LTP-3862JR LED Display Datasheet - 0.3 Inch Digit Height - AlInGaP Super Red - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTP-3862JR is a high-performance, dual-digit alphanumeric display module designed for applications requiring clear character representation. Its core function is to display alphanumeric characters (letters and numbers) using a 17-segment configuration per digit, offering greater flexibility than standard 7-segment displays. The device utilizes advanced AS-AlInGaP (Aluminum Indium Gallium Phosphide) RED SUPER LED chips, which are epitaxially grown on a GaAs substrate. This technology is known for its high efficiency and excellent luminous properties. The visual design features a black face with white segments, which significantly enhances contrast and readability under various lighting conditions. The display is categorized for luminous intensity, ensuring consistency in brightness across production batches.

1.1 Core Advantages and Target Market

The key advantages of this display stem from its design and semiconductor technology. The continuous uniform segments create a smooth, appealing character appearance without visible gaps or discontinuities. It operates with low power requirements, making it suitable for battery-powered or energy-conscious devices. The combination of high brightness and high contrast ensures legibility even in brightly lit environments. A wide viewing angle allows the displayed information to be read from various positions relative to the display surface. The solid-state reliability of LED technology offers long operational life and resistance to shock and vibration compared to other display types like vacuum fluorescent or incandescent.

This product is typically targeted at markets and applications where compact, reliable, and clear alphanumeric readouts are essential. Common applications include industrial instrumentation panels, test and measurement equipment, medical devices, point-of-sale terminals, automotive dashboard displays (for auxiliary information), and various consumer electronics where status or numeric data needs to be presented.

2. Technical Specifications Deep Dive

This section provides a detailed, objective analysis of the key technical parameters specified in the datasheet.

2.1 Photometric and Optical Characteristics

The optical performance is central to the display's functionality. The Average Luminous Intensity per Segment is specified with a minimum of 200 µcd, a typical value of 600 µcd, and no maximum listed, when driven at a forward current (I_F) of 1mA. This parameter defines the perceived brightness of each individual segment. The Luminous Intensity Matching Ratio is specified as 2:1 maximum. This is a critical parameter for display uniformity; it means the brightness of the dimmest segment will be no less than half the brightness of the brightest segment under the same conditions, ensuring a consistent look across all segments of a character.

The color characteristics are defined by wavelength parameters, measured at I_F=20mA. The Peak Emission Wavelength (λ_p) is 639 nm, which is in the red region of the visible spectrum. The Dominant Wavelength (λ_d) is 631 nm. The difference between peak and dominant wavelength relates to the shape of the emission spectrum. The Spectral Line Half-Width (Δλ) is 20 nm, indicating the spectral purity or the spread of the emitted light's wavelengths around the peak.

2.2 Electrical Parameters

The electrical specifications define the operating limits and conditions for the device. The Forward Voltage per Segment (V_F) ranges from 2.0V to 2.6V at a test current of 20mA. Designers must ensure the driving circuit can provide sufficient voltage to overcome this, typically using a current-limiting resistor or constant-current driver. The Reverse Current per Segment (I_R) is a maximum of 100 µA at a reverse voltage (V_R) of 5V, indicating the level of leakage when the LED is reverse-biased.

The Absolute Maximum Ratings set the boundaries for safe operation. The Continuous Forward Current per Segment is 25 mA at 25°C, with a derating factor of 0.33 mA/°C above that temperature. This means the maximum allowable continuous current decreases as ambient temperature increases to prevent overheating. The Peak Forward Current is 90 mA but only under specific pulsed conditions: a 1/10 duty cycle and a 0.1ms pulse width. This allows for multiplexing schemes where higher instantaneous current can be used to achieve perceived brightness while keeping average power dissipation low. The Power Dissipation per Segment is limited to 70 mW.

2.3 Thermal and Environmental Specifications

The device is rated for an Operating Temperature Range of -35°C to +105°C and an identical Storage Temperature Range. This wide range makes it suitable for applications in harsh environments, both industrial and automotive. The derating of forward current with temperature, as mentioned, is a direct thermal management consideration. The datasheet also specifies soldering conditions: the device can withstand 260°C for 3 seconds at a distance of 1/16 inch (approximately 1.59 mm) below the seating plane, which is a typical reflow soldering profile guideline.

