LTC-7500KG LED Display Datasheet - 0.72-inch Digit Height - AlInGaP Green - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTC-7500KG is a high-performance, triple-digit, seven-segment LED display module. Its primary function is to provide clear, bright numeric readouts in a wide range of electronic equipment. The core technology is based on AlInGaP (Aluminium Indium Gallium Phosphide) LED chips grown on a GaAs substrate, which is known for producing high-efficiency green light. The device features a black face with white segments, offering excellent contrast for optimal readability under various lighting conditions.

1.1 Key Features and Core Advantages

The display is designed with several key advantages that make it suitable for demanding applications. The 0.72-inch (18.4 mm) digit height provides a large, easily legible character. The segments are continuous and uniform, ensuring a consistent appearance across all digits and segments. It operates with low power requirements, contributing to energy-efficient designs. The combination of high brightness and high contrast, along with a wide viewing angle, ensures the display is visible from multiple positions. Furthermore, it offers solid-state reliability and is categorized for luminous intensity, allowing for brightness matching in multi-display setups. The package is lead-free and compliant with RoHS directives.

1.2 Device Description and Target Market

This device is specifically a multiplex common cathode display with a right-hand decimal point. The multiplex design reduces the number of required driver pins, simplifying the interfacing circuitry. Its target market includes a broad spectrum of ordinary electronic equipment where reliable numeric indication is required. This encompasses office automation equipment, communication devices, industrial control panels, instrumentation, household appliances, and consumer electronics. The design prioritizes clarity, reliability, and ease of integration.

2. Technical Parameters and Objective Interpretation

This section provides a detailed, objective analysis of the electrical, optical, and thermal characteristics of the LTC-7500KG display, based solely on the data provided in the specification sheet.

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the limits beyond which permanent damage to the device may occur. These are not operating conditions.

• Power Dissipation per Segment: 70 mW. This is the maximum power that can be safely dissipated by a single LED segment without risk of overheating.
• Peak Forward Current per Segment: 60 mA. This current is permissible only under pulsed conditions with a 1/10 duty cycle and a 0.1 ms pulse width. It is used for achieving very high instantaneous brightness, not for continuous operation.
• Continuous Forward Current per Segment: 25 mA at 25°C. This current derates linearly at a rate of 0.28 mA/°C as the ambient temperature (Ta) increases above 25°C. For example, at 85°C, the maximum allowable continuous current would be approximately 25 mA - (0.28 mA/°C * 60°C) = 8.2 mA.
• Operating and Storage Temperature Range: -35°C to +105°C. The device can be stored or operated within this full range.
• Solder Condition: The device can withstand wave soldering or reflow where the solder temperature at a point 1/16 inch (≈1.6mm) below the seating plane does not exceed 260°C for 3 seconds. The temperature of the component body itself must not exceed the maximum temperature rating during assembly.

2.2 Electrical and Optical Characteristics

These parameters are measured under standard test conditions (Ta=25°C) and represent typical performance.

• Average Luminous Intensity (I_V): This is the key brightness parameter. At a forward current (I_F) of 1 mA, the intensity is typically 1050 µcd (microcandela), with a minimum of 500 µcd. At 10 mA, the typical intensity rises significantly to 11550 µcd. Designers must select the drive current based on the required brightness and thermal considerations.
• Peak Emission Wavelength (λ_p): 571 nm (typical). This is the wavelength at which the emitted light intensity is highest.
• Spectral Line Half-Width (Δλ): 15 nm (typical). This indicates the spectral purity; a smaller value means a more monochromatic light.
• Dominant Wavelength (λ_d): 572 nm (typical). This is the wavelength perceived by the human eye, defining the green color.
• Forward Voltage per Chip (V_F): 2.6 V (typical), with a minimum of 2.05 V, at I_F=20 mA. Circuit design must account for this voltage drop and its variation from chip to chip.
• Reverse Current per Segment (I_R): Maximum 100 µA at a reverse voltage (V_R) of 5V. This parameter is for test purposes only; continuous reverse bias operation is prohibited.
• Luminous Intensity Matching Ratio: 2:1 maximum (for similar light area). This means the brightness difference between any two segments under the same drive condition (I_F=1mA) should not exceed a factor of two.
• Cross Talk: ≤ 2.5%. This specifies the maximum amount of unintended light from a non-energized segment when an adjacent segment is lit, often due to internal optical reflection.

3. Binning System Explanation

The datasheet indicates that the device is \"categorized for luminous intensity.\" This implies a binning system is in place, although specific bin codes are not listed in the provided excerpt. In LED manufacturing, binning is the process of sorting LEDs based on measured parameters like luminous intensity (brightness), forward voltage (V_F), and dominant wavelength (color).

