LTS-2801AJR LED Digital Tube Datasheet - 0.28 Inch Character Height - Super Red Color - 2.6V Forward Voltage - Technical Documentation

1. Product Overview

LTS-2801AJR is a high-performance, single-digit, seven-segment digital tube display module. Its primary function is to provide clear and reliable display of numbers and limited alphanumeric characters in electronic devices. Its core application areas include low-power instrumentation, consumer electronics, industrial control panels, and any equipment requiring bright and easily readable numeric indicators.

This device is built on advanced AlInGaP (Aluminum Indium Gallium Phosphide) LED technology. This semiconductor material system is renowned for its high efficiency and excellent color purity within the red-orange to amber spectral range. The use of a transparent GaAs substrate further enhances light extraction efficiency, thereby increasing the display's brightness. The display features a gray panel with white segment markings, providing high contrast when segments are illuminated, thus improving readability under various lighting conditions.

The defining feature of this display is its optimized design for low-current operation. It is specifically tested and screened to perform excellently even at drive currents as low as 1mA per segment, making it an ideal choice for battery-powered or energy-sensitive applications. The luminous intensity of each segment at low currents is also matched to ensure uniform and consistent illumination across the entire digit.

1.1 Key Features and Advantages

• Character Size:It adopts a 0.28-inch (7.0 mm) character height, providing clear and easily readable display in a compact area.
• Segment Quality:Each segment provides continuous, uniform light emission without visible gaps or hotspots.
• Energy Efficiency:Designed specifically for ultra-low power requirements, supporting operation starting from 1mA per segment.
• Optical Performance:Provides excellent character appearance with high brightness and high contrast against a gray panel background.
• Viewing Angle:Thanks to the LED chip structure and packaging design, it provides a wide viewing angle.
• Reliability:Benefiting from the reliability of solid-state devices, it has no moving parts and features the long service life typical of LED technology.
• Consistency:Devices are classified (binned) according to luminous intensity to ensure predictable brightness levels during production.

2. Detailed Technical Specifications

This section provides a detailed and objective analysis of the device's technical parameters based on the datasheet. Understanding these specifications is crucial for proper circuit design and ensuring reliable performance.

2.1 Absolute Maximum Ratings

These ratings define the stress limits that may cause permanent damage to the device. Operation at or beyond these limits is not guaranteed.

• Power consumption per segment:Maximum 70 mW. Exceeding this value may cause the LED chip to overheat and accelerate aging.
• Peak forward current per segment:Maximum 90 mA, but only under pulse conditions (1/10 duty cycle, 0.1ms pulse width). This allows brief periods of high brightness, such as in multiplexed displays or when used for strobe effects.
• Continuous Forward Current per Segment:Maximum 25 mA at 25°C. This rating derates linearly as ambient temperature (Ta) increases above 25°C, with a derating factor of 0.33 mA/°C. For example, at 50°C, the maximum continuous current is approximately 25 mA - (0.33 mA/°C * 25°C) = 16.75 mA.
• Reverse voltage per segment:Maximum 5 V. LEDs have a low reverse breakdown voltage. Exceeding this value may cause immediate junction failure.
• Operating and storage temperature range:-35°C to +85°C. This device is suitable for industrial-grade temperature ranges.
• Soldering temperature:Withstands up to 260°C for a maximum of 3 seconds, measured 1.6mm below the mounting plane. This is crucial for the reflow soldering process.

2.2 Electrical and Optical Characteristics (Ta=25°C)

These are typical operating parameters under specified test conditions. The design should be based on these values.

• Average Luminous Intensity (I_V):At a forward current (I_F) of 1mA, the range is from 200 μcd (minimum) to 480 μcd (typical). This confirms its excellent suitability for extremely low current applications. Intensity will vary proportionally with current.
• Peak emission wavelength (λ_p):Typical value 639 nm. This is the wavelength at which the optical power output is maximum, placing it in the "super red" region of the spectrum.
• Spectral line half-width (Δλ):Typical value 20 nm. This indicates spectral purity; a narrower width means the color is more monochromatic (purer).
• Dominant wavelength (λ_d):Typical value 631 nm. This is the single wavelength perceived by the human eye, which may be slightly different from the peak wavelength.
• Forward voltage per segment (V_F):At I_F=20mA, the range is from 2.0V (minimum) to 2.6V (typical). This is the voltage drop across the LED when it is lit. A current-limiting resistor must always be connected in series with each segment or common anode.
• Reverse current per segment (I_R):) at a reverse voltage (V_R) of 5V is a maximum of 100 μA. This is the small leakage current when the LED is reverse biased.
• Luminous Intensity Matching Ratio (I_V-m):At I_FWhen =1mA, the maximum is 2:1. This stipulates that the brightness of the darkest segment within the same digit is not less than half of the brightness of the brightest segment, ensuring uniformity.

