LTP-1457AKA LED Display Datasheet - 1.2-inch (30.42mm) Matrix Height - AlInGaP Red Orange - 2.6V Forward Voltage - 33mW Power Dissipation - English Technical Document

1. Product Overview

The LTP-1457AKA is a single-digit, alphanumeric display module built using a 5x7 dot matrix configuration. Its primary function is to visually represent characters and symbols, compatible with standard USASCII and EBCDIC code sets. The core technology utilizes AlInGaP (Aluminum Indium Gallium Phosphide) Red Orange LED chips, which are fabricated on a non-transparent GaAs substrate. This substrate choice contributes to the device's characteristic gray face and white dot color appearance. The display is categorized based on its luminous intensity, ensuring consistency in brightness for applications requiring multiple units.

The device is designed for low power consumption and offers solid-state reliability. A key mechanical feature is its stackability, allowing multiple units to be placed side-by-side horizontally to form multi-character displays without significant gaps, ideal for message boards or simple numeric readouts.

2. Technical Parameters Deep Objective Interpretation

2.1 Photometric and Optical Characteristics

The optical performance is defined under specific test conditions at an ambient temperature (Ta) of 25°C. The average luminous intensity (Iv) per dot has a typical value of 3800 µcd when driven with a peak current (Ip) of 80mA at a 1/16 duty cycle. The minimum specified value is 2100 µcd. The luminous intensity matching ratio between dots is specified at a maximum of 2:1, which defines the allowable variation in brightness across the matrix.

The color characteristics are defined by wavelength. The peak emission wavelength (λp) is typically 621 nm. The dominant wavelength (λd), which more closely correlates with perceived color, is typically 615 nm, placing it firmly in the red-orange spectrum. The spectral line half-width (Δλ) is typically 18 nm, indicating the spectral purity or bandwidth of the emitted light.

2.2 Electrical Parameters

The forward voltage (VF) for any single LED dot, measured at a forward current (IF) of 20mA, ranges from a minimum of 2.05V to a maximum of 2.6V, with a typical value provided. The reverse current (IR) for any dot, when a reverse voltage (VR) of 5V is applied, has a maximum specified value of 100 µA.

2.3 Absolute Maximum Ratings and Thermal Considerations

These ratings define the stress limits beyond which permanent damage may occur. The average power dissipation per dot must not exceed 33 mW. The peak forward current per dot is rated at 90 mA, but only under pulsed conditions: a 1/10 duty cycle with a 0.1 ms pulse width. The average forward current per dot has a derating factor; it is 13 mA at 25°C and decreases linearly by 0.17 mA for every degree Celsius increase in ambient temperature.

The device can withstand a reverse voltage of up to 5V per dot. The operating and storage temperature range is specified from -35°C to +85°C. For assembly, the solder temperature must not exceed 260°C for a maximum duration of 3 seconds, measured at a point 1.6mm (1/16 inch) below the seating plane of the component.

3. Binning System Explanation

The datasheet explicitly states that the device is "Categorized for Luminous Intensity." This indicates a binning or sorting process based on measured light output. Units are tested and grouped into specific intensity bins (e.g., a bin for 2100-2800 µcd, another for 2800-3800 µcd). This ensures that designers can select parts with consistent brightness for their application, which is critical when multiple displays are used together to avoid noticeable brightness variations. The datasheet does not specify separate bins for wavelength or forward voltage, suggesting the primary sorting criterion is luminous intensity.

4. Performance Curve Analysis

The datasheet includes a section for "Typical Electrical / Optical Characteristic Curves." While the specific graphs are not detailed in the provided text, such curves typically illustrate the relationship between key parameters. Standard curves for this type of device would likely include:

• Forward Current vs. Forward Voltage (I-V Curve): Shows the non-linear relationship between the current through the LED and the voltage across it. This is crucial for designing the current-limiting circuitry.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with current, typically in a sub-linear fashion at higher currents due to heating effects.
• Luminous Intensity vs. Ambient Temperature: Shows the decrease in light output as the junction temperature of the LED rises. AlInGaP LEDs generally exhibit less thermal quenching than older technologies like GaAsP, but output still declines with heat.
• Spectral Distribution: A graph plotting relative intensity against wavelength, showing the peak at ~621nm and the 18nm half-width.

