LTD-2701JD LED Display Datasheet - 0.28-inch Digit Height - Hyper Red - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTD-2701JD 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 devices and equipment. The core technology utilizes AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material to produce a Hyper Red emission, characterized by high brightness and excellent color purity. The device features a gray face with white segments, enhancing contrast and readability under various lighting conditions. It is designed as a common cathode type, which is a standard configuration for simplifying multiplexing drive circuits in multi-digit applications.

1.1 Key Features and Core Advantages

• Digit Height: 0.28 inches (7.0 mm), offering a balanced size for good visibility without excessive space consumption.
• Segment Uniformity: Continuous, uniform segments ensure consistent character appearance across both digits.
• Power Efficiency: Low power requirement, making it suitable for battery-powered or energy-conscious applications.
• Optical Performance: High brightness and high contrast ratio contribute to excellent character legibility.
• Viewing Angle: Wide viewing angle allows for readability from various positions.
• Reliability: Solid-state construction offers long operational life and resistance to shock and vibration.
• Binning: Devices are categorized (binned) for luminous intensity, allowing for matched brightness in multi-display setups.
• Environmental Compliance: Lead-free package compliant with RoHS (Restriction of Hazardous Substances) directives.

1.2 Target Market and Applications

This display is intended for use in ordinary electronic equipment. Typical application areas include, but are not limited to:

• Test and measurement instruments (multimeters, power supplies).
• Consumer appliances (microwaves, ovens, washing machines).
• Industrial control panels and timers.
• Communication equipment status displays.
• Automotive aftermarket accessories (e.g., voltage monitors).
• Point-of-sale terminals and basic numeric readouts.

It is specifically noted that consultation is required for applications demanding exceptional reliability where failure could jeopardize life or health, such as in aviation, medical, or critical safety systems.

2. Technical Specifications and Objective Interpretation

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 under pulsed conditions (1/10 duty cycle, 0.1 ms pulse width). This rating is for short-duration pulses, not continuous operation.
• Continuous Forward Current per Segment: 25 mA at 25°C. This current must be derated linearly by 0.33 mA/°C as ambient temperature (Ta) rises above 25°C to prevent thermal runaway.
• Operating & Storage Temperature Range: -35°C to +85°C. The device can withstand these extremes but optical performance will vary with temperature.
• Solder Condition: 260°C for 3 seconds, measured 1/16 inch (approx. 1.6 mm) below the seating plane. This guides wave or reflow soldering processes.

2.2 Electrical & Optical Characteristics

These are typical performance parameters measured at Ta=25°C under specified test conditions.

• Average Luminous Intensity (I_V): 200-600 µcd at I_F=1mA. This wide range indicates the effect of the binning process; designers should account for the minimum value for visibility calculations.
• Peak Emission Wavelength (λ_p): 650 nm. This is the wavelength at which the emitted optical power is greatest.
• Dominant Wavelength (λ_d): 639 nm. This is the single wavelength perceived by the human eye to match the color of the light, with a tolerance of ±1 nm.
• Spectral Line Half-Width (Δλ): 20 nm. This defines the spectral purity; a narrower width indicates a more monochromatic color.
• Forward Voltage per Chip (V_F): 2.1V (Min), 2.6V (Typ) at I_F=20mA, with a tolerance of ±0.1V. This is critical for driver circuit design, especially when multiplexing multiple digits, to ensure consistent current.
• Reverse Current (I_R): 100 µA maximum at V_R=5V. The datasheet explicitly warns that reverse voltage is for test purposes only and continuous reverse bias operation must be avoided.
• Luminous Intensity Matching Ratio: 2:1 maximum for similar light areas at I_F=10mA. This specifies the maximum allowable brightness variation between segments within a display.
• Cross Talk: ≤ 2.5%. This refers to unwanted illumination of a non-driven segment due to electrical leakage or optical coupling.

2.3 Binning System Explanation

The datasheet states the product is \"Categorized for Luminous Intensity.\" This implies a binning process where LEDs are sorted based on measured light output (in µcd) at a standard test current (likely 1mA or 10mA). Using displays from the same intensity bin in an assembly is strongly recommended to avoid noticeable brightness differences (hue unevenness) between adjacent units. Designers should specify the required bin or work with suppliers to ensure consistency for multi-display applications.

3. Mechanical and Packaging Information

3.1 Package Dimensions

The display conforms to a standard through-hole DIP (Dual In-line Package) format. Key dimensional notes include:

• All dimensions are in millimeters (mm).
• Standard tolerance is ±0.25 mm unless otherwise specified.
• Pin tip shift tolerance is ±0.4 mm, important for PCB hole alignment.
• Allowable defects on the display face: foreign material on segment ≤10 mils, ink contamination ≤20 mils, bubbles in segment ≤10 mils.
• Bending of the reflector is limited to ≤1% of its length.

