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

1. Product Overview

The LTP-3862JD is a compact, high-performance dual-digit alphanumeric display module. Its primary function is to present clear, readable numeric and limited alphabetic characters in electronic devices. The core application areas include instrumentation panels, industrial control systems, point-of-sale terminals, and test equipment where space is at a premium but information clarity is critical. The device is engineered for reliability and ease of integration into multiplexed drive circuits commonly found in embedded systems.

1.1 Core Advantages and Target Market

This display offers several key advantages that make it suitable for professional and industrial applications. The use of AlInGaP (Aluminum Indium Gallium Phosphide) Hyper Red LED chips provides high luminous efficiency, resulting in excellent brightness and contrast even in well-lit environments. The continuous uniform segments create a smooth, pleasing character appearance without visible gaps or discontinuities. Its low power requirement is a significant benefit for battery-operated or energy-conscious devices. The wide viewing angle ensures readability from various positions, which is essential for panel-mounted equipment. The device is categorized for luminous intensity, allowing designers to select bins for consistent brightness across multiple units in a product line. Furthermore, its lead-free package complies with modern environmental regulations (RoHS). The target market primarily includes designers and manufacturers of industrial controls, medical devices, automotive dashboards, and consumer appliances requiring a compact, reliable display solution.

2. Technical Parameters: In-Depth Objective Interpretation

The datasheet provides comprehensive electrical, optical, and mechanical specifications necessary for proper circuit design and integration.

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 320 µcd, typical of 900 µcd, and a maximum value not stated, when driven at a forward current (I_F) of 1mA. This parameter, measured using a filter approximating the CIE photopic eye-response curve, indicates the perceived brightness. The Luminous Intensity Matching Ratio of 2:1 defines the maximum allowable variation in brightness between different segments within a single device, ensuring visual uniformity. The color is defined by the Peak Emission Wavelength (λ_p) of 650 nm (nanometers) and the Dominant Wavelength (λ_d) of 639 nm, both typical at I_F=20mA. These values place the emission firmly in the hyper-red region of the spectrum. The Spectral Line Half-Width (Δλ) of 20 nm (typical) describes the spectral purity or the range of wavelengths emitted around the peak.

2.2 Electrical Parameters

Electrical specifications are crucial for designing the driver circuitry. The key parameter is the Forward Voltage per Segment (V_F), which has a typical value of 2.6V and a maximum of 2.6V at I_F=20mA. This relatively low voltage is characteristic of AlInGaP technology. The Reverse Current per Segment (I_R) is a maximum of 100 µA when a reverse voltage (V_R) of 5V is applied, indicating the leakage current in the off state. The absolute maximum ratings define the operational limits: Continuous Forward Current per Segment is 25 mA, with a derating factor of 0.33 mA/°C above 25°C ambient temperature. The Peak Forward Current per Segment is 90 mA, but only under specific conditions (1 kHz frequency, 10% duty cycle), which is relevant for multiplexed driving schemes. The Power Dissipation per Segment must not exceed 70 mW.

2.3 Thermal and Environmental Ratings

The device is rated for an Operating Temperature Range of -35°C to +85°C and an identical Storage Temperature Range. This wide range ensures reliable operation in harsh environments, from freezing industrial settings to hot enclosures. The forward current derating mentioned above is a direct thermal consideration; as ambient temperature rises, the maximum allowable continuous current must be reduced to prevent overheating and premature failure.

3. Binning System Explanation

The datasheet explicitly states that the device is Categorized for Luminous Intensity. This refers to a post-production sorting process, known as binning. During manufacturing, slight variations occur in the epitaxial growth and processing of the LED chips, leading to differences in key parameters like luminous intensity and forward voltage. To ensure consistency for the end-user, manufacturers measure each unit and sort them into predefined groups or \"bins\" based on these measurements. For the LTP-3862JD, the primary binning criterion is luminous intensity at a standard test current (likely 1mA or 20mA). This allows designers purchasing parts from the same intensity bin to achieve uniform brightness across all digits in their application, which is critical for product aesthetics and quality. The datasheet does not provide the specific bin code definitions, which would typically be found in a separate binning document.

4. Performance Curve Analysis

While the PDF shows a placeholder for \"Typical Electrical / Optical Characteristic Curves,\" such curves are standard for LED datasheets and provide vital design insight. Based on the provided tabular data and standard LED behavior, we can infer the following typical relationships:

Luminous Intensity vs. Forward Current (I-V Curve): The luminous intensity (I_V) does not increase linearly with current. It rises steeply at lower currents and tends to saturate at higher currents due to thermal and efficiency droop effects. The typical value of 900 µcd at 1mA suggests a very efficient chip. Designers would use this curve to select an operating current that provides the desired brightness without exceeding power dissipation limits.

