LTD-4708JS LED Display Datasheet - 0.4-inch Digit Height - AlInGaP Yellow - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTD-4708JS is a dual-digit, seven-segment alphanumeric display module designed for applications requiring clear, bright numeric readouts. Its primary function is to visually represent two digits (0-9) using individually addressable LED segments. The core technology utilizes Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor material to produce yellow light emission. This material system is known for its high efficiency and excellent color purity in the yellow-orange-red spectrum. The device features a gray faceplate with white segment markings, which enhances contrast and legibility under various lighting conditions. It is categorized based on luminous intensity, ensuring consistent brightness levels across production batches for uniform appearance in multi-unit applications.

2. In-Depth Technical Parameter Analysis

2.1 Photometric and Optical Characteristics

The optical performance is central to the display's functionality. At a standard test current of 1 mA per segment, the average luminous intensity ranges from a minimum of 200 μcd to a typical value of 650 μcd. The peak emission wavelength (λp) is typically 588 nm, with a dominant wavelength (λd) of 587 nm, firmly placing the output in the yellow region of the visible spectrum. The spectral line half-width (Δλ) is 15 nm, indicating a relatively narrow bandwidth and good color saturation. The luminous intensity matching ratio between segments is specified at a maximum of 2:1, which is critical for ensuring uniform brightness across all segments of a digit.

2.2 Electrical and Thermal Parameters

Electrically, each LED segment has a forward voltage (VF) ranging from 2.05V to 2.6V at a drive current of 20 mA. The absolute maximum ratings define the operational limits: the continuous forward current per segment is 25 mA at 25°C, derating linearly by 0.33 mA/°C as ambient temperature increases. The peak forward current, permissible under pulsed conditions (1/10 duty cycle, 0.1ms pulse width), is 60 mA. The maximum power dissipation per segment is 70 mW. The device can withstand a reverse voltage of up to 5V per segment, with a reverse current (IR) of less than 100 μA at this voltage. The operating and storage temperature range is specified from -35°C to +85°C, indicating robustness for industrial and consumer environments.

3. Binning System Explanation

The datasheet indicates the device is \"categorized for luminous intensity.\" This implies a binning or sorting process post-manufacturing. LEDs are typically tested and grouped (binned) based on key parameters like luminous intensity and forward voltage to ensure consistency. While specific bin code details are not provided in this excerpt, such a system allows designers to select parts with tightly matched brightness, preventing noticeable variations between digits or segments in an array, which is crucial for aesthetic and functional uniformity in final products.

4. Performance Curve Analysis

The datasheet references \"Typical Electrical / Optical Characteristic Curves.\" Although the specific graphs are not detailed in the provided text, such curves typically illustrate the relationship between forward current (IF) and luminous intensity (IV), forward voltage (VF) versus temperature, and the angular distribution of light (viewing angle pattern). These curves are essential for designers to understand the non-linear behavior of LEDs. For instance, the IV curve shows how light output increases with current but may saturate at higher currents. The temperature derating curve is vital for thermal management design to ensure longevity and stable performance.

5. Mechanical and Package Information

5.1 Dimensions and Outline

The package drawing (referenced but not shown in detail) provides the physical dimensions of the display. The primary specification is a 0.4-inch (10.0 mm) digit height. All dimensions are provided in millimeters with a standard tolerance of ±0.25 mm unless otherwise noted. This information is critical for PCB footprint design and ensuring the display fits correctly within the product enclosure.

5.2 Pin Configuration and Polarity

The device has a 10-pin configuration. It employs a duplex common cathode architecture, meaning there are two separate common cathode pins—one for each digit (pins 4 and 9). The anodes for segments A through G and the decimal point (D.P.) are on individual pins. The specific pinout is: 1(C), 2(D.P.), 3(E), 4(Cathode Digit 2), 5(D), 6(F), 7(G), 8(B), 9(Cathode Digit 1), 10(A). Correct identification of cathode and anode pins is essential to prevent reverse bias damage during circuit assembly.

6. Soldering and Assembly Guidelines

The absolute maximum ratings include a critical soldering parameter: the device can withstand a maximum solder temperature of 260°C for a maximum duration of 3 seconds, measured at 1.6mm (1/16 inch) below the seating plane. This guideline is intended for wave soldering or hand soldering processes. For reflow soldering, a profile with a peak temperature below this limit and controlled ramp rates should be used. Prolonged exposure to high temperatures can damage the internal wire bonds, LED chips, or plastic package.

