LTC-4724JS LED Display Datasheet - 0.4-inch Digit Height - AlInGaP Yellow - 2.6V Forward Voltage - 40mW Power Dissipation - English Technical Document

1. Product Overview

The LTC-4724JS is a compact, high-performance triple-digit seven-segment display module designed for applications requiring clear numeric readouts. Its primary function is to visually represent three digits (0-9) and associated decimal points using individual LED segments. The device is engineered for integration into various electronic systems where space efficiency, readability, and reliability are key considerations.

The core technology utilizes Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor material for the LED chips. This material system is known for its high efficiency and excellent performance in the yellow to red spectral region. The chips are fabricated on a non-transparent Gallium Arsenide (GaAs) substrate, which helps in directing light output forward, enhancing brightness and contrast. The display features a gray faceplate with white segment markings, providing a high-contrast background that improves character legibility under various lighting conditions.

The display employs a multiplexed common cathode configuration. This design significantly reduces the number of required driver pins compared to a static drive method. Instead of requiring a dedicated pin for each segment of each digit, the cathodes of each digit are connected together and controlled sequentially (multiplexed), while the anodes for each segment type (A-G, DP) are shared across all digits. This makes it highly efficient for microcontroller-based systems with limited I/O pins.

2. In-Depth Technical Parameter Analysis

2.1 Photometric and Optical Characteristics

The optical performance is central to the display's functionality. The key parameters are measured under standardized test conditions, typically at an ambient temperature (Ta) of 25°C.

• Average Luminous Intensity (I_V): This parameter defines the perceived brightness of a segment. With a test current (I_F) of 1mA, the typical value is 650 µcd (microcandelas), with a minimum guaranteed value of 200 µcd. The wide range indicates a categorization or binning process for intensity, which is common in LED manufacturing to ensure minimum performance levels.
• Peak Emission Wavelength (λ_p): Measured at I_F=20mA, the typical peak wavelength is 588 nanometers (nm). This places the emission firmly in the yellow region of the visible spectrum.
• Dominant Wavelength (λ_d): This is 587 nm, very close to the peak wavelength. The dominant wavelength is the single wavelength that best represents the perceived color of the light and is crucial for color-critical applications.
• Spectral Line Half-Width (Δλ): At 15 nm (typical), this parameter indicates the spectral purity or bandwidth of the emitted light. A relatively narrow half-width, as seen here, is characteristic of AlInGaP LEDs and contributes to a saturated, pure yellow color.
• Luminous Intensity Matching Ratio (I_V-m): This ratio, specified as 2:1 maximum, defines the allowable variation in brightness between different segments within the same display. A 2:1 ratio means the brightest segment should be no more than twice as bright as the dimmest segment under identical drive conditions, ensuring uniform appearance.

All luminous intensity measurements are performed using a light sensor and filter combination calibrated to approximate the CIE (Commission Internationale de l'Eclairage) standard photopic eye-response curve, ensuring the measurements correlate with human visual perception.

2.2 Electrical Characteristics and Absolute Maximum Ratings

Adherence to these limits is critical for device longevity and preventing catastrophic failure.

• Continuous Forward Current per Segment: The maximum allowable continuous DC current through any single LED segment is 25 mA at 25°C. Beyond this temperature, the rating must be derated linearly at a rate of 0.33 mA per degree Celsius increase in ambient temperature.
• Peak Forward Current per Segment: For pulsed operation, a higher current is permissible. Under a 1/10 duty cycle with a 0.1ms pulse width, the peak current can reach 60 mA. This is useful for multiplexing schemes where higher instantaneous brightness is needed during the short ON time.
• Power Dissipation per Segment: The maximum power that can be dissipated as heat by a single segment is 40 mW. This is calculated as Forward Voltage (V_F) multiplied by Forward Current (I_F). Exceeding this limit risks overheating the semiconductor junction.
• Forward Voltage per Segment (V_F): At a drive current of 20 mA, the typical forward voltage drop across an LED segment is 2.6V, with a minimum of 2.05V. This parameter is vital for designing the current-limiting circuitry in the driver.
• Reverse Voltage per Segment: The maximum reverse-bias voltage that can be applied across an LED segment is 5V. Exceeding this can cause immediate and irreversible damage to the LED due to junction breakdown.
• Reverse Current per Segment (I_R): With a 5V reverse bias applied, the leakage current is typically 100 µA or less.

2.3 Thermal and Environmental Specifications

• Operating Temperature Range: The device is specified to function correctly within an ambient temperature range of -35°C to +85°C. Performance outside this range is not guaranteed.
• Storage Temperature Range: The device can be stored without operation within the same -35°C to +85°C range.
• Solder Temperature: During assembly, the device can withstand a maximum soldering temperature of 260°C for a maximum duration of 3 seconds, measured 1.6mm below the seating plane of the package. This is critical for wave soldering or reflow processes.

