LTP-181FFM LED Dot Matrix Display Datasheet - 1.86-inch (47.4mm) Height - Green & Hyper Red - 16x16 Matrix - English Technical Document

1. Product Overview

The LTP-181FFM is a medium-sized, bi-color dot matrix display module designed for applications requiring clear alphanumeric or symbolic information display. Its core function is to provide a visual output interface composed of individually addressable light-emitting diodes (LEDs) arranged in a grid pattern.

1.1 Core Advantages and Target Market

This device is engineered with several key advantages that make it suitable for industrial, commercial, and instrumentation applications. It features a 1.86-inch (47.4 mm) character height, which offers excellent readability from a distance. The display provides high brightness and high contrast, ensuring visibility even in well-lit environments. A wide viewing angle allows the information to be seen clearly from various positions relative to the display surface.

From a reliability standpoint, it boasts solid-state reliability inherent to LED technology, meaning no moving parts and long operational life. It has low power requirements, making it energy-efficient. A significant mechanical feature is that the modules are stackable both vertically and horizontally, enabling the creation of larger display panels or multi-line displays without complex interfacing. The LEDs are also categorized for luminous intensity, ensuring consistent brightness across different units and within the matrix itself, which is critical for uniform appearance.

The target market includes applications such as public information displays, industrial control panels, test and measurement equipment, transportation signage, and any system where robust, reliable, and clear status or data presentation is required.

2. Technical Specifications Deep Dive

The LTP-181FFM is a 16 rows by 16 columns dot matrix display. It utilizes two different LED semiconductor technologies for its bi-color capability.

2.1 Device Description and Technology

The green LED chips are fabricated from Gallium Phosphide (GaP) on a GaP substrate. The red LED chips utilize Aluminum Indium Gallium Phosphide (AlInGaP) technology, specifically noted as "Hyper red," indicating high efficiency and purity in the red spectrum. These red chips are grown on a non-transparent Gallium Arsenide (GaAs) substrate. The display features a black face to enhance contrast by absorbing ambient light, and a diffusion film is added over the LEDs to blend the individual dots into a more uniform character appearance, reducing the "dotty" look.

2.2 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. They are specified at an ambient temperature (T_A) of 25°C.

• Average Power Dissipation per Dot: Green: 36 mW, Hyper Red: 40 mW.
• Peak Forward Current per Dot: Green: 100 mA, Hyper Red: 90 mA.
• Average Forward Current per Dot: Green: 13 mA, Hyper Red: 15 mA. This rating must be derated linearly above 25°C at a rate of 0.17 mA/°C for green and 0.2 mA/°C for red.
• Reverse Voltage per Dot: 5 V for both colors.
• Operating & Storage Temperature Range: -35°C to +85°C.
• Solder Temperature: 260°C for 3 seconds, measured 1/16 inch (≈1.59 mm) below the seating plane of the package.

2.3 Electrical & Optical Characteristics

These are the guaranteed performance parameters under specified test conditions at T_A = 25°C.

2.3.1 Green LED Characteristics

• Average Luminous Intensity (I_V): Typical 1400 µcd, with a minimum of 500 µcd. Test Condition: Peak current (I_p) = 35 mA, 1/16 duty cycle.
• Peak Emission Wavelength (λ_p): 565 nm (Typical). Test Condition: Forward current (I_F) = 20 mA.
• Spectral Line Half-Width (Δλ): 30 nm (Typical). I_F = 20 mA.
• Dominant Wavelength (λ_d): 569 nm (Typical). I_F = 20 mA.
• Forward Voltage (V_F) per Dot: Typical 2.6 V (Max 3.7 V) at I_F=80mA; Typical 2.1 V at I_F=20mA.
• Reverse Current (I_R) per Dot: Maximum 100 µA at V_R = 5V.
• Luminous Intensity Matching Ratio (I_V-m): Maximum 1.6:1 between any two dots. I_p = 35 mA, 1/16 duty.

2.3.2 AlInGaP Hyper Red LED Characteristics

• Average Luminous Intensity (I_V): Typical 1500 µcd, with a minimum of 500 µcd. Test Condition: I_p = 15 mA, 1/16 duty cycle.
• Peak Emission Wavelength (λ_p): 650 nm (Typical). I_F = 20 mA.
• Spectral Line Half-Width (Δλ): 35 nm (Typical). I_F = 20 mA.
• Dominant Wavelength (λ_d): 639 nm (Typical). I_F = 20 mA.
• Forward Voltage (V_F) per Dot: Typical 2.8 V (Max 3.7 V implied) at I_F=80mA; Typical 2.6 V at I_F=20mA.
• Reverse Current (I_R) per Dot: Maximum 100 µA at V_R = 5V.
• Luminous Intensity Matching Ratio (I_V-m): Maximum 1.6:1. I_p = 15 mA, 1/16 duty.

Note: Luminous intensity measurements use a sensor and filter approximating the CIE photopic eye-response curve.

3. Binning System Explanation

The datasheet indicates the LEDs are categorized for luminous intensity. This is a critical binning process.

