LTP-1557AJD LED Display Module Specification Sheet - 1.2-inch (30.42mm) Height - AlInGaP Red Light - 5x7 Dot Matrix - Chinese Technical Documentation

1. Product Overview

The LTP-1557AJD is a single-character alphanumeric display module designed for applications requiring clear and reliable character output. Its core function is to visually present ASCII or EBCDIC encoded characters through a grid of individually addressable light-emitting diodes (LEDs). Primary target markets include industrial control panels, instrumentation, point-of-sale terminals, communication equipment, and any embedded system requiring a simple, rugged user interface to display status or data. Its solid-state construction offers significant advantages in reliability and operational lifespan compared to older display technologies such as vacuum fluorescent or incandescent displays.

The core advantage of this module lies in its use of AlInGaP (Aluminum Indium Gallium Phosphide) LED technology. This semiconductor material system is renowned for producing highly efficient red and amber light. Compared to older GaAsP (Gallium Arsenide Phosphide) LEDs, AlInGaP LEDs offer superior luminous efficiency, meaning brighter output for the same electrical input power and better performance at elevated temperatures. The device features a gray panel with white dots, enhancing contrast and readability under various lighting conditions.

2. Detailed Technical Parameters

2.1 Photometric and Optical Characteristics

Optical performance is defined under standard test conditions with an ambient temperature (Ta) of 25°C. The key parameters areAverage luminous intensity (Iv)Its typical value is 2500 microcandelas (µcd), with a minimum value of 1020 µcd. This measurement was conducted under conditions of a pulse drive current (Ip) of 32mA and a duty cycle of 1/16. The use of pulse driving is common in multiplexed displays, aiming to achieve higher peak brightness while ensuring the safe average power consumption of each LED point.

Color characteristics are defined by wavelength. The device'sPeak emission wavelength (λp)is 656 nm, placing it within the red region of the visible spectrum.Dominant Wavelength (λd)is specified as 640 nm. It is important to note the distinction between the two: the peak wavelength is the point of maximum spectral power, while the dominant wavelength is the single wavelength perceived by the human eye as the color.Spectral line half-width (Δλ)It is 22 nm, indicating the spectral purity or bandwidth of the emitted light; the narrower the half-width, the more saturated and pure the color.Luminous intensity matching ratio (IV-m)Maximum 2:1, meaning the brightness variation between the brightest and darkest points in the array should not exceed this ratio, ensuring a uniform appearance.

2.2 Electrical Characteristics

Electrical parameters define the operating limits and conditions of the device. At a test current (IF) of 20mA, any single LED point'sForward Voltage (VF)Between 2.1V (minimum) and 2.6V (maximum). This forward voltage is characteristic of AlInGaP technology and is crucial for designing current-limiting circuits. When a 5V reverse bias voltage (VR) is applied,Reverse Current (IR)is a maximum of 100 µA, which indicates the leakage characteristics of the diode in the off state.

3. Absolute Maximum Ratings

These ratings define stress limits that may cause permanent damage and are not intended for continuous operation. Key limitations include:Average Power Dissipation per Point(33 mW),Peak forward current per point(90 mA) andAverage forward current per point(13 mA at 25°C, linearly derated by 0.17 mA/°C above 25°C).Reverse voltage per pointis 5V. The device'sOperating Temperature RangeIt is -35°C to +85°C, and the storage temperature range is the same. The soldering temperature must not exceed 260°C for more than 3 seconds at a point 1.6mm below the package mounting plane.

4. Explanation of the Grading System

The datasheet indicates that the deviceBinned by luminous intensity. This means the units are tested and categorized (binned) based on their measured light output. This allows designers to select components from specific intensity bins to ensure uniform brightness across multiple displays in a product, avoiding noticeable variations. While not explicitly detailed in this document, common binning parameters for such LEDs may also include forward voltage (Vf) and dominant wavelength (λd) to ensure electrical and color consistency.

