in a compact and efficient package. The core advantage of this device lies in its utilization of advanced AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for the LED chips, which is known for producing high-efficiency light emission in the yellow-orange spectrum. This technology, combined with a specific chip construction on a non-transparent GaAs substrate, contributes to the display's key performance characteristics.

The device is categorized as a common anode type, which is a standard configuration for simplifying drive circuitry in multi-segment displays. It features a right-hand decimal point for each digit, providing flexibility for displaying fractional numbers. The physical design incorporates a gray faceplate with white segment color, a combination engineered to maximize contrast and improve character legibility under various lighting conditions. The 0.56-inch digit height (14.22 mm) makes it suitable for applications where information needs to be readable from a moderate distance without requiring excessively large components.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the stress limits beyond which permanent damage to the device may occur. Operating the display continuously at or near these limits is not recommended and will likely reduce its operational lifespan.

• Power Dissipation per Segment: 70 mW. This is the maximum power that can be safely dissipated as heat by an individual LED segment without causing damage.
• Peak Forward Current per Segment: 60 mA. This current rating applies under pulsed conditions (1 kHz frequency, 10% duty cycle), allowing for higher instantaneous brightness in multiplexed driving schemes.
• Continuous Forward Current per Segment: 25 mA at 25°C. This is the maximum recommended DC current for continuous operation of a single segment. A derating factor of 0.28 mA/°C is specified, meaning the maximum allowable continuous current decreases as the ambient temperature (Ta) rises above 25°C to prevent overheating.
• Reverse Voltage per Segment: 5 V. Applying a reverse voltage greater than this value can break down the LED's PN junction.
• Operating & Storage Temperature Range: -35°C to +105°C. The device is rated for industrial-grade temperature resilience.
• Soldering Conditions: Wave soldering at 260°C for 3 seconds maximum, with the condition that the body temperature of the unit does not exceed the maximum temperature rating. This is critical for assembly to prevent thermal damage to the plastic package and internal bonds.

2.2 Electrical & Optical Characteristics

These parameters are measured under standard test conditions (Ta = 25°C) and define the typical performance of the device.

• Average Luminous Intensity (I_V): 43.75 mcd (Min), 70 mcd (Typ) at I_F = 20 mA. This is a measure of the light output power as perceived by the human eye. The test condition was revised from 1 mA to 20 mA, indicating the standard operating current for brightness specification.
• Peak Emission Wavelength (λ_p): 611 nm (Typ). This is the wavelength at which the spectral power distribution of the emitted light is at its maximum.
• Spectral Line Half-Width (Δλ): 17 nm (Typ). This parameter indicates the spectral purity or bandwidth of the emitted light, measured as the full width at half maximum (FWHM) of the emission peak.
• Dominant Wavelength (λ_d): 605 nm (Typ). This is the single wavelength that best represents the perceived color of the light, calculated from the emission spectrum and the CIE color matching functions.
• Forward Voltage per Segment (V_F): 2.05 V (Min), 2.6 V (Typ) at I_F = 20 mA. This is the voltage drop across an LED segment when operating. Designers must ensure the driving circuit can provide this voltage.
• Reverse Current per Segment (I_R): 100 μA (Max) at V_R = 5 V. This is the small leakage current that flows when the specified reverse voltage is applied.
• Luminous Intensity Matching Ratio: 2:1 (Max) for similar light area. This specifies the maximum allowable ratio between the brightest and dimmest segments within a device when driven under identical conditions, ensuring visual uniformity.

Measurement Note: Luminous intensity values are measured using a sensor and filter combination designed to approximate the CIE photopic luminosity function, which models the spectral sensitivity of the standard human eye under normal (photopic) lighting conditions.

3. Binning System Explanation

The datasheet explicitly states that the device is "Categorized for Luminous Intensity." This indicates the presence of a binning or sorting process post-manufacturing. Due to inherent variations in the semiconductor epitaxial growth and chip fabrication processes, LED parameters like luminous intensity and forward voltage can vary from batch to batch and even within a batch.

The binning process involves testing each unit and sorting them into different groups (bins) based on specific measured parameters. For the LTD-5721AKF, the primary binning criterion is Average Luminous Intensity. Units are grouped according to their measured light output at the standard test current (20mA). This ensures that customers receive displays with consistent brightness levels. While not explicitly detailed in this brief datasheet, it is common for such displays to also be binned for forward voltage (V_F) to ensure electrical consistency, and potentially for dominant wavelength (λ_d) to maintain color consistency, although the narrow half-width suggests good intrinsic color purity.

4. Performance Curve Analysis

The datasheet references "Typical Electrical/Optical Characteristic Curves" on page 5. While the specific graphs are not provided in the text, we can infer their standard content and significance based on the listed parameters.

