LTP-7188KE LED Dot Matrix Display Specification Sheet - 0.764 Inch (19.4mm) Height - AlInGaP Red Light - 2.6V Forward Voltage - 40mW Power Consumption - Technical Documentation

1. Product Overview

LTP-7188KE is a solid-state, single-plane 8x8 dot matrix display module. Its primary function is to provide a compact and reliable way to display alphanumeric characters, symbols, or simple graphics. Its core technology employs aluminum indium gallium phosphide red LED chips epitaxially grown on a gallium arsenide substrate. This material system is renowned for its high efficiency and excellent luminous intensity within the red-orange spectral range. The device features a gray panel with white luminous segments, enhancing contrast and readability under various lighting conditions. Its design is optimized for applications requiring clear visual communication within a compact form factor, and its stackability enables the construction of larger multi-character displays.

1.1 Core Advantages and Target Market

This display offers several key advantages that define its application areas. Its low power consumption makes it suitable for battery-powered or power-sensitive devices. The solid-state construction ensures high reliability and long service life, as there are no moving parts or filaments to fail. The wide viewing angle provided by the single-plane design allows for clear visibility from different positions, which is crucial for public information displays or instrumentation. Compatibility with standard character codes such as USASCII and EBCDIC simplifies integration with microcontrollers and digital systems. The device is graded by luminous intensity, allowing designers to select units with consistent brightness. Primary target markets include industrial control panels, test and measurement equipment, consumer electronics with status displays, and information signage where reliability and clarity are paramount.

2. In-depth Technical Parameter Analysis

The performance of the LTP-7188KE is defined by a comprehensive set of electrical and optical parameters. These parameters must be carefully considered during circuit design to ensure optimal performance and longevity.

2.1 Absolute Maximum Ratings

These ratings define the stress limits that may cause permanent damage to the device. They are not applicable to normal operation.

• Average power dissipation per point:40 mW. This is the maximum continuous power that a single LED element can safely dissipate, primarily in the form of heat.
• Peak forward current per point:90 mA. This is the maximum instantaneous current allowed, specified under pulse conditions of 1 kHz frequency and 18% duty cycle. Exceeding this value, even briefly, may lead to catastrophic failure.
• Average forward current per point:15 mA. This is the maximum continuous DC current recommended for a single LED to maintain reliability over its lifetime.
• Forward current derating:From 25°C, the maximum allowable current decreases by 0.2 mA for every 1°C increase in ambient temperature. This is crucial for thermal management.
• Reverse voltage per point:5 V. Applying a reverse bias voltage exceeding this value may break down the PN junction of the LED.
• Operating and storage temperature range:-35°C to +85°C. This device is rated for operation and storage over this full temperature range.
• Soldering Conditions:260°C for 3 seconds, with the soldering iron tip positioned at least 1/16 inch (approximately 1.6 mm) below the package mounting plane. This prevents thermal damage to the LED chip during assembly.

2.2 Electrical and Optical Characteristics (Ta = 25°C)

These are typical performance parameters under specified test conditions, representing the normal operating behavior of the device.

• Average Luminous Intensity per Point (I_V):630 μcd (minimum), 1650 μcd (typical). Measured at 1/16 duty cycle using 32 mA peak current (I_p). This parameter defines the perceived brightness.
• Peak emission wavelength (λ_p):632 nm (typical). The wavelength at which the optical output power is maximum. This places its emission in the red region of the visible spectrum.
• Spectral line half-width (Δλ):20 nm (typical value). A measure of spectral purity; a smaller value indicates better monochromaticity of the light source.
• Dominant wavelength (λ_d):624 nm (typical value). The single wavelength perceived by the human eye, which may differ slightly from the peak wavelength.
• Forward voltage (V_F) Any point:
  • 2.05V (min), 2.6V (typ), 2.8V (max), at I_F= 20mA condition.
  • 2.3V (min), 2.8V (typ), at I_F= 80mA (pulse) condition.
  This is the forward voltage drop when the LED is conducting current. It is crucial for designing the current limiting circuit.
• Reverse Current (I_R) Any point:100 μA (max), at V_R= 5V. A small leakage current when the LED is reverse biased.
• Luminous Intensity Matching Ratio (I_V-m):2:1 (Maximum). This parameter specifies the maximum allowable ratio between the brightest and dimmest LED points in the array, ensuring uniform appearance.

Note: Luminous intensity measurement uses sensors and filters approximating the CIE photopic response curve, ensuring relevance to human visual perception.

3. Explanation of the Grading System

The datasheet indicates that the device is "graded by luminous intensity." This means a grading system is applied, although this document does not list the specific grade codes. Typically, such grading involves:

• Luminous Intensity Binning:LEDs from a production batch are sorted into different groups (bins) based on their measured luminous intensity at a standard test current. This allows customers to purchase displays with consistent and predictable brightness levels, which is crucial to avoid noticeable variations in multi-unit assemblies.
• Wavelength Binning (implied):Although not explicitly stated as binning, the strict specifications for peak wavelength (632 nm) and dominant wavelength (624 nm) indicate tight process control. In many LED products, chips are also binned by wavelength (or chromaticity coordinates for white LEDs) to ensure color uniformity across the entire display.
• Forward voltage binning:The specified V_Frange (e.g., 2.05V to 2.8V at 20mA) shows natural variation. For designs requiring precise voltage matching, they can be binned based on the measured V_F.

