LTP-1457AKR LED Display Datasheet - 1.2-inch (30.42mm) Matrix Height - AlInGaP Super Red - 5x7 Dot Array - English Technical Document

1. Product Overview

The LTP-1457AKR is a solid-state, single-plane dot matrix display module designed for generating alphanumeric characters and simple symbols. Its core function is to provide a reliable and legible visual output in various electronic systems. The device is built around a 5x7 array of light-emitting diodes (LEDs), which is a standard configuration for character generation, compatible with common character codes like USASCII and EBCDIC. The primary application areas include industrial control panels, instrumentation readouts, point-of-sale terminals, and other embedded systems requiring a compact, low-power display solution. Its stackable horizontal design allows for the creation of multi-character displays by aligning multiple units side-by-side, facilitating the display of words and numbers.

2. Technical Specifications Deep Dive

This section provides a detailed, objective analysis of the device's key technical parameters as defined in the datasheet.

2.1 Optoelectronic Characteristics

The display utilizes AlInGaP (Aluminum Indium Gallium Phosphide) Super Red LED chips. This semiconductor material is known for its high efficiency and excellent color purity in the red-orange spectrum. The chips are fabricated on a non-transparent GaAs (Gallium Arsenide) substrate. The typical peak emission wavelength (λp) is 639 nm, with a dominant wavelength (λd) of 631 nm, placing its output firmly in the red visible region. The spectral line half-width (Δλ) is 20 nm, indicating a relatively narrow bandwidth and pure color output. The device features a gray face with white dots, which enhances contrast and readability. Luminous intensity, a critical measure of brightness, is categorized. Under a test condition of 80mA peak current and a 1/16 duty cycle, the average luminous intensity (Iv) ranges from a minimum of 2100 μcd to a typical value of 3800 μcd. The luminous intensity matching ratio between dots is specified as 2:1 maximum, ensuring uniform brightness across the character.

2.2 Electrical Parameters

The electrical characteristics define the operating limits and conditions for the display. The absolute maximum ratings must not be exceeded to ensure device reliability. The average power dissipation per LED dot is limited to 33 mW. The peak forward current per dot is 90 mA, but this is only permissible under pulsed conditions (1/10 duty cycle, 0.1 ms pulse width). The more critical parameter for continuous or multiplexed operation is the average forward current per dot, which is 13 mA at 25°C. This current rating derates linearly by 0.17 mA/°C as the ambient temperature increases above 25°C. The maximum reverse voltage that can be applied to any dot is 5 V. The forward voltage (Vf) for any dot, when driven with a 20mA current, typically ranges from 2.1V to 2.6V. The reverse current (Ir) is a maximum of 100 μA when 5V is applied in reverse bias.

2.3 Thermal and Environmental Specifications

The device is rated for an operating temperature range of -35°C to +85°C. The storage temperature range is identical. This wide range makes it suitable for applications in harsh environments. A critical assembly parameter is the solder temperature: the device can withstand a maximum temperature of 260°C for a maximum of 3 seconds, measured at a point 1.6mm (1/16 inch) below the seating plane of the package. This information is vital for defining the reflow soldering profile during PCB assembly.

3. Binning System Explanation

The datasheet explicitly states that the devices are "Categorized for Luminous Intensity." This indicates a binning or sorting process based on measured light output. Binning is a standard practice in LED manufacturing to group components with similar performance characteristics. For the LTP-1457AKR, the primary binning criterion is luminous intensity. This ensures that designers can select displays with consistent brightness levels, which is crucial for multi-unit displays where uniformity is key. While the datasheet does not detail specific bin codes or ranges beyond the min/typ values, designers should consult the manufacturer for available bins to meet specific application brightness requirements.

