LTC-2621JG LED Display Datasheet - 0.28-inch Digit Height - Green Color - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTC-2621JG is a compact, high-performance triple-digit numeric display module designed for applications requiring clear, bright numerical readouts. Its primary function is to visually represent three digits of numerical data using solid-state LED technology. The core technology employed is AlInGaP (Aluminum Indium Gallium Phosphide) epitaxial layers grown on a GaAs substrate, which is specifically engineered to produce high-efficiency green light emission. This material system is chosen for its superior luminous efficiency and color purity compared to older technologies like standard GaP, resulting in excellent brightness and character appearance even at lower drive currents. The device is categorized as a common anode, multiplexed display, meaning all the anodes for each digit are connected together internally, allowing for efficient control of multiple digits with a reduced number of microcontroller I/O pins through time-division multiplexing.

1.1 Key Features and Advantages

The display offers several distinct advantages that make it suitable for a wide range of industrial, consumer, and instrumentation applications.

• Optical Performance: It features a digit height of 0.28 inches (7.0 mm) with continuous, uniform segments, eliminating gaps for a clean, professional appearance. The combination of high brightness and high contrast ensures excellent readability under various ambient lighting conditions. A wide viewing angle allows the display to be read clearly from off-axis positions.
• Electrical Efficiency: The device has low power requirements, contributing to energy-efficient system design. The use of AlInGaP technology provides high luminous intensity with relatively low forward current.
• Reliability and Consistency: As a solid-state device, it offers high reliability with no moving parts and resistance to shock and vibration. The units are categorized for luminous intensity, ensuring consistent brightness levels between different displays, which is critical for multi-unit products.
• Environmental Compliance: The package is lead-free, complying with RoHS (Restriction of Hazardous Substances) directives, making it suitable for use in products sold in markets with strict environmental regulations.

1.2 Physical Description

The display has a gray faceplate, which helps to absorb ambient light and improve contrast. The segments themselves emit a white-colored light when powered, which shines through the gray face to create the visible characters. This combination is chosen for optimal readability. The device is a three-digit display, meaning it can show numbers from 000 to 999.

2. Technical Specifications Deep Dive

This section provides a detailed, objective analysis of the electrical, optical, and thermal parameters specified in the datasheet. Understanding these limits and characteristics is essential for reliable circuit design.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation at or beyond these limits is not guaranteed and should be avoided.

• Power Dissipation per Segment: 70 mW. This is the maximum power that can be safely dissipated as heat by a single LED segment. Exceeding this can lead to overheating and reduced lifespan or failure.
• Peak Forward Current per Segment: 60 mA (at 1 kHz, 25% duty cycle). This is the maximum instantaneous current a segment can handle under pulsed conditions. For continuous DC operation, the continuous forward current rating is the limiting factor.
• Continuous Forward Current per Segment: 25 mA at 25°C. This current must be derated linearly by 0.28 mA/°C as the ambient temperature (Ta) rises above 25°C. For example, at 85°C, the maximum allowed continuous current would be: 25 mA - [0.28 mA/°C * (85°C - 25°C)] = 25 mA - 16.8 mA = 8.2 mA.
• Reverse Voltage per Segment: 5 V. Applying a reverse bias voltage greater than this can cause breakdown and damage the LED junction.
• Operating & Storage Temperature Range: -35°C to +85°C. The device is rated to function and be stored within this broad temperature range, making it suitable for harsh environments.
• Soldering Condition: 260°C for 3 seconds, with the iron tip at least 1/16 inch (approx. 1.6 mm) below the seating plane of the component. This is a standard lead-free reflow profile guideline to prevent thermal damage during assembly.

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

These are the typical performance parameters measured under specified test conditions. Designers should use these values for circuit calculations.

