LTP-7188KE LED Dot Matrix Display Datasheet - 0.764-inch (19.4mm) Height - AlInGaP Red - 2.6V Forward Voltage - 40mW Power Dissipation - English Technical Document

1. Product Overview

The LTP-7188KE is a solid-state, single-plane 8x8 dot matrix display module. Its primary function is to provide a compact, reliable means of displaying alphanumeric characters, symbols, or simple graphics. The core technology utilizes Aluminum Indium Gallium Phosphide (AlInGaP) red LED chips epitaxially grown on a Gallium Arsenide (GaAs) substrate. This material system is known for its high efficiency and excellent luminous intensity in the red-orange spectrum. The device features a gray faceplate with white segments, which enhances contrast and readability under various lighting conditions. Its design is optimized for applications requiring clear visual communication in a compact form factor, with stackability enabling the creation of larger multi-character displays.

1.1 Core Advantages and Target Market

The display offers several key advantages that define its application space. Its low power requirement makes it suitable for battery-operated or power-sensitive devices. The solid-state construction ensures high reliability and long operational 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 various positions, which is critical for public information displays or instrumentation. Compatibility with standard character codes like USASCII and EBCDIC simplifies integration with microcontrollers and digital systems. The device is categorized for luminous intensity, allowing designers to select units with consistent brightness. The primary target markets include industrial control panels, test and measurement equipment, consumer electronics with status displays, and informational 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, which must be carefully considered during circuit design to ensure optimal performance and longevity.

2.1 Absolute Maximum Ratings

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

• Average Power Dissipation Per Dot: 40 mW. This is the maximum continuous power that can be safely dissipated by a single LED element, primarily as heat.
• Peak Forward Current Per Dot: 90 mA. This is the maximum instantaneous current allowed, specified under a pulsed condition of 1 kHz frequency and an 18% duty cycle. Exceeding this, even briefly, can cause catastrophic failure.
• Average Forward Current Per Dot: 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 Dot: 5 V. Applying a reverse bias voltage exceeding this value can break down the LED's PN junction.
• Operating & Storage Temperature Range: -35°C to +85°C. The device is rated to function and be stored within this full temperature span.
• Soldering Condition: 260°C for 3 seconds, with the iron tip positioned at least 1/16 inch (approx. 1.6mm) below the seating plane of the package. This prevents thermal damage to the LED chips during assembly.

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

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

• Average Luminous Intensity Per Dot (I_V): 630 μcd (Min), 1650 μcd (Typ). Measured with a peak current (I_p) of 32 mA at a 1/16 duty cycle. This parameter defines the perceived brightness.
• Peak Emission Wavelength (λ_p): 632 nm (Typ). The wavelength at which the optical output power is greatest. This places the emission in the red region of the visible spectrum.
• Spectral Line Half-Width (Δλ): 20 nm (Typ). A measure of the spectral purity; a smaller value indicates a more monochromatic light source.
• Dominant Wavelength (λ_d): 624 nm (Typ). The single wavelength perceived by the human eye, which may differ slightly from the peak wavelength.
• Forward Voltage (V_F) any Dot:
  • 2.05V (Min), 2.6V (Typ), 2.8V (Max) at I_F = 20mA.
  • 2.3V (Min), 2.8V (Typ) at I_F = 80mA (pulsed).
  This is the voltage drop across the LED when conducting current. It is crucial for designing the current-limiting circuitry.
• Reverse Current (I_R) any Dot: 100 μA (Max) at V_R = 5V. The small leakage current when the LED is reverse-biased.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 (Max). This specifies the maximum allowable ratio between the brightest and dimmest LED dots in the array, ensuring uniform appearance.

Note: Luminous intensity measurement uses a sensor and filter approximating the CIE photopic eye-response curve, ensuring relevance to human vision.

3. Binning System Explanation

The datasheet indicates the device is \"categorized for luminous intensity.\" This implies a binning system is applied, though specific bin codes are not listed in this document. Typically, such categorization involves:

• Luminous Intensity Binning: LEDs from a production batch are sorted into 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 critical for multi-unit assemblies to avoid noticeable variations.
• Wavelength Binning (Implied): While not explicitly stated as binned, the tight specifications on peak (632 nm) and dominant (624 nm) wavelength suggest tight process control. In many LED products, chips are also binned by wavelength (or chromaticity coordinates for white LEDs) to ensure color consistency across a display.
• Forward Voltage Binning: The specified V_F range (e.g., 2.05V to 2.8V at 20mA) shows the natural variation. For designs requiring precise voltage matching, units can be selected based on measured V_F.

