LTP-747KF LED Dot Matrix Display Datasheet - 0.7-inch (17.22mm) Digit Height - AlInGaP Yellow Orange - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTP-747KF is a compact, high-performance 5 x 7 dot matrix LED display module. Its primary function is to provide clear, legible alphanumeric character output in a variety of electronic devices and equipment. The core design philosophy centers on delivering excellent visual performance with low power consumption and high reliability, making it suitable for integration into consumer electronics, industrial control panels, instrumentation, and other applications requiring status or data display.

The device's key positioning lies in its balance of size, brightness, and efficiency. The 0.7-inch (17.22mm) character height offers a good compromise between readability and board space requirements. Utilizing advanced AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for its Yellow Orange LED chips, the display achieves high luminous intensity and excellent color purity directly from the chip material, contributing to its overall performance and longevity.

2. Technical Parameter Deep Dive

2.1 Optical Characteristics

The optical performance is defined by several key parameters measured under standard test conditions (T_A=25°C). The Average Luminous Intensity (I_V) ranges from a minimum of 630 µcd to a typical value of 1650 µcd when driven with a peak current (I_P) of 32mA at a 1/16 duty cycle. This high brightness ensures good visibility even in moderately lit environments.

The color characteristics are specified by wavelength. The Peak Emission Wavelength (λ_p) is typically 611 nm, while the Dominant Wavelength (λ_d) is typically 605 nm, defining the perceived Yellow Orange color. The Spectral Line Half-Width (Δλ) is typically 17 nm, indicating a relatively narrow spectral bandwidth which contributes to color saturation. Luminous intensity is measured using a sensor and filter combination that approximates the CIE photopic eye-response curve, ensuring the values correlate with human visual perception.

2.2 Electrical Characteristics

The electrical parameters define the operating limits and conditions for the device. The Forward Voltage per dot (V_F) typically ranges from 2.05V to 2.6V at a forward current (I_F) of 20mA. This parameter is crucial for designing the current-limiting circuitry.

The Reverse Current per dot (I_R) has a maximum value of 100 µA when a reverse voltage (V_R) of 5V is applied, indicating the leakage characteristic of the LED junction. The Luminous Intensity Matching Ratio for LEDs within a similar light area is specified at a maximum of 2:1, which is important for ensuring uniform appearance across all segments of the displayed character.

2.3 Absolute Maximum Ratings

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

• Average Power Dissipation per dot: 70 mW
• Peak Forward Current per dot: 60 mA
• Average Forward Current per dot: 25 mA (derated linearly from 25°C at 0.33 mA/°C)
• Reverse Voltage per dot: 5 V
• Operating Temperature Range: -35°C to +105°C
• Storage Temperature Range: -35°C to +105°C

3. Binning System Explanation

The datasheet indicates that the device is categorized for luminous intensity. This implies a binning process where manufactured units are sorted (binned) based on their measured light output. The specified intensity range (Min: 630 µcd, Typ: 1650 µcd) likely represents the spread across different bins. Designers can select a specific bin to ensure consistency in brightness across multiple displays in a product or to meet specific brightness requirements, though the exact bin code structure is not detailed in this document.

While not explicitly mentioned for wavelength or forward voltage in this datasheet, such categorization is common in LED manufacturing to group parts with closely matched optical and electrical characteristics, critical for applications demanding color or brightness uniformity.

4. Performance Curve Analysis

The datasheet references Typical Electrical/Optical Characteristic Curves. While the specific graphs are not provided in the text, such curves typically included in full datasheets are essential for design. They would normally illustrate:

• Forward Current vs. Forward Voltage (I-V Curve): Shows the nonlinear relationship, helping to determine the operating point and the required drive voltage for a given current.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with current, up to a point of saturation or excessive heat generation.
• Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as junction temperature rises, which is critical for thermal management design.
• Spectral Distribution: A plot of relative intensity vs. wavelength, visually confirming the peak and dominant wavelengths and the spectral width.

