LTC-2621JD-04 LED Display Datasheet - 0.28-inch Digit Height - Hyper Red (650nm) - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTC-2621JD-04 is a compact, high-performance triple-digit seven-segment display module designed for applications requiring clear numeric readouts. Its primary function is to provide a visual numeric output in electronic devices. The core advantage of this device lies in its utilization of advanced AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for the LED chips, which are fabricated on a non-transparent GaAs substrate. This combination results in the characteristic \"Hyper Red\" emission. The display features a gray face with white segments, enhancing contrast and readability. The target market includes industrial instrumentation, consumer electronics, test and measurement equipment, and any embedded system where a reliable, low-power numeric display is needed.

1.1 Key Features and Advantages

• Digit Height: 0.28 inches (7.0 mm), offering a good balance between size and visibility.
• Segment Design: Continuous uniform segments for excellent character appearance and aesthetics.
• Power Efficiency: Low power requirement, making it suitable for battery-powered or energy-conscious applications.
• Optical Performance: High brightness and high contrast ratio ensure legibility under various lighting conditions.
• Viewing Angle: Wide viewing angle allows the display to be read from off-axis positions.
• Reliability: Solid-state reliability with no moving parts, leading to long operational life.
• Quality Control: Devices are categorized for luminous intensity, ensuring consistency in brightness across production batches.

2. Technical Specifications Deep Dive

This section provides a detailed, objective analysis of the device's key technical parameters as defined in the datasheet.

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. This limits the maximum continuous power that can be dissipated as heat in a single segment.
• Peak Forward Current per Segment: 90 mA maximum, but only under specific pulsed conditions: 1/10 duty cycle and 0.1 ms pulse width. This rating is for multiplexing or short-duration high-brightness pulses.
• Continuous Forward Current per Segment: 25 mA maximum at 25°C. This current derates linearly at a rate of 0.33 mA/°C as ambient temperature (Ta) increases above 25°C. For example, at 85°C, the maximum allowable continuous current would be approximately: 25 mA - ((85°C - 25°C) * 0.33 mA/°C) = 5.2 mA.
• Reverse Voltage per Segment: 5 V maximum. Exceeding this can cause junction breakdown.
• Operating Temperature Range: -35°C to +85°C. The device is designed to function within this ambient temperature range.
• Storage Temperature Range: -35°C to +85°C.
• Solder Temperature: Maximum 260°C for a maximum of 3 seconds, measured 1.6mm below the seating plane. This is critical for wave or reflow soldering processes to prevent thermal damage.

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

These are the typical operating parameters under specified test conditions.

• Average Luminous Intensity (I_V): Ranges from 200 μcd (min) to 600 μcd (max), with a typical value implied. Measured at a forward current (I_F) of 1 mA. This is the key parameter for perceived brightness.
• Peak Emission Wavelength (λ_p): 650 nm (typical). This is the wavelength at which the spectral output is strongest, defining the \"Hyper Red\" color.
• Spectral Line Half-Width (Δλ): 20 nm (typical). This indicates the spectral purity; a smaller value means a more monochromatic light. 20nm is typical for AlInGaP red LEDs.
• Dominant Wavelength (λ_d): 639 nm (typical). This is the single wavelength perceived by the human eye that matches the color of the LED, often slightly different from the peak wavelength.
• Forward Voltage per Segment (V_F): Ranges from 2.1 V (min) to 2.6 V (max), with a typical value of 2.6 V at I_F=20 mA. This is crucial for designing the current-limiting circuitry.
• Reverse Current per Segment (I_R): 100 μA maximum at a reverse voltage (V_R) of 5V.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 maximum. This specifies the maximum allowable ratio between the brightest and dimmest segment/digit within a device, ensuring uniformity.

Note on Measurement: Luminous intensity is measured using a sensor and filter that approximates the CIE photopic eye-response curve, ensuring the measurement correlates with human brightness perception.

3. Binning and Categorization System

The datasheet explicitly states that devices are \"categorized for luminous intensity.\" This implies a binning process.

• Luminous Intensity Binning: The wide range specified for I_V (200-600 μcd) suggests production parts are tested and sorted into different intensity bins. Designers can select bins for applications requiring specific brightness levels or tight uniformity across multiple displays.
• Forward Voltage: The specified range (2.1-2.6V) may also lead to voltage binning, which can be important for power supply design in large arrays.
• Wavelength: While typical values are given for λ_p and λ_d, tight-tolerance bins for specific color coordinates might be available, though not detailed in this summary datasheet.