• Luminous Intensity Binning: LEDs are grouped into bins based on their light output at a standard test current. This ensures consistency in brightness across multiple displays used in the same product. The datasheet's 2:1 intensity matching ratio is a performance guarantee that relies on this binning.
• Forward Voltage Binning: LEDs may also be binned by their V_F. Using LEDs from the same V_F bin in a multiplexed or parallel-driven circuit helps ensure uniform current distribution and consistent brightness.
• Wavelength/Color Binning: For colored LEDs like this green AlInGaP type, binning by dominant wavelength (λ_d) ensures a consistent hue. The caution note recommending the use of \"same BIN LED display\" for multi-unit assemblies directly addresses the need to avoid \"hue uneven problems.\"

Designers should consult the manufacturer for specific bin code information when ordering for applications requiring tight color or brightness matching.

4. Performance Curve Analysis

While the provided PDF excerpt references \"Typical Electrical / Optical Characteristics Curves\" on page 7/10, the specific graphs are not included in the text content. Typically, such curves for an LED display would include:

• Relative Luminous Intensity vs. Forward Current (I-V Curve): This graph would show how light output increases with drive current. It is typically non-linear, with efficiency often dropping at very high currents.
• Forward Voltage vs. Forward Current: This shows the diode's I-V characteristic, crucial for designing the current-limiting circuitry.
• Relative Luminous Intensity vs. Ambient Temperature: This curve demonstrates how light output decreases as the junction temperature rises. It is critical for designing systems that operate over a wide temperature range.
• Spectral Distribution: A graph plotting light intensity against wavelength, showing the peak at ~571nm and the spectral width.

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

5. Mechanical and Package Information

5.1 Package Dimensions and Drawing

The LTC-7500KG is a 30-pin, dual-in-line package. Key dimensions from the drawing include:

• Overall package width: Approximately 45.72 mm.
• Digit height: 18.4 mm (0.72 inches).
• Pin spacing (pitch): 2.54 mm (0.1 inches), a standard DIP pitch.
• Row-to-row spacing: 10.16 mm (2.54 mm * 4).
• Pin diameter: 0.45 mm. The recommended PCB hole diameter is 0.9 mm to allow for easy insertion and soldering.

Tolerances for most dimensions are ±0.25 mm. Specific notes address allowable manufacturing variations such as pin tip shift (±0.4 mm), foreign material on segments, ink contamination, bubbles, and bending of the reflector.

5.2 Pin Connection and Polarity Identification

The device uses a multiplexed common cathode configuration. There are three common cathode pins, one for each digit (Digit 1, Digit 2, Digit 3). The anodes for each segment (A-G and DP) for all three digits are brought out to individual pins. This structure allows the microcontroller to illuminate one digit at a time by pulling its common cathode low while applying a high signal to the desired segment anodes. By cycling through the digits rapidly (multiplexing), all three digits appear to be continuously lit. The pinout table provides the specific mapping for all 30 pins. Pin 1 is identified in the drawing, establishing the orientation.

6. Soldering and Assembly Guidelines

Proper handling and assembly are critical for reliability.

• Soldering: The device can withstand a solder temperature of 260°C for 3 seconds at a point 1.6mm below the seating plane. Standard lead-free reflow or wave soldering profiles compatible with this requirement should be used.
• Mechanical Stress: Avoid using unsuitable tools or assembly methods that apply abnormal force to the display body, as this can cause physical damage.
• Pattern Film Application: If a decorative film is applied to the front, it uses pressure-sensitive adhesive. It is not recommended to let this film side be in close contact with a front panel/cover, as external force may cause the film to shift.

7. Storage Conditions

To prevent degradation, especially oxidation of the pins, the LED displays should be stored in their original packaging under the following conditions:

• Temperature: 5°C to 30°C.
• Relative Humidity: Below 60% RH.

Storage outside these specifications may compromise solderability and long-term performance.

8. Application Recommendations and Design Considerations

Based on the \"Cautions\" section, several critical design and application guidelines must be followed.

8.1 Circuit Design

• Drive Method: Constant current driving is strongly recommended over constant voltage driving. This ensures consistent luminous intensity regardless of variations in the forward voltage (V_F) of individual LED chips.
• Current Limiting: The circuit must be designed to supply the intended drive current across the whole range of possible V_F (2.05V to 2.6V typical).
• Safe Operating Current: The chosen continuous drive current must be derated based on the maximum expected ambient temperature in the application, using the 0.28 mA/°C derating factor from 25°C.
• Protection: The driving circuit must include protection against reverse voltages and transient voltage spikes during power-up or shutdown. Reverse bias can cause metal migration, increasing leakage current or causing short circuits.

