LTS-549AJD LED Display Datasheet - 0.52 Inch Digit Height - Hyper Red Color - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTS-549AJD is a high-performance, single-digit numeric display module designed for applications requiring clear, bright, and reliable numerical readouts. Its core function is to visually represent a single decimal digit (0-9) along with a decimal point. The device is engineered for integration into various electronic systems where space efficiency and readability are key considerations.

The primary application domains for this display include industrial instrumentation, test and measurement equipment, consumer appliances, automotive dashboards (secondary displays), and point-of-sale terminals. Its design prioritizes long-term reliability and consistent performance under standard operating conditions.

2. Technical Specifications Deep Dive

2.1 Optical Characteristics

The optical performance is defined by several key parameters measured under standard test conditions (Ta=25°C). The Average Luminous Intensity (Iv) has a typical value of 700 µcd when driven at a forward current (IF) of 1mA, with a specified range from 320 µcd (minimum) upwards. This parameter directly correlates to the perceived brightness of the segments.

The color is defined as Hyper Red, achieved using AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material. The Peak Emission Wavelength (λp) is typically 650 nm, while the Dominant Wavelength (λd) is specified at 639 nm (IF=20mA). The Spectral Line Half-Width (Δλ) is 20 nm, indicating the spectral purity of the emitted light. A Luminous Intensity Matching Ratio of 2:1 (maximum) ensures uniformity in brightness between different segments of the same digit.

2.2 Electrical Characteristics

The electrical parameters define the operating limits and conditions for the device. The Absolute Maximum Ratings must not be exceeded to prevent permanent damage. Key limits include: a Power Dissipation per Segment of 70 mW, a Peak Forward Current per Segment of 90 mA (under pulsed conditions: 1/10 duty cycle, 0.1ms pulse width), and a Continuous Forward Current per Segment of 25 mA at 25°C, derating linearly at 0.33 mA/°C above 25°C. The maximum Reverse Voltage per Segment is 5 V.

Under typical operating conditions (IF=20mA), the Forward Voltage per Segment (VF) ranges from 2.1V to 2.6V. The Reverse Current per Segment (IR) is a maximum of 100 µA when a reverse voltage (VR) of 5V is applied. These values are critical for designing the appropriate current-limiting circuitry.

2.3 Thermal and Environmental Specifications

The device is rated for an Operating Temperature Range of -35°C to +85°C and a Storage Temperature Range of -35°C to +85°C. This wide range ensures functionality in various environmental conditions. For assembly, the maximum allowable Solder Temperature is 260°C for a maximum duration of 3 seconds, measured at 1.6mm below the seating plane of the component. Adherence to these thermal limits is crucial during the reflow soldering process to avoid damaging the internal LED chips and package.

3. Binning and Classification System

The product datasheet indicates that the devices are Categorized for Luminous Intensity. This implies a binning process where units are sorted and labeled according to their measured light output (Iv) at a standard test current (typically 1mA, as per the datasheet). This allows designers to select displays with consistent brightness levels for their applications, ensuring visual uniformity in multi-digit displays or across different products. The specific bin codes or intensity ranges for commercial selection are typically defined in separate product selection guides.

4. Performance Curve Analysis

The datasheet references Typical Electrical/Optical Characteristic Curves. While the specific graphs are not detailed in the provided text, such curves standardly illustrate the relationship between key parameters. These typically include:

• Forward Current (IF) vs. Forward Voltage (VF) Curve: Shows the exponential relationship, crucial for determining the required drive voltage for a desired current.
• Luminous Intensity (Iv) vs. Forward Current (IF) Curve: Demonstrates how light output increases with current, often in a roughly linear region before saturation, informing drive current selection for target brightness.
• Luminous Intensity (Iv) vs. Ambient Temperature (Ta) Curve: Illustrates the decrease in light output as junction temperature rises, which is vital for thermal management in high-temperature or high-current applications.
• Spectral Distribution Curve: A plot of relative intensity versus wavelength, visually confirming the peak (650 nm) and dominant (639 nm) wavelengths and the spectral half-width.

These curves provide essential guidance for optimizing the display's performance in real-world circuit designs beyond the single-point data in the tables.

5. Mechanical and Package Information

5.1 Physical Dimensions

The device features a 0.52 inch (13.2 mm) digit height, which defines the physical size of the displayed character. The package dimensions are provided in a detailed drawing with all measurements in millimeters. Standard tolerances for these dimensions are ±0.25 mm (0.01") unless otherwise specified. The physical construction contributes to the wide viewing angle and excellent character appearance mentioned in the features.

5.2 Pinout and Internal Circuit

The display has a 10-pin configuration. The internal circuit diagram reveals a Common Cathode architecture. This means the cathodes (negative terminals) of all LED segments (and the decimal point) are connected internally and brought out to common pins (Pin 3 and Pin 8 in this device). Each individual segment anode (positive terminal) has its own dedicated pin. The specific pin assignment is: 1 (Segment J), 3 (Common Cathode), 4 (Segment C), 5 (Decimal Point), 6 (Segment B), 8 (Common Cathode), 9 (Segment H), 10 (Segment G). Pins 2 and 7 are noted as "No Connection" (N.C.). This configuration is optimal for multiplexing drives in multi-digit displays.