Typical curves for such a device would include:

• Forward Current vs. Forward Voltage (I-V Curve): This graph shows the non-linear relationship between the current flowing through the LED and the voltage across it. It is essential for designing the current-limiting circuitry. The curve will show a turn-on voltage (around 2V) after which current increases rapidly with a small increase in voltage.
• Luminous Intensity vs. Forward Current (I-L Curve): This plot demonstrates how light output increases with drive current. It is generally linear over a range but will saturate at very high currents due to thermal and efficiency droop effects. The curve validates the 20mA test point for the intensity specification.
• Luminous Intensity vs. Ambient Temperature: This curve shows the derating of light output as the junction temperature of the LED increases. AlInGaP LEDs are known to have a temperature-dependent efficiency, with output typically decreasing as temperature rises. This informs design for thermal management.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the peak at ~611 nm and the ~17 nm half-width, confirming the monochromatic yellow-orange emission.

5. Mechanical & Package Information

5.1 Package Dimensions

The device comes in a standard LED display package. The dimensional drawing provides critical measurements for PCB (Printed Circuit Board) footprint design and mechanical integration. Key notes from the drawing include:

• All linear dimensions are specified in millimeters (mm).
• The default tolerance for dimensions is ±0.25 mm unless a specific note states otherwise.
• A specific tolerance for pin tip shift is given as ±0.4 mm, which is important for ensuring the pins align correctly with PCB holes during automated insertion.

5.2 Pin Connection & Internal Circuit

The device has 18 pins in a dual-in-line package configuration. The internal circuit diagram and pin connection table are crucial for correct electrical interfacing.

• Circuit Type: Common Anode. This means the anode terminals of all LED segments for each digit are connected together internally. To illuminate a segment, its corresponding cathode pin must be driven low (connected to ground or a current sink) while the common anode for that digit is driven high (connected to the positive supply via a current-limiting resistor).
• Pinout: The detailed table maps each pin number to its function: cathode for specific segments (A-G, DP) of digit 1 or digit 2, or the common anode for each digit. For example, Pin 1 is the cathode for segment 'E' of Digit 1, and Pin 14 is the common anode for Digit 1. This precise mapping is essential for creating the correct drive sequence in the microcontroller or driver IC software.

6. Soldering & Assembly Guidelines

Proper handling during assembly is critical to reliability. The datasheet provides specific soldering parameters.

• Wave Soldering: The recommended condition is 260°C for a maximum of 3 seconds. The note "1/16 inch below seating plane" likely refers to the depth to which the pins should be immersed in the solder wave.
• Critical Condition: The most important caveat is that "the temperature of the unit (during assembly) [must] not over max. temperature rating." This means the body temperature of the LED display package itself must never exceed the maximum storage temperature of 105°C during the entire soldering process, including pre-heat and post-heat phases. Failure to adhere to this can cause internal delamination, lens cracking, or degradation of the LED chips.
• General Handling: Standard ESD (Electrostatic Discharge) precautions should be observed, as LED chips are sensitive to static electricity.

7. Application Recommendations

7.1 Typical Application Scenarios

The LTD-5721AKF is suited for a wide range of industrial, commercial, and instrumentation applications where a compact, bright, and reliable numeric display is required. Examples include:

• Test and Measurement Equipment: Digital multimeters, frequency counters, power supplies, sensor readouts.
• Industrial Controls: Panel meters for temperature, pressure, speed, or count displays on machinery.
• Consumer Appliances: Advanced kitchen appliances, audio equipment tuners, older model digital clocks or timers.
• Automotive Aftermarket: Gauges and display modules (though environmental specs should be verified for specific automotive requirements).

7.2 Design Considerations

• Current Limiting: LEDs are current-driven devices. A series current-limiting resistor must be used for each common anode connection (or per segment in more advanced constant-current driver designs) to set the operating current to 20 mA or less, as per the derating guidelines. The resistor value is calculated using R = (V_supply - V_F - V_{driver_sat}) / I_F.
• Multiplexing: For a two-digit display, multiplexing is the standard driving technique. The digits are illuminated one at a time in rapid succession (e.g., at a frequency >100 Hz). This requires controlling the common anode pins (digits) and the cathode pins (segments) sequentially. This method reduces the number of required driver pins and overall power consumption.
• Viewing Angle: The datasheet claims a "wide viewing angle," which is typical for LED displays with a diffused lens or face. This should be considered for the mechanical placement of the display in the end product.
• Thermal Management: While the device can operate up to 105°C, luminous efficiency decreases with temperature. For optimal brightness and longevity, providing adequate ventilation or heat sinking in the design is advisable, especially if operating near maximum current or in high ambient temperatures.

8. Technical Comparison & Differentiation

The key differentiating factors of the LTD-5721AKF compared to other numeric LED displays, particularly older technologies, include:

• AlInGaP Technology vs. Traditional GaAsP or GaP: AlInGaP LEDs offer significantly higher luminous efficiency and brightness for red, orange, and yellow colors compared to older semiconductor materials. This results in better visibility and/or lower power consumption for the same perceived brightness.
• Gray Face/White Segments: The specific color combination of the face and segments is engineered for high contrast. A gray face absorbs more ambient light than a black face, reducing reflections, while the white segment areas help diffuse the emitted yellow-orange light evenly, improving character appearance.
• Lead-Free Package (RoHS Compliance): The device is constructed to meet the Restriction of Hazardous Substances (RoHS) directive, making it suitable for products sold in markets with strict environmental regulations. This is a critical compliance differentiator.
• Solid-State Reliability: As with all LEDs, it offers advantages over mechanical displays (like flip-discs) or vacuum fluorescent displays (VFDs) in terms of shock/vibration resistance, instant-on capability, and long operational life.

