LTP-22157M LED Dot Matrix Display Datasheet - 2.2-inch (57.22mm) Height - 5x7 Array - Red-Orange & Green - English Technical Document

1. Product Overview

The LTP-22157M is a monochrome, single-plane dot matrix display module designed for alphanumeric character presentation. Its core function is to provide a visual output interface by illuminating a specific pattern of LEDs within a 5-column by 7-row grid. The device integrates two distinct LED chip technologies within a single package: red-orange LEDs and green LEDs. This dual-color capability, while not enabling multi-color per dot, allows for module-level color selection or simple two-state indication schemes. The display features a gray faceplate with white dots, which enhances contrast and readability under various lighting conditions. Its primary application is in industrial equipment, instrumentation, point-of-sale terminals, and other embedded systems requiring a simple, reliable character readout.

The fundamental advantage of this display lies in its solid-state construction, offering high reliability and long operational life compared to legacy technologies like filament-based displays. It requires relatively low power and is designed for easy electrical integration, being compatible with standard ASCII and EBCDIC character codes. The mechanical design allows for horizontal stacking, enabling the creation of multi-character displays.

2. Technical Parameters Deep Objective Interpretation

2.1 Photometric and Optical Characteristics

The optical performance is specified separately for the green and red-orange LED elements. For the Green LEDs, the typical average luminous intensity is 4800 µcd when driven with a peak current (Ip) of 80mA at a 1/16 duty cycle. The dominant wavelength (λd) is typically 569 nm, and the peak emission wavelength (λp) is 565 nm, placing it in the pure green region of the spectrum. The spectral line half-width (Δλ) is 30 nm, indicating a moderately narrow emission band.

For the Red-Orange LEDs, the typical average luminous intensity is also 4800 µcd under the same 80mA, 1/16 duty cycle drive conditions. The dominant wavelength is typically 621 nm, and the peak emission is at 630 nm, characterizing its red-orange color. The spectral line half-width is broader at 40 nm. A key parameter for display uniformity is the Luminous Intensity Matching Ratio (IV-m), which is specified as 2:1 maximum. This means the intensity of the dimmest dot in the array will be no less than half the intensity of the brightest dot under the same test conditions (IF=10mA), ensuring acceptable visual consistency across the character.

2.2 Electrical Parameters

The electrical characteristics define the operating boundaries and typical performance. The Absolute Maximum Ratings are identical for both colors: average power dissipation per dot is 36 mW, peak forward current per dot is 100 mA, and the average forward current per dot must be derated linearly from 13 mA at 25°C by 0.17 mA/°C. The maximum reverse voltage per segment is 5V. Exceeding these ratings may cause permanent damage.

The Typical Electrical Characteristics show the forward voltage (VF). For Green LEDs, VF is 2.6V typical at 20mA and 3.7V typical at 80mA. For Red-Orange LEDs, VF is 2.6V typical at 20mA and 3.4V typical at 80mA. The reverse current (IR) for any dot is a maximum of 100 µA at VR=5V. These values are critical for designing the current-limiting circuitry and power supply.

3. Thermal Characteristics

The device is rated for an operating temperature range of -35°C to +85°C and an identical storage temperature range. The derating curve for average forward current is a direct thermal specification; as ambient temperature rises above 25°C, the permissible continuous current must be reduced to prevent overheating and accelerated degradation. The soldering temperature is specified as a maximum of 260°C for a maximum of 3 seconds, measured 1.6mm below the seating plane, which is crucial for PCB assembly processes.

4. Binning System Explanation

The datasheet indicates the device is categorized for luminous intensity. This implies that units are sorted (binned) based on their measured light output. While specific bin codes are not provided in this document, such a system ensures that designers can select displays with a guaranteed minimum brightness or a tight brightness range, which is important for product consistency, especially when multiple displays are used side-by-side. There is no mention of voltage or wavelength binning in this datasheet; the dominant/peak wavelengths are given as typical values.

5. Performance Curve Analysis

The datasheet references Typical Electrical/Optical Characteristic Curves. Although the specific curves are not detailed in the provided text, such graphs typically included in full datasheets would illustrate the relationship between forward current (IF) and forward voltage (VF), the relationship between forward current and luminous intensity, and the variation of these parameters with ambient temperature. Analyzing these curves allows designers to optimize drive current for desired brightness and efficiency, and to understand how performance will shift across the operating temperature range.

6. Mechanical and Packaging Information

The display has a matrix height of 2.2 inches (57.22 mm). The package dimensions are provided in a drawing with all units in millimeters and standard tolerances of ±0.25 mm unless otherwise noted. The device features an 18-pin configuration. The pinout is clearly defined: Pins 1-4 and 9-12 are the anode rows (1-7). Pins 5-9 are the cathode columns for the Green LEDs (columns 1-5). Pins 13-17 are the cathode columns for the Red-Orange LEDs (columns 5-1, in reverse order). Pin 18 has no connection. This arrangement facilitates multiplexed driving, where a controller sequentially activates each row (anode) while providing the column (cathode) data for that row.

