LTC-3743KG LED Display Datasheet - 0.3 Inch Digit Height - AlInGaP Green - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTC-3743KG is a quadruple-digit numeric LED display module designed for applications requiring clear, bright numeric readouts. It features a digit height of 0.3 inches (7.4 mm), making it suitable for medium-sized displays in various electronic equipment. The device utilizes AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology to produce green light. This material system is known for its high efficiency and good performance across a range of operating conditions. The display has a black face with white segments, providing high contrast for excellent readability. It is constructed as a multiplex common cathode type, which is a standard configuration for multi-digit displays to minimize the number of required driver pins.

1.1 Key Features

• 0.3 Inch Digit Height: Provides a clear and easily readable character size.
• Continuous Uniform Segments: Ensures a consistent and professional visual appearance across all digits.
• Low Power Requirement: Designed for energy-efficient operation, suitable for battery-powered or low-power devices.
• Excellent Character Appearance: High contrast between the black background and illuminated white segments.
• High Brightness & High Contrast: The AlInGaP chips deliver strong luminous intensity, visible even in well-lit environments.
• Wide Viewing Angle: Allows the display to be read from a broad range of angles without significant loss of brightness or clarity.
• Solid State Reliability: LEDs offer long operational life and resistance to shock and vibration compared to other display technologies.
• Lead-Free Package: Compliant with RoHS (Restriction of Hazardous Substances) directives, making it suitable for modern electronic manufacturing.

1.2 Device Identification

The part number LTC-3743KG specifically denotes an AlInGaP green, multiplex common cathode display with a right-hand decimal point configuration. This naming convention helps in identifying the exact technology, electrical configuration, and mechanical variant.

2. Technical Parameters Deep Dive

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed.

• Power Dissipation per Segment: 70 mW. This is the maximum power that can be safely dissipated by an individual LED segment.
• Peak Forward Current per Segment: 60 mA. This is the maximum instantaneous current allowed under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). It is significantly higher than the continuous current rating.
• 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 increases above 25°C. For example, at 85°C, the maximum allowable continuous current would be approximately: 25 mA - (0.28 mA/°C * (85°C - 25°C)) = 8.2 mA.
• Operating Temperature Range: -35°C to +105°C. The device is rated to function within this ambient temperature range.
• Storage Temperature Range: -35°C to +105°C.
• Solder Conditions: The device can withstand wave soldering with the solder tip 1/16 inch (approx. 1.6 mm) below the seating plane for 3 seconds at 260°C. The temperature of the unit itself during assembly must not exceed its maximum temperature rating.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters measured at an ambient temperature (Ta) of 25°C.

• Average Luminous Intensity (Iv): 200 - 630 ucd (microcandelas) at a forward current (IF) of 1 mA. This wide range indicates a binning process for brightness.
• Peak Emission Wavelength (λp): 571 nm (typical) at IF=20mA. This is the wavelength at which the emitted light intensity is highest.
• Spectral Line Half-Width (Δλ): 15 nm (typical) at IF=20mA. This measures the spread of the emitted wavelengths; a smaller value indicates a more monochromatic (pure color) light.
• Dominant Wavelength (λd): 572 nm (typical) at IF=20mA. This is the single wavelength perceived by the human eye that best matches the color of the light.
• Forward Voltage per Chip (VF): 2.05V (Min), 2.6V (Typ), with a tolerance of ±0.1V at IF=20mA. This is a critical parameter for driver circuit design.
• Reverse Current per Segment (IR): 100 µA (Max) at a reverse voltage (VR) of 5V. This parameter is for test purposes only; continuous reverse bias operation is prohibited.
• Luminous Intensity Matching Ratio: 2:1 (Max) for similar light areas at IF=10mA. This specifies the maximum allowable brightness variation between segments to ensure uniform appearance.
• Cross Talk: ≤2.5%. This measures the unintended illumination of a non-selected segment when another is driven, which should be minimal.

3. Mechanical & Package Information

The display comes in a standard through-hole DIP (Dual In-line Package) style. Key dimensional notes include:

• All dimensions are in millimeters (mm).
• General tolerance is ±0.25 mm unless otherwise specified.
• Pin tip shift tolerance is ±0.4 mm.
• Limits are placed on foreign material (≤10 mil), bending (≤1% of reflector length), bubbles in segments (≤10 mil), and ink contamination on the surface (≤20 mil) to ensure optical quality.

4. Pin Connection & Internal Circuit

The device has 24 pins. The internal circuit is a multiplexed common cathode configuration. This means the cathodes of the LEDs for each digit are connected together (forming the digit select lines), while the anodes for each segment type (A, B, C, D, E, F, G, DP) are connected across all digits. To illuminate a specific segment on a specific digit, the corresponding digit cathode is driven low (grounded) while the corresponding segment anode is driven high (with a current-limiting resistor). The pinout table clearly defines the function of each pin, including anodes for segments, cathodes for digits, and connections for special features like the decimal points (DP1, DP2, DP3) and other indicators (UDP, LC, L1, L2, L3).

5. Performance Curve Analysis

While the specific graphs are not detailed in the provided text, typical curves for such a device would include:

• IV (Current-Voltage) Curve: Shows the relationship between forward current and forward voltage, which is non-linear. This is essential for designing the current-limiting circuitry.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with current, typically in a near-linear relationship within the operating range.
• Luminous Intensity vs. Ambient Temperature: Shows how light output decreases as the junction temperature of the LED increases. This highlights the importance of thermal management.
• Spectral Distribution: A graph plotting light intensity against wavelength, showing the peak and dominant wavelengths and the spectral half-width.

