LTS-2801AJR LED Display Datasheet - 0.28-inch Digit Height - Super Red Color - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTS-2801AJR is a high-performance, single-digit, seven-segment alphanumeric display module. Its primary function is to provide clear, reliable numeric and limited alphanumeric character representation in electronic devices. The core application is in low-power instrumentation, consumer electronics, industrial control panels, and any device requiring a bright, easily readable numeric indicator.

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

The defining characteristic of this display is its optimization for low-current operation. It is specifically tested and selected to perform exceptionally well at driving currents as low as 1mA per segment, making it ideal for battery-powered or energy-sensitive applications. The segments are also matched for consistent luminous intensity at these low currents, ensuring uniform appearance across the digit.

1.1 Key Features and Advantages

• Digit Size: Features a 0.28-inch (7.0 mm) character height, offering a compact yet legible display area.
• Segment Quality: Provides continuous, uniform light emission across each segment with no visible gaps or hotspots.
• Power Efficiency: Engineered for very low power requirement, enabling operation from 1mA per segment upwards.
• Optical Performance: Delivers excellent character appearance with high brightness and high contrast against its gray face.
• Viewing Angle: Offers a wide viewing angle due to the LED chip construction and package design.
• Reliability: Benefits from solid-state reliability with no moving parts and long operational lifetime typical of LED technology.
• Consistency: Devices are categorized (binned) for luminous intensity, ensuring predictable brightness levels in production.

2. Technical Specifications Deep Dive

This section provides a detailed, objective analysis of the device's technical parameters as defined in 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 beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed.

• Power Dissipation per Segment: 70 mW maximum. Exceeding this can lead to overheating and accelerated degradation of the LED chip.
• Peak Forward Current per Segment: 90 mA maximum, but only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). This allows for brief periods of high brightness, such as in multiplexed displays or for strobe effects.
• Continuous Forward Current per Segment: 25 mA maximum at 25°C. This rating derates linearly at 0.33 mA/°C as ambient temperature (Ta) increases above 25°C. For example, at 50°C, the maximum continuous current would be approximately 25 mA - (0.33 mA/°C * 25°C) = 16.75 mA.
• Reverse Voltage per Segment: 5 V maximum. LEDs have low reverse breakdown voltage. Exceeding this can cause immediate junction failure.
• Operating & Storage Temperature Range: -35°C to +85°C. The device is rated for industrial temperature ranges.
• Solder Temperature: Withstands a maximum of 260°C for up to 3 seconds, measured 1.6mm below the seating plane. This is critical for reflow soldering processes.

2.2 Electrical & Optical Characteristics (at Ta=25°C)

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

• Average Luminous Intensity (I_V): Ranges from 200 μcd (min) to 480 μcd (typ) at a forward current (I_F) of 1mA. This confirms its suitability for very low-current applications. The intensity will scale with current.
• Peak Emission Wavelength (λ_p): Typically 639 nm. This is the wavelength at which the optical power output is greatest, placing it in the \"super red\" region of the spectrum.
• Spectral Line Half-Width (Δλ): Typically 20 nm. This indicates the spectral purity; a narrower width means a more monochromatic (pure) color.
• Dominant Wavelength (λ_d): Typically 631 nm. This is the single wavelength perceived by the human eye, which may differ slightly from the peak wavelength.
• Forward Voltage per Segment (V_F): Ranges from 2.0V (min) to 2.6V (typ) at I_F=20mA. This is the voltage drop across the LED when illuminated. A current-limiting resistor is always required in series with each segment or common anode.
• Reverse Current per Segment (I_R): Maximum 100 μA at a reverse voltage (V_R) of 5V. This is the small leakage current when the LED is reverse-biased.
• Luminous Intensity Matching Ratio (I_V-m): Maximum 2:1 at I_F=1mA. This specifies that the brightness of the dimmest segment will be no less than half the brightness of the brightest segment within the same digit, ensuring uniformity.