3. Mechanical and Packaging Information

The LTP-3862JR comes in a standard LED display package. The datasheet includes a detailed dimensioned drawing (package dimensions). Key mechanical features include the overall footprint, the height of the package, the spacing between the two digits, and the precise location and diameter of the mounting holes or pins. The drawing specifies that all dimensions are in millimeters, with standard tolerances of ±0.25mm unless otherwise noted. This information is crucial for PCB (Printed Circuit Board) layout designers to ensure the physical footprint on the board matches the display and that there is adequate clearance around the component.

3.1 Pin Configuration and Internal Circuit

The device has a total of 20 pins. It is configured as a Multiplex Common Anode type. This means the anodes of the LEDs for each digit are connected together internally. Digit 1's common anode is on Pin 4, and Digit 2's common anode is on Pin 10. The cathodes of each individual segment (A through U, plus DP for decimal point) are brought out to separate pins. This multiplexed architecture allows control of two digits with fewer driver lines than if each segment were independently addressable. An internal circuit diagram would typically show these common anode connections for each digit and how the segment cathodes are organized. The pin connection table is essential for correctly wiring the display to a microcontroller or driver IC.

4. Performance Curve Analysis

The datasheet references typical electrical/optical characteristic curves. While the specific graphs are not detailed in the provided text, standard curves for such devices would include:

• Forward Current vs. Forward Voltage (I-V Curve): This graph shows the nonlinear relationship between the voltage across the LED and the current flowing through it. It helps designers select the appropriate current-limiting resistor value for a given supply voltage.
• Luminous Intensity vs. Forward Current: This curve shows how the light output increases with increasing drive current. It is typically linear over a range but may saturate at very high currents.
• Luminous Intensity vs. Ambient Temperature: This graph demonstrates how light output decreases as the junction temperature of the LED increases. Understanding this derating is vital for applications operating at high ambient temperatures.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the shape of the emitted light spectrum, centered around the peak wavelength of 639 nm.

These curves provide designers with a more nuanced understanding of the device's behavior under non-standard or varying conditions beyond the single-point data in the tables.

5. Application Guidelines and Design Considerations

5.1 Driving Circuit Design

To operate this multiplexed common anode display, a driver circuit is required. This typically involves using a microcontroller with sufficient I/O pins or a dedicated LED driver IC. The common anodes (Pins 4 and 10) would be connected to the microcontroller via current-sourcing transistors or directly if the MCU pins can source enough current. The segment cathodes (Pins 1-3, 5-9, 11-13, 15-20) would be connected to current-sinking drivers (like a transistor array or driver IC). The multiplexing is achieved by sequentially turning on one digit's common anode at a time while presenting the segment pattern for that digit on the cathode lines. This cycle must happen fast enough (typically >60 Hz) to avoid visible flicker. The peak current rating allows the use of higher instantaneous currents during the brief on-time of each digit to achieve a higher perceived average brightness.

5.2 Thermal and Soldering Management

While LEDs are efficient, the power dissipated (up to 70mW per segment) can lead to heating, especially when multiple segments are lit simultaneously. Adequate PCB copper area or thermal vias may be considered for the common anode pins to act as a heat sink. Strict adherence to the soldering profile (260°C for 3 seconds) is necessary to prevent damage to the internal epoxy, wire bonds, or the semiconductor die itself during assembly.

5.3 Optical Integration

The black face/white segment design offers high contrast. For further enhancement in bright ambient light, a contrast filter or a darkened cover window can be used. The wide viewing angle eliminates the need for precise alignment of the viewer with the display normal. Designers should consider the intended viewing distance and ambient light levels when selecting drive currents to ensure optimal readability without unnecessary power consumption.

6. Technical Comparison and Differentiation

The primary differentiators of the LTP-3862JR are its use of AlInGaP Super Red technology and its 17-segment architecture. Compared to older technologies like standard GaAsP or GaP LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in brighter displays at the same current or lower power consumption for the same brightness. The 17-segment format, compared to a standard 7-segment display, allows for the legible representation of the full alphabet (alphanumeric) rather than just numerals and a few letters, greatly expanding its application scope. The categorization for luminous intensity is another key point, providing a level of brightness consistency that is important for multi-digit displays where uneven brightness would be visually distracting.