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 current, typically in a sub-linear fashion, highlighting efficiency roll-off at high currents.
• Forward Voltage vs. Forward Current: Shows the diode's I-V characteristic, essential for calculating series resistor values or designing constant-current drivers.
• Relative Luminous Intensity vs. Ambient Temperature: Demonstrates how light output decreases as temperature increases, a critical factor for thermal management.
• Spectral Distribution: A plot of relative intensity vs. wavelength, showing the peak at ~650nm and the 20nm half-width.

5. Mechanical & Package Information

5.1 Package Dimensions

The device has a standard LED display package. All dimensions are in millimeters (mm). The general tolerance is ±0.25 mm (≈±0.01 inches) unless a specific feature has a different callout. The exact dimensional drawing is referenced in the datasheet but not detailed here. Key aspects would include overall length, width, and height, digit spacing, lead spacing, and lead dimensions.

5.2 Pin Connection and Internal Circuit

The LTC-2621JD-04 is a multiplex common anode device. This means the anodes of each digit are connected together internally per digit, while the cathodes for each segment type (A-G, DP) are common across digits.

Pinout (16-pin package):

• Pin 1: Cathode D
• Pin 2: Common Anode (Digit 1)
• Pin 3: Cathode D.P. (Decimal Point)
• Pin 4: Cathode E
• Pin 5: Common Anode (Digit 2)
• Pin 6: Cathode C
• Pin 7: Cathode G
• Pin 8: Common Anode (Digit 3)
• Pin 9: No Connection
• Pin 10: No Pin
• Pin 11: No Pin
• Pin 12: Cathode B
• Pin 13: Common Anode for L1, L2, L3 (likely colon or other markers)
• Pin 14: No Pin
• Pin 15: Cathode A
• Pin 16: Cathode F

Internal Circuit Diagram: The schematic shows three common anode nodes (one per digit) connected to pins 2, 5, and 8. Each segment cathode (A-G, DP) is a single node connected to its respective pin, with the LED for that segment in each digit connected between the digit's common anode and the shared segment cathode. This structure is ideal for multiplexed driving.

6. Soldering & Assembly Guidelines

The key guideline provided is the absolute maximum rating for soldering: 260°C for a maximum of 3 seconds, measured 1.6mm below the seating plane.

• Reflow Soldering: A standard lead-free reflow profile with a peak temperature not exceeding 260°C and time above 240°C kept very short should be compatible. The 1.6mm measurement point is critical for profile verification.
• Wave Soldering: Possible, but contact time and temperature must be carefully controlled to meet the 260°C/3s limit.
• Hand Soldering: Use a temperature-controlled iron. Apply heat to the PCB pad, not directly to the LED lead, and complete the joint quickly.
• Storage Conditions: Store in a dry, anti-static environment within the specified storage temperature range (-35°C to +85°C). Moisture-sensitive devices may require baking before use if exposed to humid environments.

7. Application Suggestions

7.1 Typical Application Circuits

The multiplex common anode configuration requires a driver circuit. A typical design uses:

• Microcontroller or Driver IC: To control timing and data.
• Digit Drivers: PNP transistors or dedicated high-side switches to sink current to the common anode pins (2, 5, 8, 13).
• Segment Drivers: The microcontroller ports or low-side driver ICs (like a 74HC595 shift register with open-drain outputs or a dedicated LED driver) to source current from the segment cathode pins (1, 3, 4, 6, 7, 12, 15, 16).
• Current-Limiting Resistors: One resistor is required per segment cathode line (not per segment LED) when using a constant-voltage drive. The resistor value is calculated using R = (V_supply - V_F) / I_F. For a 5V supply and I_F=10 mA with V_F=2.6V, R = (5 - 2.6) / 0.01 = 240 Ω. Constant-current drivers are preferred for better uniformity.

7.2 Design Considerations

• Multiplexing Frequency: Use a refresh rate high enough to avoid visible flicker (typically >60 Hz per digit, so >180 Hz scan rate for 3 digits).
• Peak Current vs. Brightness: To achieve high average brightness while staying within the continuous current rating, use multiplexing with a higher peak current (up to the 90mA pulsed rating). For example, driving at 1/3 duty cycle (3 digits) with 30mA peak gives an average of 10mA per segment.
• Thermal Management: Ensure the PCB layout allows for heat dissipation, especially if driving near maximum ratings. High ambient temperatures will require current derating.
• ESD Protection: LEDs are sensitive to electrostatic discharge. Handle with appropriate ESD precautions during assembly.

