LTP-747KA LED Dot Matrix Display Datasheet - 0.7-inch (17.22mm) Digit Height - Red-Orange Color - AlInGaP Technology - English Technical Document

1. Product Overview

The LTP-747KA is a single-digit, 5 x 7 dot matrix alphanumeric display module. Its primary function is to provide a clear, bright visual output for characters and symbols in various electronic applications. The core component of this display is the use of advanced Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor material for the light-emitting diode (LED) chips, which are responsible for generating the characteristic red-orange light output. This material technology is known for its high efficiency and good performance characteristics.

The device is constructed with a gray-colored faceplate and features white-colored dots or segments, which enhances the contrast and readability of the illuminated elements against the background. The display is categorized based on its luminous intensity, meaning units are binned or sorted according to their measured light output to ensure consistency within specified ranges for applications requiring uniform brightness.

2. Technical Specifications Deep Dive

This section provides a detailed, objective analysis of the key technical parameters specified in the datasheet.

2.1 Optical Characteristics

The optical performance is central to the display's function. Key parameters are measured under specific test conditions, typically at an ambient temperature (T_A) of 25°C.

• Average Luminous Intensity (I_V): This is the measure of the perceived power of light emitted by a single dot. The typical value is 3400 microcandelas (µcd), with a minimum of 1650 µcd, when driven with a peak current (I_P) of 32mA at a 1/16 duty cycle. The 1/16 duty cycle is a common multiplexing scheme for dot matrix displays, where each row is active for only 1/16th of the time to manage power and heat.
• Peak Emission Wavelength (λ_p): The wavelength at which the emission spectrum of the LED is at its maximum intensity. For the LTP-747KA, this is typically 621 nanometers (nm), placing it firmly in the red-orange region of the visible light spectrum.
• Dominant Wavelength (λ_d): This is 615 nm, which is the single wavelength that best describes the color perceived by the human eye. It is slightly different from the peak wavelength due to the shape of the LED's emission spectrum.
• Spectral Line Half-Width (Δλ): This parameter, typically 18 nm, indicates the width of the emission spectrum at half of its maximum intensity. A narrower half-width indicates a more spectrally pure, saturated color.
• Luminous Intensity Matching Ratio (I_V-m): Specified as a maximum of 2:1, this ratio defines the allowable variation in brightness between the brightest and dimmest dots on the display. A lower ratio indicates better uniformity.

2.2 Electrical Characteristics

Understanding the electrical behavior is crucial for proper circuit design and ensuring long-term reliability.

• Forward Voltage per Dot (V_F): The voltage drop across an LED when it is conducting current. The typical value is 2.6V with a maximum of 2.6V at a forward current (I_F) of 20mA. The minimum is listed as 2.05V. This range must be considered when designing the current-limiting circuitry.
• Reverse Current per Dot (I_R): The small amount of current that flows when a reverse voltage is applied. It is specified as a maximum of 100 µA at a reverse voltage (V_R) of 5V. Exceeding the absolute maximum reverse voltage can cause damage.
• Average Forward Current per Dot: The maximum continuous DC current recommended for reliable operation is 13 mA. This is distinct from the peak current used in multiplexed operation.
• Peak Forward Current per Dot: The maximum instantaneous current a dot can handle, specified as 90 mA. In multiplexed applications, the instantaneous current can be higher than the average current, but it must not exceed this peak rating.

2.3 Absolute Maximum Ratings and Thermal Considerations

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

• Average Power Dissipation per Dot: The maximum power that can be continuously dissipated by a single LED dot is 33 mW. Exceeding this can lead to overheating and reduced lifespan.
• Operating and Storage Temperature Range: The device is rated to function in ambient temperatures from -35°C to +85°C. It can also be stored within this same temperature range.
• Current Derating: The average forward current must be reduced linearly above 25°C at a rate of 0.17 mA per degree Celsius. This is a critical design rule to prevent thermal runaway at higher ambient temperatures.
• Solder Temperature: During wave or reflow soldering, the temperature at a point 1/16 inch (approximately 1.6mm) below the seating plane of the package must not exceed 260°C for more than 3 seconds. This prevents damage to the internal die and wire bonds.

3. Binning and Categorization System

The datasheet explicitly states that the device is "categorized for luminous intensity." This implies a binning process.

• Luminous Intensity Binning: After manufacture, individual displays are tested and sorted into different bins based on their measured light output. This ensures that customers receive products with consistent brightness levels. The datasheet provides the min/typ/max values (1650/3400 µcd), but specific bin codes or categories are not detailed in this excerpt. In practice, ordering information would specify the desired intensity bin.
• Wavelength/Color Binning: While not explicitly mentioned for wavelength in this sheet, it is common practice for LED manufacturers to bin devices by dominant or peak wavelength to ensure color consistency, especially in multi-unit displays. The tight typical values for λ_p (621 nm) and λ_d (615 nm) suggest good inherent color uniformity from the AlInGaP material.