7. Frequently Asked Questions (Based on Technical Parameters)

Q: What does a 2:1 Luminous Intensity Matching Ratio mean for my design?
A: It guarantees visual uniformity. In the worst case, one segment will be no dimmer than half the brightness of another segment driven identically. This prevents some characters or parts of characters from appearing noticeably dimmer than others.

Q: Can I drive this display with a 5V microcontroller directly?
A: Not directly for the segments. The forward voltage is 2.0-2.6V. Connecting a 5V MCU pin directly to a segment cathode (through a resistor) would apply ~5V reverse bias to the LED when the MCU pin is high, which exceeds the 8V reverse voltage rating and could damage the LED. You must use appropriate driver circuitry (transistors or driver ICs) to interface the MCU's logic levels with the LED current requirements.

Q: How do I calculate the current-limiting resistor value?
A: Use Ohm's Law: R = (V_supply - V_F) / I_F. For a 5V supply, a typical V_F of 2.3V, and a desired I_F of 20mA: R = (5 - 2.3) / 0.02 = 135 ohms. Use the next standard value (e.g., 150 ohms) which gives a slightly lower current, well within the safe operating area.

Q: What is the purpose of the peak forward current rating?
A: It enables multiplexing. In a multiplexed setup, each digit is only on for a fraction of the time (e.g., 1/2 duty cycle for two digits). To achieve a desired average brightness, you can use a higher instantaneous current during its short on-time. The 90mA peak rating (at 0.1ms pulse, 1/10 duty) allows this. The average current must still respect the continuous current rating when calculated over time.

8. Practical Application Example

Scenario: Designing a simple two-digit counter with microcontroller interface.
A design case would involve an 8-bit microcontroller (e.g., an ATmega328P). Two of its I/O pins would be configured as outputs to drive the common anodes (Digit 1 and Digit 2) via small NPN transistors (e.g., 2N3904) to source the required current for all lit segments in a digit. Eight other I/O pins would be used to drive the segment cathodes through a current-sinking driver IC like a ULN2003A Darlington array, which can handle the combined segment currents. The firmware would maintain a counter variable. It would separate the tens and units digits, convert each to a 17-segment pattern (using a look-up table), and then alternately enable the transistor for Digit 1 while outputting the units digit pattern, then enable Digit 2 while outputting the tens digit pattern, in a continuous loop with a short delay. The current-limiting resistors would be placed on either the common anode side (simpler, one resistor per digit) or the segment cathode side (more precise control per segment, more resistors).

9. Operating Principle Introduction

The fundamental operating principle is based on electroluminescence in a semiconductor p-n junction. The AlInGaP semiconductor material has a specific bandgap energy. When a forward voltage exceeding the junction's threshold (the forward voltage V_F) is applied, electrons from the n-type region and holes from the p-type region are injected across the junction. When these charge carriers recombine, they release energy. In a direct bandgap semiconductor like AlInGaP, this energy is released primarily as photons (light). The wavelength (color) of the emitted light is determined by the bandgap energy of the material. The 17-segment layout is a geometric arrangement of individual LED dies or chip regions within the package, each corresponding to a segment of the character. Electrical connections are made via wire bonds to the anode and cathode contacts, which are routed to the external pins of the package.

10. Technology Trends

Display technology is continuously evolving. While the AlInGaP technology in this datasheet represents a high-performance solution for red/orange/yellow colors, broader trends include the adoption of even more efficient materials and structures. For full-color or white displays, InGaN (Indium Gallium Nitride) based blue and green LEDs are dominant. There is a constant drive towards higher luminous efficacy (more lumens per watt), allowing for brighter displays or lower energy consumption. Miniaturization is another trend, with chip-scale packaging and smaller die sizes enabling displays with higher resolution or the same resolution in a smaller footprint. Furthermore, integrated solutions are becoming more common, where the LED driver circuitry, microcontroller, and sometimes even the display itself are combined into a single module or smart display, simplifying the design-in process for end-product manufacturers. The core advantages of solid-state reliability, low power, and wide viewing angle remain foundational and are enhanced by these material and integration advances.