LTP-2257KA 5x7 Dot Matrix LED Display Specification Sheet - 1.97-Inch Character Height - AlInGaP Red Orange - Technical Documentation

1. Product Overview

LTP-2257KA wani tsari ne na nuni na harafi guda, wanda aka tsara don aikace-aikacen da ke buƙatar fitarwa mai haske da amintacce. Babban aikinsa shine gabatar da bayanai a zahiri ta hanyar grid na matrix na haske wanda ya ƙunshi fitilun LED masu zaman kansu, yawanci haruffan ASCII ko EBCDIC. An tsara na'urar don haɗawa cikin tsarin da ke buƙatar mahimman abubuwa kamar ƙarancin wutar lantarki, amintaccen inganci na daskararre, da kuma faɗin kusurwar gani.

The primary markets for this component include industrial control panels, instrumentation, point-of-sale terminals, basic information displays, and embedded systems requiring simple, robust character readouts. Its stackable design allows for the creation of multi-character displays in a horizontal orientation, providing flexibility for displaying words or numbers.

Its core technical advantage lies in the use of aluminum indium gallium phosphide (AlInGaP) semiconductor material for the LED chip. This material system is renowned for generating high-efficiency light emission within the red to amber-orange spectral range, providing good visibility. The display features a black panel, which creates high contrast with the illuminated white light dots, significantly enhancing readability under various ambient lighting conditions.

2. Detailed Technical Specifications

This section provides a detailed and objective analysis of the key electrical, optical, and physical parameters defined in the specification document.

2.1 Photometric and Optical Characteristics

Optical performance is the core of display functionality. Key parameters are measured under standardized test conditions (Ta=25°C) to ensure consistency.

• Average luminous intensity (I_V):Ranges from a minimum of 2100 µcd to a maximum of 5000 µcd, with a typical value implied. This intensity is measured at I_pMeasured for each light spot under pulse drive conditions of =32mA and a duty cycle of 1/16. The 1/16 duty cycle is a typical value for multiplexed matrix driving, where each row is activated only for a portion of the time. The sensor used approximates the CIE photopic luminosity function, ensuring the measurements are relevant to human eye sensitivity.
• Peak Emission Wavelength (λ_p):The typical value is 621 nanometers (nm). This represents the wavelength at which the optical power output is greatest. It lies in the red-orange region of the visible spectrum.
• Dominant Wavelength (λ_d):615 nm. This is the single wavelength perceived by the human eye that matches the color of the LED's output. It is slightly lower than the peak wavelength, which is a common phenomenon due to the shape of the emission spectrum.
• Spectral line half-width (Δλ):Approximately 18 nm. This parameter defines the bandwidth of the emitted light, specifically referring to the width of the spectral curve at half of its maximum power. The value of 18 nm indicates that this is a relatively narrow-band monochromatic light source, which is characteristic of AlInGaP LEDs and produces saturated colors.
• Luminous intensity matching ratio (I_V-m):Maximum 2:1. This is a key parameter for display uniformity. It stipulates that the luminous intensity of any single light point shall not exceed twice that of any other light point within the same display module. This ensures consistent brightness across all segments of a character.

2.2 Electrical Characteristics

Electrical parameters define the interface and power supply requirements of the device.

• Forward Voltage (V_F):At a test current (I_F) of 20mA, the range for each light point is from 2.05V (minimum) to 2.6V (maximum). This is the voltage drop across the LED when it is conducting. Designers must ensure the drive circuit can provide this voltage. A typical value is not specified, but it lies within this range.
• Reverse Current (I_R):At a reverse voltage (V_R) of 15V, the maximum is 100 µA. This is the small leakage current that flows when the LED is reverse biased. It is usually negligible in operation but must be considered in circuit protection design.
• Average forward current per light point:The rated average current is 13 mA. However, above 25°C, a derating factor of 0.17 mA/°C must be applied linearly. This means that as the ambient temperature increases, the allowable maximum average current must be reduced to prevent overheating and premature failure. For example, at 85°C, the maximum average current is: 13 mA - [0.17 mA/°C * (85-25)°C] = 13 - 10.2 = 2.8 mA.

2.3 Absolute Maximum Ratings

These are stress limits that must not be exceeded under any conditions, even momentarily. Operation beyond these limits may cause permanent damage.

