LTD-5721AJS LED Display Datasheet - 0.56-inch Digit Height - AlInGaP Yellow - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTD-5721AJS is a high-performance, low-power seven-segment LED display module. Its primary function is to provide clear, bright numeric and limited alphanumeric character output in electronic devices. The core technology is based on Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor material, which is renowned for its high efficiency and excellent color purity in the yellow-orange-red spectrum. This specific device emits a yellow light, characterized by its dominant wavelength. The display features a light gray face and white segment color, which significantly enhances contrast and readability under various lighting conditions. It is categorized for luminous intensity, ensuring consistent brightness levels across production batches, which is crucial for applications requiring uniform visual output.

1.1 Core Advantages and Target Market

The display is engineered for applications where power efficiency, reliability, and visual clarity are paramount. Its low current requirement, with segments operational at currents as low as 1mA, makes it ideal for battery-powered or energy-conscious devices such as portable instrumentation, handheld meters, consumer electronics, and industrial control panels. The high brightness and wide viewing angle ensure that the displayed information is easily legible from various perspectives, a critical feature for panel-mounted equipment. The solid-state reliability of LED technology offers a long operational lifespan with no moving parts, making it suitable for harsh environments where mechanical wear is a concern. The continuous uniform segments contribute to an excellent character appearance, providing a clean and professional look.

2. Technical Parameter Deep-Dive

This section provides a detailed, objective analysis of the electrical and optical specifications as defined in the datasheet. Understanding these parameters is essential for proper circuit design and system integration.

2.1 Photometric and Optical Characteristics

The key optical parameters are measured under standardized test conditions (typically at an ambient temperature of 25°C). The Average Luminous Intensity (Iv) ranges from a minimum of 320 µcd to a typical 700 µcd when driven at a forward current (IF) of 1mA per segment. This parameter quantifies the perceived brightness of the light emitted. The Peak Emission Wavelength (λp) is 588 nm, indicating the wavelength at which the spectral power distribution is maximum. The Dominant Wavelength (λd) is 587 nm, which is the single wavelength perceived by the human eye that best matches the color of the emitted light. The Spectral Line Half-Width (Δλ) is 15 nm, describing the bandwidth of the emitted light; a narrower half-width indicates a more monochromatic, purer color. Luminous intensity is measured using a sensor and filter combination that approximates the CIE photopic eye-response curve, ensuring the measurements correlate with human visual perception.

2.2 Electrical Parameters

The electrical characteristics define the operating boundaries and requirements for the driver circuit. The Forward Voltage per Segment (VF) is between 2.05V (min) and 2.6V (max) at a test current of 20mA. This is the voltage drop across the LED when it is conducting. Designers must ensure the driving circuit can provide this voltage. The Reverse Current per Segment (IR) is a maximum of 100 µA when a reverse voltage (VR) of 5V is applied, indicating the level of leakage when the LED is reverse-biased. Exceeding the Absolute Maximum Ratings can cause permanent damage. These include a maximum Power Dissipation per Segment of 40 mW, a Peak Forward Current of 60 mA (under pulsed conditions), and a Continuous Forward Current of 25 mA which must be derated linearly above 25°C at a rate of 0.33 mA/°C. The maximum Reverse Voltage is 5V.

2.3 Thermal and Environmental Ratings

The device is rated for an Operating Temperature Range of -35°C to +85°C and an identical Storage Temperature Range. This wide range ensures functionality in most commercial and industrial environments. The Solder Temperature specification is critical for assembly: the device can withstand 260°C for 3 seconds at a point 1/16 inch (approximately 1.6mm) below the seating plane. This guides the reflow soldering profile to prevent thermal damage to the LED chips or package.

3. Binning System Explanation

The datasheet states the device is \"Categorized for Luminous Intensity.\" This implies a binning or sorting process post-manufacturing. While specific bin code details are not provided in this excerpt, typical categorization for such displays involves grouping units based on measured luminous intensity at a standard test current (e.g., 1mA or 20mA). This ensures that within a single production order or assembly, all digits have matched brightness, preventing uneven illumination across a multi-digit display. Designers should consult the manufacturer for the specific binning structure and codes to specify consistency requirements for their application.

4. Performance Curve Analysis

The datasheet references \"Typical Electrical/Optical Characteristic Curves\" which are essential for understanding device behavior beyond single-point specifications. Although the specific graphs are not displayed in the provided text, standard curves for such LEDs would typically include: Relative Luminous Intensity vs. Forward Current (I-V Curve): This shows how brightness increases with current, often in a sub-linear fashion, highlighting the efficiency at low currents. Forward Voltage vs. Forward Current: This curve is vital for designing current-limiting circuits or constant-current drivers. Relative Luminous Intensity vs. Ambient Temperature: This demonstrates the thermal derating of light output, which is crucial for high-temperature applications. Spectral Distribution: A graph showing the relative power across wavelengths, centered around the peak wavelength of 588 nm.

5. Mechanical and Package Information

The device is presented with a detailed package dimension drawing (all dimensions in millimeters with a standard tolerance of ±0.25mm unless noted). This drawing is critical for PCB footprint design, ensuring proper fit and alignment. The display has a digit height of 0.56 inches (14.22 mm). It is supplied in a standard dual-digit, right-hand decimal point configuration. The package includes 18 pins for electrical connection.

5.1 Pin Configuration and Polarity Identification

The pin connection table is provided. The LTD-5721AJS is a Common Anode type display. This means the anode terminals for all segments in a digit are connected together internally. Digits 1 and 2 have separate common anode pins (Pin 14 and Pin 13, respectively). Each segment (A through G, plus Decimal Point) has its own individual cathode pin. To illuminate a segment, its corresponding cathode must be connected to a lower voltage (ground) while the common anode for that digit is held at a higher voltage (supply). The right-hand decimal point is included. Pin 1 is explicitly marked as \"No Connection\" (N.C.).

