LTC-4724JF LED Display Datasheet - 0.4-inch Digit Height - Yellow-Orange Color - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTC-4724JF is a compact, high-performance triple-digit seven-segment LED display module. Its primary function is to provide clear, bright numeric readouts in various electronic devices and instrumentation. The device is built using advanced AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology, which is known for producing high-efficiency light emission in the yellow-orange spectrum. This specific material choice results in excellent luminous intensity and color purity. The display features a gray face with white segment markings, creating a high-contrast appearance that enhances readability under different lighting conditions. It is designed as a multiplex common cathode type, which is a standard configuration for multi-digit displays to minimize the number of required driver pins.

1.1 Key Features and Advantages

The LTC-4724JF offers several distinct advantages for designers and engineers:

• Compact Size with High Legibility: The 0.4-inch (10.0 mm) digit height provides a good balance between space-saving design and clear visibility, making it suitable for panel meters, test equipment, and consumer electronics where front-panel space is limited.
• Superior Optical Performance: The use of AlInGaP chips delivers high brightness and excellent contrast. The continuous, uniform segments ensure a consistent and professional character appearance without gaps or dim spots.
• Energy Efficiency: It has a low power requirement, which is beneficial for battery-powered or energy-conscious applications. The typical forward voltage is relatively low, reducing the overall power consumption of the display subsystem.
• Wide Viewing Angle: The display maintains good visibility over a broad angle, ensuring the readout can be seen from various positions, which is critical for panel-mounted equipment.
• High Reliability: As a solid-state device, it offers long operational life and robustness against vibration and shock compared to mechanical displays.
• Quality Assurance: The devices are categorized (binned) for luminous intensity. This means units are sorted based on their measured light output, allowing designers to select consistent brightness levels for their applications, preventing uneven illumination in multi-display setups.
• Environmental Compliance: The package is lead-free, complying with the RoHS (Restriction of Hazardous Substances) directive, making it suitable for use in products sold in markets with strict environmental regulations.

2. Technical Specifications and In-Depth Interpretation

This section provides a detailed analysis of the electrical and optical parameters that define the performance boundaries and operating conditions of the LTC-4724JF.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed.

• 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 can lead to overheating and accelerated degradation of the semiconductor junction.
• Peak Forward Current per Segment: 90 mA (under pulsed conditions: 1/10 duty cycle, 0.1ms pulse width). This rating is for short-duration pulses, often used in multiplexing schemes to achieve higher peak brightness.
• Continuous Forward Current per Segment: 25 mA at 25°C. This is the maximum DC current recommended for continuous operation. The datasheet specifies a derating factor of 0.33 mA/°C above 25°C. For example, at an ambient temperature (Ta) of 65°C, the maximum allowable continuous current would be: 25 mA - [ (65°C - 25°C) * 0.33 mA/°C ] = 25 mA - 13.2 mA = 11.8 mA. This derating is crucial for thermal management and long-term reliability.
• Operating & Storage Temperature Range: -35°C to +85°C. The device is rated for industrial temperature ranges, suitable for environments outside typical office conditions.
• Soldering Condition: 260°C for 3 seconds, measured 1/16 inch (approx. 1.6 mm) below the seating plane. This guides the reflow soldering profile for PCB assembly.

2.2 Electrical & Optical Characteristics (Typical at 25°C)

These are the typical performance parameters under specified test conditions, representing the expected behavior of the device.