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

3. Binning and Categorization System

The datasheet states that devices are \"categorized for luminous intensity.\" This refers to a common practice in LED manufacturing known as \"binning.\"

• Luminous Intensity Binning: Due to natural variations in the semiconductor epitaxial growth and fabrication process, LEDs from the same production batch can 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 a bin that meets their specific brightness requirements, ensuring consistency in the final product's appearance. The LTS-2801AJR's typical I_V of 480 μcd likely represents a specific bin or the center of the distribution.
• Forward Voltage Binning: While not explicitly mentioned for this part, it is also common to bin LEDs based on forward voltage (V_F). This is important for designs where power supply voltage is tightly constrained or where precise current matching across multiple LEDs is critical.
• Wavelength Binning: For color-critical applications, LEDs are also binned by dominant or peak wavelength to ensure a consistent hue. The tight typical values for λ_p (639nm) and λ_d (631nm) suggest good inherent color consistency for this AlInGaP technology.

4. Performance Curve Analysis

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

• Relative Luminous Intensity vs. Forward Current (I-V Curve): This graph would show how light output increases with forward current. It is typically non-linear, especially at very low currents. The curve confirms the device's usability at 1mA and shows the gain in brightness achievable by increasing current up 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 essential for designing the current-limiting resistor value. The curve is exponential in nature, but for design purposes, the typical V_F at the intended operating current is used.
• Relative Luminous Intensity vs. Ambient Temperature: LED light output decreases as junction temperature increases. This curve is critical 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 graph showing the relative optical power across wavelengths. It would illustrate the peak at ~639nm and the 20nm half-width, confirming the narrow, pure red emission.

5. Mechanical and Package Information

5.1 Package Dimensions

The device has a standard single-digit seven-segment LED package footprint. Key dimensional notes from the datasheet:

• All primary dimensions are provided in millimeters (mm).
• Standard tolerance on dimensions is ±0.25 mm (which is equivalent to ±0.01 inches).
• The specific dimensions (not listed in the text extract) would define the overall length, width, and height of the package, the digit window size, the lead (pin) spacing, and the lead length and diameter. These are critical for PCB footprint design and mechanical fit within an enclosure.

5.2 Pin Connection and Polarity

The LTS-2801AJR is a common anode display. This means the anode (positive side) of all LED segments is connected internally to common pins. The cathodes (negative side) of individual segments are brought out to separate pins.

Pinout (10-pin configuration):

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

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

6. Soldering and Assembly Guidelines

Adherence to these guidelines is essential for reliability and preventing damage during the assembly process.

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

7. Application Suggestions and Design Considerations

7.1 Typical Application Circuits

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

Current Limiting Resistor Calculation: This is mandatory for each common anode connection or each segment cathode (depending on the drive topology). Using the typical forward voltage (V_F = 2.6V) and a desired forward current (I_F), the resistor value R is calculated using Ohm's Law: R = (V_supply - V_F) / I_F. For a 5V supply and I_F=10mA: R = (5V - 2.6V) / 0.01A = 240 Ω. The resistor power rating should be at least I_F² * R.

7.2 Design Considerations

• Multiplexing: To control multiple digits with fewer microcontroller pins, multiplexing is used. Digits are turned on one at a time at a fast rate (e.g., 1-5 ms per digit). The LTS-2801AJR's ability to handle peak currents (90mA pulsed) makes it suitable for multiplexed applications where instantaneous brightness needs to be higher to compensate for the reduced duty cycle.
• Low-Power Design: Leverage the 1mA operating capability for battery-powered devices. At 1mA per segment and a 5V supply, power consumption per lit segment is approximately (5V - 2.6V) * 0.001A = 2.4 mW.
• Viewing Angle: Position the display considering its wide viewing angle to ensure readability for the end-user.
• Heat Management: In applications running at high continuous current or in high ambient temperatures, ensure adequate ventilation. Adhere to the current derating curve above 25°C.

