LTC-2624AJD LED Display Datasheet - 0.28-inch Digit Height - AlInGaP Red - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTC-2624AJD is a triple-digit, seven-segment alphanumeric display module designed for applications requiring clear, bright numeric readouts. Its primary function is to visually represent three digits (0-9) along with decimal points. The core technology utilizes AlInGaP (Aluminum Indium Gallium Phosphide) high-efficiency red LED chips. These chips are fabricated on a non-transparent GaAs substrate, which contributes to high contrast by minimizing internal light scattering and reflection. The display features a gray faceplate with white segment markings, enhancing readability by providing a neutral background that makes the illuminated red segments stand out prominently.

The device is engineered for low-power operation, a critical advantage for battery-powered or energy-conscious applications. It is specifically tested and characterized for excellent performance at low drive currents, with segment matching ensured even under these conditions. This allows designers to use drive currents as low as 1mA per segment while maintaining uniform brightness across all segments and digits, significantly reducing the overall system power consumption.

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 outside these limits is not advised.

• Power Dissipation per Segment: 70 mW. This is the maximum allowable power loss as heat in a single LED segment.
• Peak Forward Current per Segment: 100 mA. This is permissible only under pulsed conditions with a 1/10 duty cycle and a 0.1ms pulse width, typically used for multiplexing or short-term overdrive for higher brightness.
• Continuous Forward Current per Segment: 25 mA at 25°C. This rating derates linearly at 0.33 mA/°C as ambient temperature (Ta) increases above 25°C. For example, at 85°C, the maximum continuous current would be approximately 25 mA - (0.33 mA/°C * (85°C-25°C)) = 5.2 mA.
• Reverse Voltage per Segment: 5 V. Exceeding this voltage in reverse bias can cause junction breakdown.
• Operating & Storage Temperature Range: -35°C to +85°C. The device is rated for industrial temperature ranges.
• Solder Temperature: A maximum of 260°C for a maximum of 3 seconds, measured 1.6mm (1/16 inch) below the seating plane of the package. This is critical for wave or reflow soldering processes to prevent thermal damage to the LED chips or internal bonds.

2.2 Electrical & Optical Characteristics

These parameters are measured at Ta=25°C and define the typical operating performance.

• Average Luminous Intensity (I_V): 200 μcd (Min), 600 μcd (Typ) at I_F=1mA. This exceptionally low test current highlights the device's high efficiency. The luminous intensity is measured using a filter that approximates the photopic (CIE) eye-response curve.
• Peak Emission Wavelength (λ_p): 656 nm (Typ) at I_F=20mA. This indicates the wavelength at which the optical output power is greatest, placing it in the bright red portion of the visible spectrum.
• Spectral Line Half-Width (Δλ): 22 nm (Typ) at I_F=20mA. This parameter describes the spectral purity; a narrower half-width indicates a more monochromatic light source.
• Dominant Wavelength (λ_d): 640 nm (Typ) at I_F=20mA. This is the single wavelength perceived by the human eye, which may differ slightly from the peak wavelength.
• Forward Voltage per Segment (V_F): 2.1V (Min), 2.6V (Typ) at I_F=20mA. This is the voltage drop across an LED segment when conducting the specified current. Designers must ensure the driving circuit can provide this voltage.
• Reverse Current per Segment (I_R): 10 μA (Max) at V_R=5V. This is the leakage current when the LED is reverse-biased.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 (Max) at I_F=10mA. This specifies the maximum allowable ratio between the brightest and dimmest segment within a device, ensuring visual uniformity. A ratio of 2:1 means the brightest segment will be no more than twice as bright as the dimmest.

3. Binning System Explanation

The datasheet indicates the device is \"Categorized for Luminous Intensity.\" This implies a binning process where manufactured units are sorted (binned) based on measured luminous intensity at a standard test current (likely 1mA or 10mA). This allows customers to select parts with consistent brightness levels for their application, preventing noticeable variations between different displays in a product. While specific bin codes are not listed in this document, procurement typically involves specifying the desired intensity range.

4. Performance Curve Analysis

The datasheet references \"Typical Electrical / Optical Characteristic Curves.\" Although the specific graphs are not provided in the text, standard curves for such devices would typically include:

• I-V (Current vs. Voltage) Curve: Shows the exponential relationship between forward current and forward voltage, crucial for designing current-limiting circuitry.
• Luminous Intensity vs. Forward Current (I_V vs. I_F): Demonstrates how light output increases with drive current, usually in a near-linear relationship within the operating range.
• Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as junction temperature increases. AlInGaP LEDs generally experience a decrease in efficiency with rising temperature.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the peak at ~656nm and the ~22nm half-width.

5. Mechanical and Package Information

5.1 Package Dimensions

The device uses a standard dual in-line package (DIP) format with 26 pins. All dimensions are specified in millimeters with a general tolerance of ±0.25 mm unless otherwise noted. The key feature is the 0.28-inch (7.0 mm) digit height, which determines the physical size of each numeric character. The overall package dimensions would define the footprint on the PCB.

5.2 Pin Connection and Internal Circuit

The LTC-2624AJD is a common anode configuration. This means the anode (positive side) of all LED segments for a given digit are connected together internally and brought out to a single pin per digit (pins 1, 20). The cathodes (negative side) of individual segments (A, B, C, D, E, F, G, DP) for each digit are brought out to separate pins. The internal circuit diagram would show three independent common-anode digit blocks, each containing seven segments and a decimal point. Multiplexing is required to drive a three-digit common-anode display: the controller sequentially enables (applies a positive voltage to) one digit's common anode at a time while driving the appropriate segment cathode patterns for that digit, cycling fast enough to create a persistance-of-vision effect of all digits being continuously on.