3.2 Pin Connection and Polarity Identification

The device has 10 pins in a single row. The pinout is as follows:

• Pin 1: Anode for segment E
• Pin 2: Anode for segment D
• Pin 3: Anode for segment C
• Pin 4: Anode for segment G (center segment)
• Pin 5: Anode for Decimal Point (DP)
• Pin 6: Common Cathode for Digit 2 (right-hand digit)
• Pin 7: Anode for segment A
• Pin 8: Anode for segment B
• Pin 9: Common Cathode for Digit 1 (left-hand digit)
• Pin 10: Anode for segment F

The \"Rt. Hand Decimal\" description confirms the decimal point is associated with the right-hand digit. The common cathode configuration means all LED cathodes for one digit are connected internally. To illuminate a segment, a positive voltage must be applied to its respective anode pin while the corresponding digit's common cathode pin is pulled to ground.

3.3 Internal Circuit Diagram

The internal diagram shows two independent sets of seven LEDs (plus a decimal point LED), each set sharing a common cathode connection (Pins 6 and 9). This structure is fundamental for multiplexing: by sequentially enabling one cathode (digit) at a time and presenting the pattern for that digit on the anode lines, multiple digits can be controlled with fewer I/O pins.

4. Performance Curve Analysis

The datasheet references \"Typical Electrical / Optical Characteristics Curves.\" While the specific graphs are not detailed in the provided text, typical curves for such devices would include:

• I-V (Current-Voltage) Curve: Shows the exponential relationship between forward voltage (V_F) and forward current (I_F). The curve will shift with temperature.
• Luminous Intensity vs. Forward Current: Shows that light output is approximately linear with current over a range, but will saturate at higher currents and degrade faster due to heat.
• Luminous Intensity vs. Ambient Temperature: Demonstrates the decrease in light output as junction temperature increases, highlighting the need for thermal management and current derating.
• Spectral Distribution: A plot of relative intensity vs. wavelength, showing the peak at ~650nm and the ~20nm half-width.

These curves are essential for designing drivers that provide stable brightness over the intended operating temperature range.

5. Soldering, Assembly, and Storage Guidelines

5.1 Soldering and Assembly

• Follow the specified solder profile (260°C for 3 seconds).
• Avoid using unsuitable tools or methods that apply abnormal force to the display body.
• If a decorative film is applied, avoid having it in direct contact with a front panel/cover, as external force may shift it.

5.2 Storage Conditions

Proper storage is critical to prevent pin oxidation.

• Standard LED Display (Through-Hole): In original packaging. Temperature: 5°C to 30°C. Humidity: Below 60% RH. Long-term storage outside these conditions may require re-plating of oxidized pins. If the moisture barrier bag is opened for >6 months, baking at 60°C for 48 hours is recommended before use, with assembly within one week.
• SMD LED Displays (Note for reference): In sealed bag: 5-30°C, <60% RH. Once opened: Same conditions, but must be used within 168 hours (7 days, MSL Level 3).

6. Application Design Considerations and Cautions

6.1 Driver Circuit Design

• Constant Current Drive: Highly recommended over constant voltage drive to ensure consistent luminous intensity regardless of V_F variations between segments and over temperature.
• Current Limiting: The circuit must limit current to within the continuous rating (25mA at 25°C, derated). Exceeding this causes rapid degradation.
• Voltage Range: The driver must accommodate the full V_F range (approx. 2.0V to 2.7V per segment) to deliver the intended current.
• Reverse Voltage Protection: The circuit should protect against reverse voltages or transients during power cycling to prevent metal migration and increased leakage.
• Thermal Management: Consider maximum ambient temperature (T_a) to select a safe operating current. Heat sinking may be necessary in high-T_a environments.

6.2 Environmental and Handling Cautions

• Avoid rapid ambient temperature changes in humid environments to prevent condensation on the display.
• Select displays from the same luminous intensity bin when using two or more in one assembly to ensure uniform brightness.

