LTP-2157AKS 5x7 Dot Matrix LED Display Datasheet - 2.0-inch Height - AlInGaP Yellow - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTP-2157AKS is a monochrome dot matrix display module designed for alphanumeric character presentation. Its primary function is to provide a clear, bright visual output for applications requiring information display such as simple readouts, indicators, or basic messaging systems. The core advantage of this device lies in its utilization of Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor technology for the LED chips, which is known for producing high-efficiency light emission in the amber/yellow/red spectrum. The display features a 5x7 array configuration, which is the standard for representing ASCII characters and symbols. The physical design incorporates a black face with white dot color, enhancing contrast and readability under various lighting conditions. This product is targeted at embedded system designers, industrial control panel manufacturers, and developers of consumer electronics requiring a reliable, low-complexity display solution.

2. Technical Parameters Deep Objective Interpretation

2.1 Photometric and Optical Characteristics

The key photometric parameter is the Average Luminous Intensity (Iv), specified with a typical value of 3600 microcandelas (μcd) under a test condition of a 32mA pulse current and a 1/16 duty cycle. This indicates a high-brightness output suitable for indoor and many outdoor applications. The Peak Emission Wavelength (λp) is 588 nm, and the Dominant Wavelength (λd) is 587 nm, firmly placing the emitted light in the yellow region of the visible spectrum. The Spectral Line Half-Width (Δλ) of 15 nm denotes a relatively pure color with minimal spectral spread. The Luminous Intensity Matching Ratio between segments is specified as 2:1 maximum, ensuring uniform appearance across the display.

2.2 Electrical Parameters

The primary electrical characteristic is the Forward Voltage (Vf) per segment, which has a typical value of 2.6V and a maximum of 2.6V at a test current (If) of 20mA. This is a critical parameter for driver circuit design. The Absolute Maximum Ratings define the operational limits: an Average Forward Current per Dot of 25 mA (derating linearly by 0.28 mA/°C above 25°C), a Peak Forward Current per Dot of 60 mA, and a Reverse Voltage per Dot of 5 V. Exceeding these ratings can cause permanent damage. The Reverse Current (Ir) is specified at a maximum of 100 μA at 5V reverse bias.

2.3 Thermal and Environmental Characteristics

The device is rated for an Operating Temperature Range of -35°C to +105°C and an identical Storage Temperature Range. This wide range ensures reliability in harsh environments. The power dissipation limit is 70 mW per dot on average. The derating factor for forward current (0.28 mA/°C) is essential for calculating safe operating currents at elevated ambient temperatures to prevent overheating and ensure long-term reliability.

3. Binning System Explanation

The provided datasheet does not explicitly detail a formal binning system for wavelength, flux, or voltage. However, the specifications provide minimum, typical, and maximum values for key parameters like Luminous Intensity (2100 μcd min, 3600 μcd typ) and Forward Voltage (2.05V min, 2.6V typ/max). In practice, manufacturers often group products into bins based on measured performance to ensure consistency within a production lot. Designers should consult the manufacturer for specific binning information if tight parameter matching is required for their application.

4. Performance Curve Analysis

The datasheet references 'Typical Electrical / Optical Characteristic Curves' on the final page. While the specific graphs are not detailed in the text, such curves typically include:

• Forward Current vs. Forward Voltage (I-V Curve): This graph shows the nonlinear relationship between current and voltage for the LED. It is crucial for designing constant current drivers, as a small change in voltage can cause a large change in current.
• Luminous Intensity vs. Forward Current: This curve demonstrates how light output increases with current, usually in a roughly linear relationship within the operating range, before efficiency drops at very high currents.
• Luminous Intensity vs. Ambient Temperature: This graph shows the derating of light output as the junction temperature increases. For AlInGaP LEDs, luminous intensity typically decreases as temperature rises.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the peak at ~588 nm and the 15 nm half-width, confirming the color purity.

These curves are vital for understanding the device's behavior under non-standard conditions and for optimizing the design for performance and longevity.

5. Mechanical and Packaging Information

The LTP-2157AKS is presented in a standard dual in-line package (DIP) format suitable for through-hole PCB mounting. The package dimensions are provided in millimeters, with a general tolerance of ±0.25 mm. A key mechanical feature is the pin tip's shift tolerance of ±0.4 mm, which is important for PCB hole alignment during assembly. The device utilizes a lead-free package compliant with RoHS (Restriction of Hazardous Substances) directives. The physical appearance is characterized by a black face with white dots, which serves to absorb ambient light and improve contrast by making the unlit areas appear darker.

6. Soldering and Assembly Guidelines

The Absolute Maximum Ratings section provides specific soldering conditions: the device can be subjected to a soldering temperature of 260°C for 3 seconds, measured at a point 1/16 inch (approximately 1.6 mm) below the seating plane of the package. This is a critical parameter for wave soldering or hand soldering processes to prevent thermal damage to the LED chips or the internal wire bonds. It is imperative that the maximum temperature rating is not exceeded during the assembly process. Standard ESD (Electrostatic Discharge) precautions should be observed when handling the device.

