LTD-4608JS LED Display Datasheet - 0.4-inch Digit Height - AlInGaP Yellow - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTD-4608JS 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) and a decimal point using individual LED segments. The core technology utilizes AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material to produce yellow light emission. This material system is known for its high efficiency and excellent brightness compared to traditional LED technologies. The device features a gray faceplate with white segment markings, which enhances contrast and readability under various lighting conditions. It is categorized based on luminous intensity, allowing for selection consistency in batch production.

1.1 Core Advantages and Target Market

The display offers several key advantages that make it suitable for a range of applications. Its low power requirement makes it ideal for battery-operated or energy-sensitive devices. The high brightness and contrast, coupled with a wide viewing angle, ensure legibility from various perspectives, which is critical for consumer electronics, instrumentation, and industrial control panels. The solid-state reliability of LEDs translates to long operational life and resistance to shock and vibration, unlike mechanical or vacuum fluorescent displays. The continuous uniform segments provide a pleasing aesthetic character appearance. The primary target markets include portable electronic devices, test and measurement equipment, automotive dashboards (for non-critical indicators), home appliances, and point-of-sale terminals where clear, reliable numeric display is necessary.

2. In-Depth Technical Parameter Analysis

This section provides a detailed, objective interpretation of the key electrical and optical parameters specified in the datasheet, explaining their significance for design engineers.

2.1 Photometric and Optical Characteristics

The photometric performance is central to the display's function. The Average Luminous Intensity (Iv) is specified from 200 to 650 µcd at a forward current (IF) of 1mA. This wide range indicates a binning process; designers must account for this variation or specify tighter bins for uniform appearance across multiple displays. The Peak Emission Wavelength (λp) is 588 nm, and the Dominant Wavelength (λd) is 587 nm, both measured at IF=20mA. These values define the yellow color point. The Spectral Line Half-Width (Δλ) of 15 nm indicates a relatively narrow spectral bandwidth, resulting in a saturated yellow color. The Luminous Intensity Matching Ratio (IV-m) of 2:1 maximum defines the allowable brightness variation between segments within a single device, impacting overall uniformity.

2.2 Electrical Parameters

The electrical specifications define the operating limits and conditions. The Forward Voltage per Segment (VF) has a typical value of 2.6V at IF=20mA. This parameter is crucial for designing the current-limiting resistor network. The Reverse Current per Segment (IR) is a maximum of 100 µA at VR=5V, indicating the leakage current when the LED is reverse-biased, which is generally negligible in normal operation. These parameters must be considered alongside the absolute maximum ratings to ensure reliable operation.

2.3 Thermal and Absolute Maximum Ratings

The absolute maximum ratings define the stress limits beyond which permanent damage may occur. The Continuous Forward Current per Segment is 25 mA at 25°C, with a derating factor of 0.33 mA/°C. This means the allowable continuous current decreases as ambient temperature (Ta) increases above 25°C. For example, at 85°C, the maximum current would be approximately 25 mA - (0.33 mA/°C * (85-25)°C) = 5.2 mA. The Peak Forward Current is 60 mA but only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The Power Dissipation per Segment is 70 mW. The operating and storage temperature range is -35°C to +85°C, defining the environmental limits for use and non-operation. The solder temperature rating (260°C max for 3 seconds) is critical for PCB assembly processes.

3. Binning System Explanation

The datasheet indicates that the device is \"categorized for luminous intensity.\" This implies a binning or sorting process post-manufacturing. While specific bin codes are not provided in this document, typical binning for such displays involves sorting units based on measured luminous intensity at a standard test current (e.g., 1mA, as shown in the characteristics). This ensures that designers sourcing multiple units can achieve consistent brightness levels across their products. Engineers should consult the manufacturer for detailed binning specifications or lot-specific data if uniformity is a critical design requirement.

4. Performance Curve Analysis

The datasheet references \"Typical Electrical / Optical Characteristic Curves.\" Although the specific graphs are not detailed in the provided text, standard curves for such LEDs would typically include:

• IV Curve (Current vs. Forward Voltage): Shows the exponential relationship, helping to determine the dynamic resistance and the precise voltage drop at various operating currents.
• Luminous Intensity vs. Forward Current (Iv-IF): Demonstrates how light output increases with current, usually in a near-linear relationship within the operating range, aiding in brightness calibration and efficiency calculations.
• Luminous Intensity vs. Ambient Temperature (Iv-Ta): Shows the decrease in light output as junction temperature rises, which is vital for designing applications that operate in high-temperature environments.
• Spectral Distribution: A plot of relative intensity versus wavelength, confirming the peak and dominant wavelengths and the shape of the emission spectrum.

These curves are essential for understanding the device's behavior under non-standard conditions and for optimizing the drive circuitry for performance and longevity.

5. Mechanical and Package Information

The device package is defined by a detailed dimension drawing (in millimeters). Key features include the overall footprint, the height of the display, the spacing between the two digits, and the location and diameter of the mounting holes or pins. The pin connection diagram is crucial: it is a 10-pin configuration with two common anodes (one for each digit) and individual cathodes for segments A-G and the decimal point (D.P.). The internal circuit diagram shows the multiplexed arrangement: all corresponding segments (e.g., all 'A' segments) between the two digits are connected internally to a single cathode pin. Each digit's anode is controlled separately (Pin 9 for Digit 1, Pin 4 for Digit 2). This multiplexing design reduces the number of required driver pins from 15 (7 segments + DP per digit, plus two grounds) to 10, simplifying the interface circuitry.