4. Performance Curve Analysis

The datasheet references "Typical Electrical / Optical Characteristic Curves." While the specific graphs are not provided in the text, we can infer their standard content and significance.

• Forward Current vs. Forward Voltage (I_F-V_F) Curve: This graph shows the non-linear relationship between the current through the LED and the voltage across it. It is essential for designing the correct driver circuit. The curve will show a "knee" voltage (around the typical 2.6V) after which current increases rapidly with a small increase in voltage.
• Luminous Intensity vs. Forward Current (I_V-I_F) Curve: This plot illustrates how light output increases with driving current. It is typically linear over a range but will saturate at very high currents. It helps determine the operating point for desired brightness.
• Luminous Intensity vs. Ambient Temperature (I_V-T_A) Curve: This shows the decrease in light output as the junction temperature of the LED rises. It quantifies the thermal derating effect and is critical for applications operating in elevated temperatures.
• Spectral Distribution Curve: A plot of relative intensity versus wavelength, showing the bell-shaped curve centered around 621 nm with a half-width of 18 nm.

5. Mechanical and Packaging Information

5.1 Physical Dimensions

The display has a digit height of 0.7 inches, which is equivalent to 17.22 millimeters. The package dimensions drawing (referenced but not shown in text) would detail the overall length, width, height, lead spacing, and segment arrangement. Tolerances for all dimensions are specified as ±0.25 mm (0.01 inches) unless otherwise noted. This level of precision is important for mechanical fitting on a printed circuit board (PCB).

5.2 Pin Connection and Internal Circuit

The device has 12 pins. The pinout is clearly defined: Pin 1: Anode for Column 1, Pin 2: Cathode for Row 3, Pin 3: Anode for Column 2, and so on. The internal circuit diagram shows a common-cathode configuration for the rows. This means each of the 7 row lines is connected to the cathodes of all 5 LEDs in that row. The 5 column lines are connected to the anodes of the LEDs in each column. This matrix arrangement allows control of 35 individual dots (5x7) with only 12 pins (5+7), using multiplexing techniques.

5.3 Polarity Identification

While not explicitly shown in the text, the pin numbering and the internal circuit diagram provide the necessary information for polarity. The pinout table is the definitive guide for connecting anodes and cathodes correctly. Incorrect polarity connection (applying forward bias to the cathode) will prevent the LED from illuminating and, if the voltage exceeds the reverse voltage rating (5V), may damage it.

6. Soldering and Assembly Guidelines

The key guideline provided is the soldering temperature profile: the temperature measured 1.6mm below the package body must not exceed 260°C for more than 3 seconds. This is a standard guideline for wave soldering or reflow soldering processes. For manual soldering, a temperature-controlled iron should be used, and contact time with the leads should be minimized to prevent heat from traveling up the lead and damaging the internal chip. Proper ESD (Electrostatic Discharge) precautions should be observed during handling and assembly to prevent damage to the semiconductor junctions.

7. Application Suggestions

7.1 Typical Application Scenarios

Due to its 5x7 dot matrix format, which is ideal for generating alphanumeric characters, the LTP-747KA is well-suited for applications requiring clear, single-digit readouts. Examples include:

• Industrial control panels and instrumentation displays.
• Test and measurement equipment.
• Consumer appliances like microwave ovens, washing machines, or audio equipment.
• Point-of-sale terminals and basic information displays.
• Educational kits for learning about microcontrollers and multiplexed displays.

7.2 Design Considerations

• Driver Circuitry: A microcontroller or dedicated display driver IC is required to multiplex the rows and columns. The driver must be capable of sourcing/sinking the necessary peak currents (up to 32mA per dot as per test condition, but design should reference absolute max ratings) for the columns and rows respectively.
• Current Limiting: External current-limiting resistors are mandatory for each anode (column) line to set the forward current and protect the LEDs. The resistor value is calculated using R = (V_supply - V_F) / I_F. The use of the peak current (I_P) in the multiplexing calculation must be accounted for.
• Thermal Management: In high ambient temperature environments or high-brightness applications, ensure the average current is derated as specified (0.17 mA/°C above 25°C). Adequate spacing on the PCB can help with natural convection cooling.
• Viewing Angle: The datasheet claims a "wide viewing angle," which is beneficial for applications where the display may be viewed from off-axis positions.

