LTP-1557TBE 5x7 Dot Matrix Blue LED Display Datasheet - 1.2 Inch Height - 3.6V Forward Voltage - InGaN Blue Chip - English Technical Documentation

1. Product Overview

The LTP-1557TBE is a solid-state, alphanumeric display module designed for applications requiring clear, reliable character output. Its core function is to visually represent data, typically ASCII or EBCDIC coded characters, through a grid of individually addressable light-emitting diodes (LEDs). The primary market for this component includes industrial control panels, instrumentation, point-of-sale terminals, and various embedded systems where a simple, durable, and low-power display solution is needed.

The device's core advantage lies in its use of InGaN (Indium Gallium Nitride) blue LED chips. This semiconductor technology provides good luminous efficiency and a distinctive blue color. The display features a gray face with white dots, which enhances contrast and readability. Key features contributing to its utility are its low power requirement, wide viewing angle due to the single-plane design, solid-state reliability with no moving parts, and the ability to be stacked horizontally for multi-character displays.

2. Technical Parameters Deep Objective Interpretation

2.1 Photometric and Optical Characteristics

The optical performance is defined under specific test conditions at an ambient temperature (Ta) of 25°C. The Average Luminous Intensity (Iv) per LED chip is specified with a minimum of 5400 µcd, a typical value of 13500 µcd, and no stated maximum, when driven at a forward current (IF) of 10mA. This parameter indicates the light output power as perceived by the human eye, measured using a sensor filtered to match the CIE photopic response curve.

The Peak Emission Wavelength (λp) is typically 468 nm, which places the output in the blue region of the visible spectrum. The Spectral Line Half-Width (Δλ) is 25 nm, indicating the spectral purity or the spread of wavelengths emitted. The Dominant Wavelength (λd) is between 470 nm and 475 nm, representing the perceived color of the light. The Luminous Intensity Matching Ratio for LEDs within the same display area is 2:1 maximum, ensuring acceptable uniformity in brightness across the matrix.

2.2 Electrical Characteristics

The key electrical parameter is the Forward Voltage (VF) per chip, which ranges from 3.3V (min) to 3.6V (max) at a test current of 20mA. This is a critical design parameter for selecting appropriate current-limiting resistors or driver circuitry. The Reverse Current (IR) is specified as a maximum of 100 µA when a reverse voltage (VR) of 5V is applied. It is crucial to note that this reverse voltage condition is for test purposes only; the device is not designed for continuous operation under reverse bias.

2.3 Absolute Maximum Ratings and Thermal Considerations

These ratings define the stress limits beyond which permanent damage may occur. The Continuous Forward Current per chip is 20mA at 25°C, derating linearly by 0.21 mA/°C as temperature increases. The Peak Forward Current is 100mA but only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The maximum Power Dissipation per chip is 70 mW. The device is rated for an Operating and Storage Temperature Range of -35°C to +85°C. The Electrostatic Discharge (ESD) threshold is 2000V (Human Body Model), indicating a moderate level of sensitivity that requires proper handling procedures.

3. Mechanical and Packaging Information

3.1 Dimensions and Tolerances

The device has a matrix height of 1.2 inches (30.42 mm). All package dimensions are provided in millimeters. General tolerances are ±0.25 mm unless otherwise specified. A specific note mentions a pin tip shift tolerance of ±0.5 mm, which is important for PCB footprint design and automated assembly.

3.2 Pin Connection and Internal Circuit

The display has a 14-pin configuration. The internal circuit diagram reveals a multiplexed matrix structure. Pins are assigned to the anodes of rows 1 through 7 and the cathodes of columns 1 through 5. This X-Y select architecture allows control of any single dot (LED) by activating the corresponding row (anode) and column (cathode) lines, significantly reducing the number of required driver pins compared to a direct drive approach.

4. Soldering and Assembly Guidelines

The datasheet specifies a maximum soldering temperature of 260°C for a maximum duration of 5 seconds, measured at 1.6mm (1/16 inch) below the seating plane. This is a typical reflow soldering profile constraint for through-hole components. Adherence to this limit is necessary to prevent damage to the LED chips or the plastic package from excessive thermal stress.

5. Electrostatic Discharge (ESD) Protection

Given the ESD sensitivity rating, strict handling protocols are recommended to prevent damage from static electricity or power surges. These include: using a conductive wrist strap or anti-static gloves; ensuring all equipment, workstations, and storage racks are properly grounded; and employing an ion blower to neutralize static charges that may accumulate on the plastic lens surface during handling and storage.

6. Application Suggestions

6.1 Typical Application Scenarios

This display is ideal for applications requiring a single line or a few characters of information. Common uses include status indicators on machinery, simple readouts on test equipment, display panels for basic consumer electronics, and as building blocks for larger multi-character message boards due to their stackable design.

