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

1. Product Overview

The LTP-1457AKD is a single-digit, alphanumeric display module designed for applications requiring clear, reliable character output. Its core function is to visually represent data, typically ASCII or EBCDIC coded characters, through a grid of individually addressable light-emitting diodes (LEDs).

The device is built around a 5 column by 7 row (5x7) array of AlInGaP (Aluminum Indium Gallium Phosphide) Hyper Red LED chips. This semiconductor material is grown on a non-transparent Gallium Arsenide (GaAs) substrate, which contributes to its optical performance. The visual presentation features a gray faceplate with white dots, providing high contrast for the illuminated red elements. The primary design goals for this component are low power consumption, solid-state reliability, and a wide viewing angle achieved through a single-plane construction. It is categorized based on luminous intensity, allowing for brightness matching in multi-digit applications, and is horizontally stackable to form multi-character displays.

2. Technical Parameter Deep Dive

2.1 Absolute Maximum Ratings

These parameters define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed.

• Average Power Dissipation per Dot: 40 mW. This is the maximum continuous power each LED segment can handle without overheating.
• Peak Forward Current per Dot: 90 mA. This is permissible only under pulsed conditions with a 1/10 duty cycle and a 0.1 ms pulse width to avoid thermal overstress.
• Average Forward Current per Dot: 15 mA at 25°C. This current derates linearly above 25°C at a rate of 0.2 mA/°C. For example, at 85°C, the maximum allowable average current would be approximately: 15 mA - ((85°C - 25°C) * 0.2 mA/°C) = 3 mA.
• Reverse Voltage per Dot: 5 V. Exceeding this voltage in reverse bias can cause junction breakdown.
• Operating & Storage Temperature Range: -35°C to +85°C.
• Solder Temperature: Withstands 260°C for a maximum of 3 seconds, measured 1.6mm (1/16 inch) below the seating plane of the package.

2.2 Electrical & Optical Characteristics

These are the guaranteed performance parameters under specified test conditions at an ambient temperature (Ta) of 25°C.

• Average Luminous Intensity (I_V): Ranges from 800 μcd (min) to 2600 μcd (typ), tested at a peak current (I_p) of 32 mA with a 1/16 duty cycle. The intensity is measured using a filter that approximates the photopic (CIE) human eye response curve.
• Peak Emission Wavelength (λ_p): Typically 650 nm when driven at a forward current (I_F) of 20 mA. This is the wavelength at which the optical power output is greatest.
• Spectral Line Half-Width (Δλ): Typically 20 nm (I_F=20mA). This indicates the spread of the emitted light's wavelength around the peak.
• Dominant Wavelength (λ_d): Typically 639 nm (I_F=20mA). This is the single wavelength perceived by the human eye, which may differ slightly from the peak wavelength.
• Forward Voltage per Dot (V_F): Ranges from 2.1V to 2.8V depending on current. At I_F=20mA: 2.1V (min), 2.6V (typ). At I_F=80mA: 2.3V (min), 2.8V (typ).
• Reverse Current per Dot (I_R): Maximum 100 μA when a reverse voltage (V_R) of 5V is applied.
• Luminous Intensity Matching Ratio (I_V-m): Maximum 2:1. This specifies that the brightness difference between any two dots (or segments) on the same device under the same drive conditions will not exceed a factor of two.

3. Binning System Explanation

The datasheet indicates the device is \"Categorized for Luminous Intensity.\" This implies a binning or sorting process post-manufacturing. Due to inherent variations in the semiconductor epitaxial growth and chip processing, LEDs from the same production batch can have slightly different optical outputs. To ensure consistency in applications, especially in multi-digit displays where uniform brightness is critical, the manufactured units are tested and sorted into different \"bins\" based on their measured luminous intensity. Designers can then specify a bin code when ordering to guarantee all units in their assembly fall within a tight brightness range, preventing some characters from appearing dimmer or brighter than others. While this datasheet does not list the specific bin codes or intensity ranges, the practice is standard for ensuring visual quality.

