LTP-7357JD LED Dot Matrix Display Datasheet - 0.678 Inch (17.22mm) Height - AlInGaP Red - 5x7 Array - English Technical Document

1. Product Overview

The LTP-7357JD is a single-plane, 5x7 dot matrix LED display module designed for character and symbol presentation. Its primary function is to provide a clear, legible alphanumeric display in various electronic devices. The core advantage of this device lies in its utilization of ultra-bright AlInGaP (Aluminum Indium Gallium Phosphide) high-efficiency red LED chips, which offer superior luminous intensity and reliability compared to older LED technologies. The display features a gray face with white dots, enhancing contrast for improved readability. It is categorized for luminous intensity, allowing for selection based on brightness requirements. The target market includes industrial control panels, instrumentation, point-of-sale terminals, embedded systems, and any application requiring a compact, reliable character display interface.

1.1 Key Features and Core Advantages

The device incorporates several design features that contribute to its performance and versatility. The 0.678-inch (17.22 mm) matrix height provides a character size suitable for medium-range viewing. Its low power requirement makes it suitable for battery-powered or energy-conscious applications. The single-plane construction with a wide viewing angle ensures visibility from various positions. The solid-state reliability of LED technology guarantees a long operational lifespan with no moving parts. The 5x7 array with X-Y select architecture allows for efficient multiplexing control. Compatibility with standard USASCII and EBCDIC character codes simplifies integration with microcontrollers and processors. Finally, the stackable horizontal design enables the creation of multi-character displays by aligning multiple units side-by-side.

2. Technical Parameters Deep Objective Interpretation

The performance of the LTP-7357JD is defined by a set of electrical, optical, and thermal parameters that designers must consider for proper implementation.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operating the device continuously at or near these limits is not recommended. Key maximum ratings include an average power dissipation per dot of 33 mW, a peak forward current per dot of 90 mA, and an average forward current per dot of 13 mA at 25°C. This average current derates linearly at 0.17 mA/°C as ambient temperature increases above 25°C. The maximum reverse voltage per segment is 5 V. The device is rated for an operating temperature range of -35°C to +85°C and a storage temperature range of -35°C to +85°C. The maximum soldering temperature is 260°C for a maximum duration of 3 seconds, measured 1.6mm below the seating plane.

2.2 Electrical & Optical Characteristics

These are the typical operating parameters measured at an ambient temperature (Ta) of 25°C. The average luminous intensity (Iv) ranges from a minimum of 500 μcd to a maximum of 1200 μcd, with a typical value provided, when driven with a peak current (Ip) of 32 mA at a 1/16 duty cycle. This multiplexing scheme is common for reducing power consumption and driver complexity. The peak emission wavelength (λp) is typically 656 nm, falling within the red spectrum. The spectral line half-width (Δλ) is 22 nm, indicating the spectral purity of the emitted light. The dominant wavelength (λd) is 640 nm. The forward voltage (Vf) for any dot ranges from 2.1 V (min) to 2.6 V (max) at a forward current (If) of 20 mA. The reverse current (Ir) for any dot is a maximum of 100 μA at a reverse voltage (Vr) of 5 V. The luminous intensity matching ratio (Iv-m) between dots is 1.8:1 maximum, ensuring relatively uniform brightness across the display. It is important to note that luminous intensity is measured using a sensor and filter combination that approximates the CIE photopic eye-response curve.

3. Binning System Explanation

The datasheet indicates that the LTP-7357JD is categorized for luminous intensity. This implies a binning or sorting process based on measured light output.

3.1 Luminous Intensity Binning

While specific bin codes are not listed in the provided excerpt, the specification of a range (500-1200 μcd) suggests that devices are tested and grouped according to their actual measured intensity when driven under standard test conditions (Ip=32mA, 1/16 Duty). This allows designers to select parts that meet a minimum brightness requirement for their application, potentially affecting cost and availability. Consistency within a bin ensures uniform appearance in a multi-unit display.

4. Performance Curve Analysis

The datasheet includes a section for typical electrical and optical characteristic curves. These graphs are crucial for understanding device behavior under non-standard conditions.