• Average Luminous Intensity (I_V): 200 to 650 µcd (microcandelas) at I_F=1mA. This wide range indicates the binning process. The minimum is 200 µcd, but typical units will be brighter. The test current of 1mA is a standard low-current condition for comparing brightness.
• Peak Emission Wavelength (λ_p): 611 nm. This is the wavelength at which the spectral output of the LED is at its maximum intensity. It defines the perceived "yellow-orange" color.
• Spectral Line Half-Width (Δλ): 17 nm. This measures the spread of the emitted light's wavelengths. A value of 17 nm indicates a relatively narrow, pure color emission, which is characteristic of AlInGaP technology.
• Dominant Wavelength (λ_d): 605 nm. This is the single wavelength that best represents the perceived color of the light to the human eye, slightly different from the peak wavelength.
• Forward Voltage per Segment (V_F): 2.05V to 2.6V at I_F=20mA. This is a critical parameter for driver design. The driver circuit must be able to provide at least 2.6V to ensure the desired 20mA current flows through all segments, even those at the high end of the V_F distribution.
• Reverse Current (I_R): 100 µA maximum at V_R=5V. This specifies the maximum leakage current when the LED is reverse-biased. While small, it confirms the diode's blocking characteristic.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 maximum at I_F=10mA. This is the maximum allowable ratio between the brightest and dimmest segment within a single digit or between identical segments on different digits. A ratio of 2:1 ensures visual uniformity.

3. Binning System Explanation

The LTC-4724JF employs a binning system primarily for Luminous Intensity. As indicated by the I_V range (200-650 µcd), units are tested and sorted into different bins based on their light output at a standard test current (1mA). This allows customers to:

• Ensure Consistency: For applications using multiple displays (e.g., a multi-digit instrument), ordering parts from the same intensity bin guarantees that all digits will have matched brightness, preventing an uneven, patchy appearance.
• Select for Application Needs: A design requiring very high brightness might specify units from a higher-intensity bin, while a power-sensitive design might use a lower bin.

The datasheet does not explicitly mention separate bins for wavelength (color) or forward voltage for this specific part number, implying that the AlInGaP process yields sufficiently tight control on these parameters, or they are included within the primary intensity binning.

4. Performance Curve Analysis

While the specific graphs are not detailed in the provided text, typical curves for such a device would include:

• Current vs. Forward Voltage (I-V Curve): Shows the exponential relationship. The curve will have a "knee" around the typical V_F (2.05-2.6V). Driving with a constant current, as recommended, ensures stable brightness regardless of minor V_F variations.
• Luminous Intensity vs. Forward Current (I_V vs. I_F): Generally shows a near-linear relationship at lower currents, potentially saturating at very high currents. This graph helps determine the drive current needed to achieve a target brightness.
• Luminous Intensity vs. Ambient Temperature: Shows how light output decreases as temperature increases. This is vital for designing systems that operate in high-temperature environments, as drive current may need to be increased (within ratings) to compensate.
• Spectral Distribution: A plot of relative intensity vs. wavelength, centered around 611 nm with a width of 17 nm at half the peak intensity (FWHM).

5. Mechanical and Package Information

5.1 Package Dimensions

The LTC-4724JF comes in a standard through-hole DIP (Dual In-line Package) format. The drawing (referenced on page 3) provides all critical dimensions including overall length, width, height, digit spacing, lead spacing (pitch), and lead diameter. The note specifies that all dimensions are in millimeters with a standard tolerance of ±0.25 mm unless otherwise stated. This information is essential for PCB footprint design, panel cutout sizing, and ensuring proper mechanical fit within the end product.

5.2 Pin Connection and Internal Circuit

The device has a 14-pin configuration (with some pins marked "NO PIN"). The internal circuit diagram (page 4) reveals a multiplexed common cathode architecture:

• Common Cathodes: Pins 1, 5, and 7 are the cathodes for Digit 1, Digit 2, and Digit 3, respectively. Pin 14 is a common cathode for the three right-hand decimal points (L1, L2, L3).
• Segment Anodes: The anodes for the seven main segments (A, B, C, D, E, F, G) and the decimal points are brought out to individual pins (e.g., Pin 12 = Segment A, Pin 2 = Segment E).

To illuminate a specific segment on a specific digit, the corresponding segment anode pin must be driven high (with a current-limiting resistor), and the cathode pin for that digit must be pulled low (grounded). This multiplexing technique allows 3 digits and their segments to be controlled with only 14 pins instead of 24+ pins if each segment were independently wired.