• Average Power Consumption per Spot:Maximum 36 mW. This is the product of average forward current and forward voltage.
• Peak forward current per light point:Maximum 100 mA. This is the highest instantaneous current allowed, typically associated with very short pulses in multiplexing schemes.
• Reverse voltage per light point:Maximum 5 V. Exceeding this value may cause junction breakdown.
• Operating and storage temperature range:-35°C to +85°C. This device is rated for the industrial temperature range.
• Soldering temperature:Maximum 260°C for up to 3 seconds, measured 1.6mm (1/16 inch) below the seating plane. This is critical for wave soldering or reflow processes.

3. Grading and Classification System

The datasheet clearly states that the device is "classified by luminous intensity." This indicates that the units are sorted or "binned" based on their measured light output. The luminous intensity range (2100-5000 µcd) likely represents the distribution across multiple bins. Manufacturers typically group LEDs into tighter intensity ranges (e.g., 2100-3000 µcd, 3000-4000 µcd, 4000-5000 µcd). This allows customers to select bins according to their specific brightness uniformity requirements. For multi-unit displays, using LEDs from the same intensity bin is crucial for achieving a uniform appearance. The datasheet does not specify binning for forward voltage or wavelength, but the provided min/max ranges for V_Fand λ_pdefine the overall distribution.

4. Performance Curve Analysis

The datasheet references "Typical Electrical/Optical Characteristic Curves." Although specific graphs are not provided in the text, we can infer their standard content and significance.

• Relative Luminous Intensity vs. Forward Current (I-V Curve):This chart will show how light output increases with drive current. It is typically nonlinear, with efficiency dropping at very high currents due to thermal effects. The 32mA pulse test point is likely located within the effective linear portion of this curve.
• Forward Voltage vs. Forward Current:This curve shows the I-V characteristics of the diode. Voltage increases logarithmically with current. The specified V_Fis a point on this curve.
• Relative Luminous Intensity vs. Ambient Temperature:This is the key curve for understanding thermal performance. The light output of an LED typically decreases as the junction temperature increases. The derating factor specified for the forward current is directly related to managing this thermal effect to maintain performance and reliability.
• Spectral Distribution:A graph of relative intensity versus wavelength, showing a peak at approximately 621nm with a full width at half maximum (FWHM) of about 18nm.

5. Mechanical and Packaging Information

This device is a through-hole component featuring a standard DIP (Dual In-line Package) outline, suitable for PCB mounting.

• Dot matrix height:The defining physical characteristic is a character height of 1.97 inches (50.15 mm). This is a large-format display designed specifically for long-distance viewing.
• Package size:The datasheet includes detailed dimensional drawings. All dimensions are in millimeters, with a standard tolerance of ±0.25 mm unless otherwise specified. This drawing is crucial for PCB pad design and ensuring proper fit within the enclosure.
• Pin Connections:The device has 12 pins arranged in a single row.
  • Pins 1-7: Correspond to cathode rows 1 through 7. In a typical matrix configuration, these would be the scan lines.
  • Pin 8-12: Correspond to anode columns 5 to 1 (note the reverse order: pin 8 is column 5, pin 12 is column 1). These will be the data lines.
• Internal circuit diagram:The provided diagram illustrates the standard 5x7 matrix configuration. Each LED (light point) is located at the intersection of an anode column and a cathode row. To illuminate a specific light point, its corresponding anode line must be driven high (positive voltage) while its cathode line is driven low (ground). This matrix arrangement minimizes the number of required drive pins (12, as opposed to the 35 needed for individually addressing the light points).
• Polarity Identification:The pin definition table clearly identifies the anode and cathode connections. One end of the package may have a notch or marking to indicate the orientation of pin 1.

6. Soldering and Assembly Guide

An bayar da mahimman ƙa'idodin haɗawa don tsarin weld.

