LTP-1557AKY LED Dot Matrix Display Datasheet - 1.2 inch (30.42mm) Height - AlInGaP Amber Yellow - 5x7 Array - English Technical Document

1. Product Overview

The LTP-1557AKY is a single-digit alphanumeric display module designed for applications requiring clear, legible character output. Its core function is to visually represent information through a grid of individually addressable light-emitting diodes (LEDs).

1.1 Core Advantages and Target Market

This device offers several key advantages that make it suitable for a range of industrial and commercial applications. Its primary features include a 1.2-inch (30.42 mm) character height, which provides excellent visibility from a distance. The utilization of AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for the amber yellow LED chips results in good luminous efficiency and a distinct, easily recognizable color. The display operates with low power requirements, enhancing energy efficiency in the end application. It offers a wide viewing angle due to its single-plane construction, ensuring the displayed information is readable from various positions. The solid-state design of LEDs guarantees high reliability and long operational life with no moving parts. The device is compatible with standard character codes like USASCII and EBCDIC, simplifying integration into digital systems. Furthermore, the units are designed to be stackable horizontally, allowing for the creation of multi-character displays. The display is also categorized for luminous intensity, providing consistency in brightness across production batches. The target markets for this component include industrial control panels, instrumentation, point-of-sale terminals, medical equipment, and any embedded system requiring a robust, reliable character display interface.

2. Technical Parameters: In-Depth Objective Interpretation

The performance of the LTP-1557AKY is defined by a set of electrical, optical, and environmental parameters which are critical for proper circuit design and application.

2.1 Photometric and Optical Characteristics

The optical performance is central to its function. The typical average luminous intensity (Iv) per dot is 3800 µcd (microcandelas) under a test condition of a peak current (Ip) of 80mA with a 1/16 duty cycle. The minimum specified value is 2100 µcd. The luminous intensity matching ratio between dots is specified at a maximum of 2:1, ensuring uniform brightness across the display. The color is defined by its wavelength. The peak emission wavelength (λp) is typically 595 nanometers (nm), placing it in the amber-yellow region of the visible spectrum. The dominant wavelength (λd) is typically 592 nm. The spectral line half-width (Δλ) is typically 15 nm, indicating the spectral purity or bandwidth of the emitted light. It is important to note that the luminous intensity is measured using a sensor and filter combination that approximates the photopic (CIE) eye-response curve, ensuring the values correlate with human visual perception.

2.2 Electrical Parameters

The electrical characteristics define the operating conditions and limits. The forward voltage (Vf) for any single LED dot (at an input current of 20mA) has a typical value of 2.6V, with a maximum of 2.6V and a minimum of 2.05V. The reverse current (Ir) for any dot, when a reverse voltage (Vr) of 5V is applied, has a maximum value of 100 µA. These parameters are essential for designing the appropriate current-limiting circuitry and ensuring signal integrity.

2.3 Absolute Maximum Ratings and Thermal Considerations

These ratings specify the limits beyond which permanent damage to the device may occur. The average power dissipation per dot must not exceed 25 mW. The peak forward current per dot is rated at 60 mA, but only under specific pulsed conditions: a 1/10 duty cycle with a 0.1 ms pulse width. The average forward current per dot has a derating factor; it is 13 mA at 25°C and decreases linearly by 0.17 mA for every degree Celsius increase in ambient temperature. The maximum reverse voltage that can be applied to any dot is 5V. The device is rated for an operating temperature range of -35°C to +85°C, and a similar storage temperature range. For assembly, the maximum solder temperature is 260°C, but this should be applied for a maximum of 3 seconds at a point 1.6mm (1/16 inch) below the seating plane of the component to prevent thermal damage.

3. Binning System Explanation

The datasheet indicates that the devices are categorized for luminous intensity. This is a common binning practice in LED manufacturing to group components based on measured performance. While the specific bin codes are not detailed in this excerpt, the practice typically involves testing each unit's light output at a standard current and sorting them into bins with defined minimum and maximum intensity ranges (e.g., Bin A: 3000-3500 µcd, Bin B: 3500-4000 µcd). This allows designers to select parts that ensure consistent brightness across a multi-unit display. The tight specification on luminous intensity matching ratio (2:1 max) further supports this goal of visual uniformity.

