LTD-3506KR Dual Digit 7-Segment LED Display Datasheet - Digit Height 7.62mm - Forward Voltage 2.6V - Power 75mW - Super Red Color

1. Product Overview

The device is a dual-digit, seven-segment light-emitting diode (LED) display module. Its primary function is to provide a clear, legible numeric readout in various electronic applications. The core component utilizes advanced semiconductor materials to achieve its optical performance.

1.1 Core Advantages and Target Market

This display offers several key advantages that make it suitable for a range of applications. It features a continuous and uniform segment design, which enhances character appearance and readability. The device operates with low power requirements, contributing to energy efficiency in end products. It delivers high brightness and high contrast output, ensuring visibility even in well-lit conditions. A wide viewing angle allows the display to be read from various positions. The solid-state construction provides inherent reliability and long operational life. The luminous intensity is categorized, allowing for consistency in brightness across production batches. Finally, the package complies with lead-free requirements.

The target market for this component includes consumer electronics, industrial instrumentation, automotive dashboards, test and measurement equipment, and any device requiring a compact, reliable numeric display.

2. Technical Parameter Deep Dive

This section provides a detailed, objective analysis of the device's key technical parameters as defined in its specification sheet.

2.1 Photometric and Optical Characteristics

The optical performance is central to the display's function. The primary color emitted is in the red spectrum, achieved through specific semiconductor materials. The typical peak emission wavelength is approximately 639 nanometers (nm) when driven at a forward current of 20 milliamperes (mA). The dominant wavelength is specified at 631 nm. The spectral line half-width, which indicates the purity or breadth of the emitted color, is 240 nm. The average luminous intensity, a measure of perceived brightness, is categorized. At a forward current of 1 mA, the intensity ranges from a minimum of 350 microcandelas (μcd) to a maximum of 860 μcd. At a higher drive current of 10 mA, a typical value of 11150 μcd is noted. A luminous intensity matching ratio of 2:1 (maximum to minimum) is specified for segments within the same light area at 1 mA, ensuring visual uniformity.

2.2 Electrical Parameters

The electrical characteristics define the operating conditions and limits for the device. The absolute maximum ratings set the boundaries for safe operation. The power dissipation per segment must not exceed 75 milliwatts (mW). The peak forward current per segment is limited to 90 mA under pulsed conditions (1 kHz, 10% duty cycle). The continuous forward current per segment is rated at 25 mA at 25°C, with a derating factor of 0.33 mA per degree Celsius above 25°C. The forward voltage per segment, measured at 20 mA, has a typical value of 2.6 volts (V) and a maximum of 2.6 V (with a minimum of 2.0 V). The reverse current per segment is limited to a maximum of 100 microamperes (μA) at a reverse voltage of 5V; it is crucial to note that this is a test condition and the device is not intended for continuous reverse bias operation.

2.3 Thermal and Environmental Specifications

The device is designed to operate within an ambient temperature range of -35°C to +85°C. The storage temperature range is identical. These ratings ensure functionality in both harsh and standard environments. Specific soldering temperature profiles are provided to prevent damage during assembly: wave soldering should not exceed 260°C for a maximum of 5 seconds measured 1.6mm below the seating plane, while manual soldering should not exceed 295°C ±5°C for a maximum of 3 seconds at the same reference point.

3. Binning System Explanation

The datasheet indicates that the devices are categorized for luminous intensity. This is a common binning practice where LEDs from a production batch are sorted (binned) based on measured light output. This ensures that customers receive displays with consistent brightness levels. The specification of a 2:1 maximum-to-minimum intensity matching ratio for segments further guarantees visual uniformity within a single device. While not explicitly detailed for wavelength or forward voltage in this document, such parameters are often tightly controlled in manufacturing to meet the published typical and maximum/minimum values.

4. Performance Curve Analysis

The datasheet references typical electrical and optical characteristic curves. While the specific graphs are not provided in the text, standard curves for such devices would typically illustrate the relationship between forward current and luminous intensity (showing the light output increase with current), the relationship between forward voltage and forward current, and the variation of luminous intensity with ambient temperature. These curves are essential for designers to optimize drive conditions for desired brightness and efficiency while staying within the device's operational limits.

5. Mechanical and Packaging Information

5.1 Physical Dimensions and Tolerances

The device has a digit height of 0.3 inches (7.62 mm). The package dimensions are provided in a drawing with all measurements in millimeters. Standard tolerances are ±0.25 mm unless otherwise specified. Additional mechanical notes include a pin tip shift tolerance of ±0.4 mm, limits on foreign material and ink contamination on the segment surface, a limit on bending of the reflector, and a limit on bubbles within the segment material. A printed circuit board (PCB) hole diameter of 1.0 mm is recommended for best fit.

5.2 Pin Configuration and Polarity Identification

The device has 10 pins in a dual-in-line package configuration. It features a common cathode architecture, with one common cathode for each digit (Digit 1 and Digit 2). The internal circuit diagram shows the interconnection of the segment anodes (A, B, C, D, E, F, G) and decimal points (DP) for both digits to the specific pin numbers. The pin connection table clearly maps each pin number to its function (e.g., Pin 1: Anode for G1,G2; Pin 4: Common Cathode for Digit 2; Pin 7: Common Cathode for Digit 1). This information is critical for correct PCB layout and system interfacing.