8. Technical Comparison and Differentiation

While a direct comparison with other part numbers is not provided, the LTP-747KA's key differentiators based on its datasheet are:

• Material Technology (AlInGaP): Compared to older GaAsP or GaP LEDs, AlInGaP offers higher efficiency, better temperature stability, and superior brightness, leading to the "high brightness & high contrast" claim.
• Dot Matrix vs. Segmented Displays: A 5x7 dot matrix offers far greater flexibility than a standard 7-segment display, as it can show the full ASCII character set, symbols, and simple graphics, not just numbers and a few letters.
• Intensity Categorization: The binning for luminous intensity is a value-added feature for applications requiring uniformity across multiple units.
• Contrast Enhancement: The gray face with white dots is a design choice aimed at improving contrast when the LEDs are off, making the display appear more professional and readable in various lighting conditions.

9. Frequently Asked Questions (Based on Technical Parameters)

9.1 What is the difference between peak forward current (90mA) and the test condition current (32mA)?

The peak forward current (90mA) is an Absolute Maximum Rating—the highest instantaneous current the LED can withstand without immediate damage. The 32mA used in the luminous intensity test is a typical operating condition for measurement in a multiplexed (1/16 duty cycle) system. The average current in that case is much lower (32mA / 16 = 2mA). The design must ensure instantaneous currents stay below 90mA and average currents per dot stay below 13mA (derated for temperature).

9.2 How do I interpret the 1/16 duty cycle specification?

This indicates the standard multiplexing drive method. To control 7 rows with 5 columns, a common technique is to activate one row at a time, cycling through all 7 rows rapidly. If each row is on for an equal time, it is active for 1/7 of the time. The 1/16 duty is a conservative, standardized test condition that allows for comparison between different displays, even if the actual multiplexing scheme in your application is 1/7 or 1/8 duty.

9.3 Why is the forward voltage given as a range (2.05V min, 2.6V typ/max)?

Forward voltage (V_F) has a natural variation due to manufacturing tolerances in the semiconductor material. The circuit design must accommodate this range. The current-limiting resistor should be calculated using the maximum V_F (2.6V) to guarantee that even a device with high V_F receives sufficient voltage to turn on and achieve the desired current. Using the typical value for calculation risks under-driving some units.

10. Design and Usage Case Example

Scenario: Designing a single-digit temperature readout for an industrial controller operating in an environment up to 50°C.

1. Character Set: The 5x7 matrix can display numbers 0-9 and letters like "C" for Celsius.
2. Driver Selection: A microcontroller with at least 12 I/O pins or a dedicated display driver IC (like the MAX7219) would be used to handle the multiplexing timing.
3. Current Calculation: Target an average dot current for good brightness. Suppose we choose 8mA average. At 50°C, derating applies: Derating = (50°C - 25°C) * 0.17 mA/°C = 4.25 mA. Maximum allowed average current at 50°C = 13 mA - 4.25 mA = 8.75 mA. Our target of 8mA is safe.
4. Resistor Calculation: For a 1/7 multiplex (7 rows), the peak current per dot needs to be 8mA * 7 = 56mA to achieve an 8mA average. This is below the 90mA peak rating. Using a 5V supply and V_F(max)=2.6V, the current-limiting resistor is R = (5V - 2.6V) / 0.056A ≈ 42.9Ω. A standard 43Ω resistor would be used.
5. PCB Layout: The display footprint would match the dimension drawing. Adequate space around the package would be left for airflow.

11. Operating Principle

The LTP-747KA operates on the principle of electroluminescence in a semiconductor p-n junction. When a forward voltage exceeding the diode's built-in potential is applied (anode positive relative to cathode), electrons from the n-type AlInGaP layer recombine with holes from the p-type layer. This recombination event releases energy in the form of photons (light). The specific composition of the AlInGaP alloy (Aluminium, Indium, Gallium, Phosphorus) determines the bandgap energy of the semiconductor, which directly dictates the wavelength (color) of the emitted light—in this case, red-orange at ~621 nm. The chips are mounted on a non-transparent Gallium Arsenide (GaAs) substrate, which helps reflect light upward, improving overall light extraction efficiency from the top surface of the device. The 5x7 matrix is formed by individually addressable LEDs arranged in this grid pattern, controlled via external multiplexing circuitry that rapidly sequences power through the rows and columns to create the illusion of a stable, fully lit character.

12. Technology Trends and Context

AlInGaP LED technology, as used in the LTP-747KA, represented a significant advancement over earlier LED materials like GaAsP. It enabled higher brightness, improved efficiency, and better temperature stability, making LEDs viable for a wider range of indicator and display applications. The trend in display technology has since moved towards higher-density dot matrices, full-color RGB matrices, and the widespread adoption of organic LED (OLED) and micro-LED displays for high-resolution screens. However, single and multi-digit alphanumeric dot matrix displays like the 5x7 format remain highly relevant for cost-effective, reliable, and easily readable interfaces in industrial, appliance, and instrumentation contexts where full graphical capability is not required. The underlying drive principles—multiplexing and current control—remain fundamental to LED display design regardless of the scale or technology.