LTS-3403JR 0.8-inch Super Red LED Display Datasheet - Digit Height 20.32mm - Forward Voltage 2.6V - Power 70mW - English Technical Document

1. Product Overview

The LTS-3403JR is a single-digit, seven-segment alphanumeric display module designed for applications requiring clear, bright numeric readouts. Its primary function is to visually represent digits (0-9) and some letters using individually controllable LED segments. The core technology is based on AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material, which is engineered to emit light in the super red wavelength spectrum. This material choice offers advantages in efficiency and color purity compared to older technologies.

The device is categorized as a common-cathode display, meaning the cathodes (negative terminals) of all LED segments are connected internally and brought out to common pins. This configuration simplifies circuit design when using sink-current drivers (where the driver connects to ground). The display features a light gray face and white segment color, which enhances contrast and readability under various lighting conditions.

2. Technical Specifications Deep Dive

2.1 Photometric and Optical Characteristics

The optical performance is defined under standard test conditions at an ambient temperature (Ta) of 25°C. The key parameter, Average Luminous Intensity (Iv), has a typical value of 700 µcd when driven at a forward current (IF) of 1mA per segment. The minimum specified value is 320 µcd, and there is no maximum limit listed, indicating a focus on minimum brightness guarantees. The luminous intensity matching ratio between segments is specified at a maximum of 2:1, ensuring uniform brightness across the character.

The color characteristics are defined by the peak emission wavelength (λp) of 639 nm and a dominant wavelength (λd) of 631 nm, both measured at IF=20mA. The spectral line half-width (Δλ) is 20 nm, indicating a relatively narrow emission spectrum which contributes to the pure, saturated red color. All photometric measurements are conducted using equipment filtered to approximate the CIE standard photopic eye-response curve, ensuring the data correlates with human visual perception.

2.2 Electrical and Thermal Parameters

The Absolute Maximum Ratings define the operational limits that must not be exceeded to prevent permanent damage. The continuous power dissipation per segment is 70 mW. The maximum continuous forward current per segment is 25 mA at 25°C, derating linearly at a rate of 0.33 mA/°C as the temperature rises above 25°C. A higher Peak Forward Current of 90 mA is allowed under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The maximum reverse voltage that can be applied across a segment is 5 V.

Under standard operating conditions (Ta=25°C, IF=20mA), the typical forward voltage (VF) per segment is 2.6V, with a maximum of 2.6V and a minimum of 2.0V. The reverse current (IR) is a maximum of 100 µA when a reverse voltage (VR) of 5V is applied. The device is rated for an operating and storage temperature range of -35°C to +85°C.

3. Binning and Categorization System

The datasheet explicitly states that the device is "Categorized for Luminous Intensity." This implies that units are tested and sorted (binned) based on their measured light output at a standard test current (likely 1mA or 20mA). This allows designers to select displays with consistent brightness levels for their applications, which is critical for multi-digit displays where variation would be visually apparent. While not detailed in this specific document, typical binning for such LEDs can also include forward voltage (Vf) ranges to ensure electrical compatibility in parallel driving scenarios.

4. Performance Curve Analysis

While the specific graphs are not detailed in the provided text, typical characteristic curves for such a device would include several key plots essential for design engineers. The Forward Current vs. Forward Voltage (I-V) curve is fundamental for determining the required drive voltage and for designing current-limiting circuitry. The Relative Luminous Intensity vs. Forward Current curve shows how light output scales with drive current, highlighting the region of linear operation and potential saturation.

The Luminous Intensity vs. Ambient Temperature curve is crucial for understanding thermal derating; light output typically decreases as junction temperature increases. Finally, the Spectral Distribution graph would visualize the narrow 20 nm bandwidth around the 639 nm peak, confirming the color purity. Designers use these curves to optimize drive conditions for a balance of brightness, efficiency, and longevity.

5. Mechanical and Package Information

The display has a digit height of 0.8 inches (20.32 mm). The package dimensions are provided in a detailed drawing with all measurements in millimeters. The tolerance for most dimensions is ±0.25 mm (±0.01 inches) unless otherwise specified. The physical construction houses the AlInGaP LED chips on a non-transparent GaAs substrate within a molded plastic package. The pin configuration is designed for compatibility with standard dual in-line (DIP) sockets or direct PCB mounting.

5.1 Pin Connection and Internal Circuit

The device has 18 pins in a dual-row configuration. The pinout is as follows: Pins 4, 6, and 17 are Common Cathodes. Pins 2 (A), 3 (F), 5 (E), 7 (L.D.P. - Left Decimal Point), 10 (R.D.P. - Right Decimal Point), and 11 (D) are Anodes for specific segments and decimal points. Pins 13 (C), 14 (G), and 15 (B) are Cathodes for their respective segments. Pin 12 is noted as a Common Anode, which appears to be an error or specific to an alternate internal configuration not used in this common-cathode version; it should be verified in the circuit diagram. Pins 1, 8, 9, 16, and 18 are listed as "NO PIN" (not connected). The internal circuit diagram shows the common-cathode connection scheme for the seven main segments (A-G) and the two decimal points.

6. Soldering and Assembly Guidelines

The datasheet provides a critical soldering specification: the maximum allowable solder temperature is 260°C, and this temperature can only be applied for a maximum duration of 3 seconds. This measurement is taken at a point 1.6mm (1/16 inch) below the seating plane of the package. This guideline is essential for wave soldering or reflow soldering processes to prevent thermal damage to the LED chips, the wire bonds, or the plastic package, which could lead to reduced brightness, color shift, or catastrophic failure.

Standard ESD (Electrostatic Discharge) precautions should be observed during handling and assembly, as LED chips are sensitive to static electricity. The storage conditions align with the operating temperature range (-35°C to +85°C) and should be in a low-humidity environment to prevent moisture absorption.