6. Soldering and Assembly Guidelines

The primary guideline is the absolute maximum rating for solder temperature: 260°C for a maximum of 3 seconds, measured at the specified point below the package. This is compatible with standard lead-free reflow profiles. Designers should ensure the thermal mass of the PCB and the reflow oven profile do not expose the LEDs to excessive temperature or time above liquidus. Manual soldering with an iron should be performed quickly and with appropriate thermal management. Prolonged exposure to high humidity should be avoided before soldering, and standard ESD (Electrostatic Discharge) precautions must be observed during handling and assembly.

7. Application Suggestions

7.1 Typical Application Scenarios

This display is ideal for applications requiring clear, low-power numeric indication. Examples include: instrument panels (multimeters, power supplies, scales), consumer electronics (audio equipment, kitchen appliances), industrial control readouts, medical device displays, and portable battery-operated devices.

7.2 Design Considerations

• Drive Circuitry: Use constant current drivers or current-limiting resistors for each segment cathode. For multiplexed driving, calculate the resistor value based on the peak current required during the digit's ON time and the supply voltage minus the LED V_F.
• Multiplexing: A microcontroller with sufficient I/O pins or coupled with a decoder/driver IC (like a 74HC595 shift register with constant current outputs or a dedicated LED driver) is necessary. The refresh rate should be high enough (typically >60Hz) to avoid visible flicker.
• Viewing Angle: The datasheet claims a wide viewing angle, which is beneficial for applications where the display may be viewed from off-axis positions.
• Brightness Control: Brightness can be easily controlled by adjusting the segment current or by using pulse-width modulation (PWM) on either the segment cathodes or the digit anodes.

8. Technical Comparison and Differentiation

The key differentiating advantages of the LTC-2624AJD based on its datasheet are:

• Material Technology (AlInGaP): Compared to older GaAsP or GaP LEDs, AlInGaP offers significantly higher efficiency and brighter red emission, leading to better visibility and lower power consumption.
• Low Current Operation: Its characterization down to 1mA/segment is a standout feature, enabling ultra-low-power designs that are not feasible with displays requiring higher drive currents.
• High Contrast Design: The combination of a gray face, white segments, and a non-transparent substrate is designed to maximize contrast when the LEDs are off and on, improving readability in various lighting conditions.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this display with a 3.3V microcontroller directly?

A: Possibly, but with caution. The typical V_F is 2.6V at 20mA. If you drive a segment directly from a 3.3V GPIO pin through a resistor, the voltage drop across the resistor would only be 0.7V. To achieve 10mA, you would need a 70-ohm resistor (0.7V/0.01A). However, this leaves little headroom, and variations in V_F could cause significant current changes. For reliable operation, especially at higher currents, a supply voltage >3.6V is recommended, or use a transistor/LED driver.

Q: What is the purpose of the peak forward current rating (100mA)?

A: This allows for multiplexing schemes. If you have a 1/10 duty cycle (each digit is on 10% of the time), you can pulse a current of up to 100mA through the segment during its ON time to achieve a higher perceived average brightness than would be possible with a 25mA continuous current. The average current must not exceed the continuous rating.

Q: How do I interpret the 2:1 luminous intensity matching ratio?

A: This is a quality control parameter. It guarantees that within a single LTC-2624AJD unit, no segment will be more than twice as bright as the dimmest segment when driven under the same conditions (10mA). This ensures visual uniformity of the displayed number.

10. Practical Design Case Study

Consider designing a battery-powered digital thermometer displaying a three-digit temperature. Using a microcontroller with 12 I/O pins, you can drive the three common anodes (3 pins) and the 7 segment lines (A-G) shared across all digits (7 pins), plus one pin for decimal points if needed (total 11). The firmware multiplexes the digits. To conserve power, you drive each segment at 2mA. At this current, the luminous intensity will be proportionally lower than the 1mA spec but likely still sufficient for indoor use. Using the typical V_F of 2.6V and a 5V supply, the current-limiting resistor value would be R = (5V - 2.6V) / 0.002A = 1.2 kΩ. The average current consumption for the display (all three digits showing \"888\") would be approximately: 7 segments/digit * 2mA/segment * 1/3 duty cycle = ~4.67mA average. This low current draw is ideal for extended battery life.

11. Operational Principle

The device operates on the principle of electroluminescence in a semiconductor p-n junction. When a forward voltage exceeding the diode's turn-on threshold (approximately 2.1-2.6V) is applied across a segment (anode positive relative to cathode), electrons and holes are injected into the active region (the AlInGaP quantum well layers). These charge carriers recombine, releasing energy in the form of photons. The specific composition of the AlInGaP alloy determines the bandgap energy, which directly corresponds to the wavelength (color) of the emitted light—in this case, red at ~640-656 nm. The non-transparent GaAs substrate absorbs photons emitted downwards, improving contrast by preventing them from scattering and diluting the frontal light output.

12. Technology Trends

While this specific device uses mature and reliable AlInGaP technology, the broader trend in display components is towards even higher efficiency materials like InGaN (which can produce blue and green, and via phosphors, white) and the miniaturization of packages. There is also a trend towards integrated solutions where the driver IC is embedded within the display module itself, simplifying system design. Furthermore, the demand for lower power consumption continues to drive improvements in luminous efficacy (lumens per watt), allowing for brighter displays at the same current or the same brightness at even lower currents than specified here. The fundamental multiplexing drive scheme for multi-digit seven-segment displays remains standard due to its simplicity and I/O efficiency.