• Average Luminous Intensity (I_V): 320 μcd (Min), 692 μcd (Typ) at I_F = 1 mA. This is a measure of the light output. The wide range indicates a binning system is used; designers must account for the minimum value to ensure sufficient brightness in all units.
• Peak Emission Wavelength (λ_p): 571 nm (Typ) at I_F = 20 mA. This is the wavelength at which the LED emits the most optical power, in the green region of the spectrum.
• Spectral Line Half-Width (Δλ): 15 nm (Typ). This indicates the spectral purity; a narrower width means a more pure, saturated green color.
• Dominant Wavelength (λ_d): 572 nm (Typ). This is the single wavelength perceived by the human eye, closely matching the peak wavelength for this green LED.
• Forward Voltage per Segment (V_F): 2.05 V (Min), 2.6 V (Typ) at I_F = 20 mA. This is the voltage drop across the LED when conducting. The current-limiting resistor value must be calculated using the maximum V_F to guarantee the minimum required current.
• Reverse Current per Segment (I_R): 100 μA (Max) at V_R = 5 V. This is the small leakage current that flows when the LED is reverse-biased within its maximum rating.
• Luminous Intensity Matching Ratio: 2:1 (Max). This specifies that the brightness difference between any two segments within the "similar light area" (typically within one digit or across digits) will not exceed a factor of two. This ensures visual uniformity.

3. Binning System Explanation

The datasheet explicitly states the device is "categorized for luminous intensity." This refers to a post-production binning process.

• Luminous Intensity Binning: After manufacture, LEDs are tested and sorted (binned) based on their measured light output at a standard test current (1 mA in this case). The LTC-2621JG has a specified minimum of 320 μcd and a typical of 692 μcd. Units are grouped into bins with tighter intensity ranges (e.g., 320-400 μcd, 400-500 μcd, etc.). This allows customers to select a bin for consistent brightness across multiple displays in a product. The datasheet provides the overall range; specific bin codes would typically be available from the manufacturer for ordering.
• Forward Voltage: While not explicitly mentioned as binned, the range provided (2.05V to 2.6V) indicates natural variation. For designs where power consumption or driver circuit design is critical, consulting the manufacturer for voltage bins may be necessary.

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 / I_F Curve): This graph would show how light output increases with drive current. It is typically non-linear, with efficiency (light output per mA) often decreasing at very high currents. This curve helps designers choose an operating current that balances brightness and efficiency.
• Forward Voltage vs. Forward Current (V_F / I_F Curve): This shows the exponential I-V characteristic of the LED diode. It is crucial for designing the current-limiting circuitry.
• Relative Luminous Intensity vs. Ambient Temperature: This curve illustrates how light output decreases as the junction temperature increases. It is vital for applications operating at high ambient temperatures or high drive currents, as it may necessitate de-rating or heat sinking.
• Spectral Distribution: A graph showing the relative optical power across wavelengths, centered around 571-572 nm with a ~15 nm half-width, confirming the green color emission.

5. Mechanical and Package Information

5.1 Package Dimensions and Drawing

The device uses a standard dual in-line package (DIP) format suitable for through-hole PCB mounting. The key dimensional notes are: all dimensions are in millimeters, and the general tolerance is ±0.25 mm (approximately ±0.01 inches) unless a specific feature has a different callout. Designers must refer to the detailed mechanical drawing (not fully detailed in the text provided) for exact hole spacing, pin diameter, body width, height, and digit spacing to create accurate PCB footprints and ensure proper fit within the enclosure.

5.2 Pin Connection and Internal Circuit

The display has 16 pin positions, though not all are populated with physical pins (Pins 10, 11, and 14 are listed as "NO PIN"). Pin 9 is "NO CONNECTION." The internal circuit diagram shows a multiplexed common anode configuration.

• Common Anodes: Pins 2, 5, 8, and 13 are common anode pins. Pin 2 controls Digit 1, Pin 5 controls Digit 2, and Pin 8 controls Digit 3. Pin 13 is a common anode for the three colon indicator LEDs (L1, L2, L3).
• Segment Cathodes: The other pins are cathodes for specific segments (A, B, C, D, E, F, G, DP) and indicators. For example, to light segment 'A' on Digit 1, the circuit must connect the cathode for segment A (Pin 15) to ground while applying a positive voltage to the anode for Digit 1 (Pin 2).
• Right-Hand Decimal Point: The description notes "Rt.Hand Decimal," and Pin 3 is the cathode for D.P. (decimal point), indicating the decimal point is located to the right of the three digits.