Forward Voltage vs. Forward Current & Temperature: The forward voltage (V_F) has a negative temperature coefficient; it decreases as the junction temperature increases for a given current. This is an important consideration for thermal management and constant-current driver design. The typical V_F of 2.6V at 20mA and 25°C serves as a baseline.

Relative Intensity vs. Wavelength (Spectral Distribution): This curve would show a single, dominant peak centered around 650 nm (peak) and 639 nm (dominant), with a shape defined by the 20 nm half-width. It confirms the deep red color output of the AlInGaP material.

Luminous Intensity vs. Ambient Temperature: The light output of LEDs generally decreases as the ambient (and thus junction) temperature increases. Understanding this derating is essential for applications operating at high temperatures to ensure the display remains sufficiently bright.

5. Mechanical and Package Information

The device is described as having a \"black face and white segments,\" which provides a high contrast ratio when the segments are unlit, enhancing readability. The digit height is precisely 0.3 inches (7.62 mm). The PDF includes a section for \"Package Dimensions,\" indicating that a detailed mechanical drawing is part of the full datasheet. This drawing would specify the overall length, width, and height of the package, the segment and digit spacing, the lead (pin) dimensions, and the recommended footprint for PCB (Printed Circuit Board) layout. The pin count is 20, arranged in a dual-in-line package (DIP) format, which is standard for through-hole mounting. Accurate interpretation of this drawing is critical for PCB design, ensuring proper fit, alignment, and soldering.

6. Pin Connection and Circuit Configuration

The LTP-3862JD uses a Multiplex Common Anode configuration. This means the anodes of the LEDs for each digit are connected together internally, while the cathodes for each segment are separate. The pinout is as follows: Pin 4 is the Common Anode for Digit 1, and Pin 10 is the Common Anode for Digit 2. The remaining pins (1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 13, 15, 16, 17, 18, 19, 20) are cathodes for specific segments (A, B, C, D, E, F, G, H, K, M, N, P, R, S, T, U, and DP for the decimal point). Pin 14 is marked \"No Connection.\" This configuration is optimized for multiplexing. To illuminate a specific segment on a specific digit, the corresponding digit's common anode pin is driven high (connected to a positive voltage through a current-limiting resistor or transistor), and the corresponding segment cathode pin is driven low (sinked to ground). By rapidly cycling which digit's anode is active and setting the appropriate cathode patterns, both digits can be made to appear continuously lit to the human eye.

7. Soldering and Assembly Guidelines

The Absolute Maximum Ratings section provides a critical soldering condition: \"1/16 inch below seating plane for 3 seconds at 260°C.\" This is a directive for wave soldering or hand soldering of the through-hole pins. The \"seating plane\" is the bottom surface of the display's plastic body where it meets the PCB. The instruction means the solder wave or iron tip should contact the leads no more than 1.6 mm (1/16 inch) above the PCB surface, and the exposure to 260°C solder should not exceed 3 seconds. Exceeding this time or temperature can damage the internal wire bonds or the plastic package. For reflow soldering (if a surface-mount variant existed), a specific reflow profile with ramp-up, soak, peak temperature, and cool-down rates would be provided. Proper handling to avoid electrostatic discharge (ESD) is also implied, though not explicitly stated, as LEDs are generally sensitive to ESD.

8. Application Suggestions and Design Considerations

Typical Application Circuits: The primary application is in multiplexed displays. A microcontroller with sufficient I/O pins (or using shift registers or dedicated display driver ICs like the MAX7219) would control the anodes and cathodes. Each common anode requires a current-sourcing driver (e.g., a PNP transistor or a dedicated high-side driver), and each segment cathode requires a current-sinking driver (e.g., an NPN transistor or a low-side driver IC). Current-limiting resistors are mandatory for each segment cathode path to set the desired forward current (e.g., 10-20 mA). The resistor value can be calculated using R = (V_supply - V_F) / I_F.

Design Considerations: 1. Multiplexing Frequency: Must be high enough to avoid visible flicker, typically above 60-100 Hz. 2. Peak Current: In a multiplexed setup with a 1/2 duty cycle (for two digits), the instantaneous current per segment can be doubled to achieve the same average brightness as DC operation. Ensure the peak current does not exceed the 90 mA absolute maximum. 3. Viewing Angle: Position the display considering its wide viewing angle to maximize visibility for the end-user. 4. Thermal Management: In high ambient temperatures or at high drive currents, ensure adequate ventilation to keep the junction temperature within safe limits. 5. Contrast Enhancement: The black face helps, but for sunlight readability, a contrast filter or a darkened bezel might be necessary.

