LTP-2057AJD LED Display Datasheet - 2.0-inch Height - 5x7 Dot Matrix - AlGaAs Red - English Technical Document

1. Product Overview

The LTP-2057AJD is a single-digit, alphanumeric display module designed for applications requiring clear, legible character output. Its core function is to visually represent information by selectively illuminating a grid of light-emitting diodes (LEDs).

1.1 Core Advantages and Target Market

This device offers several key advantages that define its application space. It features a 2.0-inch (50.8 mm) character height, making it suitable for medium-distance viewing. The low power requirement is a significant benefit for battery-operated or energy-conscious systems. Its solid-state reliability ensures long operational life with no moving parts, and the wide viewing angle from its single-plane design allows for visibility from various positions. The display is stackable horizontally, enabling the creation of multi-character messages. It is compatible with standard USASCII and EBCDIC character codes, simplifying integration with microcontrollers and computers. The device is also categorized for luminous intensity, allowing for brightness matching in multi-unit applications. Its primary target markets include industrial control panels, instrumentation, point-of-sale terminals, basic information displays, and embedded systems where robust, simple character output is required.

2. Technical Specifications Deep Dive

The performance of the LTP-2057AJD is defined by a set of absolute limits and typical operating characteristics.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. They are not for continuous operation.

• Average Power Dissipation Per Dot: 33 mW
• Peak Forward Current Per Dot: 90 mA
• Average Forward Current Per Dot: 13 mA at 25°C, derating linearly at 0.17 mA/°C above 25°C.
• Reverse Voltage Per Dot: 5 V
• Operating Temperature Range: -35°C to +85°C
• Storage Temperature Range: -35°C to +85°C
• Solder Temperature: Maximum 260°C for a maximum of 3 seconds at 1.6mm (1/16 inch) below the seating plane.

2.2 Electrical and Optical Characteristics

These parameters are measured under specific test conditions (Ta=25°C) and represent typical performance.

• Average Luminous Intensity (I_V): 1300 μcd (Min), 3000 μcd (Typ) at I_p=32mA, 1/16 Duty Cycle. This is the key brightness parameter.
• Peak Emission Wavelength (λ_p): 660 nm (Typ) at I_F=20mA. This indicates the color is in the deep red spectrum.
• Spectral Line Half-Width (Δλ): 35 nm (Typ) at I_F=20mA.
• Dominant Wavelength (λ_d): 638 nm (Typ) at I_F=20mA.
• Forward Voltage (V_F) any Dot: 1.8V to 2.4V (Typ) at I_F=20mA; 2.0V to 2.7V (Typ) at I_F=80mA.
• Reverse Current (I_R) any Dot: 100 μA (Max) at V_R=5V.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 (Max) at I_p=32mA, 1/16 Duty Cycle. This specifies the maximum brightness variation between dots.

Note: Luminous intensity is measured with a light sensor and filter combination that approximates the CIE (Commission Internationale de l'\u00c9clairage) photopic eye-response curve.

3. Binning System Explanation

The datasheet indicates the device is categorized for luminous intensity. This means units are tested and sorted (binned) based on their measured brightness output under standard conditions. This allows designers to select displays with consistent brightness levels for their application, preventing noticeable variations in multi-character displays. While specific bin codes are not provided in this excerpt, the matching ratio of 2:1 defines the maximum allowable variation within a given bin.

4. Performance Curve Analysis

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

• Forward Current vs. Forward Voltage (I-V Curve): Shows the nonlinear relationship between current and voltage drop across the LED junction.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with current, typically showing a region of linear relationship before saturation.
• Luminous Intensity vs. Ambient Temperature: Illustrates the decrease in light output as junction temperature rises, a critical factor for thermal management.
• Spectral Distribution: A plot showing the relative intensity of light emitted across different wavelengths, centered around the peak wavelength of 660 nm.

These curves are essential for detailed circuit design, driver selection, and understanding performance under non-standard conditions.

5. Mechanical and Package Information

5.1 Package Dimensions

The device has a specific physical footprint. All dimensions are in millimeters with a general tolerance of ±0.25 mm (0.01\") unless otherwise specified. The exact dimensional drawing is referenced in the datasheet, detailing the overall length, width, height, lead spacing, and positioning of the display area.

5.2 Pin Connection and Polarity

The LTP-2057AJD has a 14-pin configuration. The pinout is as follows:

• Pin 1: Cathode Row 5
• Pin 2: Cathode Row 7
• Pin 3: Anode Column 2
• Pin 4: Anode Column 3
• Pin 5: Cathode Row 4
• Pin 6: Anode Column 5
• Pin 7: Cathode Row 6
• Pin 8: Cathode Row 3
• Pin 9: Cathode Row 1
• Pin 10: Anode Column 4
• Pin 11: Anode Column 3 (Note: Duplicate of Pin 4 function, likely a documentation note to verify)
• Pin 12: Cathode Row 4 (Note: Duplicate of Pin 5 function, likely a documentation note to verify)
• Pin 13: Anode Column 1
• Pin 14: Cathode Row 2

The internal circuit diagram shows a common-cathode configuration for rows, meaning each row of 5 LEDs shares a common cathode (negative) connection. The anodes (positive) for each column are separate. This matrix arrangement minimizes the number of required driver pins (12 for 35 LEDs).

