LTP-2157AKA LED Dot Matrix Display Datasheet - 2.0-inch (50.8mm) Height - Super Orange Color - 5x7 Array - English Technical Document

1. Product Overview

The LTP-2157AKA is a single-plane, 5x7 dot matrix LED display module designed for alphanumeric character presentation. Its primary function is to display characters from standard code sets such as USASCII and EBCDIC. The core advantage of this device lies in its utilization of AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for the LED chips, which provides the Super Orange emission. The display features a gray face and white dot color, enhancing contrast for improved readability. The device is categorized for luminous intensity, ensuring consistency in brightness across units. Its solid-state construction offers high reliability, and the low power requirement makes it suitable for various electronic applications.

1.1 Core Features and Target Applications

The key features defining this product include a 2.0-inch (50.8 mm) matrix character height, which offers good visibility from a distance. It operates with a single plane and provides a wide viewing angle, making the displayed information accessible from various positions. The 5x7 array with X-Y select architecture allows for efficient multiplexing control. A significant feature is its horizontal stackability, enabling the creation of multi-character displays by aligning multiple units side-by-side. The device is directly compatible with standard character codes. These characteristics make the LTP-2157AKA ideal for applications such as industrial instrument panels, point-of-sale terminals, basic information displays, test equipment readouts, and other embedded systems requiring reliable, low-to-medium complexity alphanumeric output.

2. Technical Specifications and Objective Interpretation

This section provides a detailed, objective analysis of the device's electrical, optical, and physical parameters as defined in the datasheet.

2.1 Absolute Maximum Ratings

The Absolute Maximum Ratings define the stress limits beyond which permanent damage to the device may occur. These are not conditions for normal operation.

• Average Power Dissipation Per Dot: 33 mW. This is the maximum continuous power that can be safely dissipated by a single LED dot.
• Peak Forward Current Per Dot: 90 mA. This is the maximum instantaneous current pulse a dot can handle, typically relevant for multiplexed driving schemes.
• Average Forward Current Per Dot: 13 mA at 25°C, derating linearly at 0.17 mA/°C. This is the key parameter for continuous DC operation. The derating factor is crucial for thermal management; as ambient temperature (Ta) rises, the maximum allowable continuous current must be reduced to prevent overheating.
• Reverse Voltage Per Dot: 5 V. Exceeding this voltage in reverse bias can damage the LED junction.
• Operating & Storage Temperature Range: -35°C to +85°C. The device is rated for industrial temperature ranges.
• Solder Temperature: Maximum 260°C for 3 seconds at 1.6mm below the seating plane. This defines the reflow soldering profile constraints.

2.2 Electrical & Optical Characteristics

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

• Average Luminous Intensity (I_V): 2100 μcd (Min), 4600 μcd (Typ) under a test condition of I_p=32mA at 1/16 duty cycle. This indicates the brightness of each LED dot when driven in a multiplexed configuration. The wide range suggests a binning process for intensity.
• Peak Emission Wavelength (λ_p): 621 nm (Typ). This is the wavelength at which the optical power output is maximum, defining the \"Super Orange\" color.
• Spectral Line Half-Width (Δλ): 18 nm (Typ). This measures the spectral purity; a smaller value indicates a more monochromatic light.
• Dominant Wavelength (λ_d): 615 nm (Typ). This is the single wavelength perceived by the human eye, closely related to the color point.
• Forward Voltage (V_F) any Dot: 2.05V (Min), 2.6V (Typ) at I_F=20mA; 2.3V (Min), 2.8V (Typ) at I_F=80mA. This is critical for driver circuit design, specifying the voltage drop across an LED when on.
• Reverse Current (I_R) any Dot: 100 μA (Max) at V_R=5V. This is the leakage current when the LED is reverse-biased.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 (Typ). This specifies the maximum allowable ratio between the brightest and dimmest dots in the array, ensuring uniform appearance.

3. Binning System Explanation

The datasheet indicates the device is \"Categorized for Luminous Intensity.\" This implies a binning or sorting process post-manufacturing. While specific bin codes are not listed, typical categorization for such displays involves grouping units based on measured luminous intensity under standard test conditions. This ensures that when multiple displays are used together, the brightness variation between them is minimized, providing a consistent visual output. Designers should verify the available intensity bins from the supplier for critical applications requiring matched brightness.

4. Performance Curve Analysis

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

• Forward Current vs. Forward Voltage (I_F-V_F Curve): Shows the exponential relationship, crucial for determining the required driving voltage for a given current.
• Luminous Intensity vs. Forward Current (I_V-I_F Curve): Demonstrates how light output increases with current, usually in a near-linear relationship within the operating range.
• Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as temperature increases, which is vital for thermal design.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the peak at ~621nm and the spectral width.

These curves allow designers to predict performance under non-standard conditions and optimize their driver circuitry.

5. Mechanical and Package Information

The device's package dimensions are provided in millimeters with a general tolerance of ±0.25 mm. The specific drawing is referenced but not detailed in the text. Key mechanical aspects include the overall footprint, height, and the spacing of the 14 pins. The pin arrangement is designed for through-hole mounting on a printed circuit board (PCB). The gray face and white dot color are part of the package design to improve contrast.

5.1 Pin Connection and Internal Circuit

The display has 14 pins. The internal circuit diagram shows a matrix configuration where the anodes of the LEDs are connected by rows and the cathodes by columns (or vice-versa, as per the pinout table). This is a common common-anode or common-cathode matrix architecture that minimizes the number of control pins required (5 rows + 7 columns = 12 control lines instead of 5*7=35). The pinout table specifies the function of each pin:

• Pins connect to Anode Row 1-7 and Cathode Column 1-5.
• Important Notes: Pin 4 & 11 are internally connected. Pin 5 & 12 are internally connected. This internal bridging must be considered during PCB layout and driver design to avoid short circuits.