7. Packaging and Ordering Information

The part number is clearly identified as LTP-2157AKS. The datasheet does not specify bulk packaging details such as reel quantities, tube counts, or tray configurations. For mass production, engineers must contact the supplier to obtain specifics on minimum order quantities, packaging type (e.g., anti-static tubes or trays), and labeling conventions. The 'Spec No.' and 'Effective Date' provide traceability to the specific revision of the technical documentation.

8. Application Suggestions

8.1 Typical Application Scenarios

This 5x7 dot matrix display is ideal for applications requiring simple, legible character output. Common uses include: industrial instrument panels (for displaying setpoints, status codes, or error messages), consumer appliances (microwave ovens, washing machines), basic information displays in vending machines or point-of-sale terminals, and educational electronics kits. Its yellow color is often chosen for cautionary indicators or where high visibility is needed.

8.2 Design Considerations

Designing with this display requires a multiplexed driver circuit due to its X-Y (matrix) select architecture, as shown in the internal circuit diagram. The pin connection table is essential for correctly interfacing the microcontroller or driver IC. Pins 4 & 11 and pins 5 & 12 are internally connected, which must be accounted for in the PCB layout and software scanning routine. A constant current driver is recommended to maintain consistent brightness and protect the LEDs. The design must respect the absolute maximum ratings for current and power dissipation, especially considering the derating factor at high temperatures. Heat sinking is generally not required for this low-power device under normal conditions.

9. Technical Comparison

Compared to other display technologies, this AlInGaP-based LED matrix offers distinct advantages. Versus older GaAsP or GaP LEDs, AlInGaP provides significantly higher luminous efficiency and brightness. Compared to simple 7-segment displays, a 5x7 dot matrix offers far greater flexibility in displaying alphanumeric characters and simple graphics. When contrasted with modern LCDs or OLEDs, this LED matrix is superior in terms of viewing angle, brightness, and ruggedness, though it consumes more power for a comparable display area and is limited to a single color. Its main differentiator is simplicity, reliability, and high visibility in various lighting conditions without a backlight.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Why is the forward current specified with a duty cycle (1/16)?
A: The display uses a multiplexed driving scheme. To achieve an average current per dot of, for example, 5 mA, the driver would apply a higher peak current (e.g., 80 mA) for a short period (1/16 of the scan cycle). This allows all dots to be addressed sequentially while maintaining perceived brightness and staying within the average power dissipation limits.

Q: Can I drive this display with a constant voltage source?
A: It is not recommended. LEDs are current-driven devices. Their forward voltage has a tolerance and varies with temperature. Driving with a constant voltage risks overcurrent if the Vf is at the low end of the specification, leading to reduced lifespan or failure. Always use a current-limiting resistor or, preferably, a constant current driver.

Q: What is the purpose of the internally connected pins (4/11 and 5/12)?
A> These internal connections simplify the internal bonding of the semiconductor die to the package leads and likely help in balancing current distribution within the matrix. From the user's perspective, they provide multiple connection points for the same electrical node, which can offer layout flexibility on the PCB.

11. Practical Use Case

Consider designing a simple temperature controller with a setpoint and actual temperature readout. The LTP-2157AKS can display values like \"SET 75\" and \"ACT 72\". A microcontroller would scan the 7 rows and 5 columns. The firmware would contain a font map, translating each character (e.g., 'S', 'E', 'T') into the specific pattern of 35 dots (5x7) to illuminate. The driver circuit, possibly consisting of discrete transistors or a dedicated LED driver IC, would sink current through the selected column cathodes and source current to the selected row anodes based on the microcontroller's GPIO pins. The high brightness ensures the display is readable from a distance on the control panel.

12. Principle Introduction

The device operates on the principle of electroluminescence in a semiconductor p-n junction. The AlInGaP (Aluminium Indium Gallium Phosphide) material system is a direct bandgap semiconductor. When forward biased, electrons from the n-region and holes from the p-region are injected into the active region where they recombine. The energy released during this recombination is emitted as photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, and thus the wavelength (color) of the emitted light—in this case, yellow (~587-588 nm). The 5x7 matrix is formed by arranging 35 individual LED chips (dots) in a grid, with their anodes connected in rows and cathodes connected in columns. This common-anode/common-cathode matrix structure allows control of 35 dots with only 12 pins (7 rows + 5 columns), significantly reducing the required number of driver lines compared to individually addressed LEDs.

13. Development Trends

While discrete LED dot matrix displays like the LTP-2157AKS remain relevant for specific applications, the broader trend in display technology is moving towards higher integration and functionality. Surface-mount device (SMD) packages are becoming more common for automated assembly. Integrated driver and controller chips are often combined with the LED array in a single module, simplifying the interface for the system designer (e.g., SPI or I2C communication instead of direct matrix scanning). Furthermore, full-color RGB LED matrices are increasingly popular for dynamic signage and more complex graphics. However, for simple, robust, single-color character display needs, the fundamental design represented by this product continues to be a reliable and cost-effective solution. Advances in materials may also lead to even higher efficiency and brightness from future AlInGaP or related nitride-based (InGaN) LEDs in the amber/yellow spectrum.