6. Soldering and Assembly Guidelines

The key assembly specification provided is the soldering temperature profile. The device can withstand a maximum temperature of 260°C for a maximum of 3 seconds, measured at a point 1.6mm (1/16 inch) below the seating plane of the package. This is critical for wave soldering or reflow processes. Designers must ensure their soldering profile does not exceed this limit to prevent damage to the internal LED chips or plastic package. Standard ESD (Electrostatic Discharge) precautions should be observed during handling. The storage temperature range (-35°C to +85°C) should also be adhered to for long-term reliability.

7. Application Recommendations

7.1 Typical Application Scenarios

• Industrial Control Panels: Displaying setpoints, status codes, or error messages.
• Test and Measurement Equipment: Showing numerical readings or unit identifiers.
• Consumer Electronics: Basic displays on appliances, audio equipment, or clocks.
• Embedded Systems Prototyping: A simple output device for microcontroller projects.
• Legacy System Upgrades: Replacing older incandescent or vacuum fluorescent displays.

7.2 Design Considerations

• Driver Circuit: Requires a multiplexing driver circuit (or a dedicated display driver IC) capable of sourcing/sinking the necessary column/row currents. The 1/16 duty cycle mentioned in the test condition suggests a multiplexing scheme.
• Current Limiting: External current-limiting resistors are mandatory for each anode column (or a controlled current source) to prevent exceeding the absolute maximum current ratings.
• Thermal Management: While low power, continuous operation at high ambient temperatures may require derating the forward current as specified.
• Viewing Angle: The wide viewing angle is beneficial, but the mounting position should be considered to align with the intended viewer.
• Optical Filtering: A red filter can enhance contrast in high-ambient-light conditions.

8. Technical Comparison and Differentiation

Compared to other display technologies available at its time (and similar basic modules today), the LTP-2057AJD's primary differentiators are its AlGaAs (Aluminum Gallium Arsenide) LED technology and 2.0-inch character height. AlGaAs LEDs typically offer good efficiency and a stable red color. Compared to smaller (e.g., 0.56\") or larger displays, it fits a specific niche requiring medium-size characters. Versus LCDs, it offers superior viewing angles, wider temperature range, and does not require a backlight, but consumes more power for a similarly lit area. Its simplicity and robustness are its main advantages over more complex graphic displays.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What driver voltage is required?
A: The forward voltage per LED is typically 1.8-2.4V at 20mA. A driver circuit supplying 5V is common, using dropping resistors. The driver must handle the multiplexing timing.

Q: How do I achieve the rated brightness of 3000 μcd?
A: The test condition is a peak current (I_p) of 32mA at a 1/16 duty cycle. This implies an average current per dot of 2mA. Your multiplexing driver must provide this specific pulse to achieve the typical brightness.

Q: Can I connect multiple displays together?
A: Yes, the datasheet states it is stackable horizontally. This likely means the mechanical design allows physical abutment, and the electrical design would involve connecting corresponding row and column lines in parallel, requiring a driver with higher current capability for the shared lines.

Q: What is the difference between peak and dominant wavelength?
A> Peak wavelength (660 nm) is the single wavelength where the emission spectrum is strongest. Dominant wavelength (638 nm) is the single wavelength of a pure monochromatic light that would appear to have the same color to the human eye. The difference is due to the shape of the LED's broad emission spectrum.

10. Design and Usage Case Study

Scenario: Designing a simple 4-digit production counter for a factory workstation.
Four LTP-2057AJD displays would be stacked horizontally. A microcontroller (e.g., an Arduino or PIC) would be programmed to count pulses from a sensor. The firmware would handle converting the decimal number into the appropriate segment patterns for each digit. The microcontroller's I/O pins, likely through transistor arrays or a dedicated driver IC like the MAX7219, would multiplex the displays. The 2.0-inch height ensures the count is easily visible from several feet away. The AlGaAs red LEDs provide high contrast against typical industrial backgrounds. The low average power consumption allows the unit to be powered from a standard 24V DC supply common in factories, stepped down to 5V for logic. The robust temperature range ensures reliable operation in non-climate-controlled environments.

11. Operating Principle Introduction

The LTP-2057AJD is a 5x7 dot matrix display. It contains 35 individual AlGaAs red LED chips arranged in a grid of 5 columns and 7 rows. Each LED is located at the intersection of a column anode line and a row cathode line. To illuminate a specific dot, a positive voltage (through a current limiter) is applied to its corresponding column anode, while its row cathode is connected to ground (or a low voltage). By rapidly sequencing (multiplexing) through the rows and setting the appropriate column patterns for each row, the illusion of a stable character is created. This multiplexing drastically reduces the number of required control pins from 35 to 12 (7 rows + 5 columns). The human eye's persistence of vision blends the rapidly flashing dots into a continuous image.

12. Technology Trends and Context

Displays like the LTP-2057AJD represent a mature technology. While largely superseded for new high-information-density designs by dot-matrix graphic OLEDs, LCDs, or smaller, surface-mount LED arrays, they remain relevant in specific niches. The trends influencing this segment include: a move towards surface-mount device (SMD) packages for automated assembly, the integration of driver ICs and controllers directly onto the display module (simplifying interface to a simple serial bus like I2C or SPI), and the development of displays with multiple colors or RGB LEDs in a single package. However, the fundamental advantages of simple LED dot matrix displays—extreme reliability, wide temperature range, high brightness, and simplicity—ensure their continued use in industrial, automotive, and harsh environment applications where newer technologies may be less robust. The principles of multiplexed matrix addressing remain foundational to almost all modern pixel-based displays.