These curves are essential for understanding the device's behavior under non-standard conditions (different currents, temperatures) and for optimizing the drive circuitry for efficiency and longevity.

5. Mechanical and Packaging Information

The device has a 1.2-inch matrix height, which corresponds to 30.42 mm. This refers to the height of the 5x7 array itself. The package dimensions are provided in a detailed drawing with all measurements in millimeters. The standard tolerance for these dimensions is ±0.25 mm (0.01 inches) unless otherwise noted on the drawing. The pin connection diagram is critical for interfacing. The display has 14 pins that control the 5 columns (anodes) and 7 rows (cathodes) in a multiplexed arrangement. The specific pinout is: 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, Pin 12: Cathode Row 4, Pin 13: Anode Column 1, Pin 14: Cathode Row 2. Note the non-sequential ordering, which is common in multiplexed displays to optimize internal routing.

The internal circuit diagram shows the matrix structure: five common anode columns and seven common cathode rows. Each intersection represents one LED dot. To illuminate a specific dot, its corresponding column pin must be driven high (anode), and its row pin must be driven low (cathode).

6. Soldering and Assembly Guidelines

The primary assembly constraint provided is the soldering temperature profile. The component body must not be exposed to temperatures above 260°C for more than 3 seconds during the reflow or wave soldering process. This is a standard rating for many through-hole and some surface-mount components. The measurement point is 1.6mm below the seating plane, which is typically the point where the leads exit the package body. This ensures the sensitive LED chip inside is not damaged by excessive heat conducted through the leads. For hand soldering, a temperature-controlled iron should be used, and contact time with each pin should be minimized. Proper ESD (Electrostatic Discharge) handling procedures should always be followed when working with semiconductor devices.

7. Application Suggestions

7.1 Typical Application Scenarios

This display is suited for applications requiring a single, highly legible alphanumeric character. Its stackability makes it ideal for multi-digit displays. Common uses include:

• Industrial instrument panels (for displaying setpoints, readings, error codes).
• Consumer appliances (microwave ovens, washing machines, thermostats).
• Test and measurement equipment.
• Simple information displays in vending machines or kiosks.
• Educational kits for learning about multiplexed LED driving and microcontroller interfacing.

7.2 Design Considerations

Drive Circuitry: The display requires external multiplexing driver circuitry. This can be implemented using discrete transistors, dedicated LED driver ICs (like the MAX7219), or directly from a microcontroller with sufficient current sourcing/sinking capability. The peak current rating (90mA at 1/10 duty) must be respected. A typical design would use a constant current source or a current-limiting resistor for each column (anode) and sink the current through the rows (cathodes) using transistors or GPIO pins.

Current Calculation: To achieve the typical luminous intensity of 3800 µcd, the datasheet specifies a condition of Ip=80mA at 1/16 duty cycle. The average current per dot is therefore 80mA / 16 = 5mA. The total average current for a fully lit character (all 35 dots on) would be 35 * 5mA = 175mA, but this is distributed across the multiplexed columns and rows.

Viewing Angle: The "wide viewing angle" feature is beneficial for applications where the display may be viewed from off-axis positions.

Optical Considerations: The gray face and white dots provide good contrast. Designers may consider adding a colored filter or diffuser in front of the display to enhance contrast or match a product's aesthetic, though this will reduce overall light output.

8. Technical Comparison

The LTP-1457AKA's key differentiator is its use of AlInGaP LED technology. Compared to older technologies like standard GaAsP (Gallium Arsenide Phosphide) red LEDs, AlInGaP offers significantly higher luminous efficiency. This means it can produce more light (higher luminous intensity) for the same amount of electrical current, or achieve the same brightness with lower power consumption. AlInGaP also generally has better temperature stability and longer operational lifetime. Compared to modern white LEDs or smaller pitch SMD matrix displays, this device is a larger, through-hole component offering simplicity, robustness, and high single-character visibility from a distance, often at a lower system cost for single-digit applications.