4.1 Implied Curve Information

Although the specific curves are not detailed in the text, typical plots for such devices would include the Forward Current vs. Forward Voltage (I-V curve), which shows the nonlinear relationship and helps in designing current-limiting circuitry. Luminous Intensity vs. Forward Current curves demonstrate how light output increases with current, often in a sub-linear fashion at higher currents due to heating effects. Luminous Intensity vs. Ambient Temperature curves show the derating of light output as temperature rises, which is critical for high-temperature environments. Spectral distribution plots would illustrate the concentration of emitted light around the peak and dominant wavelengths.

5. Mechanical and Packaging Information

The physical construction of the display determines its mounting compatibility and overall robustness.

5.1 Package Dimensions and Tolerances

The device's package dimensions are provided in a detailed drawing (referenced but not shown in text). All dimensions are specified in millimeters. The general tolerance for these dimensions is ±0.25 mm (equivalent to ±0.01 inches) unless a specific feature note indicates otherwise. Designers must refer to this drawing for precise hole patterns, overall height, and lead spacing to create accurate PCB footprints.

5.2 Pin Connection and Polarity

The LTP-7357JD has a 12-pin configuration. The pinout is as follows: Pin 1: Cathode Column 1, Pin 2: Anode Row 3, Pin 3: Cathode Column 2, Pin 4: Anode Row 5, Pin 5: Anode Row 6, Pin 6: Anode Row 7, Pin 7: Cathode Column 4, Pin 8: Cathode Column 5, Pin 9: Anode Row 4, Pin 10: Cathode Column 3, Pin 11: Anode Row 2, Pin 12: Anode Row 1. This arrangement facilitates the X-Y (row-column) multiplexing scheme. Correct identification of anode and cathode pins is critical to prevent reverse bias and ensure proper operation.

5.3 Internal Circuit Diagram

The internal circuit diagram (referenced) reveals the matrix organization 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 positive) while its column line is driven low (cathode grounded), with appropriate current limiting. This common-cathode per column architecture is standard for multiplexed displays.

6. Soldering and Assembly Guidelines

Proper handling during assembly is essential to maintain device integrity and performance.

6.1 Soldering Process Parameters

The absolute maximum rating specifies the soldering temperature limit: 260°C maximum for a maximum of 3 seconds, measured 1.6mm (1/16 inch) below the seating plane. This guideline is intended for wave soldering or reflow soldering processes. For reflow soldering, the entire temperature profile (preheat, soak, reflow peak, cooling) must be controlled to ensure the package and internal wire bonds are not subjected to thermal shock or excessive time above liquidus.

6.2 Handling and Storage Precautions

Although not explicitly detailed, standard ESD (Electrostatic Discharge) precautions should be observed when handling the LED display, as the semiconductor junctions can be sensitive. Storage should be within the specified temperature range of -35°C to +85°C in a low-humidity environment to prevent moisture absorption and potential popcorning during soldering.

7. Application Suggestions

The LTP-7357JD is suited for a variety of embedded display applications.

7.1 Typical Application Scenarios

Common uses include status displays on industrial equipment (e.g., temperature readouts, error codes), character readouts on medical devices, simple messaging on consumer appliances, and as part of larger segmented displays in retail or information kiosks. Its compatibility with standard character codes makes it ideal for displaying text messages from a microcontroller.

7.2 Design Considerations and Circuit Implementation

Designers must implement a multiplexing driver circuit. This typically involves a microcontroller with sufficient I/O pins or dedicated LED driver ICs capable of sink/sink current for the columns and source current for the rows. Current-limiting resistors are mandatory for each column or row line (depending on the driver topology) to set the forward current per LED segment. The 1/16 duty cycle mentioned in the test condition suggests a 4-bit binary multiplex (2^4=16 states), which is a common approach for a 5x7 matrix, often scanning 4 rows at a time or using a combination of row and column scanning. The refresh rate must be high enough (typically >60 Hz) to avoid visible flicker. Heat dissipation should be considered if operating near maximum ratings, especially in high ambient temperatures.

8. Technical Comparison and Differentiation

The LTP-7357JD offers specific advantages within its product category.