8. Technical Comparison & Differentiation

Compared to older technologies like standard GaP red LEDs or larger digit displays, the LTC-2621JD-04 offers specific advantages:

• AlInGaP vs. GaAsP/GaP: AlInGaP technology provides significantly higher luminous efficiency, resulting in higher brightness and better visibility in ambient light. The \"Hyper Red\" color is also more vibrant.
• Small Digit Height (0.28\"): Offers a space-saving solution compared to 0.5\" or larger digits, suitable for compact devices, while remaining larger and more legible than very small SMD 7-segment modules.
• Gray Face/White Segments: This finish provides a high contrast ratio when the segments are off, improving overall display aesthetics and readability compared to all-black or all-gray faces.
• Categorized Intensity: This binning provides a level of quality control and predictability not always present in lower-cost displays.

9. Frequently Asked Questions (Based on Technical Parameters)

Q1: What is the purpose of the \"common anode\" configuration?
A1: Common anode simplifies multiplexing. You turn on one digit at a time by applying a positive voltage to its anode pin while grounding the cathodes for the segments you want lit. This reduces the number of driver pins needed from (7 segments + 1 DP) * 3 digits = 24 down to 3 anodes + 8 cathodes = 11.

Q2: How do I calculate the resistor value for driving this display?
A2: Use Ohm's Law: R = (V_supply - V_F) / I_F. Use the maximum V_F (2.6V) from the datasheet to ensure enough voltage drop across the resistor even for high-V_F parts. Choose I_F based on desired brightness, staying within the continuous (25mA at 25°C) or pulsed ratings.

Q3: Can I drive this display with a 3.3V microcontroller?
A3: Possibly, but with limitations. If V_F is 2.6V, only 0.7V remains for the current-limiting resistor at 3.3V. For a 10mA current, R=70Ω. This low resistance value is feasible, but variations in V_F will cause significant brightness variation. A constant-current driver or a boost converter to provide a higher supply voltage (like 5V) is recommended for stable performance.

Q4: What does \"Luminous Intensity Matching Ratio 2:1\" mean?
A4: It means that within a single LTC-2621JD-04 unit, the brightest segment or digit will be no more than twice as bright as the dimmest segment or digit when measured under the same conditions (I_F=1mA). This ensures visual uniformity.

10. Design and Usage Case Study

Scenario: Designing a Portable Digital Multimeter Display
The LTC-2621JD-04 is an excellent candidate. Its 0.28\" digits are highly legible. The low power requirement is critical for battery life. The multiplexed design minimizes the microcontroller pin count. A design would use the microcontroller's timer to cycle through digits 1, 2, and 3 at ~200 Hz. The segment data would be looked up from a table. To conserve power, the display brightness (I_F) could be dynamically adjusted based on ambient light sensed by a phototransistor. The high contrast gray/white face ensures readability in both dark and bright workshop environments. The AlInGaP Hyper Red LEDs provide a clear, attention-grabbing readout.

11. Technology Principle Introduction

The LTC-2621JD-04 is based on AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material grown epitaxially on a GaAs (Gallium Arsenide) substrate. The \"non-transparent\" GaAs substrate is used because it absorbs the emitted light, but the AlInGaP active layer has high enough internal efficiency that sufficient light escapes from the top of the chip. Electrons and holes are injected into the active region when a forward voltage is applied across the p-n junction. Their recombination releases energy in the form of photons. The specific composition of the AlInGaP alloy determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, approximately 650 nm (red). The seven-segment format is created by placing multiple tiny LED chips (or a single chip with multiple isolated junctions) under a patterned optical lens/diffuser to form the recognizable numeric segments.

12. Technology Trends and Context

While this specific device uses through-hole technology, the underlying AlInGaP material system remains highly relevant. Trends in display technology include:

• Miniaturization: A move towards surface-mount device (SMD) packages for automated assembly, even for multi-digit displays.
• Integration: Combining the LED array with the driver IC in a single package or module to simplify design.
• Advanced Materials: Ongoing research into materials like GaN-based (for blue/green/white) and AlInGaP for higher efficiency and new colors. For red/orange/yellow, AlInGaP is the dominant high-performance technology.
• Application Shift: While discrete 7-segment displays are mature, they remain vital in applications where simplicity, cost, reliability, and high visibility are paramount (industrial controls, appliances, instrumentation). They coexist with newer technologies like OLEDs and LCDs, each serving different market niches based on factors like viewing angle, sunlight readability, power consumption, and cost.

The LTC-2621JD-04 represents a robust, well-established solution within this evolving landscape, offering a proven balance of performance, reliability, and cost for its intended applications.