LTP-2157AKY-01 LED Display Datasheet - 2.0-inch (50.8mm) Matrix Height - Amber Yellow - 5x7 Dot Array - English Technical Document

1. Product Overview

The LTP-2157AKY-01 is a 2.0-inch (50.8 mm) matrix height, 5x7 dot matrix alphanumeric display module. It is designed to provide clear, high-contrast character representation for applications requiring numeric or limited alphanumeric output. The device utilizes advanced AS-AlInGaP (Aluminum Indium Gallium Phosphide) LED chips grown on a GaAs substrate, which are known for their high efficiency and excellent brightness. The display features a black face with white dots, enhancing contrast and readability under various lighting conditions. Its primary application is in industrial instrumentation, consumer electronics, and other devices where a compact, reliable, and low-power display solution is needed.

1.1 Core Advantages

• High Brightness & Contrast: The AlInGaP technology combined with the black face/white dot design delivers superior visibility.
• Low Power Requirement: Engineered for efficient operation, making it suitable for battery-powered or energy-conscious applications.
• Solid-State Reliability: LEDs offer long operational life, shock resistance, and consistent performance compared to other display technologies.
• Excellent Character Appearance: The 5x7 dot matrix format provides well-defined, easily recognizable characters.
• X-Y Select Architecture: The matrix is organized in a row (anode) and column (cathode) configuration, allowing for efficient multiplexing and control with a reduced number of driver pins.

2. Technical Parameter Deep-Dive

This section provides a detailed, objective analysis of the key electrical and optical parameters specified in the datasheet. Understanding these values is critical for proper circuit design and ensuring long-term reliability.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation outside these limits is not advised.

• Average Power Dissipation per Dot: 35 mW. This limit is crucial for thermal management. Exceeding it can lead to overheating, reduced luminous output, and accelerated degradation of the LED chip.
• Peak Forward Current per Dot: 60 mA (at 1 kHz, 25% duty cycle). This rating is for pulsed operation. The average current under these conditions is 15 mA (60 mA * 0.25), which must still be below the average current rating.
• Average Forward Current per Dot: The base rating is 13 mA at 25°C. Importantly, it derates by 0.17 mA/°C. For example, at an ambient temperature (Ta) of 85°C, the maximum allowable average current would be: 13 mA - [0.17 mA/°C * (85°C - 25°C)] = 13 mA - 10.2 mA = 2.8 mA. This strong derating highlights the need for careful thermal design in high-temperature environments.
• Reverse Voltage per Dot: 5 V. Applying a reverse bias voltage greater than this can cause junction breakdown.
• Operating & Storage Temperature: -35°C to +85°C. The device is rated for industrial temperature ranges.
• Soldering Condition: 260°C for 3 seconds, with the iron tip at least 1/16 inch (approx. 1.6 mm) below the seating plane. This prevents excessive heat from traveling up the leads and damaging the internal LED chips.

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

These are the typical performance parameters under specified test conditions.

• Average Luminous Intensity per Dot (I_V): 1650 (Min), 3600 (Typ) µcd. Tested at a peak current (I_p) of 32 mA with a 1/16 duty cycle. The actual average current is 2 mA. The wide range indicates potential binning for brightness.
• Peak Emission Wavelength (λ_p): 595 nm (Typ). This defines the wavelength at which the spectral output is maximum, placing it in the amber-yellow region of the visible spectrum.
• Dominant Wavelength (λ_d): 592 nm (Typ). This is the single wavelength perceived by the human eye, closely matching the peak wavelength.
• Spectral Line Half-Width (Δλ): 15 nm (Typ). This indicates the spectral purity; a narrower width means a more saturated, pure color.
• Forward Voltage per Segment (V_F):
  • 2.05V (Min), 2.6V (Typ) at I_F = 20 mA.
  • 2.3V (Min), 2.8V (Typ) at I_F = 80 mA. The increase with current is due to the diode's series resistance.
• Reverse Current (I_R): 100 µA (Max) at V_R = 5V. A low reverse current is desirable.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 (Max). This specifies the maximum allowable ratio between the brightest and dimmest dot in the array, ensuring uniform appearance.

3. Binning System Explanation

While the provided datasheet does not detail a formal commercial binning structure, the specified parameter ranges imply inherent variation. Designers should be aware of the following potential variations between units or production lots:

• Wavelength/Color Bin: The typical dominant wavelength is 592 nm. Units may vary slightly around this value, affecting the precise shade of amber-yellow.
• Luminous Intensity (Brightness) Bin: The luminous intensity has a minimum of 1650 µcd and a typical value of 3600 µcd. This wide spread suggests that for applications requiring tight brightness matching, selection or binning at the assembly level may be necessary.
• Forward Voltage Bin: The forward voltage range (2.05V to 2.6V at 20mA) indicates variation. This is important for designing constant-current drivers to ensure consistent brightness across all segments without over-stressing higher V_F dots.

4. Performance Curve Analysis

The datasheet references typical characteristic curves. These graphs, though not displayed in the provided text, are essential for understanding device behavior under non-standard conditions.