6.2 Design Considerations

Driver Circuitry: A microcontroller or dedicated display driver IC is required to multiplex the rows and columns. The driver must supply the necessary current (typically 10-20mA per segment) and handle the forward voltage drop (~3.6V). Current-limiting resistors are essential for each row or column line to set the operating current.
Power Supply: The supply voltage must be higher than the LED forward voltage. A 5V supply is common, with resistors used to drop the remaining voltage.
Viewing Angle: The single-plane, wide-viewing-angle design is beneficial for applications where the display may be viewed from off-center positions.
Environmental: The specified operating temperature range makes it suitable for both indoor and many industrial environments.

7. Technical Comparison and Differentiation

Compared to older technologies like incandescent or vacuum fluorescent displays (VFDs), this LED matrix offers significantly lower power consumption, longer lifetime, and superior shock and vibration resistance due to its solid-state construction. Within the LED display category, the use of InGaN blue chips provides a different color option compared to more common red GaAsP or GaP LEDs. The 5x7 format is a standard for alphanumeric character generation, offering a good balance between resolution and pin count. Its through-hole package differentiates it from surface-mount alternatives, making it more suitable for prototyping, hobbyist projects, or applications where manual soldering might be involved.

8. Frequently Asked Questions Based on Technical Parameters

Q: What is the purpose of the 2:1 Luminous Intensity Matching Ratio?
A: This ratio ensures that the brightest dot in the display is no more than twice as bright as the dimmest dot under the same drive conditions. This is important for achieving uniform appearance across all characters and segments, preventing some dots from appearing noticeably dimmer or brighter than others.

Q: Can I drive this display with a 3.3V microcontroller pin directly?
A: No. The typical forward voltage (3.6V) is higher than 3.3V. You would need a driver circuit (like a transistor array) powered from a higher voltage supply (e.g., 5V) to switch the rows/columns. The microcontroller pins would then control these driver transistors.

Q: Why is there a note specifying that the reverse voltage is for test only?
A: LEDs are diodes and are not designed to block high reverse voltages. Applying a continuous reverse bias above a very low threshold (often just a few volts) can cause breakdown and damage the device. The 5V test condition is used to measure leakage current (IR) under a controlled, non-operational stress.

Q: How do I create a multi-character display?
A: The displays are "stackable horizontally." This means you can place multiple units side-by-side on a PCB. Their pinouts are designed so that corresponding row and column lines from adjacent units can be connected in parallel, allowing a single driver circuit to control a string of characters by scanning all their rows simultaneously while sending column data for each position in sequence.

9. Practical Design and Usage Case

Case: Designing a Simple Temperature Readout. A designer needs to show a two-digit temperature (e.g., "25") on an embedded controller. They would use two LTP-1557TBE displays. A microcontroller would be programmed to convert the temperature sensor value into ASCII codes for the numbers '2' and '5'. These codes would be translated into the specific pattern of lit dots for each character using a lookup table stored in the microcontroller's memory. The microcontroller's I/O pins, likely through external current-sinking drivers (like ULN2003 arrays for columns) and current-sourcing drivers (like transistors for rows), would multiplex the displays. It would rapidly cycle through activating Row 1 of both displays while setting the column patterns for that row for each character, then Row 2, and so on up to Row 7. This happens faster than the human eye can perceive, creating the illusion of stable characters. The gray face and white dots ensure good readability in the ambient light of the intended environment.

10. Operating Principle Introduction

The fundamental operating principle is based on electroluminescence in a semiconductor p-n junction. When a forward bias voltage exceeding the diode's turn-on threshold (the forward voltage, VF) is applied, electrons from the n-type region and holes from the p-type region are injected into the active region (the junction). Here, they recombine, releasing energy in the form of photons (light). The specific material used—InGaN in this case—determines the bandgap energy and thus the wavelength (color) of the emitted light, which is in the blue spectrum. The 5x7 matrix arrangement is a practical implementation where 35 individual LED chips (dice) are packaged together and interconnected in a row-column matrix to minimize external connections.

11. Technology Trends and Developments

While this specific through-hole, discrete LED matrix represents a mature and stable technology, the broader field of display technology continues to evolve. Trends include the migration to surface-mount device (SMD) packages for automated assembly and smaller form factors. There is also a move towards higher-density matrices and full-color RGB displays using advanced packaging techniques that integrate red, green, and blue chips into a single pixel. Furthermore, the underlying LED chip technology sees continuous improvement in efficiency (more light output per watt of electrical input) and reliability. However, the basic 5x7 alphanumeric format remains relevant for countless simple, cost-effective, and reliable display applications where high resolution or color is not required.