6. Soldering, Assembly & Storage Guidelines

6.1 Application Cautions

These are critical guidelines for reliable operation:

• Intended Use: For ordinary electronic equipment. Consult the manufacturer for safety-critical applications (aviation, medical, etc.).
• Ratings Compliance: Adherence to Absolute Maximum Ratings is mandatory to avoid damage.
• Current & Temperature: Exceeding recommended drive current or operating temperature leads to rapid light degradation or failure.
• Circuit Protection: The driving circuit must protect against reverse voltages and voltage transients during power cycling.
• Constant Current Drive: Recommended for consistent brightness and longevity, as LED brightness is a function of current, not voltage.
• Forward Voltage Range: The driver circuit must accommodate the full VF range (2.05V to 2.7V) to ensure the target current is always delivered.
• Thermal Derating: The operating current must be chosen based on the maximum expected ambient temperature, using the derating curve.
• Avoid Reverse Bias: Can cause metal migration, increasing leakage or causing shorts.
• Avoid Thermal Shock: Rapid temperature changes in humid environments can cause condensation.
• Mechanical Handling: Avoid applying abnormal force to the display body.
• Film Application: If using a pressure-sensitive film/overlay, avoid having it in direct contact with a front panel to prevent shifting.
• Binning for Multi-Displays: When using multiple displays in one assembly, select units from the same brightness/color bin to avoid uneven appearance.

6.2 Storage Conditions

Proper storage is vital to prevent oxidation of the pins and maintain solderability.

• Standard Condition (in original packaging): 5°C to 30°C, below 60% Relative Humidity (RH).
• Consequences of Improper Storage: Pin oxidation may occur, requiring re-plating before use.
• Inventory Management: Consume displays promptly; avoid long-term storage of large quantities.
• Moisture Sensitivity: If the product is not in a sealed moisture-barrier bag, or the bag has been open for more than 6 months, it is recommended to bake at 60°C for 48 hours and complete assembly within one week.

7. Application Suggestions

7.1 Typical Application Scenarios

The LTC-3743KG is well-suited for:

• Test and measurement equipment (multimeters, power supplies).
• Industrial control panels and process indicators.
• Consumer electronics like audio amplifiers, clock radios, or kitchen appliances.
• Point-of-sale terminals and informational displays.
• Any device requiring a clear, reliable, multi-digit numeric readout.

7.2 Design Considerations

• Driver IC Selection: Use a dedicated LED display driver or microcontroller with sufficient sink/source current capability and multiplexing support.
• Current Limiting: Always use series resistors or a constant-current driver for each anode line. Calculate the resistor value based on the supply voltage, LED forward voltage (use max VF for worst-case current), and desired forward current.
• Multiplexing Frequency: Choose a refresh rate high enough to avoid visible flicker (typically >60 Hz). Ensure the peak current in multiplexed operation does not exceed the absolute maximum rating.
• PCB Layout: Ensure clean power traces to the display driver to avoid noise. Follow recommended footprint from the dimensional drawing.
• Thermal Management: In high ambient temperature applications, consider reducing the drive current or improving ventilation to stay within the derated current limits.

8. Technical Comparison & Differentiation

The LTC-3743KG, based on AlInGaP technology, offers distinct advantages:

• vs. Traditional GaP (Gallium Phosphide) Green LEDs: AlInGaP typically offers higher brightness and efficiency, better temperature stability, and a more saturated green color.
• vs. Blue/White LEDs with Phosphor: This is a direct-emitting green LED, so it does not suffer from phosphor degradation over time and offers a pure spectral output without the broad spectrum of phosphor-converted white LEDs.
• vs. Larger/Smaller Displays: The 0.3-inch digit height strikes a balance between readability and compactness, fitting applications where space is a consideration but legibility from a moderate distance is required.

9. Frequently Asked Questions (FAQ)

Q: What is the purpose of the multiplex common cathode design?
A: It drastically reduces the number of pins required. A non-multiplexed 4-digit, 7-segment display would need 4*7 + 4 = 32 pins. The multiplexed version uses 7 segment lines + 4 digit lines + a few extras = 24 pins, simplifying the PCB and driver circuitry.

Q: How do I calculate the current-limiting resistor value?
A: Use Ohm's Law: R = (V_supply - VF_LED) / I_desired. For a 5V supply, a max VF of 2.7V, and a desired current of 10mA: R = (5V - 2.7V) / 0.010A = 230 Ohms. Use the next standard value (e.g., 220 Ohms) and verify the actual current.

Q: Why is constant current drive recommended over constant voltage?
A: LED luminous intensity is primarily a function of forward current (IF). The forward voltage (VF) can vary from unit to unit and with temperature. A constant current source ensures consistent brightness regardless of these VF variations, while a simple resistor with a constant voltage supply leads to brightness variations.

Q: What does \"Luminous Intensity Matching Ratio 2:1\" mean?
A: It means the brightest segment in a group should be no more than twice as bright as the dimmest segment under the same test conditions. This ensures visual uniformity across the display.

10. Operating Principle Introduction

The LTC-3743KG is based on semiconductor electroluminescence. The AlInGaP material forms a p-n junction. When a forward voltage exceeding the junction's built-in potential is applied, electrons and holes are injected into the active region where they recombine. In AlInGaP, this recombination primarily releases energy in the form of photons (light) in the green wavelength range (~572 nm). The specific alloy composition of Aluminum, Indium, Gallium, and Phosphorus determines the bandgap energy and thus the color of the emitted light. The black face and white segments are part of the package's optical system, designed to absorb ambient light (reducing reflections) and efficiently guide the internally generated light out through the desired segment shapes, creating high contrast.