LTD-2601JD LED Display Datasheet - 0.28-inch Digit Height - Hyper Red (650nm) - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The device is a dual-digit, seven-segment light-emitting diode (LED) display module. Its primary function is to provide a clear, legible numeric readout for various electronic instruments and devices. The core application is in scenarios requiring the display of two numerical digits, such as counters, timers, simple meters, or control panel indicators.

The display utilizes AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for its light-emitting elements. This material system is specifically chosen for producing high-efficiency red and amber LEDs. The chips are fabricated on a non-transparent Gallium Arsenide (GaAs) substrate, which helps in directing light output forward and can improve contrast by reducing internal reflection and light leakage. The visual presentation features a gray faceplate with white segment markings, a combination designed to offer high contrast between illuminated (red) and non-illuminated states, enhancing readability under various lighting conditions.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

These parameters define the limits beyond which permanent damage to the device may occur. Operation under or at these conditions is not guaranteed and should be avoided in normal use.

• Power Dissipation per Segment: 70 mW. This is the maximum allowable power that can be dissipated as heat by a single LED segment without risk of damage. Exceeding this limit, typically by driving the LED with excessive current, can lead to overheating, accelerated degradation of luminous output, and eventual failure.
• Peak Forward Current per Segment: 90 mA. This is the maximum instantaneous current pulse a segment can withstand. It is relevant for multiplexing schemes or pulsed operation but is not intended for continuous DC operation.
• Continuous Forward Current per Segment: 25 mA (at 25°C). This is the recommended maximum current for reliable, long-term continuous operation of a single segment. The datasheet specifies a derating factor of 0.33 mA/°C above 25°C. For example, at an ambient temperature (Ta) of 60°C, the maximum allowable continuous current would be: 25 mA - ((60°C - 25°C) * 0.33 mA/°C) ≈ 13.45 mA. This derating is crucial for thermal management and longevity.
• Reverse Voltage per Segment: 5 V. LEDs have very low reverse breakdown voltage. Applying a reverse bias greater than 5V can cause a sudden increase in reverse current, potentially damaging the PN junction. Circuit designs must ensure this limit is not exceeded, often by using protection diodes in bidirectional or multiplexed circuits.
• Operating & Storage Temperature Range: -35°C to +85°C. The device is rated for industrial temperature ranges, ensuring functionality in non-climate-controlled environments.
• Solder Temperature: Maximum 260°C for a maximum of 3 seconds, measured 1.6mm below the seating plane. This is a critical guideline for wave soldering or reflow processes to prevent thermal damage to the plastic package and internal wire bonds.

2.2 Electrical & Optical Characteristics

These parameters are measured under standard test conditions (Ta=25°C) and define the typical performance of the device.

• Average Luminous Intensity (I_V): 200 μcd (Min), 600 μcd (Typ) at I_F=1mA. This quantifies the perceived brightness of the lit segment. The wide range (200-600 μcd) indicates the device is categorized or binned for intensity. Designers must account for this variation if uniform brightness across multiple displays or digits is critical.
• Peak Emission Wavelength (λ_p): 650 nm (Typ) at I_F=20mA. This is the wavelength at which the spectral output is strongest, placing this LED in the \"hyper red\" or \"super red\" part of the spectrum, which appears as a deep, saturated red to the human eye.
• Spectral Line Half-Width (Δλ): 20 nm (Typ). This indicates the spectral purity. A value of 20nm is typical for AlInGaP LEDs and results in a relatively pure color compared to broader-spectrum sources.
• Dominant Wavelength (λ_d): 639 nm (Typ). This is the single-wavelength perceived by the human eye that best matches the color of the LED light. It is the key parameter for color specification.
• Forward Voltage per Segment (V_F): 2.1V (Min), 2.6V (Typ) at I_F=20mA. This is the voltage drop across the LED when operating. It is crucial for designing the current-limiting circuitry. The driver circuit must supply a voltage higher than the maximum V_F to ensure proper current regulation across all units and over temperature.
• Reverse Current per Segment (I_R): 100 μA (Max) at V_R=5V. This is the leakage current when the specified reverse voltage is applied.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 (Max). This specifies the maximum allowable ratio between the brightest and dimmest segment within a single device or between devices from the same batch. A ratio of 2:1 means the dimmest segment will be at least half as bright as the brightest, which is important for visual uniformity.

3. Binning System Explanation

The datasheet explicitly states the device is \"categorized for luminous intensity.\" This implies a binning or sorting process post-manufacturing.