4.1 Forward Current vs. Forward Voltage (I-V Curve)

This curve would show the exponential relationship typical of a diode. The specified V_F points at 20mA and 80mA give two data points. The curve helps determine the necessary driving voltage for a given current and allows calculation of power dissipation (V_F * I_F).

4.2 Luminous Intensity vs. Forward Current

This graph shows how light output increases with current. For LEDs, the relationship is generally linear over a range but will saturate at very high currents due to thermal and efficiency droop. Operating near the typical current (derived from the 32mA peak, 1/16 duty spec) ensures optimal efficiency and longevity.

4.3 Luminous Intensity vs. Ambient Temperature

LED light output decreases as junction temperature rises. This characteristic, coupled with the strong current derating (0.17 mA/°C), underscores the critical importance of managing the device's operating temperature to maintain consistent brightness and reliability.

4.4 Spectral Distribution

A graph of relative intensity vs. wavelength would show a peak around 595 nm with a typical half-width of 15 nm, confirming the amber-yellow color point.

5. Mechanical & Package Information

5.1 Package Dimensions

The display module has specific physical dimensions (provided in a diagram in the original datasheet). All dimensions are in millimeters with a standard tolerance of ±0.25 mm unless otherwise noted. Designers must incorporate these dimensions into their product enclosures and PCB layouts.

5.2 Pin Connection & Polarity Identification

The device has a 14-pin configuration. The pinout is as follows: 1. Anode Row 5 2. Anode Row 7 3. Cathode Column 2 4. Cathode Column 3 5. Anode Row 4 6. Cathode Column 5 7. Anode Row 6 8. Anode Row 3 9. Anode Row 1 10. Cathode Column 4 11. Cathode Column 3 (Note: Pin 4 is also Cathode Column 3; this is likely a typo in the source text. Pin 11 is presumably Cathode Column 6 or another column. The internal circuit diagram must be consulted for clarification.) 12. Anode Row 4 (Duplicate of Pin 5; likely a documentation error) 13. Cathode Column 1 14. Anode Row 2

Critical Note: The provided pin list contains apparent duplicates (Pins 4 & 11 for Column 3, Pins 5 & 12 for Row 4). The Internal Circuit Diagram referenced in the datasheet is the authoritative source for correct pin-to-segment mapping and must be used for design. The display uses a common-cathode group configuration per the \"Cathode Column\" and \"Anode Row\" description.

5.3 Internal Circuit Diagram

The schematic shows the electrical interconnection of the 35 LEDs (5 columns x 7 rows). Each LED's anode is connected to a row line, and its cathode is connected to a column line. To illuminate a specific dot, its corresponding row line must be driven high (anode), and the column line must be driven low (cathode). This matrix structure allows control of 35 dots with only 12 lines (5 rows + 7 columns), enabling efficient multiplexing.

6. Soldering & Assembly Guidelines

• Reflow Soldering: Follow the specified condition: 260°C for 3 seconds. Use a controlled thermal profile to avoid thermal shock.
• Hand Soldering: If necessary, use a temperature-controlled iron. Apply heat to the pin, not the package body, and limit contact time to prevent heat from wicking into the display.
• Cleaning: Use appropriate solvents that are compatible with the display's materials (likely epoxy and plastic). Avoid ultrasonic cleaning which may damage the internal bonds.
• Storage Conditions: Store in a dry, anti-static environment within the specified temperature range (-35°C to +85°C).

7. Application Suggestions

7.1 Typical Application Scenarios

• Industrial Panel Meters: Displaying numeric values for voltage, current, temperature, pressure, etc.
• Test and Measurement Equipment: Readouts for multimeters, oscilloscopes (for settings or basic readouts), signal generators.
• Consumer Appliances: Timers, scales, audio equipment displays.
• Medical Devices: Simple numeric readouts on monitors or diagnostic tools where reliability is key.
• Retail Equipment: Price displays, basic transaction terminals.

7.2 Design Considerations

• Driver Circuit: A microcontroller with sufficient GPIO pins or a dedicated LED driver IC with multiplexing support is required. The driver must be capable of sourcing current for the anode rows and sinking current for the cathode columns. Current-limiting resistors are mandatory for each row or column line to set the forward current.
• Current Calculation: Due to multiplexing, the instantaneous (peak) current per LED will be higher than the desired average current. For N multiplexed rows, the peak current should be approximately N times the desired average current. Ensure this peak current does not exceed the absolute maximum rating of 60 mA.
• Thermal Management: Adhere to the current derating curve. In high ambient temperatures, reduce the drive current or improve ventilation. The black face may absorb more ambient heat.
• Viewing Angle: Consider the intended viewing position. LED dot matrix displays often have a limited optimal viewing angle.
• ESD Protection: Implement standard ESD protection on control lines, especially if the display is user-accessible.