3. Binning and Categorization System

The datasheet explicitly states that the device is \"Categorized for Luminous Intensity.\" This implies a post-production sorting (binning) process. While specific bin codes are not provided in this excerpt, typical categorization for such displays involves grouping units based on measured luminous intensity at a standard test current. This ensures that customers receive displays with consistent minimum brightness levels. The specified minimum (200 µcd) and typical (650 µcd) values for I_V define the boundaries of this categorization. Designers should be aware that brightness can vary between units within the specified 2:1 matching ratio and across the intensity bins, which may affect system calibration for uniform brightness across multiple displays.

4. Performance Curve Analysis

The datasheet references \"Typical Electrical / Optical Characteristic Curves\" which are essential for detailed design work. While the specific graphs are not provided in the text, based on standard LED characteristics, these curves would typically include:

• Forward Current vs. Forward Voltage (I-V Curve): This non-linear curve shows the relationship between the voltage applied across the LED and the resulting current. It is crucial for designing constant-current drivers, as a small change in voltage can cause a large change in current (and thus brightness). The curve's knee, around the typical V_F of 2.6V at 20mA, is the normal operating region.
• Luminous Intensity vs. Forward Current (I-L Curve): This graph shows 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. The 1mA test point for I_V and the 20mA point for other parameters provide two key references on this curve.
• Luminous Intensity vs. Ambient Temperature: The light output of LEDs typically decreases as the junction temperature increases. This curve is vital for applications operating over a wide temperature range to ensure readability is maintained at high temperatures.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the peak at ~588 nm and the narrow 15 nm half-width, confirming the pure yellow color emission.

5. Mechanical and Package Information

5.1 Physical Dimensions and Tolerances

The package drawing provides critical mechanical data for PCB layout and enclosure design. All dimensions are provided in millimeters. The general tolerance for unspecified dimensions is ±0.25 mm (which is equivalent to ±0.01 inches). Designers must incorporate these tolerances into their mechanical designs to ensure proper fit. The drawing would detail the overall length, width, and height of the display module, the spacing between digits, the segment size, and the position and diameter of the mounting pins.

5.2 Pin Configuration and Connection Diagram

The pin connection table is the interface map between the internal circuitry and the external world. The LTC-4724JS uses a 15-pin arrangement (with several pins marked as \"No Connection\" or \"No Pin\").

• Common Cathodes: Pins 1, 5, 7, and 14 are cathode connections. Pin 1 is for Digit 1, Pin 5 for Digit 2, Pin 7 for Digit 3, and Pin 14 is a common cathode for the left-side decimal points (L1, L2, L3). This structure enables the multiplexing scheme.
• Segment Anodes: The remaining pins (2, 3, 4, 6, 8, 11, 12, 15) are anodes for specific segments: A, B, C, D, E, F, G, and DP (decimal point). Segments C and G are shared with the left decimal points L3 and general, respectively, as indicated in the internal circuit diagram.

The internal circuit diagram visually represents this multiplexed architecture, showing how the three digit cathodes and the shared segment anodes are interconnected. Understanding this diagram is essential for developing the correct software timing and hardware drive circuitry.

6. Soldering and Assembly Guidelines

The absolute maximum rating for soldering temperature (260°C for 3 seconds at 1.6mm below seating plane) provides clear guidance for the assembly process. This rating is compatible with standard lead-free reflow soldering profiles (which often have a peak temperature around 245-250°C). For wave soldering, the exposure time of the pins to molten solder must be controlled to stay within this limit. It is recommended to follow standard IPC guidelines for through-hole component soldering. Preheating is advised to minimize thermal shock. After soldering, the display should be allowed to cool gradually. Proper ESD (Electrostatic Discharge) handling procedures should always be followed during assembly to prevent damage to the sensitive LED junctions.

7. Application Suggestions and Design Considerations

7.1 Typical Application Scenarios

The LTC-4724JS is well-suited for a variety of applications requiring a compact, bright, and reliable numeric display. Common uses include:

• Test and Measurement Equipment: Digital multimeters, frequency counters, power supplies, where 3-digit resolution is sufficient (e.g., showing 0-999).
• Industrial Controls and Instrumentation: Panel meters for temperature, pressure, speed, or count displays.
• Consumer Electronics: Audio equipment (amplifier volume displays), kitchen appliances (timer, temperature readouts).
• Automotive Aftermarket: Gauges and displays for voltage, RPM, or temperature.

7.2 Critical Design Considerations

• Drive Circuitry: A multiplexing driver circuit is required. This typically involves a microcontroller or dedicated display driver IC that can sink current through the digit cathodes (usually via transistors) and source current to the segment anodes. Current-limiting resistors are mandatory for each segment anode (or possibly shared if using a constant-current driver) to set the I_F to a safe value, typically between 10-20 mA for a balance of brightness and longevity.
• Multiplexing Frequency: The refresh rate must be high enough to avoid visible flicker, typically above 60 Hz. With three digits, each digit is illuminated for roughly 1/3 of the cycle. The peak current can be set higher (up to the 60mA pulsed rating) to compensate for the reduced duty cycle and maintain average brightness.
• Power Supply: The forward voltage requirement (~2.6V) means the system power supply must provide a voltage higher than this to allow for the voltage drop across the current-limiting resistor and driver circuitry. A 5V supply is common and convenient.
• Viewing Angle and Contrast: The datasheet claims a \"wide viewing angle\" and \"high contrast.\" The gray face/white segments enhance contrast. For optimal viewing, the display should be mounted perpendicular to the primary viewing direction. In high-ambient-light conditions, the high brightness (650 µcd typ.) is beneficial.
• Thermal Management: While the power dissipation per segment is low, the cumulative heat from multiple segments being lit simultaneously, especially at higher currents, should be considered. Adequate ventilation in the enclosure is recommended, particularly if operating near the upper temperature limit.