4. Performance Curve Analysis

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

• Current vs. Voltage (I-V) Curve: Shows the exponential relationship between forward current and forward voltage. The \"knee\" voltage is around 1.8-2.0V for AlInGaP red LEDs. The curve is essential for selecting the appropriate current-limiting resistor or designing constant-current drivers.
• Luminous Intensity vs. Forward Current (L-I Curve): Displays how light output increases with current. It is generally linear over a wide range but will saturate at very high currents due to thermal and efficiency droop. The 1/16 duty cycle measurement point (32mA peak) is chosen to represent an equivalent average current while avoiding self-heating effects during measurement.
• Luminous Intensity vs. Ambient Temperature: Illustrates the decrease in light output as junction temperature rises. AlInGaP LEDs exhibit less thermal quenching than older technologies like GaAsP, but output still declines with temperature. This curve informs designs for high-temperature environments.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing a bell-shaped curve centered around 632 nm with a typical half-width of 20 nm.

5. Mechanical & Package Information

5.1 Package Dimensions

The device has a matrix height of 0.764 inches (19.4 mm). The package dimensions drawing (referenced but not detailed in text) would typically show the overall length, width, and thickness of the module, the spacing between the 16 pins, and the seating plane. All dimensions are in millimeters with a standard tolerance of ±0.25 mm unless otherwise specified. The physical construction enables horizontal stacking to form longer multi-character displays.

5.2 Pin Connection and Internal Circuit

The display has a 16-pin dual in-line package (DIP). The internal circuit diagram shows an 8x8 matrix where the anodes of the LEDs are connected in rows and the cathodes are connected in columns. This common-anode configuration is confirmed by the pinout:

• Pins 1, 2, 5, 7, 8, 9, 12, 14 are Anode Rows (for rows 5, 7, 8, 6, 3, 1, 4, 2 respectively).
• Pins 3, 4, 6, 10, 11, 13, 15, 16 are Cathode Columns (for columns 2, 3, 5, 4, 6, 1, 7, 8 respectively).

This X-Y select architecture allows control of 64 LEDs with only 16 pins by multiplexing. To illuminate a specific dot, its corresponding row anode must be driven high (or supplied with current), and its column cathode must be pulled low.

6. Soldering & Assembly Guidelines

Proper handling is critical to prevent damage. The key specification is the soldering condition: 260°C for a maximum of 3 seconds, with the iron tip at least 1.6mm below the package body. This prevents excessive heat from traveling up the pins and damaging the sensitive LED chips or the internal wire bonds. Wave soldering or reflow soldering profiles should be designed to not exceed this localized thermal load. During storage, the device should be kept in its original moisture-barrier bag with desiccant in a controlled environment (within the -35°C to +85°C range) to prevent moisture absorption, which can cause \"popcorning\" during soldering.

7. Application Suggestions

7.1 Typical Application Scenarios

• Industrial Control Panels: For displaying machine status, error codes, or simple numerical data.
• Test & Measurement Equipment: As a readout for multimeters, frequency counters, or power supplies.
• Consumer Electronics: In audio equipment (VU meters), appliances, or toys for status indication.
• Information Displays: Simple public signage for time, temperature, or queue numbers, especially when multiple units are stacked.
• Prototyping & Education: Ideal for learning about microcontroller interfacing, multiplexing, and display drivers.

7.2 Design Considerations

• Drive Circuitry: Must use multiplexing. A microcontroller with sufficient I/O pins or a dedicated LED driver IC (like the MAX7219) is required to scan the rows and columns.
• Current Limiting: Each column (cathode) line typically requires a series current-limiting resistor. The value is calculated based on the supply voltage, the LED forward voltage (V_F), and the desired average current (not exceeding 15mA per dot). For multiplexed operation, the peak current will be higher but the average must remain within limits.
• Power Dissipation: Calculate total power for all illuminated dots to ensure it doesn't exceed the module's thermal capacity. Consider the derating with temperature.
• Viewing Angle: The wide viewing angle is beneficial but consider the mounting orientation relative to the intended viewer.
• Refresh Rate: The multiplex scan rate must be high enough (typically >60 Hz) to avoid visible flicker.

