LTP-747KD LED Dot Matrix Display Datasheet - 0.7 Inch (17.22mm) Digit Height - Hyper Red (650nm) - 2.6V Forward Voltage - 40mW Power Dissipation - English Technical Document

1. Product Overview

The LTP-747KD is a single-digit, alphanumeric display module built using a 5x7 dot matrix configuration. The primary function of this device is to generate clearly visible characters and symbols by selectively illuminating its individual LED dots. Its core application is in scenarios requiring compact, reliable, and bright information display, such as in industrial instrumentation, consumer electronics panels, and basic signage.

The key advantage of this display lies in its utilization of Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor technology for the LED chips, specifically in the Hyper Red wavelength. This material system is known for its high efficiency and excellent performance in the red to amber spectral regions, contributing directly to the device's advertised high brightness and contrast. The display features a gray face with white dots, which enhances contrast and readability under various lighting conditions. The continuous, uniform segments ensure a cohesive and professional character appearance.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Optical Characteristics

The optical performance is central to the display's functionality. The Average Luminous Intensity (Iv) is specified with a minimum of 630 µcd, a typical value of 1238 µcd, and no maximum under a test condition of a 32mA pulse current and a 1/16 duty cycle. This pulsed driving method is common for multiplexed displays to achieve higher perceived brightness while managing power and heat. The Peak Emission Wavelength (λp) is 650 nanometers (nm), placing it in the hyper-red region of the spectrum. The Dominant Wavelength (λd) is 639 nm. It is important to note the difference: peak wavelength is the point of maximum spectral power, while dominant wavelength is the single-wavelength perception of the color by the human eye. The Spectral Line Half-Width (Δλ) is 20 nm, indicating the spectral purity or the spread of the emitted light around the peak wavelength. A Luminous Intensity Matching Ratio (Iv-m) of 2:1 maximum is specified, meaning the brightness difference between the brightest and dimmest segments in a device should not exceed this ratio, ensuring uniform appearance.

2.2 Electrical Characteristics

The electrical parameters define the operating boundaries and conditions for the device. The Forward Voltage per dot (Vf) ranges from 2.0V (min) to 2.6V (max) at a test current of 20mA DC. This is the voltage drop across the LED when it is conducting. The Reverse Current per dot (Ir) is a maximum of 100 µA when a reverse bias of 5V is applied, indicating the level of leakage when the LED is not intended to be on.

2.3 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage may occur. They are not for normal operation. Key limits include: Average Power Dissipation per dot of 40mW, Peak Forward Current per dot of 90mA, and an Average Forward Current per dot of 15mA at 25°C, derating linearly by 0.2 mA/°C above 25°C. This derating is crucial for thermal management. The maximum Reverse Voltage per dot is 5V. The device can operate and be stored within a Temperature Range of -35°C to +85°C. A soldering temperature profile is specified: 260°C for 3 seconds at 1/16 inch (approximately 1.6mm) below the seating plane.

3. Binning System Explanation

The datasheet indicates the device is categorized for luminous intensity. This implies a binning process where manufactured units are sorted (binned) based on their measured light output. This allows designers to select parts with consistent brightness levels for their application, ensuring visual uniformity across multiple displays in a product. While specific bin codes are not detailed in this excerpt, typical bins would group LEDs with similar luminous intensity values (e.g., a range around the 1238 µcd typical).

4. Performance Curve Analysis

The datasheet references Typical Electrical/Optical Characteristic Curves. Although the specific graphs are not provided in the text, such curves in LED datasheets typically include:

• Forward Current vs. Forward Voltage (I-V Curve): Shows the nonlinear relationship, essential for designing current-limiting circuitry.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with current, usually in a sub-linear fashion at higher currents due to heating.
• Luminous Intensity vs. Ambient Temperature: Shows the decrease in light output as temperature rises, a critical factor for thermal design.
• Spectral Distribution: A plot of relative intensity versus wavelength, visually showing the peak and dominant wavelengths and spectral width.

These curves are vital for understanding the device's behavior under non-standard conditions and for optimizing drive conditions for efficiency and longevity.

5. Mechanical and Packaging Information

The device is presented with a detailed dimensioned drawing. Key mechanical features include an overall digit height of 0.7 inches (17.22mm). The package is a standard LED display module format. The drawing includes critical dimensions such as overall height, width, segment spacing, and lead spacing. Tolerances are specified as ±0.25mm unless otherwise noted. The Internal Circuit Diagram shows the matrix arrangement: 5 anode columns and 7 cathode rows. This is a common common-cathode row configuration for multiplexing.

6. Pin Connection and Interface

The pinout is clearly defined with a 12-pin configuration. The connections are a mix of anode columns and cathode rows: Pin 1: Anode Column 1, Pin 2: Cathode Row 3, Pin 3: Anode Column 2, Pin 4: Cathode Row 5, Pin 5: Cathode Row 6, Pin 6: Cathode Row 7, Pin 7: Anode Column 4, Pin 8: Anode Column 5, Pin 9: Cathode Row 4, Pin 10: Anode Column 3, Pin 11: Cathode Row 2, Pin 12: Cathode Row 1. This specific arrangement must be followed in the PCB layout and driver software to correctly address each dot in the matrix. The pin numbering is likely sequential along one side of the package.

