LTC-4724JR LED Display Datasheet - 0.4-inch Digit Height - Super Red - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTC-4724JR is a compact, high-performance triple-digit seven-segment LED display module. It is designed for applications requiring clear, bright numeric readouts in a space-efficient package. The device utilizes advanced AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for its LED chips, which are fabricated on a non-transparent GaAs substrate. This construction contributes to its high efficiency and brightness. The display features a gray face with white segment markings, providing excellent contrast for optimal character legibility under various lighting conditions. Its primary design goals are low power consumption, high reliability, and consistent visual performance, making it suitable for integration into a wide range of electronic equipment.

1.1 Key Features and Advantages

• Digit Height: 0.4 inches (10.0 mm), offering a good balance between size and readability.
• Segment Uniformity: Continuous, uniform segments ensure consistent illumination across all digits and characters.
• Power Efficiency: Low power requirement, making it suitable for battery-powered or energy-conscious devices.
• Visual Quality: Excellent character appearance with high brightness and high contrast ratio.
• Viewing Angle: Wide viewing angle for visibility from various positions.
• Reliability: Solid-state construction offers long operational life and resistance to shock and vibration.
• Binning: Categorized for luminous intensity, allowing for selection of displays with matched brightness levels.
• Environmental Compliance: Lead-free package compliant with RoHS (Restriction of Hazardous Substances) directives.

1.2 Device Identification

The part number LTC-4724JR specifically denotes a multiplex common cathode display with AlInGaP Super Red LEDs and includes a right-hand decimal point. This naming convention helps in precise identification and ordering.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

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

• Power Dissipation per Segment: 70 mW. This is the maximum power that can be safely dissipated by a single LED segment without risk of overheating.
• Peak Forward Current per Segment: 90 mA. This is the maximum instantaneous current allowed under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). It is significantly higher than the continuous current rating.
• Continuous Forward Current per Segment: 25 mA at 25°C. This current derates linearly at a rate of 0.33 mA/°C as ambient temperature increases above 25°C. This derating is crucial for thermal management in the application.
• Operating & Storage Temperature Range: -35°C to +85°C. The device is rated for industrial temperature ranges.
• Solder Conditions: The device can withstand wave soldering with the pin tip 1/16 inch (approx. 1.6mm) below the seating plane for 3 seconds at 260°C. The temperature of the display body itself must not exceed its maximum temperature rating during assembly.

2.2 Electrical & Optical Characteristics

These are typical operating parameters measured at Ta=25°C, providing the expected performance under normal conditions.

• Average Luminous Intensity (Iv): 200-650 ucd (microcandelas) at a forward current (IF) of 1mA. This wide range indicates the device is binned; specific intensity values can be selected.
• Peak Emission Wavelength (λp): 639 nm (typical). This is the wavelength at which the optical power output is greatest, defining the \"super red\" color.
• Spectral Line Half-Width (Δλ): 20 nm (typical). This indicates the spectral purity or bandwidth of the emitted light.
• Dominant Wavelength (λd): 631 nm (typical). This is the wavelength perceived by the human eye, closely related to the color point.
• Forward Voltage per Chip (VF): 2.0V to 2.6V at IF=20mA. The tolerance is ±0.1V. Circuit design must accommodate this range to ensure consistent drive current.
• Reverse Current per Segment (IR): 100 µA maximum at a reverse voltage (VR) of 5V. Note that reverse voltage operation is for test purposes only and not for continuous use.
• Luminous Intensity Matching Ratio: 2:1 maximum for LEDs in similar light areas at IF=10mA. This specifies the maximum allowable brightness variation between segments.
• Cross Talk: ≤2.5%. This parameter measures unwanted electrical or optical interference between adjacent segments.

3. Binning System Explanation

The LTC-4724JR employs a binning system primarily for Luminous Intensity. As indicated by the Iv range of 200-650 ucd, displays are categorized based on their measured light output at a standard test current (1mA). This allows designers to select displays with matched brightness levels, which is critical for multi-digit applications to avoid uneven appearance. While the datasheet does not explicitly detail bins for wavelength or forward voltage, the typical and maximum/minimum values provided for λp, λd, and VF imply controlled manufacturing processes. For critical color-matching applications, consulting the manufacturer for specific binning codes is recommended.