5. Performance Curve Analysis

The datasheet references typical electrical/optical characteristic curves. Although not displayed in the provided text, such curves typically include:Forward Current vs. Forward Voltage Relationship Curve (I-V Curve)This shows the nonlinear relationship between current and voltage, which is crucial for designing drive circuits.I-L curve (Light Intensity vs. Forward Current)This shows how the light output increases with current, typically exhibiting a roughly linear region before very high currents cause a drop in efficiency.Light Intensity vs. Ambient Temperature curveThe curve shows the thermal derating characteristics of light output, which is crucial for applications operating in high-temperature environments. AlInGaP LEDs typically maintain performance better at high temperatures compared to older technologies.

6. Mechanical and Packaging Information

The device is a display with a matrix height of 1.2 inches (30.42 mm). Package dimensions are provided in the drawing, with all dimensions in millimeters. Unless otherwise specified, the tolerance is ±0.25 mm. The mechanical drawing is essential for PCB pad design and ensuring proper installation within the enclosure. The package features a specific 5x7 matrix pin arrangement, including connections for 7 row anodes and 5 column cathodes (or vice versa, depending on the internal circuit configuration).

6.1 Pin Connections and Internal Circuitry

The pin connection table lists 14 pins. The internal circuit diagram shows a common-cathode or common-anode configuration for a 5x7 matrix. Specific pin assignments are provided (e.g., Pin 1: Anode Row 5, Pin 3: Cathode Column 2). This configuration allows the display to be multiplexed. By activating one row (or column) at a time and providing the corresponding column (or row) data, all 35 dots can be controlled using only 12 I/O lines (7+5), significantly reducing the number of microcontroller pins required compared to directly driving each LED.

7. Soldering and Assembly Guide

Awọn ofin iṣẹṣiṣẹpọ pataki jẹ iṣiro otutu irinṣẹ. Awọn iye to pọju ti o ṣe pato sọ pe, ni wiwọn 1.6 mm (1/16 inṣi) labẹ iṣori fifi sori, apoti le gbaOṣuwọn otutu irinṣẹ to ga julọ ti 260°C, fun iṣẹju-aaya 3 to pọ julọ. Eyi jẹ apẹẹrẹ ti irinṣẹ igbọn omi tabi irinṣẹ ọwọ. Fun irinṣẹ atunṣe, o yẹ ki a lo iṣiro otutu ti ko ni olu ti ko ni oṣuwọn giga to 260°C. O ṣe pataki lati yẹra fun iwọn-ara gbigbona ti o pọ si lati ṣe idiwọn bibajẹ LED chip, awọn okun iṣọkan, tabi apoti plastiki. Awọn ilana ESD (Itusilẹ Ẹlẹktrọniku ti o ni ẹmi) ti o tọ gbọdọ tẹle nigbagbogbo nigba iṣẹṣiṣẹpọ.

8. Application Suggestions

8.1 Typical Application Scenarios

This display is ideal for applications requiring single characters or digits, or where multiple units can be stacked horizontally to form a multi-character display. Common uses include: digital panel meters (voltage, current, temperature), simple status indicators on industrial machinery (displaying error codes, mode numbers), basic readouts on consumer appliances, and prototyping or educational kits for learning multiplexed LED driving.

8.2 Design Considerations

Drive Circuit Design: Need to reuse the drive circuit. This typically involves a microcontroller with sufficient I/O pins or a dedicated LED driver IC (such as MAX7219 or similar devices). The circuit must include current-limiting resistors for each column or row line to set the forward current to a safe value, usually between 10-20mA per segment based on the required brightness and power consumption limits.Power supply: Must consider a forward voltage of approximately 2.4V. Typically, a 3.3V or 5V power supply is used, generating an appropriate voltage drop across the current-limiting resistor.Refresh rate：复用扫描速率必须足够高（通常>60 Hz）以避免可见闪烁。Viewing Angle: The datasheet mentions a wide viewing angle, which is very beneficial for applications where the display may be viewed from off-axis positions.