4. Performance Curve Analysis

The datasheet references typical electrical/optical characteristic curves, though they are not displayed in the provided text. Based on standard LED behavior, one would expect to see curves illustrating the relationship between forward current (If) and forward voltage (Vf), which is exponential. Another crucial curve would show luminous intensity (Iv) as a function of forward current (If), typically showing a near-linear relationship within the operating range. A third important curve would depict the variation of luminous intensity with ambient temperature (Ta), showing a decrease in output as temperature increases. These curves are vital for understanding the device's behavior under non-standard conditions and for optimizing drive circuitry for efficiency and longevity.

5. Mechanical and Package Information

The LTP-1557AKY comes in a standard LED display package. The provided content mentions a package dimensions diagram (not shown) with all dimensions specified in millimeters and standard tolerances of ±0.25 mm unless otherwise noted. The physical description states the device has a gray face and white dot color, which refers to the color of the plastic housing and the diffused lens over each LED, respectively, enhancing contrast.

5.1 Pin Connection and Internal Circuit

The device has a 14-pin configuration. The pinout is clearly defined: Pins are assigned as anodes for specific rows (1, 2, 3, 4, 5, 6, 7) and cathodes for specific columns (1, 2, 3, 4, 5). It is a common-anode configuration for the rows, meaning to light a specific dot, the corresponding column cathode must be driven low (sink current) while the corresponding row anode is driven high (source current). An internal circuit diagram (referenced but not shown) would typically illustrate this 5x7 matrix arrangement, showing how each LED is connected at the intersection of a row (anode) line and a column (cathode) line. This matrix structure significantly reduces the number of required driver pins from 35 (for individually addressed dots) to 12 (5 columns + 7 rows).

6. Soldering and Assembly Guidelines

The key assembly guideline provided is related to soldering temperature. The absolute maximum rating specifies that the solder temperature should not exceed 260°C, and this temperature should be applied for a maximum duration of 3 seconds. The measurement point for this temperature is critical: it is 1.6mm (1/16 inch) below the seating plane of the component. This guideline is intended to prevent the transfer of excessive heat to the LED chips and the internal wire bonds, which could cause degradation or failure. For modern assembly, this suggests the device is suitable for reflow soldering processes, provided the temperature profile is carefully controlled to stay within these limits. Standard ESD (Electrostatic Discharge) precautions should be observed during handling. The storage temperature range (-35°C to +85°C) should also be adhered to when the devices are not in use.

7. Application Suggestions

7.1 Typical Application Scenarios

The LTP-1557AKY is ideal for applications requiring the display of alphanumeric characters, symbols, or simple graphics. Common uses include: status displays on industrial machinery (showing error codes, machine state, or simple counts), readouts on test and measurement equipment, display panels in point-of-sale systems, information displays in medical devices, and as part of embedded systems in appliances or consumer electronics. Its stackability allows it to be used for multi-digit displays such as clocks, counters, or simple messaging boards.

7.2 Design Considerations and Circuit Interface

Designing with this display requires a microcontroller or dedicated driver IC capable of multiplexing. Since it is a matrix display, only one row is typically activated at a time in a sequential scan. The persistence of vision creates the illusion of a stable image. The driver circuit must be able to source sufficient current for the active row anode and sink the required current for the active column cathodes. Current-limiting resistors are mandatory for each column cathode line (or each LED, depending on the driver architecture) to set the operating current, typically around 20mA per dot for continuous operation, but adjustable based on the desired brightness and multiplexing duty cycle. The peak current ratings must be respected when designing the multiplexing scheme. For example, with a 1/7 duty cycle (activating one of seven rows at a time), the instantaneous current per dot can be higher to achieve the same average brightness, but it must not exceed the peak current rating of 60mA under pulsed conditions. Heat dissipation should be considered if operating near the maximum ratings or in high ambient temperatures.