7. Application Recommendations

7.1 Typical Application Scenarios

This display is suitable for a wide range of applications requiring compact, low-power numeric indicators. Common uses include instrumentation panels (e.g., multimeters, frequency counters), consumer appliances (microwaves, washing machines, thermostats), industrial control readouts, and portable electronic devices. The high brightness and wide viewing angle make it readable in both dim and brightly lit environments.

7.2 Design Considerations

Current Limiting: External current-limiting resistors are mandatory for each segment anode or common cathode line to set the desired brightness and prevent exceeding the maximum continuous forward current. The resistor value is calculated based on the supply voltage (Vcc), the LED forward voltage (VF ~2.6V max), and the desired forward current (e.g., 10-20 mA).
Multiplexing: The common cathode architecture is ideal for multiplexed drive circuits. By sequentially enabling one cathode (digit) at a high frequency (typically >100Hz) while supplying the appropriate segment data to the anodes, two digits can be controlled with a reduced number of I/O pins compared to static drive. This also reduces average power consumption.
Viewing Angle: The wide viewing angle is beneficial but must be considered during mechanical design to align the display's optimal viewing cone with the user's expected line of sight.

8. Technical Comparison and Differentiation

Compared to older technologies like standard GaAsP or GaP LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in greater brightness for the same input current. The yellow color produced is more saturated and pure. Compared to single-digit displays, this dual-digit unit saves PCB space and simplifies assembly. The categorization (binning) for luminous intensity is a key differentiator from non-binned parts, providing designers with predictable performance essential for professional-grade products.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What resistor value should I use to drive a segment at 15 mA with a 5V supply?
A: Using Ohm's Law: R = (Vcc - VF) / IF. Assuming a typical VF of 2.3V, R = (5V - 2.3V) / 0.015A ≈ 180 Ω. Always use the maximum VF from the datasheet (2.6V) for a conservative design: R = (5V - 2.6V) / 0.015A ≈ 160 Ω. A standard 150 Ω or 180 Ω resistor would be appropriate, checking the actual power dissipation in the resistor.
Q: Can I drive this display directly from a microcontroller pin?
A: No. Microcontroller pins typically cannot source or sink the required current (up to 25 mA per segment, potentially much more for multiple segments on one digit). You must use transistor drivers (for common cathode switching) and/or dedicated LED driver ICs to provide adequate current and implement multiplexing.
Q: What is the purpose of the \"Peak Forward Current\" rating?
A>This rating allows for brief current pulses higher than the DC rating, which can be used in multiplexed circuits to achieve higher peak brightness during the short ON time of each digit. The average current over time must still be within the continuous rating limits.

10. Practical Design and Usage Case

Consider designing a simple two-digit counter. The circuit would involve a microcontroller generating the count sequence. Two NPN transistors (or a dual transistor array) would be used to sink current through the common cathode pins (Digits 1 & 2), controlled by separate microcontroller GPIOs set in open-drain or open-collector mode. The seven segment anodes (A-G) would be connected to other GPIOs through individual current-limiting resistors (e.g., 150Ω). Firmware would implement multiplexing: turn on the transistor for Digit 1, set the GPIOs to light the segments needed for the first digit's value, wait a few milliseconds, then turn off Digit 1, turn on Digit 2, set the segments for the second digit's value, and repeat. This cycle creates the perception of both digits being continuously lit.

11. Operational Principle Introduction

The device operates on the principle of electroluminescence in a semiconductor p-n junction. When a forward voltage exceeding the diode's threshold (approximately 2V for AlInGaP) is applied, electrons from the n-type region and holes from the p-type region are injected into the active region. Their recombination releases energy in the form of photons (light). The specific wavelength (color) of the light is determined by the bandgap energy of the semiconductor material—AlInGaP in this case, which is engineered to emit in the yellow spectrum. Each of the seven segments (plus the decimal point) contains one or more of these tiny LED chips. The common cathode configuration means the cathodes (negative terminals) of all LEDs in one digit are connected internally, allowing the entire digit to be enabled or disabled by a single switch.

12. Technology Trends and Context

AlInGaP technology represents a significant advancement over earlier LED materials for red, orange, and yellow light. It offers higher efficiency and better temperature stability. While this datasheet is for a discrete component, the trend in display technology is towards higher integration, such as multi-digit modules with built-in drivers and serial interfaces (I2C, SPI). Furthermore, for yellow indicators, phosphor-converted white LEDs or direct-emitting InGaN-based LEDs covering a broader spectrum are sometimes used. However, for applications requiring pure, efficient yellow light with simple direct drive, AlInGaP remains a relevant and reliable choice. The principles of multiplexing, current limiting, and thermal management discussed here are fundamental and apply to a wide variety of LED-based display technologies.