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

1. Product Overview

The LTC-2624JD is a high-performance, triple-digit, seven-segment display module designed for applications requiring clear numeric readouts with low power consumption. Its primary function is to provide a visual numeric output in electronic devices such as test equipment, industrial controllers, instrumentation panels, and consumer electronics. The core advantage of this device lies in its utilization of advanced AlInGaP (Aluminum Indium Gallium Phosphide) LED technology, which offers superior luminous efficiency and color purity compared to traditional LED materials. This results in excellent character appearance, high brightness, and high contrast, making the digits easily readable even in well-lit environments. The device is categorized for luminous intensity, ensuring consistent brightness levels across production batches, which is crucial for applications requiring uniform display quality.

2. Technical Specifications Deep Dive

2.1 Optical Characteristics

The optical performance is central to the display's functionality. The device emits light in the red spectrum. The typical peak emission wavelength (λp) is 656 nanometers, with a dominant wavelength (λd) of 640 nm, producing a pure red color. The spectral line half-width (Δλ) is 22 nm, indicating a relatively narrow bandwidth which contributes to color saturation. The key parameter for brightness is the average luminous intensity (Iv), which has a minimum of 200 μcd, a typical value, and a maximum of 600 μcd when driven at a forward current (IF) of just 1 mA per segment. This low-current, high-brightness characteristic is a significant feature. Furthermore, the segments are matched for luminous intensity with a matching ratio (IV-m) of 2:1 maximum when driven at 10 mA, ensuring uniform brightness across all segments of all digits.

2.2 Electrical Characteristics

The electrical parameters define the operating conditions and power requirements. The forward voltage (VF) per segment is typically 2.6 Volts, with a maximum of 2.6V at a test current of 20 mA. The reverse current (IR) per segment is very low, with a maximum of 10 μA when a reverse voltage (VR) of 5V is applied. The device is designed for low-power operation, with segments capable of being driven effectively at currents as low as 1 mA, which is a primary design goal stated in the description. The internal circuit is configured as a common anode, meaning the anodes of the LEDs for each digit are connected together, requiring a multiplexed driving scheme where digits are illuminated sequentially at a high frequency.

2.3 Absolute Maximum Ratings

These ratings specify the limits beyond which permanent damage may occur. The maximum continuous power dissipation per segment is 75 mW. The peak forward current per segment is 100 mA, but this is only permissible under pulsed conditions with a 1/10 duty cycle and a 0.1 ms pulse width. The continuous forward current per segment must be derated linearly from 25 mA at 25°C. The maximum reverse voltage per segment is 5V. The operating and storage temperature range is from -35°C to +85°C, indicating suitability for industrial and extended environmental conditions. The maximum soldering temperature is 260°C for a maximum of 3 seconds at a distance of 1.6mm below the seating plane, which is a standard reflow soldering guideline.

3. Binning System Explanation

The datasheet indicates that the device is "categorized for luminous intensity." This implies a binning or sorting process based on measured light output. While specific bin code details are not provided in this document, such a system typically groups devices according to their measured luminous intensity at a standard test current (e.g., 1mA or 10mA). This ensures that designers and manufacturers can select displays with consistent brightness levels for their products, avoiding visible variations between different units in a single assembly. The luminous intensity matching ratio of 2:1 further guarantees that within a single device, the brightness difference between the dimmest and brightest segment will not exceed this factor.

4. Performance Curve Analysis

While the specific graphs for typical electrical/optical characteristic curves are referenced on page 5 of the datasheet but not detailed in the provided text, such curves are standard for LED components. They would typically include:

• Forward Current vs. Forward Voltage (I-V Curve): This graph shows the nonlinear relationship between the current flowing through the LED and the voltage across it. It is essential for designing the current-limiting circuitry.
• Luminous Intensity vs. Forward Current (I-L Curve): This shows how the light output increases with increasing drive current. It is crucial for determining the operating current needed to achieve a desired brightness level.
• Luminous Intensity vs. Ambient Temperature: This curve demonstrates how the light output decreases as the ambient temperature rises. Understanding this derating is vital for applications operating in high-temperature environments.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the peak at 656 nm and the shape of the emitted light spectrum.

These curves allow engineers to predict the display's behavior under various operating conditions not explicitly covered in the tabular data.

5. Mechanical and Packaging Information

The LTC-2624JD comes in a standard LED display package. The digit height is 0.28 inches (7.0 mm). The package dimensions drawing (referenced on page 2) provides the exact physical outline, pin spacing, and overall size in millimeters. Tolerances for these dimensions are typically ±0.25 mm unless otherwise specified. The device features a gray face with white segments, which enhances contrast by reducing reflected ambient light from the non-illuminated areas of the display. The pin connection table provides a complete map of the 26 pins, detailing the cathode connections for each segment (A-G, DP) of each digit (1-3) and the common anode pins for the digits. This precise mapping is critical for designing the PCB layout and the driver circuitry.

6. Soldering and Assembly Guidelines

The key assembly guideline provided is related to soldering temperature. The device can withstand a maximum soldering temperature of 260°C for a maximum duration of 3 seconds, measured at a point 1.6mm (1/16 inch) below the seating plane of the package. This is a standard specification for wave soldering or reflow soldering processes. Designers must ensure their soldering profiles do not exceed these limits to prevent damage to the internal LED chips or the plastic package. For storage, the specified temperature range is -35°C to +85°C. It is advisable to store components in a dry, anti-static environment to prevent moisture absorption and electrostatic discharge damage before use.