Measurement Instructions:Luminous intensity is measured using a sensor and filter calibrated to the CIE photopic luminous efficiency function, which approximates the sensitivity of the human eye.

3. Grading and Classification System

The datasheet indicates that the devices are "classified according to luminous intensity." This refers to the common "binning" practice in LED manufacturing.

• Luminous Intensity Binning:Due to natural variations in semiconductor epitaxial growth and the manufacturing process, LEDs from the same production batch may have slightly different brightness outputs. Manufacturers test each device and sort them into different "bins" based on their measured luminous intensity at a standard test current (e.g., 1mA or 20mA). This allows customers to select bins that meet their specific brightness requirements, ensuring consistency in the final product's appearance. The typical I_Vvalue of 480 μcd for the LTS-2801AJR most likely represents a specific bin or the center value of a distribution.
• Forward Voltage Binning:Although this model does not explicitly mention it, binning LEDs based on forward voltage (V_F) is also very common. This is crucial for designs where the power supply voltage is strictly limited or where precise matching of multiple LED currents is required.
• Wavelength Binning:For applications with strict color requirements, LEDs are also binned according to dominant wavelength or peak wavelength to ensure consistent hue. λ_p(639nm) and λ_d(631nm) have relatively narrow typical value ranges, indicating that this AlInGaP technology has good inherent color consistency.

4. Performance Curve Analysis

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

• Relative Luminous Intensity vs. Forward Current (I-V Curve):This chart will show how light output increases with forward current. It is typically nonlinear, especially at very low currents. The curve confirms the device's usability at 1mA and shows the brightness gain achievable by increasing the current to the maximum rating.
• Forward Voltage vs. Forward Current:This curve shows the relationship between the voltage across the LED and the current flowing through it. It is crucial for designing the current-limiting resistor value. The curve is essentially exponential, but for design purposes, the typical V_Fvalue at the expected operating current is often used.
• Relative luminous intensity vs. ambient temperature:LED light output decreases as junction temperature increases. This curve is crucial for understanding thermal derating. The linear derating specified for continuous current (0.33 mA/°C) is a practical simplification of this relationship to prevent overheating.
• Spectral distribution:A chart showing the relative optical power at each wavelength. It will illustrate the peak at ~639nm and a 20nm full width at half maximum, confirming its narrow and pure red light emission.

5. Mechanical and Packaging Information

5.1 Package Dimensions

The device adopts the standard single-digit seven-segment LED package outline. Key dimension descriptions in the datasheet:

• All primary dimensions are provided in millimeters (mm).
• The standard tolerance for dimensions is ±0.25 millimeters (equivalent to ±0.01 inches).
• Specific dimensions (not listed in the text excerpt) will define the package's overall length, width, and height, the digital window size, the pin pitch, and the pin length and diameter. These are crucial for PCB package design and mechanical fit within the housing.

5.2 Pin Connection and Polarity

LTS-2801AJR is aCommon AnodeDisplay. This means that the anodes (positive terminals) of all LED segments are internally connected to a common pin. The cathodes (negative terminals) of the individual segments are brought out to separate pins.

Pin Definition (10-Pin Configuration):

1. Pin 1: E Segment Cathode
2. Pin 2: D Segment Cathode
3. Pin 3: Common Anode 1
4. Pin 4: Segment C Cathode
5. Pin 5: Decimal Point (D.P.) Cathode
6. Pin 6: Segment B Cathode
7. Pin 7: Segment A Cathode
8. Pin 8: Common Anode 2
9. Pin 9: Cathode of Segment G
10. Pin 10: F segment cathode

Internal circuit diagram:The schematic shows that the two common anode pins (3 and 8) are internally connected together. This dual-anode design helps distribute current and can be used for redundancy or specific multiplexing schemes. All segment cathodes and the decimal point cathode are independent.