• Reflow solder / tafkin solder sigogi:Absolute maximum ratings specify that the device can withstand a maximum soldering temperature of 260°C for up to 3 seconds. This measurement is taken 1.6mm below the mounting plane (i.e., at the PCB level), not on the component body. This is the standard rating for leaded components and is compatible with typical wave soldering profiles. For reflow soldering using lead-free solder (with a higher melting point), the temperature profile must be carefully controlled to ensure the component body temperature does not exceed the maximum storage temperature of 85°C for an extended period, even if the leads briefly reach 260°C.
• Hand soldering:If hand soldering must be performed, a temperature-controlled soldering iron should be used. The contact time per lead should be minimized, ideally less than 3 seconds, to prevent heat from traveling up the lead and damaging the internal wire bonds or epoxy.
• Cleaning:No specific cleaning instructions are provided. Standard isopropyl alcohol or approved flux removers may be used, but strong solvents should be avoided as they may damage plastic housings or markings.
• Storage Conditions:Devices should be stored in a dry, non-condensing environment within the specified temperature range of -35°C to +85°C. It is recommended to keep components in their original moisture barrier bag until use to prevent moisture absorption, which can lead to "popcorning" during soldering.

7. Application Recommendations

7.1 Typical Application Scenarios

• Industrial Control Panel:Display setpoints, process values (temperature, pressure, speed), error codes, or machine status.
• Test and Measurement Equipment:Display numerical readings for multimeters, power supplies, or signal generators.
• Consumer Electronics (Traditional):Clocks, timers, basic calculators, or home appliance displays.
• Embedded System Prototype Development:Provide simple and direct output for microcontrollers (such as Arduino, PIC) to display debugging information or user prompts.
• Stacking multi-character displays:By placing multiple LTP-2257KA modules side by side, words, numbers, or simple scrolling messages can be created for basic information boards or signs.

7.2 Design Considerations

• Drive Circuit:A dedicated LED driver IC or a microcontroller GPIO pin with a current-limiting resistor is required. Due to the matrix configuration, a multiplexing (scanning) scheme must be adopted. The driver must supply current to the anode columns and sink current from the cathode rows. In multiplexing timing calculations, the peak current (100mA) per pixel and average current derating must be observed.
• Current Limitation:Each anode column or cathode row (depending on the drive topology) must use an external resistor to set the operating current. Its value is determined based on the supply voltage (V_CC), LED forward voltage (V_F) and the required current (I_F) calculation. For example, using a 5V power supply, V_Fis 2.3V, target I_Fis 20mA: R = (5V - 2.3V) / 0.02A = 135 ohms. A standard 150 ohm resistor would be suitable.
• Thermal Management:Although the device has low power consumption, the forward current derating curve must be followed at high ambient temperatures. If the display is enclosed, ensure sufficient airflow. The average power dissipation per light point (max. 36mW) translates to the total maximum power dissipation for the entire lit character, which should be considered in the PCB thermal design.
• Viewing Angle:The "wide viewing angle" feature is beneficial, but for optimal readability, the display should be installed facing the primary viewer. The black panel/white light point design provides good contrast at most angles.

8. Technical Comparison and Differentiation

Compared to other display technologies available at the time of its release (2000), the LTP-2257KA offered specific advantages:

• Compared to incandescent bulbs or Vacuum Fluorescent Displays (VFD):LEDs are solid-state, offering higher reliability, resistance to shock/vibration, longer lifespan (typically tens of thousands of hours), and lower operating voltage/power consumption. They also do not require a heated filament or high voltage.
• Compared to early LCDs:LEDs are self-luminous devices, meaning they generate their own light, making them clearly visible in low-light or dark conditions without a backlight. They have a wider operating temperature range and faster response time. However, they consume more power than reflective LCDs and are not suitable for complex graphics.
• Comparison with other LED technologies:Compared to older GaAsP or GaP, the use of AlInGaP material provides higher efficiency and better color purity (more saturated red-orange) at a given drive current. The specific 5x7 format and large height of 1.97 inches target applications requiring easy character reading from a distance.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive all light spots simultaneously with a constant DC current?
A: Technically possible, but extremely inefficient. If all 35 light spots are lit, it will exceed the average power rating. The standard and recommended method is to use multiplexing, i.e., lighting one row (or column) of spots at a time at a high frequency. This creates the visual illusion of a stable display while significantly reducing the average current.

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength is the position where the LED emits the maximum optical power. Dominant wavelength is the single wavelength that matches the color of the LED as perceived by the human eye. Due to the asymmetry of the LED emission spectrum, they are usually close but not identical. Dominant wavelength is more related to color perception.

