LTP-2088AKD 8x8 Dot Matrix LED Display Datasheet - 2.3 Inch Height - AlInGaP Hyper Red - 2.6V Forward Voltage - 40mW Power Dissipation - English Technical Document

1. Product Overview

The LTP-2088AKD is a single-plane, 8x8 dot matrix LED display module designed for alphanumeric and symbolic information presentation. Its primary function is to provide a reliable, low-power visual output interface in electronic systems. The core advantage of this device lies in its use of AlInGaP (Aluminum Indium Gallium Phosphide) Hyper Red LED chips, which offer a balance of performance and efficiency. The display features a gray face with white segments, enhancing contrast and readability. It is categorized for luminous intensity, ensuring consistency in brightness across production batches. The device is stackable horizontally, allowing for the creation of wider multi-character displays without complex interfacing. Its compatibility with standard character codes like USASCII and EBCDIC makes it versatile for integration into various digital systems requiring simple text output.

2. Technical Specifications Deep Dive

2.1 Optical Characteristics

The optical performance is defined at an ambient temperature (T_A) of 25°C. The key parameter, Average Luminous Intensity (I_V), has a typical value of 3500 µcd (microcandelas) under a test condition of I_p=32mA and a 1/16 duty cycle. The minimum specified value is 1650 µcd, and there is no maximum limit listed, indicating a focus on meeting a minimum brightness threshold. The device emits in the red spectrum with a Peak Emission Wavelength (λ_p) of 650 nm and a Dominant Wavelength (λ_d) of 639 nm, measured at I_F=20mA. The spectral purity is indicated by a Spectral Line Half-Width (Δλ) of 20 nm. A critical parameter for multi-dot displays is the Luminous Intensity Matching Ratio (I_V-m), which is specified as 2:1 maximum. This means the brightest dot in the array will not be more than twice as bright as the dimmest dot under the same operating conditions, ensuring uniform appearance.

2.2 Electrical Characteristics

The electrical parameters are also specified at T_A=25°C. The Forward Voltage (V_F) for any single LED dot is typically 2.6V at I_F=20mA, with a maximum of 2.8V at a higher pulse current of I_F=80mA. The minimum V_F is 2.1V at 20mA. The Reverse Current (I_R) is limited to a maximum of 100 µA when a Reverse Voltage (V_R) of 5V is applied, indicating good diode characteristics.

2.3 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage may occur. The Average Power Dissipation per dot must not exceed 40 mW. The Peak Forward Current per dot is rated at 90 mA. The Average Forward Current per dot is 15 mA at 25°C, with a derating factor of 0.2 mA/°C, meaning the allowable continuous current decreases as ambient temperature rises above 25°C. The maximum Reverse Voltage per dot is 5V. The device is rated for an Operating Temperature Range of -35°C to +85°C and an identical Storage Temperature Range. The solderability is specified for a wave or reflow process: the device can withstand 260°C for 3 seconds at a point 1/16 inch (approximately 1.59 mm) below the seating plane of the package.

3. Mechanical and Package Information

The display has a matrix height of 2.3 inches (58.42 mm). The package dimensions are provided in a detailed drawing with all measurements in millimeters. The manufacturing tolerance for these dimensions is ±0.25 mm (or ±0.01 inches) unless specifically noted otherwise on the drawing. This level of precision is important for mechanical fitting into panels or enclosures.

4. Pin Connection and Internal Circuit

The device uses a 16-pin configuration for interfacing. The pinout is designed for X-Y matrix driving. Pins 1-4 and 9-12 are the Anodes for Columns 1-4 and 8-5 respectively. Pins 5-8 and 13-16 are the Cathodes for Rows 5-8 and 4-1 respectively. This specific arrangement is crucial for designing the correct driving circuitry. The internal circuit diagram shows that the 64 LEDs (8 rows x 8 columns) are arranged in a common-cathode configuration for the rows. This means to illuminate a specific dot, its corresponding column anode must be driven high (positive voltage applied) while its row cathode is driven low (grounded). Multiplexing techniques are used to scan through rows or columns to display patterns.