4. Performance Curve Analysis

The datasheet references typical electrical/optical characteristic curves. While the specific graphs are not provided in the text, standard curves for such LEDs would typically include:

• IV (Current-Voltage) Curve: Shows the relationship between forward current (IF) and forward voltage (VF). It is non-linear, with a turn-on voltage around 1.8-2.0V for AlInGaP red LEDs.
• Luminous Intensity vs. Forward Current (Iv-IF): Demonstrates how light output increases with current, typically in a near-linear relationship within the operating range before efficiency drops at very high currents.
• Luminous Intensity vs. Ambient Temperature (Iv-Ta): Shows the derating of light output as the junction temperature increases. AlInGaP LEDs generally experience a decrease in efficiency with rising temperature.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the peak at ~639nm and the half-width of ~20nm.

These curves are essential for designing the drive circuitry to achieve desired brightness while maintaining efficiency and reliability.

5. Mechanical & Package Information

5.1 Package Dimensions

The display has a standard 15-pin dual in-line package (DIP) configuration, though not all pin positions are populated. Key dimensional notes include:

• All dimensions are in millimeters with a general tolerance of ±0.25 mm unless specified otherwise.
• Pin tip shift tolerance is ±0.4 mm.
• Specific quality criteria are defined for the display surface: foreign material on segments ≤10 mils, bending ≤1% of reflector length, bubbles in segments ≤10 mils, and ink contamination ≤20 mils.

A detailed dimensioned drawing would be required for precise PCB footprint design.

5.2 Pin Connection and Circuit Diagram

The device has a multiplexed common cathode configuration. The internal circuit diagram shows three common cathode pins (for Digit 1, Digit 2, Digit 3) and a separate common cathode for the LEDs L1, L2, L3. The anodes for segments A-G, DP (decimal point), and LEDs L1-L3 are brought out to individual pins. This configuration allows the three digits to be driven sequentially (multiplexed) to reduce the number of required driver lines.

Pinout:

1: Common Cathode Digit 1

2: Anode E

3: Anode C, L3

4: Anode D

5: Common Cathode Digit 2

6: Anode DP

7: Common Cathode Digit 3

8: Anode G

9: No Connection

10: No Connection

11: Anode B, L2

12: Anode A, L1

13: No Connection

14: Common Cathode L1, L2, L3

15: Anode F

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Parameters

The specified soldering condition is wave soldering: 1/16 inch (1.6 mm) below the seating plane for 3 seconds at 260°C. For reflow soldering, a standard lead-free profile with a peak temperature not exceeding the maximum storage temperature (85°C plus a safety margin, typically 260°C peak) should be used. The key is to prevent the body of the display from overheating.

6.2 Storage Conditions

To prevent pin oxidation and moisture absorption, the recommended storage conditions are:

Temperature: 5°C to 30°C

Humidity: Below 60% RH

The product should be kept in its original moisture-barrier packaging until use. Long-term storage of large inventories is discouraged. If the moisture barrier is compromised, the pins may require re-plating before use.

7. Application Recommendations

7.1 Typical Application Scenarios

This display is intended for ordinary electronic equipment including, but not limited to:

- Office equipment (printers, copiers, scanners)

- Communication devices

- Household appliances (microwaves, ovens, washing machines)

- Industrial control panels

- Test and measurement equipment

- Point-of-sale terminals

Important Note: For applications where failure could jeopardize life or health (aviation, medical systems, safety devices), consultation with the manufacturer is required prior to design-in.

7.2 Critical Design Considerations and Cautions

• Drive Circuitry: Constant current driving is strongly recommended over constant voltage to ensure consistent brightness and longevity. The circuit must be designed to deliver the intended current across the full VF range (2.0V-2.6V).
• Current Limiting: Never exceed the absolute maximum ratings for current. Excess current or high operating temperature leads to severe light degradation and premature failure.
• Reverse Voltage Protection: The driving circuit must protect the LEDs from reverse voltages and voltage transients during power cycling. Reverse bias can cause metal migration, increasing leakage current or causing shorts.
• Thermal Management: The safe operating current must be derated based on the maximum ambient temperature in the application environment.
• Environmental Protection: Avoid rapid temperature changes in humid environments to prevent condensation on the display.
• Mechanical Handling: Do not apply abnormal force to the display body. If an adhesive film is applied to the surface, avoid having it in direct contact with a front panel/cover as external force may shift it.
• Multi-Display Matching: When using two or more displays in one assembly, select units from the same luminous intensity bin to avoid uneven brightness (hue unevenness).
• Reliability Testing: If the end product requires drop or vibration testing, share the test conditions with the manufacturer for evaluation beforehand.