6. Soldering and Assembly Guidelines

Adherence to the specified soldering conditions is critical for long-term reliability.

• Hand Soldering: If hand-soldering is necessary, the guideline is to apply a soldering iron at 260°C for a maximum of 3 seconds per pin. The iron tip must be positioned at least 1.6 mm below the seating plane of the display body to prevent excessive heat from traveling up the pins and damaging the internal epoxy or wire bonds.
• Wave or Reflow Soldering: For automated processes, a standard lead-free temperature profile peaking at 260°C is suitable. The device's storage and operating temperature range (-35°C to +85°C) indicates it can withstand typical SMT reflow thermal cycles, though the through-hole package suggests wave soldering is the primary intended method.
• Storage Conditions: Devices should be stored in their original moisture-barrier bags in an environment within the storage temperature range (-35°C to +85°C) and at low humidity to prevent oxidation of the leads.

7. Application Suggestions

7.1 Typical Application Scenarios

The LTC-2621JG is ideal for any embedded system requiring a clear, reliable, and low-power numeric display.

• Test and Measurement Equipment: Multimeters, frequency counters, power supplies, sensor readouts.
• Industrial Controls: Panel meters for temperature, pressure, RPM, count displays on machinery.
• Consumer Appliances: Microwave ovens, digital clocks, audio equipment tuners, bathroom scales.
• Automotive Aftermarket: Gauges and displays for auxiliary systems (voltage, temperature).

7.2 Design Considerations and Driver Circuit

Designing with this display requires specific attention to driving methodology.

• Multiplexing Driver: A microcontroller must sequentially activate each digit's common anode (Pins 2, 5, 8) at a high refresh rate (typically >100 Hz) while outputting the corresponding segment cathode pattern for that digit. This persistence of vision creates the illusion of all digits being lit simultaneously. The colon anode (Pin 13) can be driven separately or included in the multiplexing sequence.
• Current Limiting: Each segment cathode line must have a series current-limiting resistor. The resistor value is calculated using R = (V_supply - V_F) / I_F. Use the maximum V_F (2.6V) from the datasheet to ensure the minimum desired I_F is always achieved. For example, with a 5V supply and a target I_F of 10 mA: R = (5V - 2.6V) / 0.01A = 240 Ω. A standard 220 Ω or 270 Ω resistor would be appropriate.
• Power Dissipation: Ensure the per-segment power (V_F * I_F) does not exceed 70 mW, and de-rate the continuous current at high ambient temperatures as described in section 2.1.
• Viewing Angle: The wide viewing angle allows flexibility in mounting position relative to the user.

8. Technical Comparison and Differentiation

Compared to other display technologies and older LED types, the LTC-2621JG offers specific advantages.

• vs. Standard GaP Green LEDs: AlInGaP technology provides significantly higher luminous efficiency, resulting in brighter displays at the same current or equivalent brightness at lower power. The color is also a more vivid, pure green.
• vs. LCD Displays: LEDs are emissive, meaning they produce their own light, offering superior brightness and readability in low-light or direct sunlight conditions without a backlight. They also have a much faster response time and a wider operating temperature range. The trade-off is generally higher power consumption when displaying many segments.
• vs. Larger or Smaller Digit Displays: The 0.28-inch height offers a good balance between visibility and board space consumption, fitting between smaller indicators and larger panel meters.
• vs. Non-Binned Displays: The categorization for luminous intensity is a key differentiator for applications requiring visual consistency across multiple units, such as in a product line or control panel with several identical readouts.

9. Frequently Asked Questions (Based on Technical Parameters)

Q1: What is the purpose of the "NO PIN" and "NO CONNECTION" pins?
A1: "NO PIN" means the physical pin is omitted from the package, leaving a gap in the pin row. "NO CONNECTION" (Pin 9) means a physical pin exists but is not electrically connected to anything inside the display. These are often included to standardize the package footprint with other displays in a family that may use those pins.