8.1 Key Differentiators

The primary differentiator is the use of AlInGaP LED technology. Compared to older GaAsP or GaP LEDs, AlInGaP provides significantly higher luminous efficiency, resulting in brighter displays at the same current or similar brightness at lower power. The gray face/white dot combination offers a professional appearance and high contrast. The wide viewing angle is beneficial for applications where the user may not be directly in front of the display. The categorization by luminous intensity provides a level of quality control and selection flexibility not always present in basic displays.

9. Frequently Asked Questions Based on Technical Parameters

Here are answers to common design questions derived from the datasheet.

Q: What is the purpose of the 1/16 duty cycle in the luminous intensity test condition?
A: It simulates a multiplexed driving scheme where each LED is only powered for 1/16th of the total scan time. The specified luminous intensity is the average value perceived by the eye under this condition. You must use multiplexing or a similar duty cycle to achieve this brightness without exceeding the average current ratings.

Q: Can I drive the LEDs with a continuous DC current instead of multiplexing?
A: Technically yes, but you must ensure the continuous forward current per dot does not exceed the average rating of 13 mA at 25°C (and must be derated for higher temperatures). This would require 35 independent current-limited channels, which is inefficient. Multiplexing is the intended and most efficient use case.

Q: The forward voltage is 2.1-2.6V. What supply voltage do I need?
A: The supply voltage must be higher than the maximum forward voltage plus the voltage drop across your current-limiting resistor and driver circuitry. A common supply voltage for such displays is 5V, which provides ample headroom.

Q: What does \"luminous intensity matching ratio of 1.8:1\" mean?
A: It means the brightest dot in the matrix will be no more than 1.8 times brighter than the dimmest dot under identical driving conditions. This ensures reasonable uniformity across the displayed character.

10. Practical Implementation Case Study

Consider designing a simple single-character display for a microcontroller-based thermostat. The goal is to show set temperature from 0 to 9.

Design Steps: 1. The microcontroller (e.g., an ATmega328P) is programmed with font data for digits 0-9 in a 5x7 bitmap format. 2. Five I/O pins are configured as column drivers (connected to cathodes, capable of sinking current). Seven I/O pins are configured as row drivers (connected to anodes, capable of sourcing current). 3. Current-limiting resistors are placed on the column lines. The resistor value is calculated based on the supply voltage (e.g., 5V), the LED forward voltage (~2.5V), and the desired peak current (e.g., 32mA for full brightness): R = (5V - 2.5V) / 0.032A ≈ 78 ohms. A standard 75 or 82 ohm resistor can be used. 4. The firmware implements a scanning routine. It sets one row line high (activates the anodes for that row), then places the pattern for that row on the five column lines (low to turn on a dot, high impedance or high to turn off). It waits a short period (e.g., 1-2 ms), then moves to the next row. Scanning all 7 rows within ~14ms achieves a refresh rate >70 Hz, eliminating flicker. 5. The display shows a stable, bright digit indicating the temperature.

11. Operational Principle Introduction

The LTP-7357JD operates on the principle of electroluminescence in a semiconductor p-n junction. When a forward bias voltage exceeding the diode's turn-on voltage (approximately 2.1-2.6V for this AlInGaP material) is applied across an individual LED, electrons and holes recombine in the active region, releasing energy in the form of photons (light). The specific material composition (AlInGaP) determines the bandgap energy and thus the wavelength (color) of the emitted light, in this case, red (~640-656 nm). The 5x7 matrix organization is an addressing scheme that reduces the number of required control pins from 35 (one per LED) to 12 (7 rows + 5 columns) through multiplexing. By rapidly sequencing through the rows and presenting the corresponding column data for each row, the human eye's persistence of vision integrates the pattern into a stable, seemingly static image.

12. Technology Trends and Context

The LTP-7357JD represents a mature technology based on AlInGaP, which was a significant advancement over earlier red LED materials. Current trends in display technology have largely moved towards higher-density dot matrix displays, full graphic OLED or LCD modules, and surface-mount device (SMD) LEDs for directly soldered matrices. However, through-hole packages like this remain relevant for prototyping, educational purposes, repair markets, and applications where extreme reliability and simplicity are valued over pixel density or color capability. The underlying LED technology continues to evolve, with ongoing research into materials like GaN-on-Si for cost reduction and efficiency improvements across the spectrum, but the fundamental multiplexing principles for matrix displays remain consistent.