Q: The forward voltage is 2.05-2.6V. Can I run it with a 3.3V logic supply?
A: Yes, absolutely. A 3.3V supply is sufficient to forward bias the LED. You need to recalculate the current-limiting resistor value based on the lower supply voltage (e.g., R = (3.3V - 2.3V) / 0.02A = 50 ohms).

Q: What does "1/16 duty cycle" mean in the luminous intensity test conditions?
A: This means the LED is driven by a 32mA current pulse, but the pulse is active only for 1/16 of the total time period. The measured intensity is the average over the entire cycle. This simulates conditions in a 1:16 multiplexing drive scheme (e.g., 7 rows + 9 blanks = 16 time slots).

10. Practical Design and Usage Cases

Case: Building a simple 4-digit voltmeter display.An engineer needs to display a voltage from 0.000 to 9.999 volts on a panel. They decided to use four horizontally stacked LTP-2257KA modules.

1. Circuit Design:A microcontroller with an ADC reads the voltage. The firmware converts the reading into four decimal digits. The microcontroller's I/O ports, combined with discrete transistors or a dedicated multiplexing driver IC (such as MAX7219), are configured to scan these four displays. The cathode rows of each display are connected in parallel, while the anode columns for each digit are controlled individually. This creates a 4-digit x 7-row matrix.
2. Current Setting:Using a 5V power supply and desiring a bright display, they selected an average current of 15mA per light point. Considering multiplexing across 4 bits and 7 lines (where the effective duty cycle for each light point is 1/28 when all are lit), the peak pulse current during its active time slot would be higher (e.g., 15mA * 28 = 420mA). However, this must be checked against the 100mA peak current rating. Therefore, they need to adjust the timing or use a lower average current to keep the peak current within specifications.
3. Thermal Considerations:This panel is designed for laboratory environments (25°C). There is no need to worry about average current derating here. However, they ensure the PCB has a ground plane to help dissipate heat from the driver circuit.
4. Results:The final product displays a clear, bright, and wide-viewing-angle 4-digit readout, meeting the requirements for a benchtop instrument.

11. How It Works

LTP-2257KA operates based on the fundamental principle of light-emitting diodes (LEDs) arranged in a passive matrix. Each of the 35 light points forming the 5x7 grid is an independent AlInGaP LED chip. When a forward bias voltage exceeding the diode junction potential (approximately 2V) is applied between a specific anode (column) and cathode (row) pair, current flows through the LED at that intersection. This current causes electrons and holes to recombine within the semiconductor's active region, releasing energy in the form of photons—i.e., light—with a wavelength characteristic of the AlInGaP material (red-orange).

矩阵组织是一种巧妙的互连方法。不是使用35根单独的导线，而是将垂直列中所有LED的阳极连接在一起，将水平行中所有LED的阴极连接在一起。要点亮单个光点，其特定的列被驱动为正，其特定的行被驱动为地。要显示一个图案（如字符），扫描算法会快速遍历各行（或各列），依次为每一行打开相应的列驱动器。在足够高的频率下（通常>100Hz），视觉暂留使整个字符看起来稳定地发光。

12. Technical Trends and Background

LTP-2257KA represents a mature and well-established display technology. At the time of its release, dot-matrix LED displays were the mainstream solution for alphanumeric output. The shift from older materials like GaAsP to AlInGaP was a significant trend, offering higher efficiency and better color.

Subsequent trends have shifted towards:
Surface Mount Device (SMD) Package:Nearly all modern equivalents are of the SMD type, enabling smaller, automated assembly.
Higher Density and Full Matrix Displays:The basic 5x7 format has largely been replaced by larger dot matrix modules (e.g., 8x8, 16x16) and full-graphic panels capable of displaying arbitrary shapes and multiple font texts.
Integrated Controller:Modern LED matrix modules typically integrate drivers, memory, and communication interfaces (such as I2C or SPI) on a single board, greatly simplifying the design process for engineers.
Alternative Technologies:For many applications requiring simple character output, low-power LCDs (with or without backlight) and OLED displays have become more prevalent, especially where power consumption, thinness, or graphical capabilities are prioritized.

Despite these trends, through-hole LED dot matrix displays like the LTP-2257KA remain relevant in educational settings, hobbyist projects, maintenance of legacy equipment, and specific industrial applications where their simplicity, ruggedness, high brightness, and wide temperature range are decisive advantages.