9. Frequently Asked Questions Based on Technical Parameters

Q: Can I drive this display with a constant DC current on each dot?
A: Technically yes, but it is highly inefficient and not recommended. The display is designed for multiplexed operation. Driving all dots continuously would exceed the average power dissipation rating (33mW per dot) if trying to achieve standard brightness, leading to overheating and rapid failure.

Q: What is the difference between peak emission wavelength and dominant wavelength?
A: Peak emission wavelength is the wavelength at which the spectral power distribution is maximum. Dominant wavelength is the single wavelength of monochromatic light that would match the perceived color of the LED. For LEDs with a relatively narrow spectrum like this one, they are often close, but dominant wavelength is more relevant for color specification.

Q: The pinout seems non-sequential. Why is it arranged this way?
A: The pin arrangement is optimized for the internal layout of the traces on the display's substrate to minimize cross-talk and simplify the connection of the LED matrix. It is essential to follow the provided pin connection table exactly; do not assume a logical sequence.

Q: How do I interpret the "Average Forward Current Derating" specification?
A: It means the safe maximum average current per dot decreases as ambient temperature rises. At 25°C, you can use up to 13 mA average current. At 85°C (the max operating temperature), the allowable current is 13 mA - [ (85-25) * 0.17 mA/°C ] = 13 mA - 10.2 mA = 2.8 mA. This derating is crucial for reliable operation in high-temperature environments.

10. Practical Use Case

Case: Designing a Single-Digit Temperature Readout for an Industrial Oven.
An engineer needs to display the setpoint temperature (0-9) on an oven that operates up to 80°C ambient inside the control panel. They select the LTP-1457AKA for its visibility and temperature range. Due to the high ambient temperature, they must derate the drive current. Targeting a lower brightness is acceptable in this controlled environment. They design a multiplexing circuit using a microcontroller, driving the columns through current-limiting resistors and the rows via NPN transistors. The firmware scans the rows at a high frequency (>100Hz). They calculate the average current per dot to be below the derated value of ~3mA at 80°C to ensure long-term reliability. The gray/white appearance provides good contrast against the oven's dark panel.

11. Operating Principle Introduction

The LTP-1457AKA operates on the principle of a multiplexed LED matrix. It contains 35 individual AlInGaP LED junctions arranged in a grid of 5 columns and 7 rows. Each LED is connected between one column line (anode) and one row line (cathode). To illuminate a specific pattern (like a number or letter), the controller does not power all dots simultaneously. Instead, it uses a technique called multiplexing or scanning. It activates one row (cathode) at a time by connecting it to ground (low logic level). Simultaneously, it applies power (high logic level) only to the column lines (anodes) that need to be lit for that particular row. This cycle repeats rapidly through all seven rows. Due to persistence of vision, the human eye perceives a stable, fully formed character. This method drastically reduces the number of required driver pins (14 instead of 35) and lowers total power consumption.

12. Technology Trends

Displays like the LTP-1457AKA represent a mature technology. Current trends in indicator and alphanumeric displays are moving towards:

• Surface-Mount Device (SMD) Packages: Smaller footprints for higher density PCB design and automated assembly.
• Higher Integration: Displays with built-in controllers, memory (for fonts), and serial interfaces (I2C, SPI) simplifying the host microcontroller's task.
• Advanced LED Materials: While AlInGaP is efficient for red/orange, newer materials like InGaN enable brighter and more efficient green, blue, and white LEDs, leading to full-color matrix displays.
• Alternative Technologies: For larger, more complex displays, OLED (Organic LED) and micro-LED technologies offer superior contrast, viewing angles, and flexibility.

However, through-hole, single-digit displays like this one remain relevant for their simplicity, durability, high single-character visibility, and cost-effectiveness in applications where only one or a few digits are needed, especially in industrial or hobbyist contexts where through-hole assembly may be preferred.