9. Technical Comparison and Differentiation

Compared to older technologies like standard GaAsP (Gallium Arsenide Phosphide) red LEDs, the AlInGaP Hyper Red used in the LTP-3862JD offers significantly higher luminous efficiency (more light output per mA of current) and better temperature stability. Compared to contemporary side-by-side 7-segment displays, the 16-segment format provides true alphanumeric capability (displaying letters A-Z, albeit some with limited legibility), whereas 7-segment displays are primarily numeric with limited alphabetic representation. Compared to dot-matrix displays, the 16-segment format is simpler to drive (fewer connections) and often provides more legible characters for single or dual-digit applications, though it is less flexible for graphics or custom fonts.

10. Frequently Asked Questions Based on Technical Parameters

Q: Can I drive this display with a constant 20mA DC current per segment without multiplexing?
A: Yes, but only for one digit at a time. Since it's a common anode multiplex design, applying DC to light both digits simultaneously would require connecting both anode pins (4 and 10) together, which is not the intended use and would prevent individual digit control. For static (non-multiplexed) drive of both digits, a common-cathode version would be more appropriate.

Q: The forward voltage is 2.6V typical. Can I run it directly from a 3.3V microcontroller pin?
A: Possibly, but with caution. The voltage drop across a microcontroller GPIO pin in output mode may be too high to provide sufficient voltage headroom (3.3V - V_{GPIO_drop} might be less than 2.6V). It is always recommended to use an external driver transistor or IC to provide adequate current sourcing/sinking capability and proper voltage.

Q: What is the difference between Peak Emission Wavelength and Dominant Wavelength?
A: Peak Emission Wavelength (λ_p) is the wavelength at which the spectral power distribution is maximum. Dominant Wavelength (λ_d) is the single wavelength of monochromatic light that matches the perceived color of the LED when compared to a standard white light source. For LEDs with a symmetric spectrum, they are often close. For this device, 650 nm vs. 639 nm indicates the spectrum is slightly asymmetric.

Q: How do I interpret the \"Luminous Intensity Matching Ratio of 2:1\"?
A: This means that within one single LTP-3862JD unit, the brightest segment will be no more than twice as bright as the dimmest segment when measured under the same conditions (I_F=1mA). This ensures visual uniformity across the display.

11. Practical Design and Usage Case

Case: Designing a Dual-Digit Temperature Readout for an Industrial Oven Controller. The requirements are: display range from -30 to 99 degrees Celsius, operation in an ambient up to 70°C, powered from a 5V rail, and controlled by a microcontroller with limited I/O. The LTP-3862JD is selected for its wide temperature range, clarity, and multiplexing capability which saves I/O pins. The design uses two PNP transistors to source current to the common anodes (pins 4 & 10) and a single 8-bit shift register (like the 74HC595) to sink current for 8 segment lines, with the remaining segments managed by a second shift register or direct MCU pins. Current-limiting resistors are calculated for an average segment current of 15mA. Considering the 70°C ambient, the forward current is derated: Max I_F = 25 mA - (0.33 mA/°C * (70-25)°C) = 25 - 14.85 = ~10.15 mA. The chosen 15mA average in multiplex mode (with a 50% duty cycle per digit) results in a peak current of 30mA, which is well below the 90mA peak rating but above the derated continuous limit. However, since the duty cycle is 50%, the average power is within safe limits. The multiplexing is done at 200 Hz to avoid flicker. A dark red filter is added over the display to enhance contrast in the bright factory environment.

12. Operating Principle Introduction

The LTP-3862JD is based on solid-state semiconductor light emission. The active material is AlInGaP (Aluminum Indium Gallium Phosphide) epitaxially grown on a GaAs (Gallium Arsenide) substrate. When a forward voltage exceeding the semiconductor's bandgap energy (approximately 2V) is applied across the P-N junction of an LED chip, electrons and holes are injected into the active region. They recombine, releasing energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, which directly correlates to the wavelength (color) of the emitted light—in this case, hyper-red at around 650 nm. Each segment of the display contains one or more of these tiny LED chips. The internal circuit diagram, hinted at in the PDF, shows how the chips for each segment are connected in parallel within a digit and how the common anode for each digit is formed. The black plastic package acts as a housing, provides mechanical protection, and incorporates the white segment diffusers which help distribute the light evenly across the segment area.

13. Technology Trends and Developments

While 16-segment displays like the LTP-3862JD remain relevant for specific applications, the broader trend in display technology is towards higher integration and flexibility. Dot-matrix LED displays and OLED (Organic Light Emitting Diode) panels are becoming more cost-effective, offering full alphanumeric and graphic capabilities. However, for simple, high-reliability, high-brightness, and low-cost numeric/alphanumeric readouts, segment displays retain significant advantages in power efficiency, simplicity, and ruggedness. The underlying LED technology continues to evolve; while AlInGaP is mature and efficient for red/orange/yellow, newer materials and chip designs focus on increasing efficiency (lumens per watt), improving high-temperature performance, and enabling even smaller package sizes. The drive towards miniaturization and surface-mount technology (SMT) is also evident, though through-hole packages like this one persist in applications requiring manual assembly or extra mechanical strength.