7. Soldering and Assembly Guidelines

The primary guideline provided is the soldering temperature specification: 260°C for 3 seconds, measured 1.6mm below the seating plane. This is a standard reflow soldering parameter for through-hole components, designed to ensure a reliable solder joint without exposing the semiconductor die to excessive heat that could degrade performance or cause failure. For manual soldering, a similar thermal profile should be approximated with a controlled iron. Standard ESD (Electrostatic Discharge) precautions should be observed during handling. The storage temperature range is -35°C to +85°C.

8. Application Suggestions

8.1 Typical Application Scenarios

This display is suited for applications requiring a single, bright, and easily readable digit or a limited set of characters. Examples include: digital panel meters for voltage, current, or temperature; simple counters or timers; status indicator panels on appliances or industrial equipment; and basic informational displays in consumer electronics.

8.2 Design Considerations

• Drive Circuitry: A microcontroller with sufficient I/O pins or a dedicated LED driver IC is required to multiplex the 5x7 matrix. The driver must source current to the anode columns and sink current from the cathode rows.
• Current Limiting: External current-limiting resistors are mandatory for each anode column (or integrated into the driver) to set the forward current to a safe value, typically between 10-20mA per dot average, considering the duty cycle.
• Multiplexing: The display is designed for multiplexed operation. The refresh rate must be high enough to avoid visible flicker (typically >60Hz). The peak current during the short ON time will be higher than the average current.
• Thermal Management: Ensure the average power dissipation per dot is not exceeded, especially in high ambient temperatures. The 0.2 mA/°C derating for forward current must be factored in.
• Viewing Angle: The wide viewing angle is beneficial for applications where the display may be viewed from off-axis positions.

9. Technical Comparison and Differentiation

The primary differentiating factors of this display are its use of AlInGaP Hyper Red technology and its specific 0.7-inch digit height. Compared to older technologies like standard GaAsP red LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in greater brightness for the same input current. The gray face/white dot combination is optimized for contrast. Compared to larger or smaller displays, the 0.7-inch size offers a balance between readability and board space. The 5x7 matrix is the standard for alphanumeric characters, providing good resolution for letters and numbers.

10. Frequently Asked Questions Based on Technical Parameters

Q: What is the difference between peak wavelength (650nm) and dominant wavelength (639nm)?

A: Peak wavelength is the physical point of highest light emission from the LED. Dominant wavelength is the perceived color by the human eye, which can differ slightly due to the shape of the emission spectrum. Both are standard specifications.

Q: How do I interpret the Average Luminous Intensity test condition (IP=32mA, 1/16 Duty)?

A: The LED is pulsed with a 32mA current, but it is only on for 1/16th of the time in a multiplexing cycle. The measured brightness is an average. The instantaneous current during the ON period is higher, but the average power is managed.

Q: Can I drive this display with a constant DC current without multiplexing?

A: Technically, yes, by turning on all desired dots continuously. However, this would greatly increase total power consumption and heat generation compared to multiplexed driving, and is not the intended or optimal use for a matrix display.

Q: What does the 2:1 Luminous Intensity Matching Ratio mean for my design?

A: It guarantees that within a single display unit, no segment will be more than twice as bright as the dimmest segment. This ensures visual consistency of the formed character.

11. Practical Design and Usage Case

Consider designing a simple digital thermometer display. A microcontroller reads a temperature sensor and drives the LTP-747KD to show values from -35 to 85 (matching its operating range). The firmware would contain a font map, translating each digit (0-9 and perhaps a minus sign) into the appropriate pattern of dots to illuminate on the 5x7 grid. The microcontroller's I/O ports, configured with appropriate current-sinking/sourcing capability, would scan through the seven cathode rows rapidly, while the five anode columns for the active row are set to pattern for the desired character. Current-limiting resistors on the anode lines would be calculated based on the supply voltage, LED forward voltage, and the desired peak pulse current (e.g., targeting ~20-30mA during the ON time to achieve good brightness while staying within ratings). The enclosure design would need to consider the wide viewing angle for easy reading.

12. Principle of Operation Introduction

The LTP-747KD operates on the principle of a light-emitting diode (LED) matrix. Each of the 35 dots is an individual AlInGaP LED. These LEDs are arranged electrically in a 5-column by 7-row grid. To illuminate a specific dot, a positive voltage must be applied to its corresponding anode column while the corresponding cathode row is connected to ground (or a lower voltage). To display a character, multiple dots are illuminated in a pattern. To manage power and pin count, multiplexing is used: the controller activates one cathode row at a time and applies the pattern for that row to the five anode columns. This cycle repeats through all seven rows so quickly that the human eye perceives a steady, complete character. The AlInGaP material emits light when electrons recombine with holes across the material's bandgap, releasing energy as photons in the red wavelength.

13. Technology Trends and Context

AlInGaP LED technology represents a significant advancement over earlier red LED materials like GaAsP, offering superior efficiency, brightness, and temperature stability. While this datasheet is from 2002, the fundamental technology remains relevant for specific color and performance needs. Current trends in display technology include a shift towards surface-mount device (SMD) packages for automated assembly, higher-density matrices, and the integration of driver electronics within the display module. Furthermore, for full-color applications, the industry has largely moved to blue InGaN LEDs with phosphors for white light or combined with red and green LEDs. However, for monochromatic red displays requiring high efficiency and reliability, particularly in industrial or outdoor settings, AlInGaP-based devices like the one described continue to be a robust and effective solution. The move towards higher integration and smarter displays is ongoing, but discrete dot matrix modules serve an important role in cost-sensitive or custom applications.