LTC-2728JS LED Display Datasheet - 0.28-inch Digit Height - AlInGaP Yellow - 2.6V Forward Voltage - 40mW Power Dissipation - English Technical Documentation

1. Product Overview

The LTC-2728JS is a quadruple-digit, seven-segment alphanumeric display module designed for applications requiring clear, bright numeric readouts. Its primary function is to visually represent numerical data through individually addressable segments. The device is constructed using advanced Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor technology for the light-emitting elements, which are mounted on a non-transparent Gallium Arsenide (GaAs) substrate. This combination results in the characteristic yellow emission. The display features a gray faceplate with white segment markings, enhancing contrast and readability under various lighting conditions.

The core advantages of this display include its excellent character appearance, achieved through continuous and uniform segments, and high brightness with strong contrast. It operates with low power requirements, making it suitable for battery-powered or energy-conscious devices. Furthermore, it offers a wide viewing angle and benefits from the solid-state reliability inherent to LED technology, ensuring long operational life and resistance to shock and vibration.

The target market for this component includes industrial control panels, test and measurement equipment, consumer electronics (such as clocks or appliances), automotive dashboards (for auxiliary displays), and any embedded system requiring a robust, legible, and efficient numeric display solution.

2. Technical Parameters Deep Objective Interpretation

2.1 Photometric and Optical Characteristics

The key optical parameters define the visual performance of the display. The Average Luminous Intensity (Iv) is specified with a typical value of 600 µcd at a forward current (IF) of 1mA, with a minimum of 200 µcd. This parameter measures the perceived brightness of the light output as seen by the human eye, calibrated using a filter that approximates the CIE photopic response curve. The Peak Emission Wavelength (λp) is 588 nm, and the Dominant Wavelength (λd) is 587 nm, both measured at IF=20mA. These values place the emission firmly in the yellow region of the visible spectrum. The Spectral Line Half-Width (Δλ) is 15 nm, indicating a relatively pure, monochromatic yellow color. The Luminous Intensity Matching Ratio between segments is specified as 2:1 maximum, ensuring uniform brightness across all segments of a digit for a consistent appearance.

2.2 Electrical Parameters

The electrical specifications govern the safe and effective driving of the LEDs. The Forward Voltage per Segment (VF) has a typical value of 2.6V at IF=20mA, with a maximum of 2.6V. This is the voltage drop across an illuminated segment. The Reverse Current per Segment (IR) is a maximum of 10 µA when a reverse voltage (VR) of 5V is applied, indicating the leakage current in the off state. The Continuous Forward Current per Segment is rated at 25 mA maximum at 25°C, with a derating factor of 0.33 mA/°C. This means the maximum allowable continuous current decreases as ambient temperature rises above 25°C to prevent overheating. For pulsed operation, a Peak Forward Current per Segment of 60 mA is allowed under specific conditions (1/10 duty cycle, 0.1ms pulse width). The Power Dissipation per Segment is limited to 40 mW.

2.3 Thermal and Absolute Maximum Ratings

These ratings define the operational limits beyond which permanent damage may occur. The Operating and Storage Temperature Range is from -35°C to +85°C. This wide range makes the display suitable for harsh environments. The maximum Reverse Voltage per Segment is 5V; exceeding this can break down the LED junction. A critical handling specification is the Solder Temperature: the device can withstand a maximum of 260°C for up to 3 seconds, measured at a point 1.6mm (1/16 inch) below the seating plane of the package. This is crucial for guiding reflow soldering processes.

3. Binning System Explanation

Based on the provided datasheet, explicit binning codes for wavelength (or color temperature), luminous flux, or forward voltage are not detailed. The specifications provide minimum, typical, and maximum values for key parameters like luminous intensity (200-600 µcd) and forward voltage (2.05-2.6V). In a production context, manufacturers often group LEDs into tighter performance bins within these ranges to ensure consistency within a single batch or for specific customer requirements. Designers should consult the manufacturer for available binning options if precise color matching or intensity uniformity beyond the published min/max specs is critical for the application.