4. Performance Curve Analysis

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

• Current vs. Voltage (I-V) Curve:It shows the exponential relationship between forward current and forward voltage. For AlInGaP red LEDs, the "knee" voltage is approximately 1.8-2.0V. This curve is crucial for selecting the appropriate current-limiting resistor or designing a constant-current driver.
• Luminous Intensity vs. Forward Current (L-I curve):It shows how the light output increases with current. It is typically linear over a wide range but saturates at very high currents due to thermal effects and efficiency droop. The measurement point at a 1/16 duty cycle (32mA peak) was chosen to represent the equivalent average current while avoiding self-heating effects during measurement.
• Luminous Intensity vs. Ambient Temperature:It illustrates that light output decreases as junction temperature increases. AlInGaP LEDs exhibit less thermal quenching compared to older technologies like GaAsP, but output still declines with temperature. This curve provides a reference for design in high-temperature environments.
• Spectral Distribution:A graph showing the relationship between relative intensity and wavelength, displaying a bell-shaped curve centered at 632 nm with a typical full width at half maximum of 20 nm.

5. Mechanical and Packaging Information

5.1 Package Dimensions

The dot matrix height of this device is 0.764 inches (19.4 mm). The package outline drawing (mentioned but not detailed in the text) typically shows the module's overall length, width, and thickness, the spacing between the 16 pins, and the mounting plane. Unless otherwise specified, all dimensions are in millimeters, with a standard tolerance of ±0.25 mm. Its physical structure supports horizontal stacking to form longer multi-character displays.

5.2 Pin Connections and Internal Circuitry

This display uses a 16-pin dual in-line package. The internal circuit diagram shows an 8x8 matrix where the LED anodes are connected by rows and the cathodes by columns. The pin arrangement confirms this common-anode configuration:

• Pins 1, 2, 5, 7, 8, 9, 12, 14 are anode rows (corresponding to rows 5, 7, 8, 6, 3, 1, 4, 2 respectively).
• Pins 3, 4, 6, 10, 11, 13, 15, 16 are cathode columns (corresponding to columns 2, 3, 5, 4, 6, 1, 7, 8 respectively).

This XY selection architecture uses multiplexing to control 64 LEDs with only 16 pins. To illuminate a specific point, its corresponding row anode must be driven high (or supplied with current), and its column cathode must be pulled low.

6. Welding and Assembly Guide

Proper handling is crucial to prevent damage. The key specification is the soldering condition: 260°C for a maximum of 3 seconds, with the soldering iron tip at least 1.6 mm from the package body. This prevents excessive heat from traveling along the leads and damaging the sensitive LED chip or internal bond wires. Wave or reflow soldering profiles should be designed not to exceed this localized thermal load. During storage, devices should be kept in their original moisture barrier bag with desiccant, in a controlled environment (within the range of -35°C to +85°C), to prevent moisture absorption, which can cause "popcorn" effect during soldering.

7. Application Recommendations

7.1 Typical Application Scenarios

• Industrial Control Panel:Used to display machine status, error codes, or simple numerical data.
• Test and Measurement Equipment:As a reading display for multimeters, frequency meters, or power supplies.
• Consumer Electronics:Used for status indication in audio equipment (VU meters), household appliances, or toys.
• Information Display:Simple public signage for time, temperature, or queue numbers, especially when multiple units are stacked.
• Prototyping and Education:Excellent for learning microcontroller interfacing, multiplexing, and display drivers.

7.2 Design Considerations

• Drive Circuit:Multiplexing must be used. A microcontroller with sufficient I/O pins or a dedicated LED driver IC (such as MAX7219) is required to scan the rows and columns.
• Current Limitation:Each column (cathode) line typically requires a series current-limiting resistor. Its resistance is calculated based on the supply voltage, LED forward voltage (V_F) and the desired average current (not exceeding 15mA per point). For multiplexed operation, the peak current will be higher, but the average must remain within the limit.
• Power Consumption:Calculate the total power of all illuminated points to ensure it does not exceed the module's thermal capacity. Consider derating with temperature.
• Viewing Angle:A wide viewing angle is beneficial, but the installation orientation relative to the intended observer must be considered.
• Refresh Rate:多路复用扫描速率必须足够高（通常>60 Hz）以避免可见闪烁。

8. Technical Comparison and Differentiation

Compared to older 8x8 dot matrix displays using discrete LEDs or different semiconductor materials (such as GaAsP), the LTP-7188KE offers distinct advantages:

• Material (AlInGaP vs. GaAsP):AlInGaP provides significantly higher luminous efficiency and better performance at high temperatures, resulting in a brighter display with the same input power.
• Integration Level:As a monolithic module with a gray panel/white luminous segments, it offers better contrast, more consistent dot matrix arrangement, and simpler assembly compared to building a display using 64 individual LEDs.
• Reliability:Compared to filament-based or vacuum fluorescent displays, solid-state structures possess excellent resistance to shock and vibration.
• Low power consumption:Although specific efficiency figures are not provided, the low V_Fand good luminous intensity indicate superior electro-optical conversion efficiency compared to incandescent or VFD alternatives.