6. Soldering and Assembly Guidelines

The primary guideline provided is for the soldering process: the device can withstand a maximum solder temperature of 260°C for a maximum of 3 seconds, measured 1.6mm (1/16 inch) below the seating plane. This is a standard reflow profile constraint. For wave soldering, standard practices for through-hole components should be followed. General handling precautions for static-sensitive devices (ESD) should be observed, although not explicitly stated for this LED product. Storage should be within the specified temperature range of -35°C to +85°C in a dry environment.

7. Application Suggestions and Design Considerations

7.1 Typical Application Circuits

The LTP-2157AKA requires an external driver circuit. Due to its matrix structure, multiplexing is the standard driving method. This involves sequentially activating one row (or column) at a time while providing the appropriate data signals to the columns (or rows). A microcontroller with sufficient I/O pins or a dedicated LED display driver IC (like the MAX7219 or similar) is typically used. The driver must supply the correct current, respecting the peak and average current ratings. Current-limiting resistors are mandatory for each column or row line to set the forward current (I_F). The value is calculated using the formula: R = (V_supply - V_F - V_{driver_sat}) / I_F.

7.2 Design Considerations

• Multiplexing Frequency: Must be high enough to avoid visible flicker (typically >60 Hz).
• Current Calculation: Use the average current rating (13mA max at 25°C) for DC calculations. In multiplexed mode with N rows, the peak current per dot can be up to N * I_avg, but must not exceed the 90mA peak rating.
• Thermal Management: If operating at high ambient temperatures, the forward current must be derated as per the 0.17 mA/°C factor.
• Voltage Supply: Must account for the highest V_F under operating conditions and any drops in the driver circuit.
• PCB Layout: Ensure correct pin mapping according to the connection table. Note the internally connected pins (4-11 and 5-12) to avoid layout errors.

8. Technical Comparison and Differentiation

Compared to older technology like standard GaAsP or GaP LEDs, the AlInGaP technology in the LTP-2157AKA offers significantly higher luminous efficiency, resulting in brighter output for the same current, and better color purity. Compared to simple 7-segment displays, the 5x7 dot matrix format provides true alphanumeric capability, allowing for the display of letters, numbers, and simple symbols. The 2.0-inch height is larger than many common character displays, offering superior visibility. The horizontal stackability is a key differentiator from displays with fixed multi-character modules, providing design flexibility.

9. Frequently Asked Questions (Based on Technical Parameters)

Q1: Can I drive this display with a constant DC current on all dots simultaneously?
A: Theoretically possible but impractical. It would require 35 independent current-limited channels. Multiplexing is the standard and efficient method.

Q2: What is the difference between Peak Emission Wavelength and Dominant Wavelength?
A: Peak wavelength is where the most optical power is emitted. Dominant wavelength is the single-wavelength equivalent perceived by the human eye. They are often close but not identical, especially for broader spectra.

Q3: How do I interpret the 1/16 duty cycle in the luminous intensity test condition?
A: The intensity is measured when the LED is pulsed with a 32mA current in a waveform with a 1/16 duty cycle. This simulates a multiplexed driving scheme where each row is active for 1/16th of the total cycle time. The reported intensity value is the average over time.

Q4: Why are pins 4 & 11 and 5 & 12 internally connected?
A> This is likely due to the internal layout of the matrix to simplify the chip bonding or substrate routing. Electrically, it means these pin pairs are shorted together. In your circuit, you must connect them to the same node.

10. Practical Use Case Example

Scenario: Designing a simple 4-digit temperature readout for an industrial oven.
The system uses a microcontroller with a temperature sensor. Four LTP-2157AKA displays are stacked horizontally. The microcontroller's firmware contains a font map for digits 0-9, the degree symbol, and 'C'. Using a multiplexing routine, it cycles through the four displays (acting as four sets of rows/columns), calculating the appropriate column data for each row based on the current digit to be shown. Current-limiting resistors are placed on the column lines. The refresh rate is set to 100 Hz to eliminate flicker. The high brightness and wide viewing angle ensure the temperature is readable from various positions on the factory floor. The industrial temperature rating of the display ensures reliable operation in the hot environment near the oven.

11. Operating Principle Introduction

The LTP-2157AKA is based on semiconductor electroluminescence. The AlInGaP chip structure forms a p-n junction. When a forward voltage exceeding the junction's threshold is applied, electrons and holes recombine in the active region, releasing energy in the form of photons. The specific alloy composition of AlInGaP determines the bandgap energy, which directly corresponds to the orange wavelength of light emitted (~621 nm). The 5x7 matrix is formed by individually addressable LED dice placed at the intersections of row and column conductors on a substrate. By selectively applying voltage to a specific row and column, only the LED at that intersection is forward-biased and lights up.

12. Technology Trends and Context

AlInGaP technology represents a significant advancement in visible LED efficiency for red, orange, and yellow colors. It has largely superseded older technologies like GaAsP. Current trends in display technology are moving towards higher-density matrices (e.g., 8x8, 16x16) and full-color RGB matrices. However, single-color, low-resolution dot matrix displays like the 5x7 remain highly relevant for cost-sensitive, reliability-critical applications where simple alphanumeric information is sufficient. Their advantages include simplicity, robustness, low power consumption, and excellent longevity. The principle of matrix addressing remains fundamental to larger and more complex display technologies, including OLED and microLED displays.