LTC-2621JE LED Display Datasheet - 0.28-inch Digit Height - AlInGaP Red - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTC-2621JE is a compact, high-performance triple-digit numeric display module. Its primary function is to provide clear, bright numeric readouts in a variety of electronic equipment. The core technology utilizes AlInGaP (Aluminum Indium Gallium Phosphide) red LED chips, which are fabricated on a non-transparent GaAs substrate. This material system is known for its high efficiency and excellent color purity in the red spectrum. The device features a gray face with white segments, which enhances contrast and improves readability under various lighting conditions. It is categorized for luminous intensity, ensuring consistent brightness levels across production batches.

1.1 Core Advantages and Target Market

The display is designed for applications where space is limited but high visibility is critical. Its key advantages stem from its solid-state LED construction, offering superior reliability and longevity compared to other display technologies like VFDs or LCDs. The primary target markets include industrial instrumentation, test and measurement equipment, point-of-sale terminals, medical devices, and automotive dashboard displays. The device's low power requirement makes it suitable for both line-powered and portable battery-operated devices.

2. Technical Parameter Deep-Dive

This section provides an objective and detailed interpretation of the key technical parameters listed in the datasheet.

2.1 Photometric and Optical Characteristics

The luminous intensity is a critical parameter. At a standard test current of 1mA, the typical average luminous intensity (Iv) is 900 \u00b5cd, with a minimum of 320 \u00b5cd. This categorization ensures a minimum brightness level. At a higher drive current of 10mA, the typical intensity rises significantly to 12,000 \u00b5cd, demonstrating the device's capability for high-brightness applications. The dominant wavelength (\u03bbd) is specified as 624 nm, and the peak emission wavelength (\u03bbp) is 632 nm at 20mA, placing it firmly in the red color region. The spectral line half-width (\u0394\u03bb) of 20 nm indicates a relatively pure, saturated red color. Luminous intensity matching between segments is guaranteed to be within a 2:1 ratio at 1mA, ensuring uniform appearance across the display.

2.2 Electrical Parameters

The forward voltage (Vf) per segment is typically 2.6V with a maximum of 2.6V at a forward current (If) of 20mA. This is a standard voltage for AlInGaP LEDs. The reverse current (Ir) is specified at a maximum of 100 \u00b5A when a reverse voltage (Vr) of 5V is applied, indicating the diode's leakage characteristics. The absolute maximum ratings define the operational limits: a continuous forward current of 25 mA per segment (derated linearly above 25\u00b0C at 0.33 mA/\u00b0C), a peak forward current of 90 mA for pulsed operation (1/10 duty cycle, 0.1ms pulse width), and a maximum reverse voltage of 5V. The power dissipation per segment is limited to 70 mW.

2.3 Thermal and Environmental Specifications

The device is rated for an operating temperature range of -35\u00b0C to +85\u00b0C, making it suitable for harsh environments. The storage temperature range is identical. A critical assembly parameter is the solder temperature: the device can withstand a maximum of 260\u00b0C for a maximum of 3 seconds, measured 1.6mm (1/16 inch) below the seating plane. This is a standard requirement for lead-free reflow soldering processes.

3. Binning System Explanation

The datasheet indicates the device is \"categorized for luminous intensity.\" This implies a binning system where units are sorted and labeled based on their measured light output at a specific test current (likely 1mA). Bins ensure that designers receive LEDs with consistent brightness, which is crucial for multi-digit displays to avoid uneven illumination. While the specific bin code structure is not detailed in this excerpt, typical bins are defined by a range of luminous intensity values (e.g., Bin A: 320-450 \u00b5cd, Bin B: 450-600 \u00b5cd, etc.). There is no mention of voltage or wavelength binning for this specific part, suggesting tight control on those parameters during manufacturing.

4. Performance Curve Analysis

The datasheet references \"Typical Electrical / Optical Characteristic Curves.\" Although the specific graphs are not provided in the text, we can infer their standard content and significance for design.