4. Performance Curve Analysis

The datasheet references "Typical Electrical / Optical Characteristic Curves" on the final page. Although the specific graphs are not provided in the text, typical curves for such devices would include:

• Forward Current vs. Forward Voltage (I-V Curve): This graph shows the relationship between the current flowing through an LED and the voltage across it. It is non-linear, with a turn-on voltage (around 1.8-2.0V for AlInGaP red) after which current increases rapidly with small voltage increases. This curve is essential for designing the current-limiting circuitry.
• Luminous Intensity vs. Forward Current: This plot demonstrates how light output increases with drive current. It is generally linear over a range but will saturate at very high currents. It helps optimize the trade-off between brightness and power consumption/heat.
• Luminous Intensity vs. Ambient Temperature: This curve shows the derating of light output as the junction temperature of the LED increases. LED efficiency drops with rising temperature, so thermal management is important for maintaining consistent brightness.
• Spectral Distribution: A graph plotting relative intensity against wavelength, showing the peak at ~639nm and the shape of the emission spectrum.

5. Mechanical and Packaging Information

The device is presented with a package dimensions drawing (details not fully specified in text, but tolerances are ±0.25 mm). The physical construction houses the 5x7 LED array. The pin connection table is crucial for interfacing. The display uses a row-cathode, column-anode configuration common in multiplexed LED matrices. There are 14 pins in total: 7 pins are connected to the cathodes of the LED rows (Rows 1-7), and 5 pins are connected to the anodes of the LED columns (Columns 1-5). Two pins are noted as duplicates (Pin 4 and Pin 11 are both Anode Column 3; Pin 5 and Pin 12 are both Cathode Row 4), which is likely for layout flexibility or internal connection. The internal circuit diagram would show each of the 35 LEDs (5 columns x 7 rows) with its anode connected to a column line and its cathode connected to a row line, forming a matrix that can be addressed by selecting one row and one column at a time.

6. Soldering and Assembly Guidelines

Based on the absolute maximum ratings, key assembly guidelines can be derived. For wave or reflow soldering, the peak body temperature must not exceed 260°C, and the time above this temperature should be limited to 3 seconds. It is recommended to follow standard JEDEC/IPC guidelines for soldering surface-mount components. The device should be stored in its original moisture-barrier bag until use. After opening, if the device is not used immediately, it may require baking according to the moisture sensitivity level (MSL) specified on the bag label (not provided in this datasheet excerpt). Handling should be done with care to avoid mechanical stress on the package and contamination of the optical surface.

7. Packaging and Ordering Information

The part number is LTP-1457AKR. The "LTP" prefix likely denotes the product family (LED dot matrix), "1457" may refer to the 1.2-inch size and 5x7 format, and "AKR" could indicate the color (AlInGaP Super Red) and possibly a specific bin or revision. The datasheet does not specify standard packaging quantities (e.g., tape and reel, tray) or include a label diagram. For volume production, designers must contact the manufacturer to obtain details on packaging options, reel specifications, and part number variations for different intensity bins.

8. Application Recommendations

8.1 Typical Application Scenarios

This display is ideal for applications requiring a simple, low-cost, and reliable alphanumeric readout. Examples include: digital clocks, thermostats, blood pressure monitors, multimeter displays, industrial timer/counter panels, basic status indicators on machinery, and educational electronics kits. Its compatibility with standard character codes makes it easy to interface with microcontrollers that have built-in character generators.

8.2 Design Considerations

• Drive Circuitry: The matrix must be multiplexed. A microcontroller or dedicated driver IC is required to sequentially activate rows (sinking current) while providing data on the columns (sourcing current). This reduces the required number of control pins from 35 (one per LED) to 12 (7 rows + 5 columns).
• Current Limiting: External current-limiting resistors are mandatory for each column (anode) line to set the forward current for the LEDs. The resistor value is calculated using R = (Vcc - Vf) / If, where Vf is the LED forward voltage (~2.6V max), If is the desired forward current (≤13mA average per dot), and Vcc is the supply voltage.
• Multiplexing Frequency: The refresh rate must be high enough to avoid visible flicker, typically above 60 Hz. With 7 rows, the row scan rate should be >420 Hz (7 * 60).
• Power Dissipation: Ensure the average power per dot (If * Vf) and the total package power do not exceed ratings, especially at high ambient temperatures. The derating curve for average current must be respected.
• Viewing Angle: The datasheet mentions a "wide viewing angle," which is typical for single-plane, non-lensed LED matrices. Consider the required viewing cone for the end application.