• Luminous Intensity Binning: Due to inherent variations in the semiconductor epitaxial growth and chip fabrication processes, the light output of individual LEDs can vary. Manufacturers test and sort (bin) LEDs into groups based on their measured luminous intensity at a standard test current (e.g., 1mA). The LTD-2601JD's specified range of 200-600 μcd likely encompasses several intensity bins. For applications requiring consistent brightness across multiple displays, specifying a tighter bin or purchasing from the same production lot is advisable.
• Forward Voltage Binning: While not explicitly mentioned for this product, it is common practice to bin LEDs for forward voltage (V_F) as well. The specified V_F range of 2.1V to 2.6V indicates potential variation. In designs where multiple segments are driven in parallel from a constant voltage source, V_F variation can lead to uneven current distribution and thus uneven brightness. Using a constant current driver for each segment or series string mitigates this issue.
• Wavelength Binning: The dominant wavelength is specified as a typical value (639nm). For most red display applications, slight variations in the exact shade of red are acceptable. For critical color-matching applications, a product with a specified wavelength binning would be required.

4. Performance Curve Analysis

The datasheet references \"Typical Electrical / Optical Characteristic Curves.\" While the specific graphs are not provided in the text, standard curves for such LEDs can be inferred and are critical for design.

• Forward Current vs. Forward Voltage (I-V Curve): This curve is exponential. A small increase in voltage beyond the knee (around 2V) causes a large increase in current. This underscores why LEDs must be driven by a current-limited source, not a simple voltage source, to prevent thermal runaway.
• Luminous Intensity vs. Forward Current (I-L Curve): For AlInGaP LEDs, light output is approximately linear with current over a wide range (e.g., from 1mA to 20-30mA). This allows brightness to be easily controlled via pulse-width modulation (PWM) or analog current adjustment.
• Luminous Intensity vs. Ambient Temperature: The light output of LEDs decreases as junction temperature increases. While the derating curve for current is provided, the efficiency (lumens per watt) also drops with temperature. This must be considered in high-temperature environments.
• Spectral Shift vs. Current/Temperature: The peak and dominant wavelengths of an LED can shift slightly with changes in drive current and junction temperature. For this hyper-red LED, the shift is usually minor but can be relevant for precise colorimetric applications.

5. Mechanical & Package Information

5.1 Package Dimensions

The device features a standard dual-in-line package (DIP) format suitable for through-hole PCB mounting. The digit height is specified as 0.28 inches (7.0 mm). The dimensional drawing indicates a 10-pin configuration. All dimensions are provided in millimeters with a standard tolerance of ±0.25 mm unless otherwise noted. Key mechanical features include the overall length, width, and height of the package, the spacing between the two digits, the segment size and spacing, and the pin diameter and spacing (pitch). The exact footprint is essential for PCB layout.

5.2 Pin Connection & Internal Circuit

The device has a \"Duplex Common Anode\" configuration with a \"Right Hand Decimal\" point. This is detailed in the pin connection table:

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

The \"common anode\" structure means all the LED segments within one digit share a common positive connection (the anode). To illuminate a specific segment, its corresponding cathode pin must be connected to a lower voltage (ground) while the common anode for that digit is held at a positive voltage. The internal circuit diagram would show two separate common anode nodes (one for each digit) with the cathodes of the corresponding segments (A-G, DP) connected to their respective pins. This configuration is ideal for multiplexing.

6. Soldering & Assembly Guidelines

Adherence to the specified soldering profile is paramount to ensure reliability.

• Process: The device is suitable for wave soldering or manual soldering processes.
• Critical Parameter: The maximum solder temperature is 260°C, and the maximum time at that temperature is 3 seconds. This is measured 1.6mm below the seating plane (i.e., at the PCB level, not at the iron tip).
• Thermal Stress: Exceeding these limits can cause several failures: melting or deformation of the plastic package, degradation of the internal epoxy lens, breaking of the delicate gold wire bonds connecting the LED chip to the lead frame, or thermal shock to the semiconductor chip itself.
• Recommendation: Use a temperature-controlled soldering iron. For wave soldering, ensure the conveyor speed and preheat zones are calibrated so the component body does not exceed the thermal limit. Allow adequate cooling time before handling.
• Cleaning: If cleaning is necessary, use solvents compatible with the LED's epoxy package. Avoid ultrasonic cleaning as the high-frequency vibrations can damage the internal wire bonds.
• Storage: Store in a dry, anti-static environment within the specified temperature range (-35°C to +85°C) to prevent moisture absorption (which can cause \"popcorning\" during reflow) and electrostatic discharge damage.