9. FAQ (Based on Technical Specifications)

• Q: Can I drive this display with a 5V microcontroller?A: Yes, but you cannot connect the LEDs directly to the GPIO pins. You must use current-limiting resistors, and you may also need transistor drivers for the rows/columns, as the GPIO pins cannot provide/sink the required high peak current (up to 80mA per dot when multiplexed).
• Q: What is the difference between peak emission wavelength and dominant wavelength?A: Peak wavelength is the physical peak of the emission spectrum. Dominant wavelength is the perceived color point on the CIE chromaticity diagram. They are usually slightly different; dominant wavelength is more relevant to color perception.
• Q: Why is the average luminous intensity measured at a 1/16 duty cycle?A: This test condition simulates an LED being active in a fully multiplexed 8x8 array (one row lit at a time). It allows measurement at a higher, easily measurable peak current (32mA) while representing the much lower average current (2mA) present in actual use, thereby avoiding measurement errors caused by self-heating.
• Q: How to calculate the resistance value for a constant voltage power supply?A: Use the formula R = (V_{Power Supply}- V_F) / I_F. For a 5V power supply, the typical V_Fis 2.6V, and the expected I_FFor 10mA: R = (5 - 2.6) / 0.01 = 240 Ω. For a conservative design, the maximum V_Fvalue should be used to ensure the current does not exceed the limit.

10. Practical Application Case Analysis

Scenario: Design a simple 4-digit voltmeter reading display.

1. Hardware Setup:Four LTP-7188KE displays are stacked horizontally. A microcontroller (e.g., Arduino or PIC) reads the analog voltage via its ADC.
2. Interface:The 8 row pins of each display are connected in parallel. The 8 column pins of each display are connected to independent I/O lines or shift registers, allowing individual control of each display's columns. This creates a matrix of 32 columns (4 displays * 8 columns) by 8 rows.
3. Software:The microcontroller converts the ADC reading into four decimal digits. It uses a multiplexing routine: activate row 1, then set the column pattern for the first segment of all four digits, wait a very short time, deactivate row 1, activate row 2, set the new column pattern, and so on, cycling through all 8 rows. This loop repeats rapidly.
4. Current Design:If the target average current is 5mA per lit point, and assuming the worst case of 8 points lit per row (one point per digit), the peak current per column driver will be 8 * 5mA = 40mA, which is within the peak rating of the device. Select appropriate drivers (e.g., ULN2003 for columns, transistors for rows) to handle this current.
5. Results:A stable, bright 4-digit display shows the voltage value, and due to the persistence of vision effect, all digits appear to be displayed simultaneously.

11. Working Principle

The LTP-7188KE operates based on the principle of electroluminescence in a semiconductor PN junction. When a forward bias voltage exceeding the diode turn-on voltage (approximately 1.8-2.0V for AlInGaP) is applied, electrons from the n-type region and holes from the p-type region are injected into the active region (quantum wells within the AlInGaP layer). Here, they undergo radiative recombination, releasing energy in the form of photons. The specific wavelength of 632 nm is determined by the bandgap energy of the AlInGaP alloy composition. The 8x8 matrix arrangement and common-anode wiring are internally implemented via metal traces on the substrate, allowing for external control via multiplexing to minimize the required number of connection pins.

12. Technical Trends and Background

Ko da yake wannan takamaiman sashi yana wakiltar cikakkiyar fasahar nuni, yana wanzuwa a cikin abubuwan da ke ci gaba da haɓaka. Amfani da AlInGaP yana wakiltar ci gaba idan aka kwatanta da tsohuwar LED na GaAsP, yana ba da ingantacciyar inganci da kwanciyar hankali na zafi. Halin yanzu na nunin nuni da sauƙaƙan nunin matrix sun haɗa da:

• Matsakaicin girma da ƙaramin tazara:Modern modules can integrate more LEDs in a smaller area to achieve higher resolution.
• Surface Mount Technology:Newer designs typically use SMT packaging for automated assembly, while this DIP component is suitable for through-hole mounting.
• Integrated Drive:Some contemporary dot matrix displays come with a built-in driver IC, simplifying the interface to a simple serial data connection.
• Alternative Technology:For applications requiring higher brightness, different colors, or flexibility, technologies such as OLED or Micro-LED are emerging. However, for many rugged, cost-sensitive, and simple applications that demand high reliability and standard red display, traditional LED dot matrix modules like the LTP-7188KE remain a practical and effective solution.

This device embodies reliable, easy-to-understand technology and continues to serve in numerous applications where its combination of performance, simplicity, and cost is optimal.