6. Soldering, Assembly, and Storage Guidelines

6.1 Soldering and Assembly

• Reflow Soldering: Follow the specified condition: 260°C for 3 seconds. This should be integrated into a standard lead-free reflow profile.
• Mechanical Stress: Avoid applying abnormal force to the display body during assembly. Use suitable tools to prevent cracking the epoxy package or damaging the internal wire bonds.
• Condensation: Avoid rapid temperature changes in humid environments to prevent condensation from forming on the display, which could cause electrical shorts or corrosion.
• Film Application: If using a decorative film or filter, note that pressure-sensitive adhesive is used. Avoid letting the film side press directly against a front panel, as external force may shift it.

6.2 Storage Conditions

Proper storage is critical to prevent oxidation of the tin-plated leads, which can cause poor solderability.

• For Through-Hole Displays (LTC-4724JF): Store in original packaging at 5°C to 30°C and below 60% RH. If the moisture barrier bag is opened for more than 6 months, bake at 60°C for 48 hours before use and assemble within one week.
• General Principle: Consume inventory promptly. Long-term storage of large quantities is discouraged. If pins appear oxidized, re-tinning may be required before assembly.

7. Application Suggestions and Design Considerations

7.1 Typical Application Scenarios

The LTC-4724JF is ideal for applications requiring clear, reliable numeric displays, such as:

• Digital panel meters (voltage, current, temperature)
• Test and measurement equipment
• Industrial control system readouts
• Consumer appliances (microwaves, scales, audio equipment)
• Medical devices (where exceptional reliability is not the sole responsibility of this component - see Cautions)

7.2 Critical Design Considerations

• Driver Circuit Design:
  • Constant Current Drive: Highly recommended over constant voltage drive. It ensures consistent segment brightness regardless of V_F variations and provides inherent protection against thermal runaway.
  • Current Limiting Resistors: If using a simple resistor-based drive, calculate the resistor value based on the supply voltage (V_CC), the maximum expected V_F (2.6V), and the desired I_F. Example: For V_CC=5V and I_F=10mA, R = (5V - 2.6V) / 0.01A = 240Ω. Use the next standard value (e.g., 240Ω or 220Ω).
  • Voltage Headroom: The driver (microcontroller pin or dedicated IC) must be able to source enough voltage to overcome the highest V_F in the circuit. A 3.3V system might struggle with segments at 2.6V V_F after accounting for driver saturation voltage.
  • Reverse Voltage Protection: The circuit should prevent reverse bias across the LEDs during power-up/down sequences. This can be achieved with careful power sequencing or by adding a protection diode in parallel with the display (reverse-biased during normal operation).
• Thermal Management: Adhere to the current derating curve. In high ambient temperature environments, reduce the drive current or improve ventilation to keep the LED junction temperature within safe limits.
• Multiplexing Driver: Use a dedicated display driver IC or microcontroller with multiplexing support. Ensure the scanning frequency is high enough (typically >60Hz) to avoid visible flicker. The peak pulse current can be higher than the DC rating (as per the 90mA rating) to maintain average brightness.

8. Technical Comparison and Differentiation

Compared to older technologies like standard GaP (Gallium Phosphide) or GaAsP (Gallium Arsenide Phosphide) red/yellow LEDs, the AlInGaP technology in the LTC-4724JF offers:

• Higher Efficiency and Brightness: More light output per milliamp of current.
• Better Color Saturation: Narrower spectral width (17 nm) for a purer, more defined yellow-orange color.
• Superior Temperature Stability: AlInGaP generally maintains its brightness and color better over temperature ranges than older technologies.

Compared to white LEDs with filters, it offers a simpler, more efficient solution when a specific monochromatic output is desired.