7. Soldering and Assembly Guidelines

The key assembly guideline is the soldering temperature profile: the component body must not be exposed to temperatures exceeding 260°C for more than 3 seconds during reflow or wave soldering. The measurement point is 1.6mm (1/16 inch) below the seating plane, which corresponds roughly to the PCB surface. Standard ESD (Electrostatic Discharge) precautions should be observed during handling, as LEDs are sensitive to static electricity. For storage, the recommended range is -35°C to +85°C in a low-humidity environment.

8. Application Suggestions

8.1 Typical Application Scenarios

This display is ideal for applications requiring simple, low-cost alphanumeric readouts. Examples include: status displays on industrial control panels, basic readouts on test and measurement equipment, simple messaging on consumer appliances, and character-based indicators in legacy or cost-sensitive systems. The horizontal stackability feature allows creation of multi-digit displays for counters, timers, or basic data presentation.

8.2 Design Considerations

Drive Circuitry: The display requires an external multiplexing driver circuit. Each LED dot is addressed by its row (anode) and column (cathode). The driver must supply sufficient peak current (up to the rated 80mA for full brightness) in short pulses, as the average current is limited by the duty cycle. Proper current-limiting resistors or constant-current drivers are essential for each cathode line to set the current and protect the LEDs.

Microcontroller Interface: The multiplexing can be managed by a microcontroller with sufficient I/O pins or via dedicated display driver ICs (e.g., MAX7219). The refresh rate must be high enough (typically >60Hz) to avoid visible flicker.

Color Selection: The designer must choose to use either the green or red-orange LEDs by connecting to the corresponding cathode pins. They cannot be mixed at the individual dot level.

Viewing Angle: The datasheet mentions a \"wide viewing angle,\" but does not specify a value. For critical viewing angle applications, this should be verified or tested.

9. Technical Comparison

Compared to modern graphic OLED or TFT displays, this dot matrix is severely limited in resolution, color capability, and information density. Its advantages are extreme simplicity, robustness, wide operating temperature range, low cost, and high brightness. Compared to other LED dot matrix displays of the same era, its key differentiator is the inclusion of two distinct LED colors in one package, offering design flexibility. The 2.2-inch character height is relatively large, making it suitable for applications where readability from a distance is important.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive both the red and green LEDs at the same time to create yellow?
A: No. The red-orange and green LEDs are separate chips connected to different cathode pins for each column. You can only enable one color set for the entire display at a time. You cannot mix colors per dot.

Q: What does \"1/16 Duty\" mean in the luminous intensity test condition?
A: It means the LED is pulsed on for 1/16th of the total cycle time. The specified luminous intensity (4800 µcd) is the average intensity over the full cycle. The peak instantaneous intensity during the on-time is much higher. This is standard for multiplexed displays.

Q: How do I calculate the required current-limiting resistor?
A: Use the formula: R = (Vcc - VF - Vdrop) / IF. Where Vcc is your supply voltage, VF is the LED forward voltage from the datasheet (use max value for safety, e.g., 3.7V for green at 80mA), Vdrop is any voltage drop across the driving transistor, and IF is your desired forward current (e.g., 20mA for lower brightness). Ensure the resistor's power rating is sufficient: P = IF^2 * R.

Q: The pinout shows cathode columns for red and green are in reverse order. Is this a mistake?
A: No. This is the documented pin connection. The internal circuit diagram (referenced in the datasheet) would show how the anodes and cathodes are interconnected. The designer must follow this pinout precisely when designing the PCB and writing the driving software.

11. Practical Use Case

Case: Industrial Temperature Controller Readout. A system monitors oven temperature and needs to display it on a panel visible from several meters away. Two LTP-22157M displays are used, stacked horizontally. The microcontroller reads a temperature sensor, converts the value to ASCII characters, and drives the displays via a multiplexing routine. The red-orange LEDs are chosen for their high visibility. The drive current is set to 60mA per dot at a 1/8 duty cycle, providing bright, clear numbers that meet the intensity requirement. The design uses the wide operating temperature range to ensure reliability inside the industrial enclosure.

12. Principle Introduction

A 5x7 dot matrix display is a grid of 35 independently addressable LEDs. To display a character, a specific pattern of these dots is illuminated. Due to pin limitations, the LEDs are not individually wired. Instead, they are arranged in a matrix configuration. All LEDs in the same row share a common anode connection, and all LEDs in the same column share a common cathode connection (for a given color). To light a specific dot, its corresponding row line is driven high (anode activated), and its column line is driven low (cathode activated). To display a full character, the controller rapidly cycles through each row (1-7), activating it while supplying the pattern data for that row on the five column lines. This multiplexing technique allows control of 35 dots with only 12 pins (7 rows + 5 columns).

13. Development Trends

Displays like the LTP-22157M represent a mature, legacy technology. The trend in alphanumeric displays has moved towards higher integration and intelligence. Modern modules often include the driver IC, controller, and sometimes even a font library within the display package, communicating via simple serial interfaces (I2C, SPI). This drastically reduces the design complexity for the system engineer. Furthermore, there is a shift towards multi-color and full-graphic capabilities in similarly sized packages, such as OLED displays, which can show custom graphics, multiple lines of text, and varied colors. However, for applications demanding very high brightness, extreme environmental robustness, lowest possible cost, or simple replacement in existing designs, traditional LED dot matrix displays like this one remain a viable and reliable solution.