9. Frequently Asked Questions (Based on Technical Parameters)

Q1: What is the purpose of the "Luminous Intensity Matching Ratio" of 2:1?
A1: This ratio ensures visual consistency. It guarantees that within a single display unit, no segment will be more than twice as bright as any other segment when driven under identical electrical conditions. This prevents uneven or "patchy" looking numbers.

Q2: Can I drive this display with a 5V supply?
A2: Yes, a 5V supply is very common. However, you must use a current-limiting resistor in series with each common anode. Using the typical V_F of 2.6V and a target I_F of 20 mA, the resistor value would be approximately (5V - 2.6V) / 0.02A = 120 Ohms. A standard 120Ω or 150Ω resistor would be suitable, adjusting for actual V_F and desired brightness.

Q3: What does "Common Anode" mean for my circuit design?
A3: In a common anode configuration, you supply positive voltage to the common pin of the digit you want to activate. You then sink current to ground through the cathode pins of the segments you wish to light on that digit. Your driving circuit (microcontroller or driver IC) must be configured to source current for the anodes and sink current for the cathodes.

Q4: Why is the Peak Wavelength (611nm) different from the Dominant Wavelength (605nm)?
A4: This is normal for LEDs. The peak wavelength is the literal highest point on the emission spectrum curve. The dominant wavelength is calculated from the entire spectrum and the human eye's color response; it's the single wavelength of pure light that would appear to have the same color. The difference accounts for the shape and asymmetry of the LED's actual emission spectrum.

10. Design and Usage Case Study

Scenario: Designing a Simple Digital Voltmeter Readout.
A designer is creating a 0-20V DC voltmeter. The analog-to-digital converter (ADC) outputs a binary-coded decimal (BCD) value. This BCD data needs to be converted to 7-segment format and displayed on two digits (e.g., 19.99V).

Implementation:
1. A microcontroller with sufficient I/O pins (or a dedicated BCD-to-7-segment decoder/driver IC) is used.
2. The microcontroller's I/O pins are connected to the segment cathodes (A-G, DP) of the LTD-5721AKF.
3. Two additional microcontroller pins are connected to the two common anodes (Digit 1 & Digit 2).
4. In software, a multiplexing routine is written. It first calculates which segments to light for Digit 1 (tens place), enables (sets high) the Digit 1 anode pin, and sets the corresponding segment cathode pins low. After a short delay (e.g., 5ms), it disables Digit 1, calculates the segments for Digit 2 (units place), enables the Digit 2 anode, and sets its segment pins low. This cycle repeats rapidly.
5. Current-limiting resistors (e.g., 150Ω) are placed on the common anode lines between the microcontroller pins and the display. The value is chosen based on the supply voltage (e.g., 5V) and the desired segment current (~20mA).
6. The gray face/white segment design ensures the displayed voltage is easily readable under the bright lighting conditions of a workshop bench.

11. Technology Principle Introduction

The core light-emitting component is an AlInGaP LED chip. AlInGaP is a III-V compound semiconductor. By precisely controlling the ratios of Aluminum (Al), Indium (In), Gallium (Ga), and Phosphorus (P) during the crystal growth process (typically via Metal-Organic Chemical Vapor Deposition - MOCVD), engineers can tune the bandgap of the material. The bandgap energy directly determines the wavelength (color) of the photons emitted when electrons recombine with holes across the junction.

In the LTD-5721AKF, the composition is tuned for emission in the yellow-orange region (~605-611 nm). The chips are fabricated on a non-transparent Gallium Arsenide (GaAs) substrate. The "gray face" of the display is part of the plastic package molding, which includes a diffuser to spread the light from the small chip across the larger segment area uniformly. The internal circuit uses wire bonding to connect the anodes and cathodes of the multiple LED chips (one per segment per digit) to the appropriate package pins, forming the common anode matrix described in the pinout.

12. Technology Trends

While discrete LED numeric displays like the LTD-5721AKF remain relevant for specific applications, broader trends in display technology have shifted. For new designs, designers often consider:

• Integrated Dot-Matrix LED Displays: These offer alphanumeric and symbolic capability beyond just numbers, providing greater flexibility in a similar footprint.
• OLED (Organic LED) Displays: Offer superior contrast, wider viewing angles, and thinner form factors, though historically with different lifetime and cost profiles for industrial use.
• TFT-LCD Modules: Provide full graphics capability, color, and the ability to display complex information, though they require more complex driving electronics and a backlight.
• Trends within LED Displays: Continued improvement in efficiency (lumens per watt) for all LED colors, the development of even more robust and temperature-resistant packages, and the integration of driver electronics directly into the display module to simplify system design.

The enduring value of devices like the LTD-5721AKF lies in their simplicity, robustness, high brightness, low cost for numeric-only applications, and ease of interface with microcontrollers, ensuring their place in the electronics ecosystem for dedicated readout functions.