These curves allow engineers to predict performance under non-standard conditions and optimize their driver circuit and thermal design.

5. Mechanical and Packaging Information

The LTP-747KF comes in a standard LED display package. Key dimensional notes specify that all dimensions are in millimeters, with a general tolerance of ±0.25 mm unless stated otherwise. A specific tolerance for pin tip shift is ±0.4 mm, which is important for PCB footprint design and automated assembly processes.

The package features a gray face with white dots, which enhances contrast and improves character legibility by reducing reflected ambient light from the non-active areas. The mechanical drawing (referenced but not detailed in text) would show the exact outline dimensions, seating plane, lead spacing, and overall height.

6. Pin Connection and Internal Circuit

The device has a 12-pin configuration. The pinout is as follows: Pin 1: Anode Column 1, Pin 2: Cathode Row 3, Pin 3: Anode Column 2, Pin 4: Cathode Row 5, Pin 5: Cathode Row 6, Pin 6: Cathode Row 7, Pin 7: Anode Column 4, Pin 8: Anode Column 5, Pin 9: Cathode Row 4, Pin 10: Anode Column 3, Pin 11: Cathode Row 2, Pin 12: Cathode Row 1.

This multiplexed arrangement (5 anode columns, 7 cathode rows) is standard for a 5x7 matrix. It allows control of 35 individual LEDs (dots) with only 12 pins, significantly reducing interconnect complexity compared to a direct drive approach. The internal circuit diagram would show each LED dot connected between a specific anode column and cathode row. To illuminate a particular dot, its corresponding anode line must be driven high (with current limiting) while its cathode line is pulled low.

7. Soldering and Assembly Guidelines

The datasheet provides specific soldering conditions: 1/16 inch (approximately 1.6mm) below the seating plane for 3 seconds at 260°C. This is a critical parameter for wave soldering or hand soldering processes to prevent thermal damage to the LED chips or the plastic package. Exceeding this temperature or time can lead to delamination, cracked epoxy, or degraded LED performance.

It is also emphasized that the temperature during assembly must not exceed the maximum temperature rating specified in the Absolute Maximum Ratings section. Proper handling to avoid electrostatic discharge (ESD) is also a standard precaution, though not explicitly stated here, as LEDs are semiconductor devices.

8. Application Suggestions

8.1 Typical Application Scenarios

The LTP-747KF is well-suited for applications requiring compact, low-power numeric or limited alphanumeric readouts. Examples include:

• Test and Measurement Equipment: Digital multimeters, frequency counters, power supplies for displaying values.
• Consumer Electronics: Audio equipment (amplifier level displays), kitchen appliances (timer, temperature).
• Industrial Controls: Panel meters, process controllers, timer displays.
• Embedded Systems: Status indicators for prototypes or development boards.

8.2 Design Considerations

• Drive Circuitry: A microcontroller with sufficient I/O pins or a dedicated LED driver IC with multiplexing support is required. The driver must supply the correct peak current (e.g., 20-32mA) at the specified duty cycle (e.g., 1/16) to achieve the rated brightness without exceeding average current limits.
• Current Limiting: Series resistors or constant current drivers are necessary for each anode column or each LED to set the forward current accurately and protect the LEDs.
• Refresh Rate: The multiplexing scheme requires a sufficiently high scan frequency (typically >100Hz) to avoid visible flicker.
• Thermal Management: Although power dissipation is low per dot, the collective heat from multiple illuminated dots in a high ambient temperature environment must be considered. Adequate ventilation or heatsinking may be needed for continuous high-brightness operation.

9. Technical Comparison and Differentiation

Compared to older technologies like standard GaAsP or GaP LEDs, the use of AlInGaP material offers significant advantages: Higher luminous efficiency (more light output per mA of current), better temperature stability (less intensity drop with heat), and superior long-term reliability. The gray face/white dot design provides a higher contrast ratio than all-red or all-green packages, improving readability.

