LTP-1557AKA LED Dot Matrix Display Datasheet - 1.2 inch (30.42mm) Height - AlInGaP Red Orange - 5x7 Array - English Technical Document

1. Product Overview

The LTP-1557AKA is a single-digit, alphanumeric display module designed for applications requiring clear, reliable character output. Its core function is to visually represent information through a grid of individually controllable light-emitting diodes (LEDs).

1.1 Core Advantages and Target Market

This device offers several key advantages that make it suitable for a range of industrial and commercial applications. Its primary benefits include a low power requirement, which is essential for battery-operated or energy-sensitive systems. The solid-state reliability of LED technology ensures long operational life and resistance to shock and vibration compared to filament-based or other mechanical displays. The single-plane, wide viewing angle design provides good visibility from various positions, which is crucial for user interfaces. Finally, its compatibility with standard character codes (USASCII and EBCDIC) and horizontal stackability simplifies integration into systems requiring multi-digit displays. Typical target markets include instrumentation panels, point-of-sale terminals, industrial control systems, and test equipment where durable, legible character output is needed.

2. Technical Specifications Deep Dive

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

2.1 Photometric and Optical Characteristics

The optical performance is defined at an ambient temperature (Ta) of 25°C. The device utilizes AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material for its LED chips, which are fabricated on a non-transparent GaAs substrate. This material choice is known for high efficiency in the red-orange spectrum. The display has a gray face with white dot color for contrast.

• Average Luminous Intensity (I_V): Ranges from a minimum of 2100 μcd to a typical value of 3800 μcd. This measurement is taken under specific drive conditions: a peak current (I_p) of 80mA with a 1/16 duty cycle. The intensity is measured using a sensor and filter approximating the CIE photopic eye-response curve, ensuring the value correlates with human brightness perception.
• Wavelength Characteristics:
  • Peak Emission Wavelength (λ_p): Typically 621 nm, indicating the strongest point of light emission in the red-orange region.
  • Dominant Wavelength (λ_d): Typically 615 nm. This is the single wavelength perceived by the human eye to match the color of the light, which may differ slightly from the peak wavelength.
  • Spectral Line Half-Width (Δλ): Typically 18 nm. This parameter defines the bandwidth of the emitted light, indicating the range of wavelengths around the peak. A narrower half-width indicates a more spectrally pure color.
• Luminous Intensity Matching Ratio (I_V-m): Has a maximum ratio of 2:1. This specifies the allowable variation in brightness between the brightest and dimmest dots in the array, ensuring uniform appearance.

2.2 Electrical Parameters

All electrical characteristics are also specified at Ta=25°C.

• Forward Voltage per Dot (V_F): Typically 2.6V, with a maximum of 2.6V, when driven at a forward current (I_F) of 20mA. This is the voltage drop across an LED when it is illuminated.
• Reverse Current per Dot (I_R): Maximum of 100 μA when a reverse voltage (V_R) of 5V is applied. This indicates the level of leakage current when the LED is reverse-biased.

2.3 Absolute Maximum Ratings and Thermal Considerations

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

• Average Power Dissipation per Dot: 33 mW maximum.
• Peak Forward Current per Dot: 90 mA maximum, but only under pulsed conditions (1/10 duty cycle, 0.1 ms pulse width). This allows for higher instantaneous brightness.
• Average Forward Current per Dot: The rating is 13 mA at 25°C. Crucially, this rating derates linearly at a rate of 0.17 mA/°C as the ambient temperature increases above 25°C. This is a critical design parameter for thermal management.
• Reverse Voltage per Dot: 5 V maximum.
• Operating & Storage Temperature Range: -35°C to +85°C.
• Solder Temperature: The device can withstand a maximum soldering temperature of 260°C for a maximum of 3 seconds, measured 1.6mm (1/16 inch) below the seating plane of the package.