• Luminous Intensity Binning: The specified matching ratio of 1.6:1 maximum ensures that within a single display module, no individual LED dot is more than 60% brighter than the dimmest dot under the same drive conditions. This is essential for achieving uniform brightness across characters and the entire display area, preventing "hot spots" or dim segments.
• Wavelength: While typical values for peak (565nm, 650nm) and dominant (569nm, 639nm) wavelengths are given, production variation is managed to ensure the green and red colors fall within acceptable visual bands. The spectral half-width data (30nm, 35nm) indicates the color purity.
• Forward Voltage: The specified ranges (e.g., 2.1V to 3.7V for green at high current) account for natural variation in semiconductor manufacturing. Drive circuitry must be designed to accommodate this range to ensure consistent brightness.

4. Performance Curve Analysis

The datasheet references Typical Electrical/Optical Characteristic Curves. While the specific graphs are not detailed in the provided text, standard curves for such devices typically include:

• I-V (Current-Voltage) Curve: Shows the relationship between forward current and forward voltage for a single LED dot. It is non-linear, with a turn-on/threshold voltage (around 1.8-2.0V for these colors) after which current increases rapidly with small voltage increases. This curve is crucial for designing current-limiting circuitry.
• Luminous Intensity vs. Forward Current (I_F): Displays how light output increases with current. It is generally linear over a wide range but will saturate at very high currents due to thermal effects.
• Luminous Intensity vs. Ambient Temperature: Shows how light output decreases as the junction temperature of the LED rises. This derating is directly related to the average current derating specified in the Absolute Maximum Ratings.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the peak and dominant wavelengths and the spectral half-width, confirming the color characteristics.

5. Mechanical and Packaging Information

5.1 Package Dimensions

The datasheet includes a detailed mechanical drawing (not rendered here). Key notes from the drawing specify that all dimensions are in millimeters (mm) and the default tolerance is ±0.25 mm (0.01 inch) unless a specific feature note states otherwise. This drawing defines the overall footprint, mounting hole positions, LED matrix viewing area, and the precise location and pitch of the 48 pins.

5.2 Pin Connection and Circuit Diagram

The device has a 48-pin dual-in-line package. The pinout is complex due to the multiplexed 16x16 matrix. Pins are designated as either Common Anode for Rows or Cathode for Columns, with specific pins for Green and Red LEDs. For example, Pin 3 is Cathode Column 1 for Green, while Pin 11 is Cathode Column 1 for Red. This arrangement allows the controller to select a row (by applying a positive voltage to its common anode) and then illuminate specific green or red dots in that row by sinking current through the corresponding column cathode pins.

An internal circuit diagram is referenced, which would typically show the interconnection of all 256 LEDs (16x16), clarifying which anode rows and cathode columns control each specific LED dot for both colors.

6. Soldering and Assembly Guidelines

The primary guidance provided is the soldering temperature profile: 260°C for 3 seconds, measured at a point 1/16 inch (1.59 mm) below the package body. This is a standard wave soldering or hand soldering reference point to prevent excessive heat from damaging the internal LEDs or plastic package. For reflow soldering, a standard lead-free profile with a peak temperature around 260°C would be applicable, but the specific time above liquidus (TAL) should be controlled to meet the 3-second guideline at the pin level.

Handling should follow standard ESD (Electrostatic Discharge) precautions for semiconductor devices. Storage should be within the specified -35°C to +85°C temperature range in a low-humidity environment.

7. Application Suggestions

7.1 Typical Application Scenarios

• Industrial Control Panels: Displaying machine status, production counts, error codes, or setpoint values.
• Test and Measurement Equipment: Showing numerical readings, units, and mode indicators.
• Information Displays: In public spaces for simple messages, queue numbers, or transportation schedules.
• Stacked Display Systems: Multiple modules can be combined to show longer text messages, larger fonts, or multi-line data.

7.2 Design Considerations

• Drive Circuitry: A microcontroller with sufficient I/O pins or dedicated LED display driver ICs (like MAX7219 or similar multiplexing drivers) is required to manage the 16:1 multiplexing (16 rows). The driver must supply the peak current needed for the selected dots (e.g., 80mA per dot, divided by duty cycle).
• Current Limiting: External current-limiting resistors or constant-current drivers are mandatory for each cathode column (or groups thereof) to prevent exceeding the Absolute Maximum Current and to set the desired brightness. Calculations must use the maximum V_F to ensure safe current under all conditions.
• Thermal Management: The average current derating with temperature must be observed. In high ambient temperatures, the multiplexing duty cycle or peak current may need to be reduced to keep junction temperature within safe limits and maintain brightness consistency.
• Viewing Angle: The wide viewing angle is beneficial but should be considered during mechanical enclosure design to align with the intended viewer positions.