7. Application Suggestions

7.1 Typical Application Circuits

The common anode configuration lends itself perfectly to multiplexed drive schemes, which drastically reduce the number of required microcontroller I/O pins.

• Multiplexing (Time-Division): Connect the two common anodes (Pins 6 & 9) to separate microcontroller pins configured as outputs. Connect all segment cathodes (Pins 1-5, 7, 8, 10) to microcontroller pins via current-limiting resistors (or to the outputs of a dedicated LED driver IC like a 74HC595 shift register or a MAX7219). The software rapidly alternates between turning on Digit 1's anode (and driving the segments for the first digit's number) and Digit 2's anode (and driving the segments for the second digit's number). At a high enough frequency (e.g., >100 Hz), persistence of vision makes both digits appear continuously lit. This is the most common and efficient driving method.
• Current Limiting: Whether using multiplexing or static drive, a current-limiting resistor is mandatory for each segment cathode path. The resistor value is calculated using Ohm's Law: R = (V_supply - V_F) / I_F. For a 5V supply, a typical V_F of 2.6V, and a desired I_F of 10mA: R = (5 - 2.6) / 0.01 = 240 Ω. A 220 Ω or 270 Ω resistor would be suitable. The resistor's power rating should be at least I_F² * R.
• Driver ICs: For systems with many digits or to offload processing from the main microcontroller, dedicated LED driver ICs are highly recommended. They handle multiplexing, current regulation, and sometimes even digit decoding (converting a number 0-9 to the correct segment pattern).

7.2 Design Considerations

• Viewing Angle & Readability: The datasheet claims a \"wide viewing angle\" and \"high contrast.\" The gray face/white segment design contributes to this. For optimal readability, consider the display's orientation relative to the expected viewer position.
• Brightness Control: Brightness can be controlled globally by adjusting the drive current (within limits) or, more commonly and efficiently, by using PWM on the segment or anode drivers. PWM allows for dimming without changing the color point significantly.
• Power Sequencing & Protection: Ensure the circuit does not apply reverse voltage or excessive current during power-up/power-down transients. In multiplexed circuits, ensure software never enables two anodes simultaneously with conflicting segment patterns, as this could create a low-impedance path between power and ground.
• Heat Dissipation: While the power per segment is low, the total power for a fully lit digit (all 7 segments + DP) at 20mA could be around 8 segments * 2.6V * 0.02A = 0.416W. Ensure adequate ventilation if multiple displays are used in a confined space.

8. Technical Comparison & Differentiation

Compared to other seven-segment display technologies, this AlInGaP hyper-red LED display offers distinct advantages:

• vs. Older GaAsP/GaP Red LEDs: AlInGaP technology provides significantly higher luminous efficiency (more light output per unit of electrical power), resulting in the \"high brightness\" claimed. It also offers better color saturation (a deeper, purer red) and typically better stability over temperature and lifetime.
• vs. Liquid Crystal Displays (LCDs): LEDs are emissive, meaning they produce their own light. This makes them clearly visible in low-light or no-light conditions without a backlight, unlike reflective LCDs. They also have a much faster response time and a wider operating temperature range. The trade-off is higher power consumption for a given area of illumination.
• vs. Other LED Colors (e.g., Standard Red, Green, Blue): The hyper-red (650nm) wavelength is near the peak sensitivity of the human eye's photopic (bright light) vision, making it appear very bright for a given radiant power. It also has excellent atmospheric penetration, which can be a factor for long-distance viewing.
• Key Product Features Recap: The combination of 0.28\" digit height, continuous uniform segments (no visible breaks in the segment shape), low power requirement, high brightness/contrast, wide viewing angle, and solid-state reliability defines this product's market position as a robust, high-performance numeric display for industrial, commercial, and hobbyist applications.