9. Technical Comparison

Compared to other display technologies, this LED dot matrix offers distinct advantages and trade-offs. Versus 7-segment LED displays, the 5x7 dot matrix can display the full alphanumeric character set and some symbols, whereas 7-segment displays are limited primarily to numbers and a few letters. However, 5x7 displays require more complex drive electronics. Compared to LCDs, LEDs are emissive (produce their own light), offering superior brightness and wide viewing angles without a backlight, making them readable in direct sunlight. LCDs, however, consume significantly less power for static content and can display more complex graphics. Versus older incandescent or vacuum fluorescent displays (VFDs), LEDs have much higher reliability, faster response time, lower voltage operation, and are solid-state with no filaments or glass to break.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this display with a constant DC current on each LED?

A: Technically yes, but it would require 35 independent drivers, which is impractical. Multiplexing (scanning) is the standard and intended method of operation, drastically reducing component count.

Q: Why is the peak current (90mA) so much higher than the average current (13mA)?

A> In a multiplexed system, each LED is only on for a fraction of the time (duty cycle). To achieve a perceived brightness equivalent to a lower constant current, a higher pulsed current is used during its brief "on" time. The 90mA rating ensures the LED can handle these brief pulses without damage.

Q: The pinout shows duplicate connections for Anode Column 3 and Cathode Row 4. Which one should I use?

A: You can use either of the duplicate pins. They are electrically connected inside the package. This is often done to provide layout flexibility on the PCB, allowing the routing to come from two different sides.

Q: How do I calculate the brightness for my application?

A> The perceived brightness in a multiplexed setup depends on the peak current (Ip) and the duty cycle. For example, with a 1/7 duty cycle (7 rows) and a peak current of 80mA, the average current per dot is ~11.4mA (80mA / 7). You would then reference the luminous intensity vs. current curve to estimate light output at that average current level.

11. Practical Design and Usage Example

Consider designing a simple single-digit clock display using a microcontroller. The microcontroller's I/O ports would be configured to drive the matrix. Seven pins would be set as open-drain or current-sinking outputs connected to the row cathodes. Five pins would be set as standard push-pull outputs connected to the column anodes, each with a series current-limiting resistor (e.g., (5V - 2.4V) / 0.013A ≈ 200Ω). Firmware would contain a font map—a lookup table defining the 5x7 pattern for each character (0-9, A-Z). The main loop would implement a timer interrupt. In the interrupt service routine, the microcontroller would: 1) turn off all columns for the previous row, 2) advance to the next row, 3) fetch the column data (5 bits) for the desired character for that row, 4) apply this data to the column pins, and 5) enable (sink current on) the current row cathode. This sequence repeats at a high frequency, creating a stable, flicker-free character.

12. Operating Principle

The fundamental operating principle is based on electroluminescence in a semiconductor p-n junction. When a forward voltage exceeding the diode's turn-on voltage is applied, electrons from the n-type material recombine with holes from the p-type material in the active region (the AlInGaP quantum well structure). This recombination releases energy in the form of photons (light). The specific wavelength (color) of the light is determined by the bandgap energy of the semiconductor material, which is engineered in AlInGaP to produce red light. The 5x7 matrix arrangement is an addressing scheme. By organizing the LEDs in a grid, a large number of pixels (35) can be controlled with a relatively small number of control lines (12). This is achieved through multiplexing, where only one row is powered at a time, but the scanning happens so quickly that the human eye perceives all LEDs in a character as being continuously lit due to persistence of vision.

13. Technology Trends

While discrete 5x7 dot matrix displays like the LTP-1457AKR remain relevant for specific, cost-sensitive applications, broader display technology trends are evident. There is a move towards higher integration, such as displays with built-in controller chips (e.g., HDSP-2112 series) that handle character generation and multiplexing, simplifying the host microcontroller's task. For new designs requiring more than a few characters, graphic OLED or TFT LCD modules are becoming more cost-competitive and offer vastly superior capabilities for graphics and custom fonts. In the LED technology itself, the use of AlInGaP represents an advancement over older GaAsP (Gallium Arsenide Phosphide) red LEDs, offering higher efficiency and better temperature stability. The ongoing trend across all LED applications is towards higher luminous efficacy (more light output per watt of electrical input), driven by improvements in epitaxial growth, chip design, and packaging.