7. Technical Comparison and Differentiation

Compared to older GaAsP or GaP LED technologies, the AlInGaP (Aluminum Indium Gallium Phosphide) used in the LTD-2701JD offers significant advantages:

• Higher Efficiency & Brightness: AlInGaP provides superior luminous efficacy, resulting in higher brightness for the same drive current.
• Better Color Purity: The Hyper Red emission (639-650nm dominant) is more saturated and visually distinct than standard red LEDs.
• Improved Temperature Stability: While all LEDs lose efficiency with heat, AlInGaP generally has better performance retention compared to older materials.
• The common cathode design with separate digit cathodes is a standard but effective approach for multiplexing, differentiating it from common anode types or displays with internally multiplexed controllers.

8. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this display directly from a 5V microcontroller pin?
A: No. Without a current-limiting resistor, connecting 5V directly to an anode would likely destroy the LED due to excessive current. You must use a series resistor or, preferably, a constant current driver. The resistor value depends on your supply voltage, the LED's V_F, and the desired I_F.

Q: Why is constant current drive recommended?
A: LED brightness is primarily a function of current, not voltage. The forward voltage (V_F) can vary from chip to chip and decreases with rising temperature. A constant current source ensures stable brightness by automatically adjusting the voltage to maintain the set current, compensating for these variations.

Q: What does \"1/10 Duty Cycle, 0.1ms Pulse Width\" mean for the Peak Current rating?
A: This means you can briefly pulse the LED with up to 90mA, but the pulse must be no wider than 0.1 milliseconds, and the average current over time must not exceed the equivalent of a 1/10 duty cycle (e.g., 0.1ms on, 0.9ms off). This is not for continuous illumination.

Q: How do I control the two digits independently?
A> You use multiplexing. In a cycle: 1) Set the anode pins (1,2,3,4,5,7,8,10) to the pattern for Digit 1. 2) Pull Cathode Pin 9 (Digit 1) low (ground) while keeping Cathode Pin 6 (Digit 2) high (disconnected). 3) Illuminate for a short time (e.g., 5ms). 4) Turn off Digit 1. 5) Set the anodes to the pattern for Digit 2. 6) Pull Cathode Pin 6 low and Pin 9 high. 7) Illuminate. Repeat this cycle rapidly (>60Hz) to create the illusion of both digits being on continuously.

9. Practical Design and Usage Case

Case: Designing a Simple Digital Voltmeter Readout (0-99V).

1. Component Selection: The LTD-2701JD is chosen for its 2-digit capability, good brightness, and through-hole package for prototyping.
2. Driver Circuit: A microcontroller (e.g., an ATmega328P) is used. Its I/O pins cannot source/sink enough current for all segments at once. Therefore, a multiplexing scheme is implemented using two NPN transistors (e.g., 2N3904) to sink the cathode currents for Digits 1 and 2. The segment anodes are connected to the microcontroller via current-limiting resistors (e.g., 150Ω for a 5V supply, targeting ~20mA per segment: R = (5V - 2.6V) / 0.02A ≈ 120Ω, using 150Ω for safety).
3. Software: The firmware reads the voltage via an ADC, converts it to two BCD digits, and drives the display using a timer interrupt for multiplexing at 100Hz.
4. Considerations: The forward voltage tolerance means brightness may vary slightly between segments. Using constant current drivers (like dedicated LED driver ICs) instead of resistors would improve uniformity. The storage advice is followed by ordering small quantities to avoid long-term inventory.

10. Operating Principle Introduction

A light-emitting diode (LED) is a semiconductor p-n junction diode. When a forward voltage exceeding the junction's built-in potential is applied, electrons from the n-region and holes from the p-region are injected across the junction. When these charge carriers recombine in the active region, energy is released in the form of photons (light). The specific wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material. AlInGaP has a bandgap corresponding to red light. In a seven-segment display, multiple individual LED chips are mounted and wired to form the standard segments (A-G and DP). The common cathode configuration internally connects all the cathodes of the LEDs belonging to one digit.

11. Technology Trends

The LED display industry continues to evolve. While through-hole displays like the LTD-2701JD remain relevant for prototyping, repairs, and certain applications, broader trends include:

• Miniaturization & SMD Dominance: Surface-mount device (SMD) packages are becoming standard for automated assembly, offering smaller size and lower profile.
• Integrated Controllers: Displays with built-in driver ICs (like MAX7219 compatible modules) simplify microcontroller interfacing by handling multiplexing and decoding internally.
• Higher Efficiency Materials: Ongoing development of materials like InGaN for blue/green and improved AlInGaP and phosphor-converted white LEDs push efficiency (lumens per watt) higher.
• Flexible and Novel Form Factors: Developments in flexible substrates and micro-LEDs enable new display shapes and ultra-high densities.

For its category, the LTD-2701JD represents a mature, reliable solution based on well-understood AlInGaP technology, suitable where its specific form factor and electrical interface are required.