8. Technical Comparison and Differentiation

The LTC-4724JR differentiates itself through several key technologies:

1. Chip Technology: Uses AlInGaP on a non-transparent GaAs substrate. Compared to older GaAsP or GaP technologies, AlInGaP offers significantly higher efficiency, brightness, and better temperature stability for red and amber LEDs.

2. Optical Design: The gray face with white segments provides superior contrast compared to all-black or all-gray faces, enhancing readability.

3. Package: The lead-free, RoHS-compliant package meets modern environmental standards. Its multiplexed pinout reduces the required microcontroller I/O lines compared to static-drive displays.

These features combine to offer a display with high brightness, good reliability, and design flexibility for cost-sensitive yet performance-oriented applications.

9. Frequently Asked Questions (Based on Technical Parameters)

Q1: What is the difference between peak wavelength (639nm) and dominant wavelength (631nm)?

A: Peak wavelength is the physical peak of the spectral output. Dominant wavelength is the single wavelength perceived by the human eye that matches the color of the light source. They are often close but not identical due to the shape of the emission spectrum.

Q2: Can I drive this display with a 5V microcontroller pin directly?

A: No. The forward voltage is only 2.0-2.6V. Connecting a 5V source directly without a current-limiting resistor would destroy the LED. You must use a series resistor or, preferably, a constant current driver to limit the current to a safe value (e.g., 10-20mA).

Q3: Why is constant current drive recommended?

A: LED brightness is primarily a function of current, not voltage. The forward voltage (VF) has a tolerance and varies with temperature. A constant current source ensures the brightness remains stable regardless of these VF variations, leading to more uniform and predictable performance.

Q4: How do I implement the multiplexing?

A: To display a number on three digits, you would rapidly cycle (multiplex) between them. For example, turn on the segment anodes for Digit 1, enable its common cathode, wait a short time, then disable that cathode. Next, set the anodes for Digit 2, enable its cathode, and so on. The cycling is fast enough (typically >100Hz) that the human eye perceives all digits as continuously lit.

10. Practical Design and Usage Case

Scenario: Designing a simple 3-digit voltmeter display.

1. Microcontroller: Select an MCU with enough I/O lines: 7 segment lines (A-G) + 1 decimal point line + 3 digit select lines (common cathodes) = 11 lines minimum.

2. Drive Circuit: Since MCU pins cannot source/sink enough current for all segments at once, use transistor arrays (e.g., ULN2003) to sink the cathode currents for each digit. The segment anode currents can be sourced from the MCU pins if within limits, or via additional drivers.

3. Current Limiting: Place a current-limiting resistor in series with each segment anode line. Calculate the resistor value based on your supply voltage (Vcc), the LED forward voltage (use max VF=2.6V for worst-case), and desired current (e.g., 10mA): R = (Vcc - VF) / IF.

4. Software: Implement a timer interrupt for multiplexing. In the interrupt service routine, turn off the previous digit, update the segment pattern for the next digit from a lookup table, and turn on its cathode.

5. Thermal Consideration: Ensure the display is not placed near other heat-generating components. If the ambient temperature is expected to be high, consider reducing the drive current below the maximum to derate the power dissipation.

11. Operating Principle Introduction

The LTC-4724JR is based on semiconductor electroluminescence. When a forward voltage exceeding the diode's turn-on threshold is applied across the AlInGaP p-n junction, electrons and holes are injected into the active region. Their recombination releases energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, which defines the wavelength (color) of the emitted light—in this case, super red (~631-639nm). The non-transparent GaAs substrate helps reflect light upward, improving light extraction efficiency. The seven-segment format is a standardized pattern where different combinations of the seven independently controllable segments (A through G) are illuminated to form the numerals 0-9 and some letters.

12. Technology Trends

The LED display industry continues to evolve. While this product uses mature and reliable AlInGaP technology, broader trends influencing this sector include:

Increased Efficiency: Ongoing material science research aims to improve the internal quantum efficiency (IQE) and light extraction efficiency (LEE) of LEDs, leading to higher brightness at lower currents.

Miniaturization: There is a constant drive for smaller pixel/digit pitches and lower profile packages to enable more compact devices.

Integration: Trends include integrating the driver ICs directly into the display module (\"COG\" or Chip-on-Glass) to simplify system design and reduce component count.

Advanced Colors & Flexibility: Development of full-color, dot-matrix, and even flexible LED displays is expanding application possibilities beyond traditional segmented numeric readouts.

The LTC-4724JR represents a well-optimized solution within the established segment of mid-size, high-reliability, multiplexed numeric displays.