6. Welding and Assembly Guide

Adherence to these guidelines is crucial to ensure reliability and prevent damage during the assembly process.

• Reflow Soldering:This device can withstand a peak temperature of up to 260°C for a maximum duration of 3 seconds. This temperature should be measured 1.6mm below the package body (the mounting plane on the PCB). The standard lead-free reflow profile (IPC/JEDEC J-STD-020) is generally applicable, but the specific 260°C/3-second limit must be observed.
• Hand soldering:If hand soldering must be performed, use a temperature-controlled soldering iron. Limit the contact time per pin to 3-5 seconds to prevent excessive heat transfer through the pin to the LED chip.
• Cleaning:Post-soldering cleaning uses appropriate, non-aggressive solvents. Avoid ultrasonic cleaning unless verified safe for the package.
• ESD (Electrostatic Discharge) Precautions:Although not explicitly stated, LEDs are semiconductor devices and may be sensitive to ESD. It is recommended to implement standard ESD handling procedures (grounded workstations, wrist straps) during assembly.
• Storage Conditions:Store the device in its original moisture barrier bag. The ambient temperature should be within the specified storage temperature range (-35°C to +85°C), and low humidity should be maintained to prevent pin oxidation.

7. Application Suggestions and Design Considerations

7.1 Typical Application Circuit

Direct Drive by Microcontroller:For a common anode display, the common pin is connected to a positive supply voltage (e.g., +5V) through a current-limiting resistor, or more commonly, to a microcontroller GPIO pin configured to output a logic "high" (or driven by a PNP transistor for higher current). Each segment cathode pin is connected to a GPIO pin of the microcontroller. To illuminate a segment, its corresponding cathode pin is driven to logic "low" (ground), thereby completing the circuit.

Current-limiting resistor calculation:This is required for each common anode connection or each segment cathode (depending on the driving topology). Using a typical forward voltage (V_F= 2.6V) and the desired forward current (I_F), the resistance value R can be calculated using Ohm's law: R = (V_{Power supply}- V_F) / I_F. For a 5V power supply and I_F=10mA: R = (5V - 2.6V) / 0.01A = 240 Ω. The resistor's power rating should be at least I_F²* R.

7.2 Design Considerations

• Reuse:To control multiple digits with fewer microcontroller pins, multiplexing technology is required. The digits are illuminated one by one at a fast rate (e.g., 1-5 milliseconds per digit). The LTS-2801AJR's ability to handle peak current (90mA pulses) makes it suitable for multiplexing applications, where instantaneous brightness needs to be higher to compensate for the reduced duty cycle.
• Low-Power Design:Design battery-powered devices utilizing its 1mA operating capability. At 1mA per segment and a 5V supply, the power consumption per lit segment is approximately (5V - 2.6V) * 0.001A = 2.4 mW.
• Viewing Angle:Consider its wide viewing angle when placing the display to ensure readability for the end user.
• Thermal Management:In applications operating under continuous high current or high ambient temperatures, ensure adequate ventilation. Adhere to the current derating curve above 25°C.

8. Technical Comparison and Differentiation

Although no direct comparison with other models is provided, the key differentiating characteristics of the LTS-2801AJR can be inferred from its specifications:

• Comparison with standard red GaAsP/GaP LEDs:Compared to older LED materials, using AlInGaP technology provides significantly higher luminous efficiency (more light output per mA of current) and better color purity (more saturated red). This results in higher brightness and lower power consumption.
• Compared to larger size digital displays:The 0.28-inch digits strike a balance between size and readability, making them suitable for compact devices where using larger size displays (e.g., 0.5-inch or 1-inch) is physically impractical.
• Compared to displays not subjected to low-current testing:Explicit testing and screening for excellent low-current (1mA) characteristics is a key feature. Not all seven-segment displays can guarantee uniform brightness and proper operation at such low drive levels.
• Compared to common-cathode displays:When interfacing with microcontrollers whose source current capability is superior to their sink current capability (though many modern MCUs are symmetrical), a common-anode configuration is generally preferred. The specific choice depends on the driver circuit design.