8. Technical Comparison and Differentiation

Compared to generic single-color or smaller dot matrix displays, the LTP-181FFM offers distinct advantages:

• Bi-Color Capability: The use of dedicated Green and high-efficiency AlInGaP Hyper Red LEDs allows for two-color information presentation (e.g., green for normal status, red for alarms/warnings), enhancing information density and clarity.
• Large Character Height (1.86\"): Provides superior long-distance readability compared to smaller 5x7 or 8x8 matrices, filling a niche between small indicators and large signage.
• Intensity Binning: The guaranteed 1.6:1 intensity matching ratio is a mark of quality, ensuring professional-grade display uniformity that cheaper, unbinned displays may lack.
• Stackable Design: The mechanical design facilitates easy assembly of multi-module displays, a feature not always present in displays meant for standalone use.

9. Frequently Asked Questions (Based on Technical Parameters)

Q1: What is the difference between "peak" and "dominant" wavelength?
A: Peak wavelength (λ_p) is the wavelength at which the emitted light has its maximum intensity. Dominant wavelength (λ_d) is the wavelength of the monochromatic light that matches the perceived color of the LED. For LEDs, λ_d is often more relevant to human color perception.

Q2: Why is the test current for luminous intensity different for Green (35mA) and Red (15mA)?
A: This reflects the different efficiencies of the two semiconductor technologies. The AlInGaP Hyper Red LED is more efficient, producing its typical luminous intensity (1500 µcd) at a lower drive current than the GaP Green LED needs for its typical intensity (1400 µcd).

Q3: How do I calculate the required series resistor for a column?
A: Use Ohm's Law: R = (V_supply - V_F - V_{drop_driver}) / I_F. Use the maximum V_F from the datasheet (e.g., 3.7V at 80mA for green) to ensure the current never exceeds the limit even with a low-V_F LED. Account for the voltage drop of the column driver transistor/MOSFET (V_{drop_driver}). The current I_F is the desired per-dot peak current (e.g., 80mA), but remember this current is shared across all dots in a column that are active during a single row's time slice in a multiplexed design.

Q4: What does "1/16 DUTY" mean in the test conditions?
A: It indicates the display is being driven in a multiplexed mode with a 1/16 duty cycle. This is standard for a 16-row matrix. Each row is powered on for only 1/16th of the total refresh cycle time. The luminous intensity is measured under this condition, which is how the display will be used in practice. The peak current during the "on" time is higher than the average current to compensate for the low duty cycle and achieve the desired average brightness.

10. Design and Usage Case Study

Scenario: Designing a Multi-Line Production Counter Display.
An engineer needs a display for a factory floor showing the current production count and target for a machine. They choose two LTP-181FFM modules stacked vertically.

Implementation: A single microcontroller drives both displays. The firmware manages a 16-row multiplexing routine, refreshing each row sequentially. The top module displays "COUNT: [number]" in green. The bottom module displays "TARGET: [number]" in green. If the machine stops due to an error, the relevant line or a separate "ERROR" message can flash in red on the corresponding module. The stackable design simplifies mechanical mounting. The high brightness and wide viewing angle ensure the information is visible to operators from various points on the floor. The intensity binning guarantees both modules have a consistent, uniform appearance side-by-side.

11. Operating Principle Introduction

The LTP-181FFM operates on the principle of LED matrix multiplexing. It is not practical to have 256 individual wires (for a 16x16 monochrome) or more for bi-color. Instead, the LEDs are arranged in a grid where the anodes of all LEDs in a single row are connected together (Common Anode Row), and the cathodes of all LEDs in a single column for a specific color are connected together (Cathode Column).

To illuminate a specific dot (e.g., the green dot at Row 5, Column 3), the controller performs these steps in rapid succession within the refresh cycle: 1) It sets the Common Anode for Row 5 to a positive voltage (e.g., +5V). 2) It connects the Cathode for Column 3 (Green) to ground (0V), completing the circuit and allowing current to flow through that specific green LED. All other rows are off, and all other column lines are held high (open circuit). By scanning through all 16 rows very quickly (e.g., at 100Hz or more), the persistence of vision creates the illusion that all desired dots in the 16x16 matrix are lit simultaneously. The bi-color capability simply adds a separate set of cathode pins for the red LEDs, which are controlled independently.

12. Technology Trends

While the LTP-181FFM uses established GaP (Green) and AlInGaP (Red) technologies, the broader LED display field is evolving. Trends include:

• Higher Efficiency Materials: The shift from AlInGaP on GaAs to even more efficient structures or the use of InGaN-based materials for red LEDs (though challenging) to improve efficiency and color gamut.
• Integrated Drivers: Newer display modules often incorporate the multiplexing driver IC and sometimes even a microcontroller interface (like I2C or SPI) directly on the module PCB, significantly simplifying the external circuit design compared to bare LED matrices like the LTP-181FFM.
• Surface-Mount Technology (SMT): Many modern LED matrices use SMT LEDs and packages, allowing for lower profile, automated assembly, and potentially higher resolution. The through-hole design of the LTP-181FFM is robust and suited for applications where manual soldering or repair might occur.
• Full-Color RGB Matrices: For more advanced graphical or multi-color text applications, matrices with integrated red, green, and blue (RGB) LEDs in each pixel are becoming more common, though they require more complex driving electronics.

The LTP-181FFM represents a reliable, high-performance solution in its class, balancing size, brightness, bi-color functionality, and design flexibility for a wide range of embedded display applications.