LTP-3786JD-03 LED Display Datasheet - 0.54-inch Digit Height - Hyper Red - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTP-3786JD-03 is a dual-digit, 14-segment alphanumeric display designed for applications requiring clear character representation. It features a digit height of 0.54 inches (13.8 mm), making it suitable for medium-sized readouts in various electronic equipment. The device utilizes AlInGaP (Aluminum Indium Gallium Phosphide) Hyper Red LED chips fabricated on a GaAs substrate, offering a specific spectral output. The display has a light gray face with white segments, enhancing contrast and readability.

1.1 Core Features and Advantages

• Character Appearance: Continuous, uniform segments contribute to excellent character definition and appearance.
• Optical Performance: High brightness and high contrast ratio ensure visibility in various lighting conditions.
• Viewing Angle: A wide viewing angle allows the display to be read from different positions.
• Power Efficiency: Low power requirement, typical of LED technology.
• Reliability: Solid-state construction offers long operational life and resistance to shock and vibration.
• Consistency: Devices are categorized (binned) for luminous intensity, aiding in achieving uniform brightness across multiple units in an assembly.

1.2 Target Applications

This display is intended for use in ordinary electronic equipment. This includes, but is not limited to, office automation equipment, communication devices, household appliances, instrumentation panels, and consumer electronics where clear numeric and limited alphabetic readouts are needed.

2. Technical Specifications Deep Dive

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation should be maintained within these limits.

• Power Dissipation per Chip: 70 mW
• Peak Forward Current per Chip: 90 mA (under pulsed conditions: 1/10 duty cycle, 0.1 ms pulse width)
• Continuous Forward Current per Chip: 25 mA at 25°C. A derating factor of 0.33 mA/°C applies above 25°C.
• Reverse Voltage per Chip: 5 V
• Operating & Storage Temperature Range: -35°C to +85°C
• Solder Condition: 260°C for 3 seconds, with the solder point at least 1/16 inch (≈1.6 mm) below the device's seating plane.

2.2 Electrical & Optical Characteristics (Ta=25°C)

These are the typical performance parameters under specified test conditions.

• Average Luminous Intensity (I_V): 200-520 µcd (microcandelas) at a forward current (I_F) of 1 mA. Measured with a filter approximating the CIE photopic eye-response curve.
• Peak Emission Wavelength (λ_p): 650 nm at I_F=20 mA.
• Dominant Wavelength (λ_d): 639 nm at I_F=20 mA, with a tolerance of ±1 nm. This defines the perceived color.
• Spectral Line Half-Width (Δλ): 20 nm at I_F=20 mA, indicating the spectral purity.
• Forward Voltage per Segment (V_F): 2.1V to 2.6V at I_F=20 mA. Tolerance is ±0.1V.
• Reverse Current per Segment (I_R): Maximum 100 µA at a reverse voltage (V_R) of 5V.
• Luminous Intensity Matching Ratio (I_V-m): Maximum 2:1 ratio between segments at I_F=1 mA, ensuring brightness uniformity.
• Crosstalk: ≤ 2.5%, minimizing unwanted illumination of non-selected segments.

3. Mechanical and Package Information

3.1 Package Dimensions

The display is provided in a standard dual-digit package with 18 pins. 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.
• Recommended PCB hole diameter for the pins is 1.0 mm.
• Quality criteria are defined for foreign material (≤10 mil), ink contamination (≤20 mil), bubbles in segments (≤10 mil), and reflector bending (≤1% of length).

3.2 Pin Configuration and Internal Circuit

The device features a common anode configuration. There are two common anode pins: one for Character 1 (pin 16) and one for Character 2 (pin 11). All other pins (except pin 3, which is No Connection) are cathodes for individual segments (A through P, and D.P. for the decimal point). The internal circuit diagram shows the independent LED chips for each segment, connected to their respective common anodes. This structure allows multiplexing for driving the two digits.

4. Application Guidelines and Cautions

4.1 Design and Usage Considerations

• Application Scope: Suitable for ordinary electronic equipment. Not recommended for safety-critical applications (aviation, medical life-support, etc.) without prior consultation.
• Drive Circuit Design:
  • Constant Current Drive: Highly recommended to maintain consistent luminous intensity and color.
  • Voltage Range: The circuit must accommodate the full V_F range (2.1V-2.6V) to ensure the desired current is delivered under all conditions.
  • Protection: The circuit should protect against reverse voltages and transient voltage spikes during power cycling.
  • Thermal Management: Operating current must be derated based on the maximum ambient temperature to prevent light degradation or failure.
• Avoid Reverse Bias: Can cause metal migration, increasing leakage current or causing shorts.
• Environmental: Avoid rapid temperature changes in humid environments to prevent condensation on the display.
• Mechanical Handling: Do not apply abnormal force to the display body during assembly.
• For Multi-Displays: Use displays from the same luminous intensity bin (BIN) to avoid uneven brightness (hue) across an assembly.