9. Frequently Asked Questions (Based on Technical Specifications)

Q: Can I drive this display directly with a 3.3V microcontroller system?
A: Yes, but the current-limiting resistor must be recalculated. Using V_{Power supply}=3.3V, V_F=2.6V, and I_F=5mA: R = (3.3V - 2.6V) / 0.005A = 140 Ω. Please verify if the light output at 5mA meets your application requirements.

Q: Why are there two common anode pins (3 and 8)?
A: They are internally connected. This provides flexibility for PCB routing and helps distribute the total anode current (the sum of all lit segment currents) across two pins, thereby reducing the current density per pin and improving reliability.

Q: What is the difference between Peak Wavelength (639nm) and Dominant Wavelength (631nm)?
A: Peak Wavelength is the physical location where the optical power output is highest. Dominant Wavelength is the single wavelength that would produce the same color perception to the human eye, calculated based on the full spectrum. The sensitivity of the human eye influences this calculation, resulting in different values.

Q: How to light up the decimal point?
A: The decimal point is an independent LED, with its cathode on pin 5. To light it up, connect the common anode to V+, and drive pin 5 to ground (through a current-limiting resistor, which can be shared with the segments or independent).

10. Practical Application Examples

Scenario: Design a simple battery-powered digital thermometer.

1. Component Selection:LTS-2801AJR is chosen for its low-current operation characteristics, which maximize battery life. Select a microcontroller with at least 8 I/O pins (7 for segments, 1 for common anode control).
2. Circuit Design:The common anode pins (3 and 8) are connected together and then connected to a GPIO pin of the microcontroller via a PNP transistor (to handle the total current when all segments are lit). Each segment cathode (pins 1, 2, 4, 5, 6, 7, 9, 10) is connected to a separate GPIO pin of the microcontroller. Place a current-limiting resistor between the microcontroller's positive power rail and the emitter of the PNP transistor (or in series with each cathode if driving directly). Calculate the resistor value based on the desired brightness (e.g., 2mA per segment).
3. Software:The microcontroller reads the temperature sensor, converts the value into a decimal number, and looks up the corresponding segment pattern (e.g., a "seven-segment font" table). Then, while setting the common anode control pin to a high level to display the digit, it drives the corresponding cathode pins to a low level.
4. Result:A clear and easy-to-read temperature display with extremely low power consumption, suitable for portable devices.

11. Introduction to Technical Principles

The core technology is AlInGaP LED. Light is generated through a process called electroluminescence. When a forward voltage is applied across the semiconductor P-N junction, electrons from the N-type material recombine with holes from the P-type material in the active region. This recombination releases energy in the form of photons (light particles). The specific wavelength (color) of the light is determined by the bandgap energy of the semiconductor material, which is achieved by precisely controlling the proportions of aluminum, indium, gallium, and phosphorus during crystal growth. Compared to an absorbing substrate, the transparent GaAs substrate allows more of the generated light to escape from the chip, thereby improving overall external efficiency. The light from these tiny chips is then shaped and directed by the plastic encapsulation to form the recognizable seven-segment pattern.

12. Industry Trends and Development

The development of seven-segment displays follows broader LED technology trends. While the basic form factor remains highly useful, the underlying technology continues to advance. AlInGaP itself represents a significant leap over older materials. Current trends may include:

• Higher Efficiency:Continuous research on epitaxial structures and light extraction technologies drives the increase in lumens per watt, making displays brighter at the same current or extending battery life.
• Integration:Some modern displays integrate the driver IC ("controller") directly into the package, simplifying the interface for system designers (though this is more common in dot-matrix and character displays than in basic seven-segment units).
• Alternative Colors & Materials:Although this model uses AlInGaP to produce red light, other materials such as InGaN are used for blue, green, and white LEDs. The principle of low current, high brightness operation applies to these technologies.
• Durability in Specific Environments:For harsh environments, improvements in package sealing and materials enhance resistance to moisture, chemicals, and extreme temperatures.

LTS-2801AJR focuses on proven AlInGaP technology optimized for low-current performance, representing a mature, reliable, and highly practical solution in this continuously evolving technological landscape.