9. Technical Comparison and Differentiation

The main differentiation of the LTP-1557AJD lies in its use ofAlInGaP LED technologyCompared to displays using old-style GaAsP or standard red GaP LEDs, AlInGaP offers:Higher luminous efficiency: More light output per unit of electrical power, resulting in lower power consumption at the same brightness or higher brightness at the same power consumption.Better high-temperature performance: AlInGaP LEDs experience less efficiency degradation at higher junction temperatures, making them more suitable for industrial environments.Superior color saturation: Their spectral characteristics typically produce a deeper, visually more vivid red.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Why use pulsed current (1/16 duty cycle) instead of DC to test luminous intensity?
A: This reflects its intended multiplexed mode of operation. Testing under pulsed conditions simulates real-world usage and allows for specifying a higher, more relevant peak brightness that a user will perceive.

Q: Can I drive each point with a constant DC current?
A: Technically yes, but it is extremely inefficient. This would require 35 independent current-limiting drivers. Multiplexing is the standard and expected method, which significantly reduces the number of components and power consumption in the drive circuit.

Q: What is the purpose of the intensity matching ratio (2:1)?
A: It ensures visual uniformity. Without binning, some points might be noticeably brighter or darker than others, resulting in uneven and unprofessional-looking characters.

Q: How to understand the derating factor (0.17 mA/°C) for average forward current?
A: This means for every 1°C increase in ambient temperature (above 25°C), the maximum safe continuous current per point must be reduced by 0.17 mA. For example, at 50°C (25 degrees above 25°C), the maximum current would be 13 mA - (25 * 0.17 mA) = 8.75 mA per point.

11. Practical Design Case Study

Consider using the LTP-1557AJD to design a single-digit temperature display for an incubator. A microcontroller (e.g., ATmega328P) reads the temperature sensor. Its seven I/O pins are configured as outputs to drive the row anodes (via small NPN transistors or a ULN2003 Darlington array for higher current capability). Another five I/O pins drive the column cathodes directly or via transistors. The firmware rapidly scans the seven rows. For each row, it outputs a 5-bit pattern on the column pins, corresponding to the segments that need to be lit on that specific row to form the desired digit (0-9). Current-limiting resistors are placed on the column lines. The scanning routine runs in a timer interrupt to ensure a consistent, flicker-free refresh rate of approximately 100 Hz. The AlInGaP technology ensures the display remains clearly readable even when the internal ambient temperature of the incubator rises.

12. Introduction to Working Principles

LTP-1557AJD is based onMultiplexed 5x7 dot matrixprinciple. Internally, 35 LEDs are arranged in a grid, with their anodes connected by rows and cathodes by columns (or vice versa in a common-anode configuration). To illuminate a specific point, a voltage is applied to its corresponding row line (making it high for common-cathode types), while its corresponding column line is pulled low (sinking current). To display a pattern or character, the controller rapidly cycles (scans) through each row. When a specific row is activated, the controller sets the appropriate column lines to create the pattern for that row. The persistence of vision of the human eye merges these rapidly changing row images into a stable, complete character. This method reduces the number of required control lines from 35 (one per LED) to just 12 (rows + columns).

13. Technology Trends

Ingawa maonyesho ya alama ya 5x7 tofauti kama LTP-1557AJD bado yanatumika katika matumizi maalum, yanayohusisha gharama, au rahisi, mwelekeo mpana wa teknolojia ya maonyesho umebadilika kuelekea suluhisho za ushirikiano.Maonyesho ya Kudhibiti UshirikianoModuli za kisasa za LCD (Maonyesho ya Kioevu-Kioo) na OLED (Diodi ya Mwanga wa Kikaboni) kwa kawaida hujumuisha chip ya kudhibiti iliyojengwa ndani, inayoshughulikia uzalishaji wa herufi na ukarabati, kupitia mawasiliano rahisi ya serial (I2C, SPI) au interface sambamba, ikirahisisha sana uundaji wa programu.Higher Resolution and Graphic DisplayFor more complex information, small graphic OLED or TFT-LCD modules are now common, offering pixel-addressable graphic capabilities.Surface Mount Technology (SMT)Newer LED indicators and displays primarily use SMT packages (e.g., 0805, 0603 LEDs arranged in matrices) for automated assembly, while through-hole packages like this product are more typical for prototyping or manual assembly. The underlying AlInGaP and InGaN (for blue/green/white light) LED chip technology continues to advance, offering increasingly higher efficiency and reliability.