8.2 Thermal and Environmental Management

• Thermal Management: Exceeding the recommended operating current or temperature will lead to severe light output degradation or premature failure. Adequate ventilation or heat sinking may be necessary in high-temperature environments.
• Condensation: Avoid rapid changes in ambient temperature, especially in high-humidity environments, as this can cause condensation to form on the display, potentially leading to electrical or optical issues.

8.3 Testing and Matching

• Mechanical Testing: If the end product incorporating this display must pass drop or vibration tests, the test conditions should be shared with the supplier for evaluation and recommendations prior to design finalization.
• Display Matching: For applications using two or more displays in one set (e.g., a multi-digit panel), it is recommended to use displays from the same manufacturing bin to avoid noticeable differences in brightness or hue.

9. Technical Comparison and Differentiation

While a direct comparison with other models is not provided in the datasheet, the LTC-7500KG's key differentiators can be inferred from its specifications:

• Technology: The use of AlInGaP on GaAs substrate for green light offers high efficiency and good temperature stability compared to older technologies.
• Package: The 0.72-inch digit height in a standard 30-pin DIP package offers a balance between size and readability, fitting well into many existing product form factors.
• Optical Performance: The combination of high typical brightness (11550 µcd @10mA), high contrast (black face/white segments), and wide viewing angle is a strong package for user interfaces.
• Compliance: Lead-free and RoHS-compliant packaging meets modern environmental regulations.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this display with a 5V microcontroller pin directly?
A: No. The typical forward voltage is 2.6V, and a series current-limiting resistor is always required to set the correct current. Driving it directly from a 5V pin would likely exceed the absolute maximum current and destroy the LED.

Q: Why is the peak current (60mA) so much higher than the continuous current (25mA)?
A: LEDs can handle short, high-current pulses because the heat generated does not have time to raise the junction temperature to a dangerous level. The 1/10 duty cycle and 0.1ms pulse width ensure the average power remains within safe limits. This is used for applications requiring very high peak brightness.

Q: What does \"common cathode\" mean for my driver circuit?
A: In a common cathode display, all the cathodes (negative sides) of the LEDs for one digit are connected together. To light a segment, you apply a positive voltage (through a resistor) to its anode and connect the corresponding digit's common cathode to ground. This is the opposite of a common anode display.

Q: How do I achieve uniform brightness across all three digits?
A: Use multiplexing. Turn on only one digit at a time by enabling its common cathode. Illuminate the desired segments on that digit. Cycle through the three digits rapidly (e.g., at 100Hz or faster). The persistence of vision makes all digits appear steadily lit. Ensure the peak current during each digit's brief on-time provides the desired average brightness.

11. Practical Application Example

Scenario: Designing a digital timer display.
A designer is creating a countdown timer that displays minutes and seconds (MM:SS). They would need two LTC-7500KG units. The microcontroller (e.g., an ARM Cortex-M or PIC) would have 6 common cathode control lines (one per digit) and 8 segment control lines (7 segments + decimal point). The firmware would implement a multiplexing routine. The drive current would be set via current-limiting resistors or, preferably, a constant current driver IC. The current value would be chosen based on the required brightness and the maximum ambient temperature inside the timer enclosure. To ensure visual consistency, the designer would specify to the supplier that both displays should be from the same intensity and wavelength bin.

12. Operating Principle Introduction

The LTC-7500KG operates on the principle of electroluminescence in a semiconductor p-n junction. When a forward voltage exceeding the diode's threshold is applied, electrons from the n-type AlInGaP layer recombine with holes from the p-type layer, releasing energy in the form of photons (light). The specific composition of the AlInGaP semiconductor determines the wavelength (color) of the emitted light, in this case, green (~572 nm). Each digit is composed of seven bar-shaped LED segments (A through G) and a decimal point (DP). By selectively energizing these segments, any numeric digit from 0 to 9 can be formed. The multiplexing scheme electronically shares the segment driver lines across all digits, significantly reducing the required number of microcontroller I/O pins.

13. Technology Trends

LED display technology continues to evolve. While the LTC-7500KG uses mature and reliable AlInGaP technology, broader industry trends include:

• Increased Efficiency: Ongoing material science research aims to improve the lumens-per-watt (efficacy) of all LED colors, reducing power consumption for the same light output.
• Miniaturization: There is a trend towards smaller pixel pitches and higher-density displays, though for large-digit applications like this, readability remains paramount.
• Integration: Some modern displays integrate the driver ICs directly into the module package, simplifying external circuitry. The LTC-7500KG represents a traditional, discrete approach offering maximum design flexibility.
• Color Options: While this is a monochrome green display, there is a wide availability of seven-segment displays in other colors (red, yellow, blue, white) using different semiconductor materials like InGaN for blue/white.

The LTC-7500KG occupies a well-established niche for applications requiring robust, highly legible, and reliable numeric indication without the cost and complexity of a full graphic display.