6. Soldering and Assembly Guidelines

Adherence to the soldering specifications is mandatory to prevent damage. The key parameter is the maximum allowable solder temperature of 260°C for 3 seconds, measured 1.6mm below the seating plane. This translates to a standard lead-free reflow profile with a peak temperature likely not exceeding 250-255°C at the component body to provide a safety margin. Standard ESD (Electrostatic Discharge) precautions should be observed during handling. For storage, the specified range of -35°C to +85°C in a dry environment should be maintained.

7. Application Suggestions

7.1 Typical Application Scenarios

This display is perfectly suited for a wide range of applications including: Test and Measurement Equipment: Digital multimeters, oscilloscopes, frequency counters. Industrial Controls: Process indicators, timer displays, control panel readouts. Consumer Electronics: Audio equipment displays, appliance controls. Medical Devices: Portable monitors, diagnostic equipment. Automotive Aftermarket: Gauges and instrumentation.

7.2 Design Considerations

Driver Circuit: Use constant-current drivers or appropriate current-limiting resistors for each segment cathode. Calculations must account for the forward voltage (VF) and desired current (IF). For low-power operation, driving at 1-5mA per segment is feasible as per the datasheet. Multiplexing: Since the two digits have separate common anodes, they can be easily multiplexed. This involves sequentially enabling one digit's anode at a time while presenting the segment data for that digit on the cathode lines. Multiplexing reduces the required number of driver pins and can lower total power consumption. Viewing Angle: The wide viewing angle allows for flexible panel mounting. Brightness Matching: Specify intensity binning if consistent brightness across multiple units is critical for the application.

8. Technical Comparison and Differentiation

Compared to older technologies like standard red GaAsP LEDs, the AlInGaP-based LTD-5721AJS offers significantly higher luminous efficiency, resulting in greater brightness at the same current or equivalent brightness at lower current. The yellow color provides excellent contrast against dark backgrounds and is often chosen for its high visibility. The low current capability (down to 1mA) is a key differentiator from displays that require higher drive currents, enabling longer battery life in portable devices. The categorization for luminous intensity provides an advantage in applications requiring visual consistency over displays without such sorting.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this display with a 3.3V microcontroller? A: Yes. The maximum forward voltage is 2.6V. When using a series current-limiting resistor, a 3.3V supply provides sufficient headroom (3.3V - 2.6V = 0.7V) to reliably control the current.

Q: What is the purpose of the \"Luminous Intensity Matching Ratio\" of 2:1? A: This ratio (Iv-m) indicates that within a single device, the luminous intensity of any segment will not be less than half the intensity of the brightest segment. It ensures uniformity within one digit.

Q: How do I connect this for a common anode display? A: Connect the common anode pin(s) to your positive supply voltage (through a driver transistor if multiplexing). Connect each segment cathode pin to a current sink (e.g., a microcontroller I/O pin with sufficient current capability or a driver IC) that pulls it low to turn the segment ON.

10. Practical Design Case

Consider designing a simple two-digit counter powered by a 5V supply and controlled by a microcontroller. The microcontroller's I/O pins cannot source/sink enough current for the LEDs. Therefore, a driver IC like a 74HC595 shift register or a dedicated LED driver (e.g., MAX7219) would be used to sink current for the cathodes. Two NPN transistors (e.g., 2N3904) would be used to switch the 5V supply to the common anodes (Digits 1 & 2) under microcontroller control for multiplexing. Current-limiting resistors would be placed on the cathode lines. The resistor value (R) is calculated using Ohm's Law: R = (Vcc - VF - Vce_sat) / IF. Assuming Vcc=5V, VF=2.2V (typical), Vce_sat of the driver ~0.2V, and a desired IF=5mA: R = (5 - 2.2 - 0.2) / 0.005 = 520 Ohms. A standard 510 or 560 Ohm resistor would be suitable. The microcontroller firmware would alternate between enabling Digit 1 and Digit 2 at a fast rate (e.g., 100Hz each) while updating the segment data synchronously, creating the illusion of both digits being constantly lit.

11. Technology Principle Introduction

The LED chips in this display are fabricated from AlInGaP (Aluminium Indium Gallium Phosphide) epitaxially grown on a non-transparent Gallium Arsenide (GaAs) substrate. When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region where they recombine. In AlInGaP, this recombination releases energy primarily in the form of photons in the yellow-orange-red spectrum (around 587-590 nm for yellow). The non-transparent substrate helps direct more of the generated light out of the top of the chip, improving external quantum efficiency compared to some older designs. The seven-segment format is created by placing multiple such LED chips (or a single chip with multiple electrically isolated junctions) in the pattern of seven bars (segments) and a decimal point. By selectively energizing these segments, numeric characters (0-9) and some letters can be formed.

12. Technology Trends

While AlInGaP remains a dominant technology for high-efficiency red, orange, and yellow LEDs, the broader display technology landscape is evolving. For seven-segment applications, the trend continues towards even lower operating currents and voltages to support ultra-low-power IoT and wearable devices. There is also a move towards higher integration, with displays incorporating the driver IC and sometimes a microcontroller into the same package, simplifying design. In terms of materials, while AlInGaP is mature, research into perovskite LEDs and other novel semiconductors may offer future alternatives. However, for standard indicator and numeric display applications requiring reliability, specific color points, and cost-effectiveness, AlInGaP-based displays like the LTD-5721AJS are expected to remain prevalent for the foreseeable future.