5. Binning System Explanation

The datasheet explicitly states that the device is "Categorized for Luminous Intensity." This indicates a binning process where manufactured units are sorted based on their measured light output (in µcd) under standard test conditions. Units falling within specific intensity ranges are grouped together. This allows designers to select displays with consistent brightness for a given application, preventing noticeable variations between different units in a product. While not detailed in this document, typical binning for such displays might involve several intensity grades (e.g., high-brightness, standard-brightness).

6. Performance Curve Analysis

The datasheet references "Typical Electrical / Optical Characteristic Curves." These graphs, typically included in fuller datasheet versions, would visually represent the relationship between key parameters. Expected curves include: Forward Current vs. Forward Voltage (I-V Curve), showing the exponential relationship and allowing for driver voltage calculation; Luminous Intensity vs. Forward Current, showing how light output increases with current, often in a sub-linear fashion at higher currents; Luminous Intensity vs. Ambient Temperature, showing the decrease in output as temperature rises; and possibly the Spectral Distribution curve, depicting the relative power across wavelengths centered around 650 nm. Analyzing these curves is essential for optimizing drive conditions and understanding performance under non-standard temperatures.

7. Soldering and Assembly Guidelines

The primary guideline provided is the Absolute Maximum Rating for solder temperature: 260°C for 3 seconds, measured 1.59mm (1/16") below the package seating plane. This is a standard rating for wave or reflow soldering processes. Designers must ensure their soldering profile does not exceed this limit to prevent damage to the internal LED chips, wire bonds, or the plastic package. For manual soldering, a temperature-controlled iron should be used with minimal contact time. Proper ESD (Electrostatic Discharge) handling procedures should always be followed during assembly, as LEDs are sensitive to static electricity.

8. Application Suggestions

8.1 Typical Application Scenarios

This 8x8 dot matrix is ideal for applications requiring compact, low-resolution text or simple graphics. Common uses include: industrial control panels for displaying status codes or simple messages; test and measurement equipment for showing numeric values or units; consumer electronics like simple scoreboards or information displays; and educational kits for learning about microcontroller interfacing and multiplexing.

8.2 Design Considerations

Drive Circuitry: A microcontroller with sufficient I/O pins or dedicated LED driver ICs (like shift registers with constant-current outputs) are required. The circuit must implement multiplexing to cycle through the 8 rows (or columns).
Current Limiting: Resistors or constant-current drivers are mandatory for each anode column (or each dot, depending on design) to set the forward current and prevent exceeding the Absolute Maximum Ratings.
Power Dissipation: The 40mW per dot and 15mA average current limits must be respected in the multiplexing scheme. For example, with a 1/8 duty cycle multiplex, the instantaneous current per dot can be higher than 15mA, but the *average* over the full cycle must be calculated to stay within limits.
Viewing Angle: The "wide viewing angle" feature is beneficial, but the exact angular distribution of light is not specified. For wide-viewing applications, prototype evaluation is recommended.
Stacking: The horizontal stackability feature simplifies creating multi-digit displays. Mechanical alignment and electrical connection between modules need to be planned.

9. Technical Comparison and Differentiation

The key differentiator of the LTP-2088AKD is its use of AlInGaP Hyper Red technology. Compared to older technologies like standard GaAsP (Gallium Arsenide Phosphide) red LEDs, AlInGaP offers significantly higher luminous efficiency. This means it can produce more light (higher luminous intensity) for the same amount of electrical current, directly contributing to its "low power requirement" feature. It also typically offers better wavelength stability over temperature and lifetime. The gray face/white segment design improves contrast compared to all-red or all-green packages, especially under high ambient light conditions. The explicit luminous intensity categorization (binning) is an advantage for applications requiring uniformity.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the difference between Peak Emission Wavelength (650nm) and Dominant Wavelength (639nm)?
A: Peak wavelength is the point of maximum power in the spectral output. Dominant wavelength is the single wavelength of monochromatic light that would produce the same perceived color (hue) as the LED's output. The difference is due to the shape of the LED's spectral curve, which has some width.