4.1 Forward Current vs. Forward Voltage (I-V Curve)

This curve is fundamental. It shows the relationship between the current flowing through an LED segment and the voltage across it. For AlInGaP LEDs, the curve exhibits a sharp turn-on at approximately 1.8-2.0V, after which the voltage increases only slightly with a large increase in current. Designers use this curve to select appropriate current-limiting resistors for their driving circuitry to ensure stable operation and prevent thermal runaway.

4.2 Luminous Intensity vs. Forward Current

This graph shows how light output scales with drive current. Typically, it is nearly linear at lower currents but may show signs of efficiency droop (reduced efficacy) at very high currents due to thermal and electrical effects. The curve helps designers balance brightness requirements with power consumption and device longevity.

4.3 Luminous Intensity vs. Ambient Temperature

LED light output decreases as junction temperature increases. This curve quantifies that relationship, showing the relative luminous intensity as a function of ambient (or case) temperature. It is critical for applications operating over a wide temperature range, as it informs necessary brightness compensation or derating.

4.4 Spectral Distribution

A spectral plot would show the relative power emitted across wavelengths, centered around 632 nm with the specified 20 nm half-width. This confirms the color point and purity.

5. Mechanical and Package Information

5.1 Dimensions and Outline Drawing

The device features a standard LED display package. The digit height is 0.28 inches (7.0 mm). The package dimensions are provided in millimeters with a general tolerance of \u00b10.25 mm (0.01\") unless otherwise noted. The drawing would typically show the overall length, width, and height of the package, the digit spacing, the segment dimensions, and the lead spacing (pitch).

5.2 Pin Configuration and Polarity Identification

The device has a 16-pin configuration, though not all positions are populated (pins 9, 10, 11, 14 are listed as \"No Connection\" or \"No Pin\"). It is a multiplex common anode type. This means the anodes of the LEDs for each digit are connected together internally (pins 2, 5, 8 for digits 1, 2, 3 respectively, and pin 13 for the left-side colon/indicators L1, L2, L3). The cathodes for individual segments (A-G, DP) are shared across all digits. Pin 1 is identified as the cathode for segment D. Proper identification of pin 1 is crucial for correct orientation during PCB assembly. The right-hand decimal point (DP) is controlled via its own cathode on pin 3.

6. Soldering and Assembly Guidelines

The key guideline provided is the maximum soldering temperature profile: 260\u00b0C peak temperature for a maximum of 3 seconds, measured at a point 1.6mm below the seating plane of the package. This is a standard JEDEC reflow profile for components sensitive to thermal stress. It is strongly recommended to follow the manufacturer's suggested reflow profile if provided in a separate application note. General handling precautions apply: avoid mechanical stress on the leads and the glass/epoxy face, store in anti-static and moisture-controlled environments if specified, and use proper ESD precautions during handling.

7. Application Suggestions

7.1 Typical Application Circuits

The LTC-2621JE requires external driver circuitry due to its multiplexed common anode design. A typical implementation uses a microcontroller with sufficient I/O pins or a dedicated LED display driver IC (like the MAX7219 or similar). The microcontroller would sequentially enable one digit's common anode (by driving it high) while outputting the cathode pattern for the desired segments of that digit. This process repeats rapidly for all three digits, relying on persistence of vision to create a stable, flicker-free image. Current-limiting resistors are mandatory on each segment cathode line (or within the driver IC) to set the forward current, typically between 5-20 mA depending on the required brightness.

7.2 Design Considerations

• Multiplexing Ratio: With 3 digits, the multiplexing duty cycle is 1/3. To achieve the same average brightness as a statically driven digit, the peak pulse current can be up to three times higher, but it must not exceed the absolute maximum peak current rating of 90 mA.
• Refresh Rate: The digit scan frequency should be high enough to avoid visible flicker, typically above 60 Hz per digit, resulting in a total display refresh rate >180 Hz.
• Viewing Angle: The datasheet claims a wide viewing angle. For optimal readability, the display should be mounted perpendicular to the primary viewing direction.
• Power Sequencing: Ensure the driver circuit does not apply reverse voltages or excessive current surges during power-up or power-down.