4. Performance Curve Analysis

The datasheet references typical electrical/optical characteristic curves. While the specific graphs are not reproduced in the text, standard curves for such devices would typically include: Forward Current (IF) vs. Forward Voltage (VF): This curve shows the exponential relationship, crucial for designing current-limiting circuitry. Luminous Intensity (Iv) vs. Forward Current (IF): This shows how light output increases with current, usually in a roughly linear region before efficiency drops at very high currents. Luminous Intensity (Iv) vs. Ambient Temperature (Ta): This curve demonstrates the negative temperature coefficient of LEDs, where light output decreases as junction temperature rises. Spectral Power Distribution: A plot showing the relative intensity of light emitted across wavelengths, centered around 588 nm with the specified 15 nm half-width. Understanding these relationships is essential for optimizing drive conditions for brightness, efficiency, and longevity.

5. Mechanical and Packaging Information

The display has a digit height of 0.28 inches (7.0 mm). The package dimensions are provided in a detailed drawing with all measurements in millimeters. Tolerances are generally ±0.25 mm unless otherwise specified. The device is a 16-pin dual in-line package (DIP). The internal circuit diagram reveals a multiplexed common cathode configuration. This means the cathodes of the LEDs for each digit are connected together (four common cathode pins: Digit 1, 2, 3, and 4), while the anodes for each segment type (A through G, plus DP) are connected across all digits. This structure allows for multiplexing, where digits are illuminated one at a time in rapid succession to create the perception of all digits being on continuously, significantly reducing the number of required driver pins.

6. Soldering and Assembly Guidelines

The key guideline provided is the solder heat resistance: the component can withstand a peak temperature of 260°C for a maximum of 3 seconds, measured 1.6mm below the package body. This is a standard rating for wave or reflow soldering. For reflow profiles, a standard lead-free profile with a peak temperature not exceeding 260°C is applicable. Precautions include avoiding mechanical stress on the pins during insertion, ensuring proper alignment before soldering, and preventing excessive solder bridging between pins. The device should be stored in its original moisture-barrier bag until use, within the specified storage temperature range of -35°C to +85°C, and in a low-humidity environment to prevent moisture absorption.

7. Packaging and Ordering Information

The part number is LTC-2728JS. The description associated with this part number is \"AlInGaP Yellow, Multiplex Common Cathode, Right Hand Decimal.\" This indicates the LED material, the electrical configuration, and the position of the decimal point. Specific packaging details such as tube quantities, tray counts, or reel specifications are not included in the provided excerpt. The label would typically include the part number, lot code, and date code. For ordering, the base part number LTC-2728JS is used.

8. Application Recommendations

8.1 Typical Application Scenarios

This display is ideal for any application requiring a clear, multi-digit numeric readout. Common uses include: digital panel meters for voltage, current, or frequency; timers and clocks; production line counters; medical device readouts (e.g., blood pressure monitors); household appliance displays (ovens, microwaves, washing machines); and automotive aftermarket gauges.

8.2 Design Considerations

Drive Circuitry: Due to its common cathode multiplexed design, a dedicated display driver IC (like a MAX7219 or a microcontroller with multiplexing software) is almost always required. Each digit is turned on by sinking current through its common cathode pin while sourcing current to the appropriate segment anode pins. Current Limiting: External current-limiting resistors are mandatory for each segment anode line (or possibly for each common cathode, depending on the driver architecture) to set the forward current to a safe value, typically between 5-20 mA depending on the desired brightness and power budget. The resistor value can be calculated using R = (Vcc - VF) / IF. Refresh Rate: When multiplexing, the refresh rate per digit should be high enough to avoid visible flicker, typically above 60 Hz per digit (so a total cycle rate >240 Hz for 4 digits). Viewing Angle: The wide viewing angle allows for flexible mounting positions. Power Sequencing: Ensure the driver circuit does not apply reverse voltage or excessive current during power-up or power-down.

9. Technical Comparison

Compared to other seven-segment technologies, AlInGaP yellow LEDs offer distinct advantages. Versus traditional red GaAsP or GaP LEDs, AlInGaP provides significantly higher luminous efficiency, resulting in greater brightness for the same drive current. It also offers better temperature stability and longer lifetime. Compared to blue or white LEDs with filters, AlInGaP yellow is a direct-emission color, avoiding the efficiency losses associated with phosphor conversion. The 0.28-inch digit height is a common size, offering a good balance between readability and board space consumption, being larger than 0.2-inch displays for easier viewing and smaller than 0.5-inch displays for compactness. The multiplexed common cathode design is standard for multi-digit displays, minimizing pin count compared to a non-multiplexed (static drive) design which would require many more I/O lines.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the \"Right Hand Decimal\" in the description?
A: This specifies the physical position of the decimal point segment. \"Right Hand\" means the decimal point is located to the right of the digit. Some displays offer left-hand or center decimal points.