3. Binning System Explanation

The datasheet indicates the device is categorized for luminous intensity. This refers to a manufacturing binning process. During production, LEDs exhibit natural variations in performance. Devices are tested and sorted (binned) based on their measured luminous intensity. This allows customers to select parts within a specific brightness range (e.g., the 2100-3800 μcd range specified), ensuring consistency in the brightness of the final product. The datasheet does not specify separate bins for wavelength or forward voltage, suggesting primary sorting is based on light output.

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 typically included in full datasheets are essential for design. Engineers would expect to see:

• Relative Luminous Intensity vs. Forward Current (I-V Curve): Shows how light output increases with drive current, helping to set the operating point for desired brightness.
• Relative Luminous Intensity vs. Ambient Temperature: Illustrates how light output decreases as temperature rises, critical for applications in non-climate-controlled environments.
• Forward Voltage vs. Forward Current: Provides detailed V_F characteristics for accurate driver design.
• Spectral Distribution: A graph showing the relative power emitted across wavelengths, confirming the peak and dominant wavelength values.

These curves allow designers to predict performance under real-world, non-ideal conditions beyond the single-point data given in the tables.

5. Mechanical and Package Information

5.1 Physical Dimensions

The device is described as having a 1.2 inch (30.42 mm) matrix height. This refers to the height of the 5x7 dot array itself. A detailed package dimension drawing is referenced, with all dimensions in millimeters and standard tolerances of ±0.25 mm unless otherwise noted. This drawing is crucial for PCB (Printed Circuit Board) footprint design and mechanical integration.

5.2 Pin Connection and Internal Circuit

The device uses a 14-pin configuration. The pinout table clearly defines the function of each pin, specifying connections to specific anode rows (1-7) and cathode columns (1-5). This common-cathode per column architecture (where multiple LED anodes in a column share a common cathode pin) is standard for multiplexed matrix displays. An internal circuit diagram is referenced, which would visually show this row-anode, column-cathode matrix arrangement, confirming the multiplexing scheme. Correct interpretation of this pinout is essential for designing the driving circuitry.

6. Soldering and Assembly Guidelines

The key assembly specification provided is the reflow soldering profile limit: a maximum temperature of 260°C for a maximum duration of 3 seconds, measured at a point 1.6mm below the package body. This information is vital for process engineers to set up soldering ovens to prevent thermal damage to the LED chips or the package. For storage, the specified range of -35°C to +85°C should be maintained to preserve device integrity before use.

7. Application Recommendations

7.1 Typical Application Scenarios

This display is ideal for applications requiring a single, highly legible character or symbol. Examples include status indicators on industrial machinery (showing codes like 'A', 'C', 'F'), digit positions in larger multi-digit displays (when stacked), simple readouts on test equipment, or as part of a user interface on specialized devices.

7.2 Design Considerations

• Drive Circuitry: A microcontroller or dedicated display driver IC is required to perform multiplexing. The circuit must sequentially activate the correct row anode and column cathode pins to illuminate the desired dot pattern for each character. Current-limiting resistors are mandatory for each anode or column line to set the forward current.
• Current Calculation: The average current per dot must be respected. For multiplexed N rows, the instantaneous current can be higher, but the average current over time must not exceed the rated 13 mA (derated for temperature). For example, with 1/7 duty cycle multiplexing, the peak current could be up to ~91mA to achieve a 13mA average, but this must also stay below the 90mA peak rating.
• Thermal Management: The derating of average forward current (0.17 mA/°C) must be factored into the design if the operating ambient temperature is expected to exceed 25°C significantly. Adequate board layout and possibly heatsinking may be necessary in high-temperature environments.
• Viewing Angle: Leverage the wide viewing angle by positioning the display for optimal visibility by the intended user.

8. Technical Comparison and Differentiation

Compared to older technologies like incandescent or vacuum fluorescent displays (VFDs), the LTP-1557AKA offers superior shock/vibration resistance, lower power consumption, and longer lifetime. Compared to other LED matrix displays, its use of AlInGaP technology for red-orange offers higher efficiency and potentially better color stability over time and temperature compared to older GaAsP (Gallium Arsenide Phosphide) red LEDs. The specific combination of a 1.2" character height, 5x7 resolution, and the defined brightness/intensity binning are its key differentiating physical and performance specs within the LED matrix display category.