6. Soldering and Assembly Guidelines

As noted in the Absolute Maximum Ratings, the component can withstand a solder temperature of 260°C maximum for 3 seconds maximum. This is a standard rating for lead-free reflow soldering processes. The measurement point is critical: 1.6mm below the seating plane. Designers must ensure their reflow profile does not exceed this limit to prevent package cracking, delamination, or damage to the wire bonds and semiconductor dies inside. For manual soldering, a controlled-temperature iron should be used with minimal contact time. Proper ESD (Electrostatic Discharge) handling procedures should always be followed during assembly.

7. Application Suggestions

7.1 Typical Application Circuits

Given its common cathode design, the LTS-549AJD is ideally driven by a microcontroller or dedicated display driver IC. A typical circuit involves connecting the common cathode pins (3 & 8) to ground (or a current sink on the driver). Each segment anode pin is connected to the driver output through a current-limiting resistor. The resistor value (R) is calculated based on the supply voltage (Vcc), the desired forward current (IF, e.g., 20mA for full brightness), and the LED's forward voltage (VF, use max 2.6V for safety): R = (Vcc - VF) / IF. For a 5V supply and 20mA current, R ≈ (5 - 2.6) / 0.02 = 120 Ω.

7.2 Design Considerations

• Current Limiting: Always use external current-limiting resistors. Driving the LEDs directly from a voltage source or a microcontroller pin without a resistor will cause excessive current flow, leading to immediate failure.
• Multiplexing: For multi-digit displays, a multiplexing technique is used where digits are illuminated one at a time rapidly. The common cathode design is perfect for this. The driver sequentially grounds the cathode of each digit while presenting the segment data for that digit on the anode lines.
• Power Dissipation: Ensure the calculated power per segment (VF * IF) does not exceed the maximum rating of 70 mW, especially in high-temperature environments. Consider derating the forward current if the ambient temperature is high.
• Viewing Angle: The wide viewing angle is beneficial, but the display's orientation in the final product should be considered to maximize readability for the end-user.

8. Technical Comparison and Differentiation

The LTS-549AJD utilizes AlInGaP (Aluminum Indium Gallium Phosphide) technology for its red emission. Compared to older technologies like GaAsP (Gallium Arsenide Phosphide), AlInGaP offers significantly higher luminous efficiency, resulting in greater brightness for the same drive current, and better temperature stability. The "hyper red" designation indicates a specific, deeper shade of red with a dominant wavelength around 639-650 nm, which may offer different aesthetic or functional properties compared to standard red LEDs. The use of a non-transparent GaAs substrate helps improve contrast by reducing internal light scattering and reflection, contributing to the "high contrast" feature.

9. Frequently Asked Questions (FAQ)

Q: Can I drive this display directly from a 5V microcontroller pin?
A: No. You must use a current-limiting resistor in series with each segment. A microcontroller pin cannot safely source 20mA continuously, and without a resistor, the LED would draw excessive current and be destroyed.

Q: What is the difference between 'Peak Wavelength' and 'Dominant Wavelength'?
A: Peak Wavelength (λp) is the wavelength at which the emission spectrum has its maximum intensity. Dominant Wavelength (λd) is the single wavelength of monochromatic light that matches the perceived color of the LED. For this red LED, λp is 650 nm (physical peak), but the human eye perceives it as equivalent to a 639 nm pure red light.

Q: The datasheet shows two common cathode pins (3 and 8). Do I need to connect both?
A: Yes, for optimal performance and current distribution, it is recommended to connect both common cathode pins to ground (or the current sink). This ensures even brightness across all segments.

Q: How do I calculate the resistor value for a brightness lower than the typical 20mA?
A: Use Ohm's Law with your desired forward current (IF). For example, for 10mA at 5V: R = (5V - 2.6V) / 0.01A = 240 Ω. Refer to the Iv vs. IF curve (conceptual) to estimate the corresponding brightness reduction.

10. Operational Principles

The LTS-549AJD is a solid-state light-emitting device. Its operation is based on electroluminescence in a semiconductor p-n junction made of AlInGaP materials. When a forward voltage exceeding the junction's threshold (approximately 2.1V) is applied, electrons from the n-type region and holes from the p-type region are injected into the active region. When these charge carriers recombine, they release energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, in the hyper red spectrum. The light is emitted through the top surface of the chip, which is part of a segment shaped like a numeral, and passes through the gray face with white segments for contrast enhancement.

11. Technology Trends

While discrete single-digit LED displays like the LTS-549AJD remain relevant for specific applications requiring simplicity, robustness, and direct readability, the broader trend in display technology is towards integration and miniaturization. This includes the widespread adoption of dot-matrix LED displays, OLEDs, and LCDs that offer greater flexibility in showing alphanumeric characters and graphics. Furthermore, surface-mount device (SMD) LED packages have largely replaced through-hole types in mass-produced consumer electronics due to automated assembly advantages. However, through-hole displays like this one maintain a strong position in industrial, automotive, and retrofit applications where through-hole PCB mounting is preferred for mechanical strength, serviceability, or legacy design compatibility. The underlying AlInGaP material technology continues to be refined for higher efficiency and reliability.