8. Technical Comparison and Differentiation

While a direct comparison with other part numbers is not provided, the LTS-2801AJR's key differentiators can be inferred from its specifications:

• vs. Standard Red GaAsP/GaP LEDs: The use of AlInGaP technology provides significantly higher luminous efficiency (more light output per mA of current) and better color purity (more saturated red) compared to older LED materials. This results in higher brightness and lower power consumption.
• vs. Larger Digit Displays: The 0.28-inch digit offers a balance between size and readability, suitable for compact devices where a larger display (e.g., 0.5-inch or 1-inch) would be physically impractical.
• vs. Displays without Low-Current Testing: The explicit testing and selection for excellent low-current (1mA) characteristics is a key feature. Not all seven-segment displays guarantee uniform brightness and proper operation at such low drive levels.
• vs. Common Cathode Displays: The common anode configuration is often preferred when interfacing with microcontrollers that source current better than they sink it (though many modern MCUs are symmetrical). The choice depends on the driver circuit design.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this display directly from a 3.3V microcontroller system?
A: Yes, but you must recalculate the current-limiting resistor. Using V_supply=3.3V, V_F=2.6V, and I_F=5mA: R = (3.3V - 2.6V) / 0.005A = 140 Ω. Verify that the light output at 5mA is sufficient for your application.

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

Q: What is the difference between peak wavelength (639nm) and dominant wavelength (631nm)?
A: Peak wavelength is where the optical power output is physically highest. Dominant wavelength is the single wavelength that would produce the same color perception to the human eye, calculated from the full spectrum. The human eye's sensitivity affects this calculation, causing the values to differ.

Q: How do I achieve a decimal point?
A: The decimal point is a separate LED with its own cathode on Pin 5. To illuminate it, connect the common anodes to V+, and drive Pin 5 to ground (through a current-limiting resistor, shared with the segments or separate).

10. Practical Application Example

Scenario: Designing a simple battery-powered digital thermometer.

1. Component Selection: The LTS-2801AJR is chosen for its low-current operation to maximize battery life. A microcontroller with at least 8 I/O pins is selected (7 for segments, 1 for common anode control).
2. Circuit Design: The common anode pins (3 & 8) are connected together and then to a GPIO pin of the microcontroller via a PNP transistor (to handle the combined segment current if all are on). Each segment cathode (Pins 1,2,4,5,6,7,9,10) is connected to a separate microcontroller GPIO pin. A current-limiting resistor is placed between the microcontroller's positive supply rail and the emitter of the PNP transistor (or in series with each cathode if driving directly). The value is calculated for a desired brightness at, for example, 2mA per segment.
3. Software: The microcontroller reads the temperature sensor, converts the value to a decimal number, and looks up the corresponding segment patterns (e.g., a \"7-segment font\" table). It then drives the appropriate cathode pins low while setting the common anode control pin high to display the digit.
4. Result: A clear, readable temperature display with minimal power draw, suitable for a portable device.

11. Technology Principle Introduction

The core technology is the AlInGaP LED. Light is produced 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 engineered by precisely controlling the ratios of Aluminum, Indium, Gallium, and Phosphide during crystal growth. The transparent GaAs substrate allows more of the generated light to escape from the chip compared to absorbing substrates, increasing overall external efficiency. The light from these tiny chips is then shaped and directed by the plastic package to form the recognizable seven-segment pattern.

12. Industry Trends and Developments

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

• Even Higher Efficiency: Ongoing research into epitaxial structures and light extraction techniques pushes for more lumens per watt, enabling brighter displays at the same current or longer battery life.
• Integration: Some modern displays integrate the driver IC (a \"controller\") directly into the package, simplifying interfacing for the system designer (though this is more common in dot-matrix and alphanumeric displays than in basic seven-segment units).
• Alternative Colors & Materials: While this part uses AlInGaP for red, other materials like InGaN are used for blue, green, and white LEDs. The principle of low-current, high-brightness operation applies across these technologies.
• Niche Durability: For harsh environments, developments in package sealing and materials improve resistance to moisture, chemicals, and temperature extremes.

The LTS-2801AJR, with its focus on proven AlInGaP technology optimized for low-current performance, represents a mature, reliable, and highly practical solution within this ongoing technological landscape.