Q: Can I drive this display with a constant voltage source?
A: No. LEDs are current-driven devices. A constant voltage source without a series current-limiting resistor will likely allow excessive current to flow, destroying the LED segment. Always use a current-limiting scheme.

Q: What does \"1/10 Duty Cycle, 0.1ms Pulse Width\" mean for the Peak Forward Current?
A: This rating allows a higher instantaneous current (60 mA) only if the pulse is very short (0.1ms) and the LED is off for much longer (giving a 10% duty cycle). This lets you achieve a brief burst of higher brightness for multiplexing or strobe effects without overheating the chip. For steady-state illumination, you must use the Continuous Forward Current rating (25 mA max).

Q: Pins 4, 9, 10, and 12 are listed as \"NO PIN.\" What does this mean?
A: These are physically absent pins. The package has a 16-pin footprint, but only 12 pins are actually present and electrically connected. This is a common practice to standardize package size while accommodating different internal circuit configurations.

Q: How do I calculate the total power consumption?
A: For a multiplexed display, power is not simply the sum of all segments. In a typical multiplexing scheme, only one digit is on at a time. Therefore, the instantaneous power is roughly the power for one fully lit digit (e.g., 8 segments * IF per segment * VF). The average power is this value divided by the number of digits (for equal on-times).

11. Practical Use Case

Case: Designing a 4-Digit Voltmeter Readout. A designer is building a digital voltmeter to display 0.00V to 19.99V. They select the LTC-2728JS for its brightness and readability. They use a microcontroller with an analog-to-digital converter (ADC) to measure voltage. The microcontroller's firmware handles converting the ADC reading to BCD (Binary-Coded Decimal) format. Four I/O pins are configured as open-drain outputs to drive the common cathode pins (Digits 1-4). Seven other I/O pins (plus one for the decimal point) are configured as push-pull outputs to drive the segment anodes (A-G, DP) through individual 100Ω current-limiting resistors (calculated for Vcc=5V, VF~2.6V, IF~20mA). The firmware implements a timer interrupt that cycles through the four digits at a rate of 1 kHz (250 Hz per digit). In the interrupt routine, it turns off all digits, outputs the segment pattern for the next digit, and then turns on that digit's cathode. This creates a stable, flicker-free display showing the measured voltage.

12. Principle Introduction

The operating principle is based on electroluminescence in a semiconductor p-n junction. The AlInGaP (Aluminium Indium Gallium Phosphide) crystal structure is a direct bandgap semiconductor. When forward-biased, electrons from the n-type region and holes from the p-type region are injected into the active region where they recombine. The energy released during this recombination is emitted as photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, which directly corresponds to the wavelength (color) of the emitted light—in this case, yellow (~587-588 nm). The non-transparent GaAs substrate absorbs any light emitted downwards, improving contrast by preventing internal reflection that could cause a \"washed-out\" appearance. The seven-segment format is a standardized pattern where seven independently controlled bar-shaped LEDs (segments) can be illuminated in different combinations to form the numerals 0-9 and some letters.

13. Development Trends

The trend in seven-segment displays and similar discrete LED indicators continues towards higher efficiency, lower power consumption, and improved reliability. While the fundamental AlInGaP technology is mature, process refinements lead to better internal quantum efficiency and light extraction. There is a growing integration of driver electronics, moving towards \"intelligent\" displays with built-in controllers, I2C or SPI interfaces, and even ambient light sensors for automatic brightness adjustment, reducing the design burden on the system microcontroller. In terms of form factor, there is constant pressure for thinner packages and smaller pixel pitches for higher-density information display. However, for standard industrial readouts, the classic through-hole DIP package, as used by the LTC-2728JS, remains popular due to its robustness, ease of hand-soldering for prototyping, and proven reliability in demanding environments.