Q: How do I calculate the required series resistor for a dot?
A: Use Ohm's Law: R = (V_supply - V_F) / I_F. For a 5V supply, typical V_F of 2.6V, and desired I_F of 20mA: R = (5 - 2.6) / 0.02 = 120 Ω. Use the maximum V_F (2.8V) for a conservative design ensuring current never exceeds the target.

Q: Can I drive it with a constant voltage without current limiting?
A: No. LED forward voltage has tolerance and decreases with temperature. A constant voltage near V_F can cause thermal runaway, where increasing current heats the LED, lowering V_F, causing more current, leading to failure. Always use current limiting.

Q: What does a 2:1 Luminous Intensity Matching Ratio mean for my design?
A> It guarantees visual uniformity. In the worst case, one dot may be twice as bright as another. For most alphanumeric displays, this ratio is acceptable and not distracting. For graphics requiring precise gray levels, it may be a consideration.

11. Design and Usage Case Study

Scenario: Building a 4-character alphanumeric display for a temperature controller.
Design: Four LTP-2088AKD modules are stacked horizontally. A single microcontroller (e.g., an ATmega328P) is used. Due to limited I/O, two 8-bit serial-in/parallel-out shift registers (like 74HC595) are used to drive the 32 column anodes (8 columns x 4 displays). The 8 row cathodes (common across all displays due to stacking) are driven directly by 8 microcontroller pins configured as open-drain/sinking outputs, each with a transistor for higher current capability.
Software: The firmware implements a multiplexing routine. It sets the pattern for one row (via the shift registers) and then activates (grounds) only that corresponding row cathode. It cycles through all 8 rows rapidly (e.g., 1-2 kHz scan rate). The persistence of vision creates the illusion of a stable image.
Current Calculation: To display all dots in a row at maximum brightness, the instantaneous current per dot might be set to 25mA. With a 1/8 duty cycle, the average current per dot is 25mA / 8 = 3.125mA, well below the 15mA average rating. The total supply current peaks when a full row is lit: 8 dots/display * 4 displays * 25mA = 800mA. The power supply and row driver transistors must be sized accordingly.

12. Operating Principle

The LTP-2088AKD is based on the principle of electroluminescence in a semiconductor p-n junction. The AlInGaP material system is a direct bandgap semiconductor. When forward biased (positive voltage on the anode relative to the cathode), electrons from the n-type region and holes from the p-type region are injected into the active region. When these charge carriers recombine, they release energy in the form of photons (light). The specific composition of Aluminum, Indium, Gallium, and Phosphide determines the bandgap energy, which in turn dictates the wavelength (color) of the emitted light—in this case, red at approximately 650 nm. The non-transparent GaAs substrate helps reflect light upward, improving the external light extraction efficiency from the top of the chip. The 8x8 matrix is formed by individually wiring 64 of these tiny LED chips in a row-column grid pattern within the single package.

13. Technology Trends

Discrete dot matrix displays like the LTP-2088AKD represent a mature technology. Current trends in display technology are moving towards higher integration and different form factors. Integrated LED dot matrix modules with built-in controllers (I2C or SPI interface) are becoming more common, simplifying the design effort for the end user. For new designs requiring small alphanumeric displays, segmented LCDs or OLEDs often offer lower power consumption and more flexible formatting. However, traditional LED dot matrices retain advantages in specific niches: extremely high brightness for outdoor or high-ambient-light viewing, wide operating temperature ranges, long lifetime, and robustness in harsh industrial environments. The underlying AlInGaP LED chip technology continues to improve, with ongoing research into increasing efficiency (lumens per watt) and improving color purity, which benefits all red LED applications, including matrix displays.