8. Technical Comparison & Differentiation

Compared to other display technologies of its era (like vacuum fluorescent displays (VFDs) or smaller LCDs), the LTP-2157AKY-01 offers distinct advantages:

• vs. VFDs: Lower operating voltage, no filament or high-voltage driver required, more rugged, longer lifetime, and better performance in low-temperature environments.
• vs. LCDs: Much higher brightness and contrast, self-illuminating (no backlight needed), wider operating temperature range, and faster response time. The trade-off is higher power consumption and limited ability to display complex graphics.
• vs. Standard GaP or GaAsP LEDs: The use of AlInGaP technology provides significantly higher luminous efficiency and brightness, resulting in better visibility in brightly lit conditions.

9. Frequently Asked Questions (Based on Technical Parameters)

Q1: Can I drive this display with a constant 20mA per dot?
A: Not directly in a static mode for all dots simultaneously, as this would exceed the average power dissipation limit (35 mW/dot * 35 dots = 1.225W, and 20mA * 2.6V = 52mW/dot). You must use multiplexing. In a 1/7 duty cycle multiplex (illuminating one row at a time), the peak current per dot could be ~140mA to achieve a 20mA average, which exceeds the 60mA peak rating. Therefore, you must design the multiplexing scheme and peak current carefully to stay within both average and peak limits.

Q2: Why are there duplicate pin assignments in the list?
A: The textual pin list in the provided content likely contains documentation errors. The definitive reference is the Internal Circuit Diagram in the original datasheet. Always use the schematic for your PCB design.

Q3: How do I calculate the necessary current-limiting resistor?
A: For a constant voltage supply (V_CC), use Ohm's Law: R = (V_CC - V_F - V_CE(sat)) / I_F. Where V_F is the LED forward voltage (use max value for safety, e.g., 2.8V), V_CE(sat) is the saturation voltage of the column driver transistor (if used), and I_F is the desired forward current. For a multiplexed design, I_F is the peak current.

Q4: What is the difference between peak and dominant wavelength?
A: Peak wavelength (λ_p) is the physical point of maximum spectral emission. Dominant wavelength (λ_d) is the psychophysical correlate, representing the single wavelength that would match the perceived color. They are often very close for monochromatic LEDs.

10. Practical Design Case Study

Scenario: Designing a simple digital voltmeter readout using the LTP-2157AKY-01, driven by a 5V microcontroller system in an environment up to 50°C.

1. Driver Selection: Choose a microcontroller with at least 12 free GPIO pins or pair a smaller MCU with a serial-to-parallel shift register and transistor arrays for row/column driving.
2. Current Limit: Determine max average current per dot at 50°C: 13 mA - [0.17 mA/°C * (50-25)] = 13 mA - 4.25 mA = 8.75 mA.
3. Multiplexing Scheme: Use 1:7 row multiplexing. To achieve an average of 8.75 mA, the peak current during its active row time should be ~61.25 mA (8.75 * 7). This is slightly above the 60 mA peak rating. Therefore, reduce the target average to ~8.5 mA, giving a peak of 59.5 mA.
4. Resistor Calculation: Assuming a column driver V_CE(sat) of 0.2V and a V_F(max) of 2.8V. For a 5V supply driving the anode: R = (5V - 2.8V - 0.2V) / 0.0595 A ≈ 33.6Ω. Use a standard 33Ω resistor. Power rating: P = I² * R = (0.0595)² * 33 ≈ 0.117W. A 1/4W resistor is sufficient.
5. Software: Implement a timer interrupt to cycle through the 7 rows, turning on the appropriate column drivers for each row based on the character font map.

11. Operating Principle

The device operates on the principle of electroluminescence in a semiconductor p-n junction. When a forward bias voltage exceeding the diode's turn-on voltage is applied across an individual LED cell (anode row positive, cathode column negative), electrons and holes recombine in the active AlInGaP region, releasing energy in the form of photons at a wavelength determined by the material's bandgap (~592-595 nm, amber-yellow). The 5x7 matrix is addressed by selectively activating one row (anode) at a time while providing sink paths on the columns (cathodes) for the dots that should be illuminated in that row. This process (multiplexing) happens faster than the human eye can perceive, creating a stable image of all desired dots.

12. Technology Trends

While this specific product utilizes mature AlInGaP-on-GaAs technology, the broader field of LED displays has evolved significantly. Current trends relevant to this product category include:

• Miniaturization: Dot matrix displays are available in much smaller pixel pitches and package sizes.
• Full-Color RGB Matrices: Modern displays often integrate red, green, and blue LEDs in each pixel, enabling full-color graphics.
• Integrated Drivers: Newer modules often include the driver IC and controller onboard, communicating via serial interfaces (I2C, SPI), vastly simplifying the host system design compared to direct GPIO multiplexing.
• Higher Efficiency Materials: The shift from AlInGaP to even more efficient materials like InGaN for certain colors, and ongoing improvements in internal quantum efficiency and light extraction.
• Alternative Technologies: For alphanumeric displays, OLED (Organic LED) technology offers similar self-emissive benefits with potentially thinner form factors and wider viewing angles, though historically with different lifetime and cost considerations.

The LTP-2157AKY-01 represents a robust, proven solution for applications where its specific combination of size, color, simplicity, and reliability meets the design requirements.