Within the 0.7-inch 5x7 matrix category, key differentiators for this part would be its specific luminous intensity binning, the low forward voltage typical of AlInGaP, and the wide operating temperature range (-35°C to +105°C), which exceeds that of many common displays, making it robust for industrial environments.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the 1/16 duty cycle specification for luminous intensity?
A: The display uses multiplexing. Each dot is only powered on for a fraction of the time (1/16th in this test condition). The luminous intensity is measured during its brief "on" pulse (peak current). The perceived average brightness is lower. This specification allows designers to calculate the effective average light output.

Q: Can I drive this display with a constant DC current instead of multiplexing?
A: Technically, yes, but it is highly inefficient. It would require 35 independent current-limited channels instead of 12 multiplexed lines, greatly increasing circuit complexity and cost. Multiplexing is the intended and optimal method.

Q: The forward voltage is 2.6V max at 20mA. Can I power it directly from a 3.3V microcontroller pin?
A: No. You must always use a series current-limiting resistor (or active constant-current circuit). Connecting it directly would attempt to draw excessive current, potentially damaging both the LED and the microcontroller pin. The resistor value is calculated as R = (V_supply - V_F) / I_F.

Q: What does "Lead-Free Package (according to RoHS)" mean?
A: It signifies that the device is compliant with the Restriction of Hazardous Substances directive. The materials used in its construction, including solder plating on the leads, do not contain prohibited substances like lead, mercury, or cadmium above allowed limits, making it suitable for sale in regulated markets.

11. Design and Usage Case Example

Case: Designing a Simple Digital Timer Display. A designer needs to show minutes and seconds (MM:SS) on a product. Two LTP-747KF displays could be used for the minutes and two for the seconds. A low-cost microcontroller would be programmed to manage the timing function. Its I/O ports would be connected to the anode and cathode lines of all four displays through appropriate current-limiting resistors. The firmware would implement the timing algorithm and a multiplexing routine that cycles through the four displays and the relevant segments of each digit at a high speed (e.g., 200Hz). The gray face of the display would ensure good contrast against the product's enclosure. The designer would select a luminous intensity bin appropriate for the expected ambient light conditions of the timer's use.

12. Operating Principle Introduction

The LTP-747KF operates on the fundamental principle of a Light Emitting Diode (LED) and time-division multiplexing. Each of the 35 dots in the 5x7 grid is an individual AlInGaP LED. When forward-biased (positive voltage applied to the anode relative to the cathode), electrons and holes recombine within the semiconductor's active region, releasing energy in the form of photons (light) at a wavelength determined by the bandgap of the AlInGaP material, resulting in yellow-orange light.

The multiplexing scheme reduces the number of required control pins. The anodes of all LEDs in a vertical column are connected together, and the cathodes of all LEDs in a horizontal row are connected together. By sequentially activating one anode column at a time while selectively enabling the cathode rows for the dots that should be lit in that column, and repeating this cycle rapidly, the illusion of a stable, fully formed character is created. The human eye's persistence of vision blends the rapidly flashing individual dots into a continuous image.

13. Technology Trends

While discrete LED dot matrix displays like the LTP-747KF remain relevant for specific applications due to their simplicity, robustness, and wide viewing angle, several trends are notable. There is a general shift towards integrated display modules that include the driver IC, controller, and sometimes a character generator ROM, simplifying the interface for the host system (e.g., SPI, I2C).

For alphanumeric output, OLED (Organic LED) and advanced LCD modules offer higher resolution, full graphic capability, and lower power consumption in some static display scenarios. However, traditional LED matrices maintain advantages in extreme temperature tolerance, very high brightness for outdoor use, and long-term reliability where pixel burn-in or limited lifetime might be concerns for other technologies. The underlying AlInGaP LED chip technology continues to improve, offering ever-higher efficiencies and more consistent color production.