6. Soldering and Assembly Guidelines

As mentioned in the thermal specifications, strict adherence to the soldering temperature and time limits is paramount to prevent thermal damage to the LED chips, wire bonds, or plastic package. The recommended PCB hole size (1.0 mm) should be used to ensure proper mechanical alignment and solder joint formation. Designers should follow standard ESD (electrostatic discharge) precautions during handling. For storage, the specified temperature range of -35°C to +85°C should be maintained in a dry environment.

7. Application Suggestions

7.1 Typical Application Scenarios

This dual-digit display is ideal for applications requiring a compact, two-digit numeric readout. Common uses include: digital multimeters, frequency counters, clock displays (showing minutes or seconds), temperature controllers, small-scale weighing scales, battery charge level indicators, and control panel status displays.

7.2 Design Considerations and Notes

When integrating this display, several factors must be considered. Current Limiting: External current-limiting resistors are mandatory for each segment anode or common cathode line to set the desired brightness and ensure the continuous forward current per segment does not exceed 25 mA (derated for temperature). The value can be calculated using the supply voltage, the LED forward voltage (Vf ~2.6V), and the target current. Drive Circuitry: A microcontroller or dedicated display driver IC is needed to multiplex the two digits. This involves sequentially enabling one common cathode at a time while presenting the segment data for that digit, at a frequency high enough to avoid visible flicker (typically >60 Hz). Cross-talk: The datasheet specifies a cross-talk specification of ≤2.5%. This refers to unintended illumination of a segment in the non-selected digit due to leakage or capacitive coupling. Proper multiplexing timing and drive strength help minimize this effect. Viewing Angle: The wide viewing angle is beneficial but should be considered during mechanical enclosure design to align with the user's typical line of sight.

8. Technical Comparison and Differentiation

Compared to older technologies like single-color GaP LEDs, the use of AlInGaP material offers superior brightness and efficiency for red emission. The gray face with white segments is a design choice that enhances contrast compared to all-black or all-gray faces, especially in ambient light. The categorization for luminous intensity is a key differentiator that provides predictable brightness levels, which is not always guaranteed with unbinned displays. The lead-free package ensures compliance with modern environmental regulations (RoHS).

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What resistor value should I use to drive a segment at 10 mA from a 5V supply?
A: Using Ohm's Law: R = (Vsupply - Vf) / I. R = (5V - 2.6V) / 0.01A = 240 Ohms. A standard 240Ω or 220Ω resistor would be appropriate.

Q: Can I drive this display with a constant voltage without current limiting?
A: No. LEDs are current-driven devices. Applying a constant voltage near or above Vf without a series resistor will result in excessive current, potentially exceeding the absolute maximum rating and destroying the segment.

Q: What does "common cathode" mean for my circuit design?
A: In a common cathode display, all the cathodes (negative terminals) of the LEDs for one digit are connected together internally. To illuminate a digit, you must connect its common cathode pin to ground (logic low) and apply a positive voltage (through a current-limiting resistor) to the anode of the segment you wish to light. This is the opposite of a common anode display.

Q: How do I achieve decimal points?
A> The internal circuit diagram shows decimal point (DP) anodes for each digit. These are controlled independently just like the main segments (A-G). To light a decimal point, you must drive its corresponding anode pin while the common cathode for its digit is active.

10. Practical Design and Usage Case

Consider designing a simple two-digit counter using a microcontroller. The microcontroller's I/O pins would be connected to the segment anodes (A1/A2 through G1/G2, and DP1/DP2) via current-limiting resistors. Two other I/O pins would be connected to the two common cathode pins (Digit 1 and Digit 2 Cathode). The firmware would implement a multiplexing routine: set the segment pattern for Digit 1 on the anode lines, enable (ground) the Digit 1 cathode pin for a few milliseconds, then disable it. Next, set the segment pattern for Digit 2, enable the Digit 2 cathode pin, and repeat. The cycle must be fast enough to appear as a steady, two-digit number to the human eye. The current per segment must be calculated based on the resistor value and the duty cycle of the multiplexing to ensure the average power dissipation remains within limits.

11. Operating Principle Introduction

The device operates on the principle of electroluminescence in a semiconductor p-n junction. When a forward voltage exceeding the junction's built-in potential is applied (the forward voltage Vf), electrons and holes are injected into the active region where they recombine. In an AlInGaP (Aluminum Indium Gallium Phosphide) LED, this recombination event releases energy in the form of photons (light) in the red wavelength range. The specific composition of the AlInGaP layers determines the exact color (wavelength) of the emitted light. Each segment of the display contains one or more of these tiny LED chips. The plastic package serves to encapsulate the chips, provide mechanical protection, and act as a lens to shape the light output for optimal viewing.

12. Technology Trends and Developments

While this specific device uses AlInGaP technology for red emission, the broader LED display market continues to evolve. Trends include the development of even higher efficiency materials, leading to lower power consumption for the same brightness. There is a push towards higher pixel density and full-color capability in multi-segment and dot-matrix displays. Integration of driver electronics directly into the display package ("intelligent displays") simplifies system design. Furthermore, advancements in packaging materials aim for improved thermal management, allowing for higher drive currents and brightness, and enhanced reliability over a wider temperature range. The fundamental principle of solid-state light emission remains, but performance and integration levels continue to increase.