LTP-7357KS LED Dot Matrix Display Datasheet - 0.678-inch (17.22mm) Height - AlInGaP Yellow - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTP-7357KS is a compact, single-plane 5x7 dot matrix LED display module. Its primary function is to display alphanumeric characters and symbols, making it suitable for applications requiring clear, legible information presentation in a limited space. The core advantage of this device lies in its utilization of Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor technology for the LED chips, which provides efficient light emission in the yellow spectrum. The display features a gray face and white dot color, enhancing contrast for improved readability. Its design targets embedded systems, industrial control panels, instrumentation, consumer electronics, and any application where a small, reliable character display is needed.

2. In-Depth Technical Parameter Analysis

2.1 Photometric and Optical Characteristics

The optical performance is central to the display's functionality. The device emits light in the yellow wavelength region. The typical peak emission wavelength (λp) is 588 nm, with a dominant wavelength (λd) of 587 nm, indicating a pure yellow hue. The spectral line half-width (Δλ) is 15 nm, which describes the spectral purity of the emitted light. The key parameter for brightness is the average luminous intensity (Iv), which ranges from a minimum of 630 μcd to a maximum of 1650 μcd under a test condition of a 32mA pulse current and a 1/16 duty cycle. A luminous intensity matching ratio of 2:1 (maximum to minimum) is specified for LEDs within the same "similar light area" bin, ensuring acceptable uniformity across the display matrix.

2.2 Electrical Characteristics and Ratings

Understanding the electrical limits is crucial for reliable operation. The Absolute Maximum Ratings define the boundaries beyond which permanent damage may occur. The average power dissipation per LED dot must not exceed 70 mW. The peak forward current per dot is limited to 60 mA, while the average forward current per dot is rated at 25 mA at 25°C, derating linearly by 0.28 mA/°C as ambient temperature increases. The maximum reverse voltage that can be applied to any segment is 5 V. The forward voltage (Vf) for any dot, measured at a forward current (If) of 20 mA, typically falls between 2.05 V and 2.6 V. The reverse current (Ir) is guaranteed to be less than or equal to 100 μA when a reverse voltage (Vr) of 5 V is applied.

2.3 Thermal and Environmental Specifications

The device is designed for robust operation across a wide temperature range. The operating temperature range is specified from -35°C to +105°C, and the storage temperature range is identical. This wide range makes it suitable for both commercial and industrial environments. The derating curve for average forward current is a critical design consideration to prevent thermal runaway; as the ambient temperature rises above 25°C, the permissible continuous current must be reduced accordingly.

3. Binning System Explanation

The datasheet indicates that the product is "Categorized for Luminous Intensity." This refers to a binning process where manufactured LEDs are sorted based on their measured light output (luminous intensity) into different groups or "bins." The specified intensity range of 630 μcd to 1650 μcd likely encompasses multiple bins. Designers can select parts from a specific bin to ensure consistent brightness across multiple displays in a system. The note about adjusting the epoxy ratio to "narrow the bin grade" in the revision history suggests efforts were made to improve consistency and reduce the spread of optical parameters within a production batch.

4. Performance Curve Analysis

While the provided PDF excerpt mentions "Typical Electrical / Optical Characteristic Curves" on the final page, the specific graphs are not included in the text content. Typically, such curves for an LED display would include:

• Forward Current vs. Forward Voltage (I-V Curve): Shows the nonlinear relationship between current and voltage, essential for designing the current-limiting driver circuit.
• Luminous Intensity vs. Forward Current (L-I Curve): Illustrates how light output increases with current, helping to optimize drive conditions for desired brightness and efficiency.
• Luminous Intensity vs. Ambient Temperature: Demonstrates the decrease in light output as junction temperature rises, critical for thermal management in high-temperature applications.
• Spectral Distribution: A graph plotting relative intensity against wavelength, showing the peak and shape of the yellow emission.

Designers should consult the full datasheet with graphs to make precise calculations for their specific operating conditions.

5. Mechanical and Package Information

5.1 Physical Dimensions and Tolerances

The display has a matrix height of 0.678 inches (17.22 mm). The package drawing (referenced but not detailed in text) would show the overall length, width, and height, lead spacing, and seating plane. Key dimensional notes from the datasheet include: all dimensions are in millimeters with a general tolerance of ±0.25 mm unless stated otherwise. A specific revision updated the width tolerance from 12.6mm ±0.1mm to 12.6mm +0.18/-0.25mm. Pin tip shift tolerance is ±0.4 mm. Additional quality notes limit foreign material on segments, ink contamination, bending, and bubbles within the epoxy.

5.2 Pinout and Connection Diagram

The device has a 12-pin configuration for X-Y (matrix) addressing. The pin connections are 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. An internal circuit diagram (referenced on page 3) visually represents the 5x7 matrix, showing how the 5 cathode columns and 7 anode rows interconnect the 35 individual LED dots.

5.3 Polarity and Orientation

The device uses a common-cathode configuration per column. Each of the five columns has a common cathode connection, and each of the seven rows has a common anode connection. To illuminate a specific dot, its corresponding cathode column must be driven low (grounded), and its corresponding anode row must be driven high with a current-limited voltage source. Proper orientation during PCB mounting is typically indicated by a notch, bevel, or pin 1 indicator on the package.