9. Frequently Asked Questions (Based on Technical Parameters)

1. Q: Can I drive this display with a constant DC current on each dot? A: Technically yes, but it is highly inefficient for a matrix. It would require 35 individual current-limiting circuits (5x7). Multiplexing is the standard and intended method, significantly reducing the required driver pins and components.
2. Q: The max average current is 13mA, but my multiplexing scheme uses a 1/16 duty cycle. What peak current can I use? A: You can calculate the allowable peak current: I_peak = I_avg / Duty Cycle. For 1/16 duty, I_peak = 13mA / 0.0625 = 208mA. However, you must also ensure this peak current does not exceed the absolute maximum peak current rating of 90mA. Therefore, the 90mA limit is the governing constraint in this case.
3. Q: What is the difference between peak wavelength and dominant wavelength? A: Peak wavelength is the physical wavelength where the LED emits the most optical power. Dominant wavelength is the perceptual single wavelength that matches the color the human eye sees. They often differ slightly due to the shape of the LED's emission spectrum.
4. Q: The storage temperature is the same as operating temperature. Does this mean I can leave it powered on at -35°C? A: The operating range indicates the device will function within specifications across that range. However, performance (like luminous intensity) will vary with temperature. The storage range simply indicates the conditions under which the unpowered device will not be damaged. Reliable operation at extreme ends of the range should be verified in the application.

10. Design and Usage Case Study

Scenario: Designing a single-digit error code display for an industrial sensor. The sensor has a microcontroller that detects various fault conditions (e.g., Overload, Sensor Fail, Calibration Error). Each fault is assigned an alphanumeric code ('O', 'F', 'C'). The LTP-1557AKA is chosen for its durability in an industrial setting. The microcontroller's I/O pins, insufficient to drive 35 dots directly, are connected to a dedicated LED driver IC. The driver handles the multiplexing, retrieving the correct 5x7 font pattern from a lookup table in memory based on the error code. A current-limiting resistor network is calculated based on the desired brightness, the forward voltage, the supply voltage, and the multiplexing duty cycle, carefully ensuring the peak and average current limits are not exceeded. The display provides an immediate, clear visual indication of the fault type to maintenance personnel.

11. Operating Principle Introduction

The LTP-1557AKA is a passive matrix LED display. It contains 35 independent AlInGaP LED chips arranged in a grid of 5 columns and 7 rows. Each LED is connected between one row anode and one column cathode. To illuminate a specific dot, a positive voltage is applied to its corresponding row anode pin, while its corresponding column cathode pin is connected to ground (or a lower voltage). The internal semiconductor structure of each LED chip consists of P-type and N-type AlInGaP layers forming a PN junction. When forward-biased (anode positive relative to cathode), electrons and holes recombine in the junction, releasing energy in the form of photons (light) at a wavelength determined by the bandgap energy of the AlInGaP material. The display is multiplexed: instead of lighting all desired dots simultaneously, the controller rapidly cycles through the rows (or columns), lighting only the dots in the active row that are part of the character. This happens faster than the human eye can perceive, creating the illusion of a stable, fully lit character while drastically reducing the number of required driver pins from 35 to 12 (7 rows + 5 columns).

12. Technology Trends and Context

Displays like the LTP-1557AKA represent a mature, well-established technology. The trend in information display has largely moved towards higher-density, multi-color, and graphical solutions like OLEDs, TFT LCDs, and finer-pitch LED matrices. However, single-character or small digit displays like this remain highly relevant in specific niches due to their simplicity, robustness, high brightness, wide operating temperature range, and low cost for applications that do not require complex graphics. The underlying AlInGaP material technology itself was a significant advancement over older GaAsP, offering improved efficiency and color purity for red, orange, and amber LEDs. Future developments in this segment focus on further increasing efficiency (lumens per watt), improving uniformity, and potentially integrating the driver electronics more closely with the display package to simplify end-user design. For ultra-low-power or sunlight-readable applications, these types of discrete LED arrays continue to be a preferred choice over more complex display technologies.