4.2 Storage and Handling Conditions

• Standard Storage (in original packaging): Temperature: 5°C to 30°C. Humidity: Below 60% RH. Long-term storage outside these conditions can lead to pin oxidation.
• Post-Open Storage (for SMD types, reference): If the moisture barrier bag is opened, the device should be used within 168 hours (MSL Level 3) under the same temperature/humidity conditions.
• Baking: If an unsealed package has been stored for over 6 months, baking at 60°C for 48 hours is recommended before assembly, which should be completed within one week.

5. Performance Curves and Characteristics Analysis

The datasheet references typical performance curves (though not displayed in the provided text). These curves are crucial for design and typically include:

• Forward Current vs. Forward Voltage (I-V Curve): Shows the nonlinear relationship, essential for selecting current-limiting resistors or designing constant-current drivers.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with current, aiding in brightness calibration and efficiency analysis.
• Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as temperature rises, critical for thermal design in high-temperature environments.
• Spectral Distribution: A graph of relative intensity vs. wavelength, confirming the dominant and peak wavelengths and the spectral half-width.

Designers should consult the full datasheet graphs to understand these relationships quantitatively for their specific operating conditions.

6. Technical Comparison and Differentiation

The LTP-3786JD-03 differentiates itself through several key aspects:

• Chip Technology: Uses AlInGaP Hyper Red chips, which generally offer higher efficiency and better temperature stability compared to older GaAsP or GaP technologies for red/orange colors.
• Optical Design: The light gray face with white segments is engineered for high contrast, improving readability compared to displays with black faces or diffused segments.
• Quality Control: The specification of tight tolerances for segment defects (bubbles, contamination) and the categorization for luminous intensity (BINning) indicate a focus on optical consistency and quality.
• Package: The 18-pin, through-hole design with separate common anodes for each digit provides flexibility in multiplexing drive circuits.

7. Frequently Asked Questions (FAQs)

7.1 How do I drive this display?

Use a multiplexing technique. Sequentially enable one common anode (digit) at a time while applying the correct cathode pattern for the desired segments on that digit. The cycle must be fast enough to avoid flicker (typically >60 Hz). A constant current driver per segment or a current-limited supply is recommended.

7.2 What is the purpose of the intensity BIN code?

The BIN code groups displays based on their measured luminous intensity at a standard test current. Using displays from the same BIN in a multi-unit application ensures uniform brightness across all digits, preventing a patchy appearance.

7.3 Can I use a simple resistor to limit current?

Yes, for simple applications. Calculate the resistor value using R = (V_supply - V_F) / I_F. Use the maximum V_F from the datasheet (2.6V) to ensure the minimum current is met under worst-case conditions. However, for best consistency across segments and temperatures, a constant current circuit is superior.

7.4 Why is reverse voltage protection important?

Applying a reverse bias beyond the absolute maximum rating (5V) can cause immediate damage. Even smaller reverse voltages, if sustained or repetitive (e.g., from inductive kickback in a circuit), can degrade the LED over time through electromigration, leading to increased leakage or failure.

8. Practical Application Example

Scenario: Designing a simple two-digit counter.

1. Microcontroller Interface: Connect the two common anode pins (11, 16) to two GPIO pins configured as current-sourcing outputs. Connect the 16 segment cathode pins to GPIO pins configured as current-sinking outputs, possibly through transistors or a driver IC for higher current.
2. Current Limiting: Implement constant current sinks for each cathode line, set to 10-15 mA for a good balance of brightness and longevity, staying well below the 25 mA continuous rating.
3. Software: Create a look-up table mapping numbers 0-9 to the appropriate segment patterns (A-G). In the main loop, enable Digit 1, output the pattern for the tens place, wait 1-5 ms, disable Digit 1, enable Digit 2, output the pattern for the ones place, wait 1-5 ms, and repeat. This creates a stable, flicker-free display.
4. Thermal Consideration: If the enclosure might get hot (e.g., >50°C), consider reducing the drive current slightly using the derating factor (0.33 mA/°C above 25°C) to ensure reliability.

9. Operating Principle and Technology Trends

9.1 Basic Operating Principle

An LED is a semiconductor diode. When a forward voltage exceeding its bandgap is applied, electrons and holes recombine in the active region (the AlInGaP layer in this case), releasing energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy and thus the wavelength (color) of the emitted light, which is in the hyper-red spectrum for this device. The 14-segment layout allows the formation of numerals and a limited set of alphabetic characters by selectively illuminating combinations of the segments.

9.2 Industry Trends

While through-hole displays like the LTP-3786JD-03 remain relevant for prototyping, repair, and certain industrial applications, the broader trend in display technology is towards surface-mount device (SMD) packages for automated assembly and miniaturization. Additionally, there is a continuous drive for higher efficiency (more lumens per watt), which for red LEDs involves optimizing the AlInGaP epitaxial structure and improving light extraction from the chip. For alphanumeric displays, dot-matrix panels are increasingly common as they offer full alphanumeric and graphic capability, though segmented displays retain advantages in cost, simplicity, and clarity for dedicated numeric readouts.