8. Technical Comparison and Differentiation

Compared to other display technologies like LCDs or vacuum fluorescent displays (VFDs), this LED dot matrix offers distinct advantages: superior brightness and visibility in both low-light and high-ambient-light conditions, a wider operating temperature range, faster response time, and higher reliability due to its solid-state nature. Within the LED dot matrix category, the use of AlInGaP technology for amber yellow provides better efficiency and color stability compared to older technologies like GaAsP. The specific 1.2-inch height, 5x7 array, and amber color differentiate it from smaller or larger displays, or those with different colors (e.g., red, green) or array configurations (e.g., 5x8, 8x8).

9. Frequently Asked Questions Based on Technical Parameters

Q: What is the purpose of the 1/16 duty cycle mentioned in the luminous intensity test condition?
A: The 1/16 duty cycle (a short pulse) is used during testing to prevent heating of the LED junction, which would lower the output. It allows measurement of the intrinsic brightness at a specific current without thermal effects. In actual multiplexed operation, a similar pulsed drive is used.

Q: Can I drive this display with a constant DC current without multiplexing?
A: Technically, yes, by turning on each desired dot continuously. However, this would require 35 individual driver channels and would consume significantly more power. Multiplexing is the standard and efficient method.

Q: The pin list shows two pins for "Anode Row 4" (pins 5 and 12) and two for "Cathode Column 3" (pins 4 and 11). Is this an error?
A> This is likely not an error but a design feature. Multiple pins for the same electrical node (row or column) are common in matrix displays. They serve to lower the current density through a single pin/connector, improve reliability, and provide mechanical symmetry in the package. Internally, these pins are connected together.

Q: How do I calculate the appropriate current-limiting resistor value?
A> You need the supply voltage (Vcc), the desired forward current per dot (If, e.g., 20mA), and the typical forward voltage of the LED (Vf, e.g., 2.6V). The formula is R = (Vcc - Vf) / If. Remember that in a multiplexed circuit, Vcc is the voltage applied to the active row anode, and the resistor is placed on the column cathode side.

10. Practical Design and Usage Case

Consider designing a simple 4-digit counter using four LTP-1557AKY displays. The displays would be stacked horizontally. A microcontroller would be programmed to manage the multiplexing. It would have 7 output pins connected to the row anodes of all displays in parallel. It would have 4 sets of 5 column cathode pins (20 pins total), but these can be managed by external shift registers or port expanders to save microcontroller I/O. The firmware would sequentially activate each of the 7 rows. For each row, it would output the pattern for that row for all four digits to the column drivers. This happens so quickly (e.g., scanning all 7 rows 100 times per second) that the human eye perceives a stable, four-digit number. The current for each column would be set by resistors to achieve the desired brightness, considering the 1/7 duty cycle per dot. The design must ensure the peak current per dot during its active pulse does not exceed the 60mA rating.

11. Operating Principle Introduction

The LTP-1557AKY operates on the principle of electroluminescence in a semiconductor p-n junction, specifically using AlInGaP materials. When a forward voltage exceeding the diode's threshold is applied, electrons and holes recombine in the active region, releasing energy in the form of photons (light). The specific composition of the AlInGaP layers determines the wavelength (color) of the emitted light, in this case, amber yellow. The 5x7 matrix arrangement is an efficient electrical configuration. Each LED is connected between one of seven row lines (anodes) and one of five column lines (cathodes). By selectively applying a positive voltage to a specific row and grounding a specific column, only the LED at that intersection turns on. A controller rapidly sequences through this process for all desired dots to form characters.

12. Technology Trends and Context

While discrete LED dot matrix displays like the LTP-1557AKY remain relevant for specific, often industrial, applications requiring high brightness and robustness, broader display technology has evolved. Surface-mount device (SMD) LED arrays and integrated LED display modules with built-in controllers (I2C, SPI) are now common, offering easier integration and higher resolution in smaller packages. Furthermore, organic LED (OLED) and micro-LED technologies are advancing for high-density, flexible displays. However, for simple, reliable, low-cost character display needs in harsh environments, traditional through-hole LED dot matrices like this one continue to be a viable and dependable solution. The AlInGaP technology used here represents an advancement over older LED materials, offering better efficiency and color performance.