9. Frequently Asked Questions (Based on Technical Parameters)

• Q: Can I drive this display directly from a 5V microcontroller pin? A: No. A microcontroller pin can typically source or sink 20-40mA, which is within the segment's current limit. However, the pin's output voltage is 5V (or 3.3V), and the LED's forward voltage is only ~2.6V. Connecting them directly would attempt to force a very high, destructive current through the LED. You must always use a series current-limiting resistor.
• Q: Why is there a \"Typical\" and \"Maximum\" forward voltage? A: Due to manufacturing variations, the actual V_F of individual LEDs varies. The driver circuit must be designed to accommodate the maximum V_F to ensure all units light up. If your supply voltage is too close to the typical V_F, units with higher V_F may be dim or not light at all.
• Q: What does \"categorized for luminous intensity\" mean for my design? A: It means displays you purchase may have different brightness levels. If you are using multiple displays side-by-side and require uniform appearance, you should either specify a tight brightness bin from your supplier, purchase from the same manufacturing lot, or implement individual brightness calibration/compensation in your drive circuitry (e.g., using PWM with different duty cycles per display).
• Q: How do I calculate the appropriate current-limiting resistor? A: Use the formula: R = (V_supply - V_{F_max}) / I_{F_desired}. Use V_{F_max} (2.6V) for a conservative design that works for all units. Choose I_{F_desired} based on your required brightness, but do not exceed the continuous current rating (25mA at 25°C, derated for temperature).
• Q: Can I use this outdoors? A: The operating temperature range (-35°C to +85°C) suggests it can handle a wide range of ambient conditions. However, the plastic package may not be rated for prolonged UV exposure, which can cause yellowing and reduced light output. For direct outdoor sunlight use, a display with a UV-stable package or a protective filter is recommended.

10. Practical Design Case Study

Scenario: Designing a simple two-digit count-up timer for a laboratory instrument, powered by a 5V rail, controlled by a microcontroller with limited I/O pins.

Implementation:

1. Circuit: The two common anodes are connected to two separate GPIO pins on the microcontroller, configured as digital outputs. The eight segment cathodes (A-G and DP) are connected to eight other GPIO pins, each through a 220Ω current-limiting resistor. No external driver IC is used to minimize cost and complexity.
2. Software: The microcontroller maintains two variables for the tens and units digits (0-9). A timer interrupt fires every 5ms. In the interrupt service routine:
   • It turns off both anode pins (to prevent ghosting).
   • It looks up the segment pattern for the current \"active digit\" (alternating between tens and units).
   • It sets the eight segment cathode pins to the correct pattern (0=on, 1=off for common anode).
   • It turns on the anode pin for the active digit.
   • It toggles the active digit for the next cycle.
   This creates a 100Hz multiplexing frequency (2 digits * 5ms = 10ms per full cycle), which is flicker-free.
3. Brightness: The drive current is approximately (5V - 2.6V) / 220Ω ≈ 10.9mA per segment, which is safe and provides good brightness. If dimming is needed, the software can implement PWM by skipping some of the 5ms display cycles.
4. Result: A reliable, clear, two-digit display using only 10 microcontroller I/O pins, with minimal external components.

11. Operating Principle

The device operates on the principle of electroluminescence in a semiconductor PN junction. The active region is composed of AlInGaP layers. When a forward bias voltage exceeding the junction's built-in potential is applied (approximately 2.1-2.6V), electrons from the N-type material and holes from the P-type material are injected into the active region. There, they recombine radiatively; the energy released from the recombination of an electron-hole pair is emitted as a photon. The specific composition of the AlInGaP alloy determines the bandgap energy, which in turn dictates the wavelength (color) of the emitted light—in this case, approximately 650 nm (red). The non-transparent GaAs substrate absorbs photons emitted downwards, improving overall efficiency and contrast by reducing internal loss and preventing light emission from the back of the chip. The light is then shaped and directed by the epoxy lens of the package to form the recognizable seven-segment pattern.

12. Technology Trends

While this specific product represents mature and reliable technology, the broader field of display technology continues to evolve. Trends influencing numeric displays include:

• Increased Integration: Modern solutions often integrate the LED dice, current drivers, multiplexing logic, and sometimes even a microcontroller interface (I2C, SPI) into a single \"intelligent display\" module, simplifying design and reducing board space.
• Advancements in Efficiency: Ongoing research in semiconductor materials, including further refinements to AlInGaP and the development of materials for other colors, continues to push the limits of luminous efficacy (lumens per watt), allowing for brighter displays at lower power or reduced heat generation.
• Miniaturization & New Form Factors: While through-hole DIP packages remain popular for robustness and ease of prototyping, surface-mount device (SMD) versions of seven-segment displays are common, enabling smaller, automated assembly. Flexible and transparent substrate technologies are also emerging for novel applications.
• Competition from Alternative Technologies: For applications requiring more information (text, graphics) or lower power consumption in well-lit conditions, organic LED (OLED) and advanced reflective display technologies are alternatives, though traditional LED seven-segment displays maintain a strong position in applications prioritizing simplicity, ruggedness, high brightness, and low cost for numeric-only output.