4. Performance Curve Analysis

The final page of the datasheet is dedicated to \"Typical Electrical / Optical Characteristic Curves.\" These graphs are invaluable for understanding device behavior beyond the single-point specifications listed in the tables. While the specific curves are not detailed in the provided text, typical plots for such a device would include:

• Forward Current vs. Forward Voltage (I-V Curve): Shows the nonlinear relationship between current and voltage across the LED junction. It helps in designing the current-limiting circuitry.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with current, typically in a sub-linear fashion at higher currents due to heating and efficiency droop.
• Luminous Intensity vs. Ambient Temperature: Illustrates the decrease in light output as the junction temperature rises, which is critical for applications operating over a wide temperature range.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the shape and width of the emitted red light spectrum.

These curves allow engineers to predict performance under their specific operating conditions, which may differ from the standard test conditions.

5. Mechanical & Package Information

The LTP-1457AKD's physical construction is defined by its package dimensions and internal circuitry.

5.1 Package Dimensions

The device has a matrix height of 1.2 inches (30.42 mm). A detailed dimensioned drawing is provided on page 2 of the datasheet. All dimensions are specified in millimeters, with a general tolerance of ±0.25 mm (±0.01 inches) unless a specific feature calls for a different tolerance. This drawing is essential for PCB (Printed Circuit Board) footprint design, ensuring the component fits correctly and aligns with the board's solder pads.

5.2 Internal Circuit & Pinout

The display uses a common-cathode configuration for the rows. The internal circuit diagram shows a 5x7 matrix where each LED (dot) is formed at the intersection of an anode (column) line and a cathode (row) line. To illuminate a specific dot, its corresponding column anode must be driven high (with appropriate current limiting), while its row cathode must be pulled low.

The pin connection table is crucial for interfacing:
- Pins 1, 2, 5, 7, 8, 9, 12, 14 connect to Cathode Rows (1-7).
- Pins 3, 4, 6, 10, 11, 13 connect to Anode Columns (1-5).
Note: There is a discrepancy in the provided list where Pin 11 is listed as \"ANODE COLUMN 3\" and Pin 4 is also \"ANODE COLUMN 3\". In a standard 5x7 matrix with 12 pins (14 pins with 2 possibly unused), this is likely a documentation error; one should be Column 1, 2, 3, 4, or 5. The actual datasheet diagram must be consulted for the correct, unambiguous mapping. Proper multiplexing drive circuitry is required to sequentially activate rows and columns to form characters without ghosting.

6. Soldering & Assembly Guidelines

The key assembly specification provided is the soldering temperature profile. The device can withstand a peak temperature of 260°C for a maximum duration of 3 seconds. This is measured at a point 1.6mm below the package body's seating plane, which corresponds roughly to the PCB surface or the solder joint itself. This rating is compatible with standard lead-free (SnAgCu) reflow soldering processes. Designers must ensure their reflow oven profile does not exceed this time-at-temperature limit to prevent damage to the LED chips, internal wire bonds, or the plastic package material. Standard ESD (Electrostatic Discharge) precautions should be observed during handling.

7. Application Suggestions

7.1 Typical Application Scenarios

This display is suited for applications requiring a single, highly legible character or symbol. Its stackable nature allows it to be used in multi-character setups. Common uses include:
- Instrumentation panels (voltmeters, multimeters, frequency counters).
- Industrial control system status indicators.
- Point-of-sale terminal displays.
- Simple message boards or scoreboards when multiple units are combined.
- Embedded system user interfaces for status codes or single-digit output.

7.2 Design Considerations

• Drive Circuitry: A microcontroller with sufficient I/O pins or a dedicated LED display driver IC (like a MAX7219 or similar) is needed for multiplexing. Each pin will sink or source current for multiple LEDs, so ensure the MCU or driver's per-pin current limits are not exceeded.
• Current Limiting: External current-limiting resistors are mandatory for each anode column (or a constant current driver) to set the forward current (I_F) to a safe value, typically between 10-20 mA for continuous operation, considering the derating with temperature.
• Power Dissipation: Calculate the total power dissipation, especially when multiple dots are illuminated simultaneously. Ensure it remains within the device's and the PCB's thermal limits.
• Viewing Angle: The wide viewing angle is beneficial for applications where the display may be viewed from the side.
• Brightness Consistency: Specify an intensity bin when ordering for multi-unit applications to ensure visual uniformity.

8. Technical Comparison & Differentiation

The LTP-1457AKD's primary differentiators are its use of AlInGaP Hyper Red technology and its specific mechanical/electrical format.