8. Technical Comparison & Differentiation

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

• Material (AlInGaP vs. GaAsP): AlInGaP provides significantly higher luminous efficiency and better performance at elevated temperatures, resulting in brighter displays for the same input power.
• Integration: As a monolithic module with a gray face/white segments, it offers better contrast, more consistent dot alignment, and easier assembly than building a display from 64 individual LEDs.
• Reliability: Solid-state construction offers superior shock and vibration resistance compared to filament-based or vacuum fluorescent displays (VFDs).
• Low Power: While specific efficiency numbers aren't given, the low V_F and good luminous intensity indicate good power-to-light conversion compared to incandescent or VFD alternatives.

9. Frequently Asked Questions (Based on Technical Parameters)

• 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 likely transistor drivers for the rows/columns, as the GPIO pins cannot source/sink the required peak currents (up to 80mA per dot in multiplexing).
• Q: What is the difference between Peak Emission Wavelength and Dominant Wavelength? A: Peak wavelength is the physical peak of the light spectrum emitted. Dominant wavelength is the perceived color point on the CIE chromaticity diagram. They often differ slightly; dominant wavelength is more relevant for color perception.
• Q: Why is the Average Luminous Intensity measured at a 1/16 duty cycle? A: This test condition simulates one LED being active in a fully multiplexed 8x8 array (1 row on at a time). It allows measurement at a higher, easily measurable peak current (32mA) while representing the much lower average current (2mA) that would be present in actual use, avoiding measurement errors from self-heating.
• Q: How do I calculate the resistor value for a constant voltage supply? A: Use R = (V_supply - V_F) / I_F. For a 5V supply, a typical V_F of 2.6V, and a desired I_F of 10mA: R = (5 - 2.6) / 0.01 = 240 Ω. Use the maximum V_F for a conservative design to ensure current doesn't exceed limits.

10. Practical Application Case Study

Scenario: Designing a Simple 4-Digit Voltmeter Readout.

1. Hardware Setup: Four LTP-7188KE displays are stacked horizontally. A microcontroller (e.g., an Arduino or PIC) reads an analog voltage via its ADC.
2. Interfacing: The 8 row pins of each display are connected in parallel. The 8 column pins of each display are connected to separate I/O lines or a shift register, allowing individual control of each display's columns. This creates a 32-column (4 displays * 8 cols) by 8-row matrix.
3. Software: The microcontroller converts the ADC reading to four decimal digits. It uses a multiplexing routine: it activates Row 1, then sets the column patterns for the first segment of all four digits, waits a short time, deactivates Row 1, activates Row 2, sets the new column patterns, and so on through all 8 rows. This cycle repeats rapidly.
4. Current Design: If targeting an average current of 5mA per lit dot, and assuming a worst-case of 8 dots lit per row (one per digit), the peak current per column driver would be 8 * 5mA = 40mA, which is within the device's peak rating. Appropriate drivers (e.g., ULN2003 for columns, transistors for rows) are selected to handle this current.
5. Result: A stable, bright, 4-digit display showing the voltage value, with all digits appearing simultaneously due to the persistence of vision effect.

11. Operating Principle

The LTP-7188KE operates on the principle of electroluminescence in a semiconductor PN junction. When a forward bias voltage exceeding the diode's 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 (the quantum wells in the AlInGaP layer). Here, they recombine radiatively, 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 implemented internally via metal traces on the substrate, allowing external control via multiplexing to minimize the number of required connection pins.

12. Technology Trends and Context

While this specific part represents mature display technology, it exists within evolving trends. The use of AlInGaP represents an advancement over older GaAsP LEDs, offering better efficiency and thermal stability. Current trends in indicator and simple matrix displays include:

• Higher Density & Smaller Pitch: Modern modules may pack more LEDs into a smaller area for higher resolution.
• Surface-Mount Technology (SMT): Newer designs often use SMT packages for automated assembly, whereas this DIP part is suited for through-hole mounting.
• Integrated Drivers: Some contemporary matrix displays come with built-in driver ICs, simplifying the interface to a simple serial data connection (SPI/I2C).
• Alternative Technologies: For applications requiring higher brightness, different colors, or flexibility, technologies like OLED (Organic LED) or micro-LED are emerging. However, for many rugged, cost-sensitive, and simple applications requiring high reliability and a standard red display, traditional LED dot matrix modules like the LTP-7188KE remain a practical and effective solution.

This device exemplifies a reliable, well-understood technology that continues to serve numerous applications where its combination of performance, simplicity, and cost is optimal.