9. Frequently Asked Questions (Based on Technical Parameters)

• Q: Can I drive this display directly from a 5V microcontroller pin? A: Possibly, but with caution. You must use a current-limiting resistor. Calculate the value based on the pin's output high voltage (which may be less than 5V) and the LED's V_F. Ensure the microcontroller pin can sink/source the required current (e.g., 10-20mA per segment), which may exceed the pin's maximum rating, requiring a transistor or driver IC.
• Q: Why is constant current drive recommended? A: LED brightness is primarily controlled by current, not voltage. The V_F can vary from unit to unit and with temperature. A constant current source automatically adjusts the voltage to maintain the set current, ensuring stable, predictable brightness and protecting the LED from overcurrent conditions.
• Q: What does "categorized for luminous intensity" mean for my design? A: It means you should specify and purchase units from the same intensity bin code if using multiple displays in one product. This prevents noticeable brightness differences between digits or displays. Consult the supplier for specific bin availability.
• Q: The storage instructions mention baking. Is this always necessary? A: Baking is a moisture removal process ("bake-out") for components that have absorbed moisture from the air during prolonged storage. It prevents "popcorning" (package cracking) during the high-temperature soldering process. If the parts are used soon after the sealed bag is opened, baking is typically not needed. Follow the guidelines in section 6.2.

10. Practical Design and Usage Case

Scenario: Designing a 3-digit DC voltage meter display.

1. Microcontroller & Driver: Select a microcontroller with enough I/O pins or use a dedicated multiplexing LED driver (e.g., MAX7219, TM1637) to control the segment anodes and digit cathodes.
2. Current Setting: Decide on the operating current. For good brightness indoors, 10-15mA per segment is often sufficient. Use the derating formula to check if this is safe at your maximum expected ambient temperature (e.g., 50°C).
3. Resistor Calculation: If the driver uses resistor current limiting, calculate as shown in section 7.2. If using a constant-current driver, set the current to the desired value.
4. PCB Layout: Place the current-limiting resistors close to the driver IC or microcontroller, not necessarily right at the display pins. Ensure the traces to the common cathode pins can handle the sum of the currents of all segments in one digit (e.g., if all 7 segments + DP are on at 10mA each, the cathode trace must handle 80mA).
5. Software: Implement a multiplexing routine that cycles through digits 1, 2, and 3 rapidly. The duty cycle for each digit is 1/3, so to achieve the same average brightness as a static display, the peak current during its active time can be up to 3 times higher (but must not exceed the 90mA peak rating).
6. Testing: Verify brightness uniformity. If digits appear uneven, check for consistent V_CC at the display pins, verify resistor values, and ensure all segments of the display are from the same intensity bin.

11. Operating Principle

The LTC-4724JF is based on the principle of electroluminescence in a semiconductor PN junction. When a forward bias voltage exceeding the diode's turn-on voltage (approximately 2V for AlInGaP) is applied, electrons from the N-type material and holes from the P-type material recombine in the active region (the quantum well structure of the AlInGaP layer). This recombination event releases energy in the form of photons (light). The specific composition of the Aluminum, Indium, Gallium, and Phosphide atoms in the crystal lattice determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, yellow-orange at ~611 nm. The non-transparent GaAs substrate helps reflect light upward, improving the overall light extraction efficiency from the top surface of the chip.

12. Technology Trends

While seven-segment displays remain a staple for numeric readouts, the underlying LED technology continues to evolve. AlInGaP represents a mature, high-performance technology for red, orange, and yellow colors. Current trends in display technology include:

• Integration: Moving towards displays with integrated driver ICs ("intelligent displays") that simplify the interface for the main controller, requiring only serial data (I2C, SPI) instead of many parallel pins.
• Miniaturization & Density: Development of smaller pixel pitches and higher-density multi-digit or dot-matrix modules using advanced packaging.
• Material Advancements: Ongoing research into materials like GaN-based compounds for broader color gamuts and higher efficiencies, though these are more prevalent in blue/green/white LEDs.
• Flexible & Novel Form Factors: Exploration of displays on flexible substrates for non-flat surfaces.

For applications requiring simple, reliable, and bright numeric indication, through-hole AlInGaP seven-segment displays like the LTC-4724JF continue to be a robust and cost-effective solution.