8. Technical Comparison and Differentiation

The key differentiating factors of the LTC-4724JS lie in its material technology and package. Compared to older technologies like standard GaP or GaAsP LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in greater brightness for the same drive current. The yellow color produced is also more saturated and pure. Compared to contemporary alternatives, its 0.4-inch digit height offers a specific balance between size and readability. The multiplexed common cathode design is a standard for multi-digit displays, but the specific pinout and internal circuit (including the shared cathode for left decimals) are unique to this part number and must be matched by the driver software. The categorization for luminous intensity provides a level of quality control that may not be present in all displays.

9. Frequently Asked Questions (Based on Technical Parameters)

• Q: Can I drive this display with a 3.3V microcontroller? A: Possibly, but careful design is needed. The typical V_F is 2.6V. After accounting for a small voltage drop in the driver transistor and a current-limiting resistor, the headroom from a 3.3V supply may be very tight or insufficient, especially considering V_F variation. A 5V supply is more reliable. You may need a level-shifter or a driver IC powered from a separate 5V rail.
• Q: Why is the peak current (60mA) higher than the continuous current (25mA)? A: LEDs can handle higher instantaneous currents if the duty cycle is low, as the average power dissipation and junction temperature remain within safe limits. This is exploited in multiplexing to achieve higher perceived brightness.
• Q: What is the purpose of the \"No Connection\" pins? A: They are likely mechanical placeholders to fit a standard 15-pin DIP (Dual In-line Package) footprint. They provide physical stability during soldering but have no electrical function. Do not connect them to any circuit.
• Q: How do I calculate the value of the current-limiting resistor? A: Use Ohm's Law: R = (V_supply - V_F - V_{driver_drop}) / I_F. For a 5V supply, a V_F of 2.6V, a driver drop of 0.2V, and a desired I_F of 15mA: R = (5 - 2.6 - 0.2) / 0.015 = 146.7 Ω. A standard 150 Ω resistor would be appropriate. Always verify power dissipation in the resistor: P = I² * R.

10. Practical Design and Usage Example

Consider designing a simple 3-digit voltmeter using a microcontroller. The microcontroller's ADC reads a voltage, converts it to a number between 0 and 999, and needs to display it.

1. Hardware Interface: Three microcontroller I/O pins are configured as outputs to control NPN transistors (or a transistor array) that sink current from the three digit cathode pins (1,5,7). Eight other I/O pins (or a shift register to save pins) are configured as outputs to source current to the eight segment anode pins (A,B,C,D,E,F,G,DP) through individual 150Ω current-limiting resistors.
2. Software Routine: The main loop implements the multiplexing. It turns off all digit cathodes. It then sets the segment pattern on the anode pins for Digit 1 (e.g., to show \"5\"). It then enables (provides a ground path via the transistor) the cathode for Digit 1. It waits for a short time (e.g., 2-3 ms). It then disables Digit 1, sets the segment pattern for Digit 2, enables the Digit 2 cathode, waits, and repeats for Digit 3. This cycle repeats continuously. The peak current per segment can be set to ~20mA. With a 1/3 duty cycle, the average current is ~6.7mA, well within the continuous rating.
3. Result: Due to persistence of vision, all three digits appear to be lit simultaneously and steadily, displaying the measured voltage.

11. Technology Principle Introduction

The LTC-4724JS is based on solid-state lighting technology using AlInGaP (Aluminium Indium Gallium Phosphide) semiconductors. When a forward voltage exceeding the diode's bandgap voltage is applied, electrons and holes are injected into the active region of the semiconductor structure. They recombine, releasing energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, which directly dictates the wavelength (color) of the emitted light—in this case, yellow (~587-588 nm). The non-transparent GaAs substrate absorbs any light emitted backwards, improving overall efficiency by reducing internal reflections that don't contribute to useful forward light output. The seven-segment format is a standardized method of forming numeric characters by selectively illuminating seven independent bar-shaped LED segments (labeled A through G).

12. Technology Trends and Context

While this specific part uses mature AlInGaP technology, the broader LED display landscape continues to evolve. Trends include the adoption of even more efficient materials like InGaN for blue/green/white, the development of chip-on-board (COB) and surface-mount device (SMD) packages for higher density and smaller footprints, and the integration of drivers and controllers directly into the display module (intelligent displays). However, for specific applications requiring a pure, efficient yellow color in a standard through-hole package, AlInGaP-based displays like the LTC-4724JS remain a reliable and cost-effective solution. Their simplicity, robustness, and ease of interface with basic microcontrollers ensure their continued relevance in many industrial and consumer designs where custom graphic displays are unnecessary.