Q2: How do I calculate the appropriate current-limiting resistor?
A2: Use the formula R = (V_supply - V_F) / I_F. Always use the maximum V_F from the datasheet (2.6V) in your calculation to guarantee the desired minimum current flows under all conditions. Choose a standard resistor value equal to or slightly lower than your calculated value.

Q3: Can I drive this display with a constant DC current without multiplexing?
A3: Technically yes, but it is highly inefficient. You would need to connect all three digit anodes together and supply current to each segment cathode continuously. This would draw 3x the current (for three identical digits) compared to a multiplexed design and would likely exceed the maximum continuous current ratings if all segments were on. Multiplexing is the intended and optimal method.

Q4: What does "luminous intensity matching ratio 2:1" mean in practice?
A4: It means that within a defined "similar light area" (likely within one display), the dimmest segment will be no less than half as bright as the brightest segment. This ensures the number "8" (all segments on) looks uniform, not with some segments noticeably dimmer than others.

10. Design and Usage Case Study

Scenario: Designing a Digital Voltmeter Readout
A designer is creating a 0-30V DC voltmeter. The microcontroller's ADC reads the voltage, converts it to a value between 0.00 and 30.00, and needs to display it on three digits and a decimal point (showing tenths of a volt, e.g., "12.3").

1. Hardware Interface: The designer uses 4 microcontroller pins configured as digital outputs to control the three digit anodes (Pins 2,5,8) and the colon/decimal anode (Pin 13). 8 other pins are configured as digital outputs (or use a shift register) to control the segment cathodes (A-G, DP).
2. Software Routine: The firmware runs a timer interrupt at 500 Hz. In each interrupt cycle:
   - Turn OFF all anode pins.
   - Output the segment pattern for Digit 1 (the hundreds place) to the cathode pins.
   - Turn ON the anode pin for Digit 1 (Pin 2).
   - Wait a short delay.
   - Repeat for Digit 2 (tens place, Pin 5) and Digit 3 (ones place, Pin 8), including the decimal point cathode (Pin 3) when Digit 2 is active.
3. Current Calculation: Targeting a segment current of 5 mA for good brightness and low power, using a 5V supply: R = (5V - 2.6V) / 0.005A = 480 Ω. A 470 Ω resistor is placed in series with each of the 8 segment cathode lines.
4. Result: The display shows a stable, bright, 3-digit voltage reading with a decimal point, consuming minimal microcontroller I/O and power.

11. Technical Principle Introduction

The core operating principle is based on electroluminescence in a semiconductor PN junction. In the AlInGaP material system, when a forward voltage exceeding the junction's built-in potential (approximately 2V) is applied, electrons from the N-type region and holes from the P-type region are injected across the junction. When these charge carriers recombine in the active region (the quantum wells of the AlInGaP epitaxial layer), they release energy in the form of photons (light particles). The specific composition of the Aluminum, Indium, Gallium, and Phosphide atoms determines the bandgap energy of the semiconductor, which directly dictates the wavelength (color) of the emitted light. For the LTC-2621JG, this composition is tuned to produce photons with a wavelength around 572 nm, which the human eye perceives as green light. The gray faceplate acts as a contrast-enhancing filter, absorbing ambient light to make the emitted green segments appear brighter and sharper.

12. Technology Trends and Context

Displays like the LTC-2621JG represent a mature and highly optimized segment of optoelectronics. The trend in such indicator-class displays has been towards increased efficiency (more light per watt), improved consistency through advanced binning, and compliance with environmental regulations (lead-free, halogen-free). While newer technologies like OLEDs offer flexibility and high contrast, traditional segmented LED displays maintain strong positions in applications requiring high brightness, extreme reliability, wide temperature operation, and low cost per digit. The move to AlInGaP from older GaP:N was a significant step in green and yellow LED performance. Future developments may focus on further efficiency gains and integration, such as displays with built-in drivers or serial interfaces (like I2C or SPI), reducing the microcontroller overhead required for multiplexing. However, the basic through-hole, multiplexed common anode display remains a fundamental and widely used component due to its simplicity, robustness, and direct interface capability with general-purpose microcontrollers.