• vs. Standard GaAsP or GaP Red LEDs: AlInGaP LEDs generally offer higher luminous efficiency, better temperature stability, and a more saturated, pure red color (dominant wavelength ~639nm) compared to older technologies, which may appear more orange.
• vs. Larger or Smaller Dot Matrix Displays: The 1.2\" height and 5x7 format represent a specific size and resolution trade-off, offering good legibility at a moderate distance. Smaller formats save space but reduce readability; larger formats are more visible from afar but consume more power and board area.
• vs. Integrated Controller Displays: This is a \"raw\" LED array. Displays with integrated controllers (I2C, SPI) simplify the microcontroller interface but may be less flexible or more expensive. The LTP-1457AKD offers direct control at the cost of more complex driver circuitry.

9. Frequently Asked Questions (Based on Parameters)

Q: Can I drive this display with a 5V microcontroller directly?
A: Possibly, but with caution. The typical V_F is 2.1-2.8V. A 5V MCU pin would apply 5V to the anode, which without a current-limiting resistor would destroy the LED. You must use a series resistor. The calculation is: R = (V_supply - V_F) / I_F. For a 5V supply, V_F=2.6V, and I_F=20mA, R = (5 - 2.6) / 0.02 = 120 Ω. Also, ensure the MCU can sink/source the required multiplexed current.

Q: What does \"1/16 Duty Cycle\" mean in the test condition for luminous intensity?
A: It means the LED is pulsed on for 1/16th of the total cycle time. For multiplexed displays, this is a common drive method. The peak current during the on-time (32 mA in the test) is higher than what could be used for DC operation to achieve a perceived brightness equivalent to a lower DC current. The average current is (Peak Current * Duty Cycle) = 32mA * (1/16) = 2 mA.

Q: How do I create characters like letters and numbers?
A: You need a font table or character generator in your software. This is a lookup table that defines which dots (anode/column, cathode/row combinations) to illuminate for each ASCII or EBCDIC code. For example, the character \"A\" would map to a specific pattern across the 5 columns and 7 rows.

10. Design and Usage Case Study

Scenario: Designing a Single-Digit RPM Indicator for a Motor Controller.
The display needs to show a number from 0-9 representing a speed range. A low-cost microcontroller with 12 I/O pins is selected.
Implementation: 7 pins are configured as open-drain outputs to drive the cathode rows (sinking current). 5 pins are configured as digital outputs to drive the anode columns via current-limiting resistors (sourcing current). The firmware contains a 5x7 font map for digits 0-9. It runs a timer interrupt that sequentially activates each row (1-7) by pulling its cathode pin low. For the active row, the firmware sets the 5 anode pins high according to the font pattern for the digit to be displayed in that specific row. This multiplexing happens faster than the human eye can perceive (e.g., >100 Hz), creating a stable, flicker-free image. The average current per LED is kept at 10 mA (peak current adjusted for duty cycle) to ensure long-term reliability within the power dissipation limits.

11. Operating Principle

The fundamental principle is electroluminescence in a semiconductor p-n junction. The AlInGaP material has a direct bandgap. When forward-biased (positive voltage on the anode relative to the cathode), electrons are injected from the n-type region into the conduction band, and holes are injected from the p-type region into the valence band. These charge carriers recombine in the active region near the junction. In a direct bandgap material like AlInGaP, a significant portion of these recombinations are radiative, meaning they release energy in the form of photons (light). The wavelength (color) of this light is determined by the bandgap energy (E_g) of the semiconductor material, according to the equation λ ≈ hc/E_g. For AlInGaP tuned for red light, this results in photons with a wavelength around 650 nm. The 5x7 matrix arrangement is simply a grid of these individual p-n junction LEDs, with their anodes and cathodes connected in a crossed pattern to minimize the number of required driver pins.

12. Technology Trends

While the LTP-1457AKD represents a mature and reliable technology, the broader field of display technology continues to evolve. Discrete LED dot matrix displays of this type face competition from integrated modules using surface-mount device (SMD) LEDs, which can be smaller and offer higher resolution. Furthermore, organic LED (OLED) and micro-LED technologies are advancing, promising thinner, more efficient, and higher-contrast displays. For the specific niche of simple, rugged, single-character or low-resolution multi-character displays, AlInGaP and similar III-V semiconductor LEDs remain highly relevant due to their proven reliability, wide operating temperature range, high brightness, and cost-effectiveness for industrial and instrumentation applications. The trend in this segment is towards higher efficiency (more light per watt) and tighter binning for color and brightness consistency.