8. Technical Comparison and Differentiation

Compared to older technologies like red GaAsP (Gallium Arsenide Phosphide) LEDs, the AlInGaP technology in the LTC-2621JE offers significantly higher luminous efficiency, resulting in greater brightness for the same drive current or lower power consumption for the same brightness. The color is a more saturated, \"true\" red compared to the orange-red hue of many GaAsP LEDs. Compared to contemporary side-glow or dot-matrix displays, this device offers a classic, highly legible 7-segment format ideal for numeric data. Its main differentiator is the combination of a small 0.28\" digit size with the performance benefits of AlInGaP material.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this display with a constant DC voltage without current limiting?
A: No. LEDs are current-driven devices. Applying a constant voltage, especially one near or above the forward voltage, will cause current to rise uncontrollably, potentially destroying the LED segments. Always use a series current-limiting resistor or a constant-current driver.

Q: The luminous intensity is specified at 1mA and 10mA. Can I interpolate for other currents?
A: Approximately, yes. The relationship is roughly linear at lower currents. However, for precise design, especially at higher currents, refer to the typical luminous intensity vs. forward current curve if available.

Q: What is the purpose of the \"No Connection\" pins?
A: They are likely mechanical placeholders to maintain a standard 16-pin DIP (Dual In-line Package) footprint for compatibility with standard sockets and PCB layouts, even though the internal circuitry does not use them.

Q: How do I control the colon indicators (L1, L2, L3)?
A> The colon segments share a common anode on pin 13. Their individual cathodes are tied to the cathodes of segments A, B, and C (pins 15, 12, and 6 respectively). To light, for example, L1, you would enable the common anode on pin 13 while driving the cathode for segment A (pin 15) low.

10. Design and Usage Case Study

Case: Designing a Portable Digital Multimeter Display
A designer is creating a compact digital multimeter. Key requirements are low power consumption for battery life, high brightness for outdoor use, and a small form factor. The LTC-2621JE is an excellent candidate. The designer chooses a drive current of 8 mA per segment in multiplex mode. Using a 1/3 duty cycle, the peak pulse current is 24 mA, well within the 90 mA limit. A microcontroller with built-in LED driver segments is used. The gray face/white segment design provides high contrast even in direct sunlight. The low forward voltage minimizes power loss in the driver circuitry. The 0.28\" digit size allows for a compact PCB layout while maintaining good readability. The wide operating temperature range ensures reliable operation from a cold garage to a hot car dashboard.

11. Operating Principle Introduction

The LTC-2621JE is based on semiconductor electroluminescence. The AlInGaP chip structure forms a p-n junction. 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 into the active region where they recombine. In AlInGaP, this recombination primarily releases energy in the form of photons (light) in the red wavelength range (~624-632 nm). The non-transparent GaAs substrate absorbs any downward-emitted light, improving overall light extraction efficiency from the top of the chip. The light passes through an epoxy lens molded into the desired segment shape, which also provides environmental protection.

12. Technology Trends and Context

AlInGaP technology represented a significant advancement in visible LED performance, particularly for red, orange, and yellow colors, when it was commercialized in the 1990s. It largely replaced the less efficient GaAsP and GaP technologies for high-performance applications. The trend in display modules has been towards higher integration (incorporating the driver IC into the display package), surface-mount packages for automated assembly, and the development of full-color RGB dot matrix displays. However, simple, reliable, and cost-effective 7-segment displays like the LTC-2621JE remain highly relevant for applications where only numeric information is required, due to their unsurpassed legibility, simplicity of interface, and proven reliability in field applications. The ongoing development in LED materials, such as micro-LEDs, focuses on ultra-high density and efficiency, but for standard segmented displays, AlInGaP and InGaN (for blue/green) continue to be the workhorse technologies.