6. Soldering and Assembly Guidelines

The primary assembly consideration is the soldering process. The absolute maximum rating specifies that the soldering temperature must not exceed 260°C for a maximum of 3 seconds, measured at 1.6mm (1/16 inch) below the seating plane. This is a standard rating for wave soldering or hand soldering. For reflow soldering, a standard lead-free profile with a peak temperature below 260°C should be used, ensuring the time above liquidus is controlled to minimize thermal stress on the LED chips and plastic package. Proper handling to avoid electrostatic discharge (ESD) is recommended, although the datasheet does not specify an ESD rating. Storage should be within the specified temperature range (-35°C to +85°C) in a low-humidity environment to prevent moisture absorption, which could cause \"popcorning\" during reflow.

7. Application Recommendations

7.1 Typical Application Scenarios

This display is well-suited for any application requiring a compact, bright, two-digit numeric readout. Examples include: digital multimeters, bench power supplies, frequency counters, clock displays (minutes/seconds), scoreboards, production line counters, and status indicators on network or audio equipment. Its yellow color is often chosen for cautionary indicators or to provide a distinct visual contrast against other displays.

7.2 Design Considerations

• Drive Circuitry: Use a multiplexing driver circuit. Each digit is illuminated alternately at a high frequency (typically >100Hz) to create the perception of both digits being on continuously. This requires microcontroller GPIO pins or a dedicated display driver IC (like a 7447 decoder or a MAX7219) capable of sinking the segment current and sourcing the digit anode current.
• Current Limiting: External current-limiting resistors are mandatory for each cathode line (segments) or integrated into the driver. The resistor value is calculated as R = (Vcc - VF) / IF, where VF is the forward voltage (use max value for worst-case current calculation), Vcc is the supply voltage, and IF is the desired forward current (not exceeding the continuous rating).
• Brightness Control: Average brightness can be controlled by adjusting the IF current or by using pulse-width modulation (PWM) on the drive signals.
• Viewing Angle: Position the display considering its wide viewing angle to ensure visibility for the end-user.

8. Technical Comparison and Differentiation

Compared to other display technologies, this AlInGaP LED display offers distinct advantages. Versus older GaAsP (Gallium Arsenide Phosphide) red LEDs, AlInGaP provides significantly higher luminous efficiency and brightness for the same current, and better temperature stability. Compared to LCD (Liquid Crystal Display) modules, it does not require a backlight, offers wider viewing angles, operates faster in cold temperatures, and is more robust mechanically. The primary trade-off is higher power consumption when displaying many segments compared to LCDs. Within the LED segment display market, its key differentiators are the specific 0.4-inch digit height, the AlInGaP yellow color, the duplex common anode configuration, and the categorized luminous intensity ensuring quality consistency.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: How do I connect this display to a microcontroller?
A: You need at least 10 GPIO pins. Connect the common anode pins (4 & 9) to microcontroller pins configured as outputs set HIGH to enable a digit. Connect the segment cathode pins (1,2,3,5,6,7,8,10) to pins configured as outputs set LOW to turn on a segment. You must multiplex by rapidly enabling one digit, setting its segments, then switching to the other digit. Using a dedicated driver IC is highly recommended to reduce MCU load.

Q: Why is the forward current derated with temperature?
A: As temperature increases, the LED's internal efficiency drops, and more electrical power is converted to heat instead of light. This heat, if not managed, can raise the junction temperature further, leading to accelerated degradation or failure. Derating the current limits the heat generated, keeping the junction temperature within safe limits.

Q: What does a \"Luminous Intensity Matching Ratio of 2:1\" mean?
A: It means that within a single display unit, the brightness of the dimmest segment will be no less than half the brightness of the brightest segment. A ratio of 1:1 would be perfect uniformity; 2:1 is a common specification ensuring acceptable visual consistency.

10. Practical Design and Usage Case

Case: Designing a Simple Two-Digit Counter. The goal is to count from 00 to 99. A low-cost microcontroller (e.g., an ATtiny) generates the control signals. The circuit uses eight 180Ω current-limiting resistors (one per segment cathode, calculated for a 5V supply, VF=2.6V, IF~13mA). Two NPN transistors (e.g., 2N3904) are used as high-side switches for the common anode pins, controlled by two more MCU pins. The firmware implements a timer interrupt at 2ms. In the interrupt service routine, it disables the currently displayed digit, updates the segment pattern for the next digit based on the count value, enables the transistor for that digit, and then exits. The main loop increments the count variable every second. This design efficiently uses MCU resources and provides a stable, flicker-free display.

11. Operating Principle Introduction

The device operates on the principle of electroluminescence in a semiconductor p-n junction. When a forward voltage exceeding the diode's turn-on voltage (approximately 2.05-2.6V) is applied across a segment (from the common anode to its specific cathode), electrons and holes recombine in the active AlInGaP region. This recombination releases energy in the form of photons, producing yellow light with a wavelength centered around 588 nm. The seven segments (A through G) are individual LED chips arranged in a \"8\" pattern. By selectively energizing different combinations of these segments, all numeric digits from 0 to 9 can be formed. The duplex common anode configuration means all LEDs for one digit share a common positive voltage connection, which is switched to enable that digit during multiplexing.

12. Technology Trends and Developments

While this specific device uses established AlInGaP technology, the broader field of LED displays continues to evolve. Trends include the adoption of even more efficient materials like InGaN (Indium Gallium Nitride) for a wider color gamut, though AlInGaP remains dominant for red, orange, and yellow. There is a move towards higher density multi-digit modules and displays with integrated drivers and controllers (\"intelligent displays\") to simplify system design. Miniaturization is another trend, with smaller digit heights becoming available for portable devices. Furthermore, advancements in packaging aim to improve thermal management, allowing for higher brightness at given current levels or improved longevity. The fundamental multiplexing principle remains standard due to its efficiency in pin reduction.