6. Soldering and Assembly Guidelines

The datasheet provides a specific soldering condition: the leads can be subjected to a soldering iron temperature of 260°C for 3 seconds, measured 1/16 inch (approximately 1.6 mm) below the seating plane of the package. This is a critical parameter to prevent thermal damage to the internal epoxy, wire bonds, and semiconductor dies during hand soldering or rework. For wave or reflow soldering processes, a standard lead-free (RoHS compliant) profile with a peak temperature not exceeding the maximum rating should be used. The device itself is confirmed as a lead-free package compliant with RoHS directives.

7. Packaging and Ordering Information

The part number is LTP-7357KS. The "KS" suffix may indicate specific binning or optical characteristics. Standard packaging for such components is typically in anti-static tubes or trays to protect the leads and window from damage and electrostatic discharge (ESD). The reel or tube quantity should be confirmed with the manufacturer or distributor. Labels on the packaging will include the part number, lot code, and date code for traceability.

8. Application Suggestions

8.1 Typical Application Scenarios

This display is ideal for applications requiring a simple, low-power character readout. Examples include: status indicators on network equipment, parameter displays on power supplies or test equipment, simple message displays on appliances, clock readouts, and basic user interface panels in industrial controls. Its stackable horizontal feature allows multiple units to be placed side-by-side to form longer messages or larger numeric displays.

8.2 Design Considerations and Driver Circuitry

Driving a 5x7 matrix requires a multiplexing scheme. A microcontroller with sufficient I/O pins or a dedicated LED driver IC (like a MAX7219 or similar) is necessary. The driver must cycle through the five columns rapidly, energizing the appropriate seven row anodes for each column. The 1/16 duty cycle mentioned in the test condition is a common multiplexing ratio (1/5 for columns * some persistence factor). The driver must supply pulsed current, not continuous DC, to each LED. The peak current per dot can be higher than the average rating to achieve the desired brightness within the multiplexing duty cycle, but it must not exceed the 60mA absolute maximum. Careful calculation of current-limiting resistors is required based on the forward voltage and the desired pulse current. Heat sinking may be necessary if operating near maximum ratings or in high ambient temperatures.

9. Technical Comparison and Differentiation

The key differentiator of the LTP-7357KS is its use of AlInGaP technology for yellow emission. Compared to older technologies like GaAsP (Gallium Arsenide Phosphide), AlInGaP offers higher efficiency, better temperature stability, and more consistent color output. The gray face/white dot combination provides a high-contrast, non-glare appearance when off, which is preferable in many professional and consumer applications over a black or clear face. The wide operating temperature range and solid-state construction give it an advantage in reliability over other display technologies like vacuum fluorescent displays (VFDs) or liquid crystal displays (LCDs) in harsh environments, though it lacks the flexibility of a graphical pixel matrix.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength (λp) is the wavelength at which the emission spectrum has its maximum intensity. Dominant wavelength (λd) is the single wavelength of monochromatic light that would match the perceived color of the LED. For a narrow spectrum like this, they are very close (588nm vs. 587nm).

Q: Can I drive this display with a constant DC current on each LED?
A: Technically yes, but it is highly inefficient and would require 35 individual current-limiting circuits. Multiplexing (scanning) is the standard and practical method, allowing control of 35 LEDs with only 12 pins.

Q: The luminous intensity is tested at 1/16 duty cycle. What does this mean for my design?
A: This is the test condition used to specify brightness. In your multiplexing design, you will have a similar duty cycle (e.g., 1/5 per column). To achieve the specified brightness, your driver's pulse current during the active time slot should be set to 32mA (the test condition current). The average current will be much lower.

Q: Is a heat sink required?
A: For normal operation within the specified average current and temperature limits, a dedicated heat sink is not typically required for the display itself. However, proper PCB layout with adequate copper area for the power and ground traces helps dissipate heat. If driving at maximum ratings in a high ambient temperature, thermal analysis is recommended.

11. Practical Design and Usage Case

Consider designing a simple temperature controller with a setpoint and actual temperature readout. Two LTP-7357KS displays could be used side-by-side. A microcontroller reads a temperature sensor, performs a PID calculation, and drives a heater relay. It also drives the two LED displays via a multiplexing driver circuit to show the setpoint and current temperature. The yellow color is easily visible in various lighting conditions. The design must include current-limiting resistors on the anode rows. The firmware must implement the character font map (converting ASCII codes to the 5x7 patterns for digits, 'C' for Celsius, etc.) and the scanning routine to refresh the displays at a rate high enough to avoid flicker (typically >60 Hz).

12. Operating Principle Introduction

The LTP-7357KS is based on semiconductor electroluminescence. The AlInGaP chip structure consists of multiple epitaxial layers grown on a GaAs substrate. When a forward voltage exceeding the diode's threshold is applied, electrons and holes are injected into the active region where they recombine, releasing energy in the form of photons (light). The specific alloy composition of Aluminium, Indium, Gallium, and Phosphide determines the bandgap energy, which directly corresponds to the wavelength (color) of the emitted light—in this case, yellow. The 5x7 matrix is formed by 35 of these individual LED chips, electrically connected in a grid pattern of rows and columns to allow independent control via multiplexing.

13. Technology Trends and Context

While dot matrix displays like the LTP-7357KS remain relevant for specific, cost-sensitive, or low-information-density applications, the broader trend in display technology is towards higher integration and flexibility. Graphical OLED and TFT-LCD modules are becoming more affordable and offer pixel-addressable graphics. However, for simple, bright, rugged, and low-power character-only displays, LED dot matrices retain advantages. The use of AlInGaP represents an advancement over older LED materials, offering better performance. Future developments in this niche may focus on even higher efficiency, wider viewing angles, integrated drivers, and surface-mount packages for easier assembly, though the fundamental multiplexed matrix approach is well-established.