7. Application Recommendations

7.1 Typical Application Scenarios

This display is ideal for any battery-powered or low-power device requiring a clear, multi-digit numeric readout. Common applications include portable multimeters, digital thermometers, clock displays, process control indicators, battery charge level indicators, and settings displays on consumer appliances. Its low current operation makes it suitable for devices where power conservation is a priority.

7.2 Design Considerations

• Driver Circuitry: As a common-anode display, it requires a multiplexed driver. A microcontroller with sufficient I/O pins or a dedicated display driver IC (like a MAX7219 or similar) must be used to sequentially power the common anode of each digit while sinking current through the appropriate segment cathodes.
• Current Limiting: External current-limiting resistors are mandatory for each segment cathode line (or built into the driver IC) to set the forward current to the desired value (e.g., 1-20 mA). The resistor value is calculated using the formula R = (Vcc - VF) / IF, where Vcc is the supply voltage to the common anode, VF is the forward voltage of the LED (typ. 2.6V), and IF is the desired segment current.
• Refresh Rate: When multiplexing three digits, the refresh rate per digit must be high enough to avoid visible flicker, typically above 60 Hz per digit, resulting in a total multiplexing frequency >180 Hz.
• Viewing Angle: The datasheet mentions a wide viewing angle, but for optimal placement, consider the typical viewing direction of the end-user relative to the display panel.

8. Technical Comparison and Differentiation

The primary differentiating factors of the LTC-2624JD are its material technology and low-current performance. Compared to displays using older GaAsP or GaP LED technology, AlInGaP offers significantly higher luminous efficiency, resulting in brighter output at the same current or equivalent brightness at much lower current. The specific mention of being "tested and selected for it’s excellent low current characteristics" and applicability at 1mA per segment highlights its optimization for energy-efficient designs. The gray face/white segment design also provides a higher contrast ratio compared to all-black or all-gray displays, improving readability. The categorization for luminous intensity provides an added level of quality control and consistency not always found in basic display modules.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this display with a 5V microcontroller directly?

A: No, you cannot connect the segments directly to a microcontroller pin. You need current-limiting resistors in series with each segment cathode. Furthermore, due to the common anode configuration and multiplexing requirement, you will likely need transistor arrays or a driver IC to handle the segment currents and digit switching.

Q: What is the difference between peak wavelength (656 nm) and dominant wavelength (640 nm)?

A: Peak wavelength is the wavelength at which the emission spectrum has its maximum intensity. Dominant wavelength is the single wavelength of monochromatic light that matches the perceived color of the LED. The difference is due to the shape of the LED's emission spectrum. Both indicate a red color.

Q: The max continuous current is 25 mA, but the test condition for VF is 20 mA. Which should I use for design?

A: For reliable long-term operation, it is prudent to design for a current at or below the typical test condition of 20 mA. Operating at the absolute maximum of 25 mA leaves no margin and may reduce lifetime. The 1 mA applicability shows it is designed for much lower currents, so choose a current based on your required brightness and power budget.

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

A: This means that within one display unit, the luminous intensity of the dimmest segment will be no less than half the intensity of the brightest segment when measured under the same conditions (IF=10mA). This ensures visual uniformity.

10. Practical Design and Usage Case

Consider designing a portable digital multimeter. The primary requirements are low power consumption for long battery life and a clear display under various lighting conditions. The LTC-2624JD is an excellent choice. The design would involve a microcontroller with a built-in analog-to-digital converter to measure voltage/current/resistance. The microcontroller's I/O ports, through a series of current-limiting resistors (calculated for ~5-10 mA per segment to balance brightness and power), would connect to the segment cathodes. Three NPN transistors (or a single transistor array) would be used to switch the common anode of each digit to the supply voltage (e.g., 3.3V or 5V) under software control. The firmware would implement multiplexing, converting the measured value into the appropriate segment patterns for each digit and cycling through them rapidly. The low 1mA capability allows for a dimming mode to further save power when full brightness is not needed.

11. Technology Principle Introduction

The LTC-2624JD is based on AlInGaP semiconductor material grown on a non-transparent GaAs substrate. AlInGaP is a direct bandgap semiconductor from the III-V group. When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region. They recombine radiatively, releasing energy in the form of photons. The specific composition of Aluminum, Indium, Gallium, and Phosphide determines the bandgap energy, which directly dictates the wavelength (color) of the emitted light—in this case, red. The non-transparent substrate helps direct more of the generated light out of the top of the device, improving external efficiency. The individual LED chips are then mounted and wire-bonded within the plastic package to form the seven segments and decimal points for each digit.

12. Technology Trends and Context

While seven-segment LED displays remain a robust and cost-effective solution for numeric readouts, the broader display technology landscape has evolved. The trend in many consumer and industrial applications is towards dot-matrix OLED or LCD displays that can show alphanumeric characters and graphics. However, for applications where only numbers are needed, extreme reliability is required, operation over a wide temperature range is necessary, or very high brightness and viewing angles are critical, LED seven-segment displays like the LTC-2624JD maintain a strong position. The ongoing development in LED materials, like AlInGaP and InGaN (for blue/green), continues to improve their efficiency, brightness, and color range. Furthermore, the drive towards IoT and low-power devices aligns well with the inherent low-current capabilities of modern LED displays.