7. Application Suggestions

7.1 Typical Application Scenarios

This display is ideal for any embedded system requiring a clear, low-power numeric indicator. Common applications include instrument panels (multimeters, oscilloscopes), industrial control equipment, consumer appliances (microwaves, ovens, washing machines), medical devices, and point-of-sale terminals. Its low current operation (effective down to 1mA/segment) makes it suitable for battery-powered portable devices where power conservation is critical.

7.2 Design Considerations and Driving Methods

To drive this common-cathode display, a current-sinking driver IC (like a 74HC595 shift register with open-drain outputs or a dedicated LED driver) is typically used. The common cathode pins are connected to the driver's ground switches, while the segment anode pins are connected to a current-limited voltage source, often through series resistors. The value of the current-limiting resistor (R) is calculated using the formula: R = (Vcc - Vf) / If, where Vcc is the supply voltage, Vf is the forward voltage of the segment (use max value for safety), and If is the desired forward current.

For multiplexing multiple digits (a common technique to save pins and power), the cathodes of each digit are switched sequentially at a high frequency while the corresponding segment data is presented on the common anode lines. The low forward voltage and good efficiency of the AlInGaP technology are beneficial here, as they reduce power dissipation in the drivers during multiplexing.

8. Technical Comparison and Advantages

The LTS-3403JR offers several distinct advantages. The use of AlInGaP technology provides higher luminous efficiency and better temperature stability compared to older GaAsP (Gallium Arsenide Phosphide) red LEDs. This results in the "High Brightness & High Contrast" and "Solid State Reliability" claimed in the features. The "Continuous Uniform Segments" feature indicates a well-designed package with minimal gaps between segment elements, creating a more cohesive character appearance.

The "Low Power Requirement" and ability to operate effectively at 1mA/segment is a significant advantage for energy-sensitive designs. The "Wide Viewing Angle" is a function of the LED chip technology and the lens design of the package, making the display readable from off-axis positions. When compared to vacuum fluorescent or LCD displays, this LED module offers superior brightness, faster response time, and wider operating temperature range, though at the cost of higher power consumption per segment if driven at high currents.

9. Frequently Asked Questions (Based on Technical Parameters)

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

A: Possibly, but with caution. The typical Vf is 2.6V. A 3.3V supply leaves only 0.7V for the current-limiting resistor and driver transistor saturation. At 1mA, a resistor of (3.3V - 2.6V) / 0.001A = 70 ohms would be needed. This is feasible, but the brightness will be at the lower end. For 20mA drive, the voltage margin is too small for reliable operation; a higher supply voltage (e.g., 5V) or a dedicated driver with external supply is recommended.

Q: What is the difference between peak wavelength and dominant wavelength?

A: Peak wavelength (λp) is the wavelength at which the emission spectrum has its maximum intensity. Dominant wavelength (λd) is the single wavelength of monochromatic light that, when combined with a specified white reference, matches the perceived color of the LED. For a narrow-spectrum LED like this, they are often close, but λd is more relevant for color perception.

Q: Why are there three common cathode pins?

A: Having multiple common cathode pins helps distribute the total cathode current (which is the sum of currents from all lit segments) across several pins and internal bond wires. This reduces current density in any single connection, improving reliability and allowing for higher multiplexing currents.

10. Design and Usage Case Study

Consider designing a simple 4-digit voltmeter using a microcontroller. The LTS-3403JR displays would be ideal. The design would involve four display units. The segment anodes (A-G, DP) of all four digits would be connected in parallel to 8 output pins of the microcontroller via current-limiting resistors (e.g., 150 ohms for ~20mA drive from a 5V supply). Each digit's common cathode pin would be connected to an NPN transistor (like a 2N3904), whose base is controlled by a separate microcontroller pin.

The microcontroller software would implement time-division multiplexing. It would calculate the digit to be displayed, set the appropriate segment pattern on the anode lines, turn on the transistor for that specific digit (connecting its cathode to ground), wait for a short persistence time (1-5 ms), then turn that digit off and move to the next digit. This cycle repeats rapidly (>60 Hz), creating the illusion of all digits being continuously lit. The low current operation allows the use of small, low-cost transistors and keeps power consumption manageable.

11. Operating Principle

The device operates on the principle of electroluminescence in a semiconductor p-n junction. The AlInGaP crystal structure is engineered with a specific bandgap energy. When a forward voltage exceeding the junction's threshold is applied, electrons from the n-type region and holes from the p-type region are injected into the active region. When these charge carriers recombine, they release energy in the form of photons (light). The wavelength (color) of this light is directly determined by the bandgap energy of the AlInGaP material. The non-transparent GaAs substrate helps reflect light upward, increasing the external efficiency. Each segment of the display contains one or more of these tiny LED chips, which are wire-bonded to the package leads and encapsulated in a plastic lens that shapes the light output.

12. Technology Trends

While discrete seven-segment LED displays remain relevant for specific applications, the broader trend in display technology is towards integration and miniaturization. Surface-mount device (SMD) LED packages have largely replaced through-hole types like this in high-volume consumer electronics for their smaller footprint and suitability for automated assembly. Furthermore, the functionality of multi-digit numeric displays is increasingly being absorbed into larger, more versatile dot-matrix OLED or LCD graphic modules, which can show numbers, text, and graphics.

However, for applications requiring extreme brightness, wide temperature range, long lifetime, and simplicity, discrete LED segment displays like the LTS-3403JR maintain a strong value proposition. Advances in materials, like the shift from GaAsP to AlInGaP documented here, continue to improve their efficiency and reliability. The core principle of a current-driven, solid-state light source remains at the heart of both discrete displays and modern high-resolution LED video walls.