LTP-3862JS 0.3-inch 17-Segment Alphanumeric LED Display Datasheet - 7.62mm Digit Height - Yellow (587nm) - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTP-3862JS is a high-performance, dual-digit alphanumeric display module designed for applications requiring clear, bright character readouts. Its primary 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 core advantage of this device lies in its use of advanced AS-AlInGaP (Aluminum Indium Gallium Phosphide) LED chips grown on a GaAs substrate, which are known for their high efficiency and excellent color purity in the yellow spectrum. The display features a black face with white segments, providing high contrast for optimal readability. Its target market includes industrial control panels, test and measurement equipment, medical devices, instrumentation, and any embedded system where compact, reliable, and bright alphanumeric indication is required.

2. In-Depth Technical Parameter Analysis

2.1 Photometric and Optical Characteristics

The optical performance is central to the display's functionality. At a standard test current of 1mA per segment, the average luminous intensity (Iv) ranges from a minimum of 320 \u00b5cd to a typical value of 800 \u00b5cd. This high brightness ensures visibility in various ambient lighting conditions. The device emits yellow light with a dominant wavelength (\u03bbd) of 587 nanometers (nm) and a peak emission wavelength (\u03bbp) of 588 nm, measured at a drive current of 20mA. The spectral line half-width (\u0394\u03bb) is 15 nm, indicating a relatively pure and saturated yellow color. A key parameter for display uniformity is the luminous intensity matching ratio, which is specified at 2:1 maximum. This means the brightness difference between the brightest and dimmest segment under identical conditions will not exceed a factor of two, contributing to a consistent visual appearance across all characters.

2.2 Electrical and Thermal Parameters

The electrical characteristics define the operating boundaries and power requirements. The absolute maximum ratings set the limits for safe operation: power dissipation per segment is 70 mW, the peak forward current per segment (at 1kHz, 10% duty cycle) is 60 mA, and the continuous forward current per segment is 25 mA at 25\u00b0C. This current derates linearly at 0.33 mA per degree Celsius above 25\u00b0C, which is a critical consideration for thermal management in the application design. The maximum reverse voltage per segment is 5V. Under typical operating conditions (I_F=20mA), the forward voltage (V_F) per segment ranges from 2.0V to 2.6V. The reverse current (I_R) is a maximum of 100 \u00b5A at the full reverse voltage of 5V. The device is rated for an operating and storage temperature range of -35\u00b0C to +85\u00b0C, making it suitable for a wide range of environmental conditions.

3. Binning and Categorization System

The datasheet explicitly states that the devices are "Categorized for Luminous Intensity." This indicates that the LTP-3862JS units are sorted (binned) based on their measured light output at the standard test condition. This binning process ensures that customers receive displays with consistent brightness levels. While the specific bin codes or intensity ranges are not detailed in this excerpt, typical categorization for such displays involves grouping them into different intensity grades (e.g., standard brightness, high brightness). Designers should consult the manufacturer's full binning documentation to select the appropriate grade for their specific contrast and visibility requirements, especially when multiple displays are used in a single product.

4. Performance Curve Analysis

The datasheet references "Typical Electrical / Optical Characteristic Curves," which are essential for detailed design work. Although the specific graphs are not provided in the text, these curves typically include:
Forward Current vs. Forward Voltage (I-V Curve): This graph shows the relationship between the current flowing through an LED segment and the voltage across it. It is non-linear, and the curve helps designers select the appropriate current-limiting resistor value to achieve the desired brightness while staying within the electrical ratings.
Luminous Intensity vs. Forward Current: This curve illustrates how the light output increases with drive current. It is generally linear over a range but will saturate at higher currents. This information is crucial for pulse-width modulation (PWM) dimming designs.
Luminous Intensity vs. Ambient Temperature: This graph shows how light output decreases as the junction temperature of the LED increases. Understanding this derating is vital for applications operating at high ambient temperatures to ensure the display remains sufficiently bright.

5. Mechanical and Package Information

The LTP-3862JS is a through-hole display package. The provided "Package Dimensions" diagram (details in millimeters) is critical for PCB (Printed Circuit Board) layout. The display has 20 pins arranged in two rows. The dimensional drawing includes the overall length, width, and height of the package, the spacing between pins (pitch), the distance between rows of pins, and the seating plane. Tolerances for all dimensions are \u00b10.25 mm unless otherwise specified. The pinout is clearly defined, with pins 4 and 10 serving as the common anodes for Digit 1 and Digit 2, respectively. All other pins (except pin 14, which is No Connection) are cathodes for specific segments (A through U, DP). The "Rt. Hand Decimal" note in the part description suggests the inclusion of a right-hand decimal point, which is controlled via the DP cathode pin.

6. Soldering and Assembly Guidelines

The datasheet provides specific soldering conditions to prevent damage to the LED components during assembly. The recommended condition is to solder at 260\u00b0C for a maximum of 3 seconds, with the stipulation that this applies to a point 1/16 inch (approximately 1.59 mm) below the seating plane of the display. This is a standard wave soldering or hand soldering guideline meant to limit the heat transferred to the sensitive LED chips and the plastic housing. For reflow soldering processes, a compatible solder paste and a profile that does not exceed the maximum storage temperature of 85\u00b0C for the device body should be used. Proper handling to avoid electrostatic discharge (ESD) is also implied, as with all semiconductor devices.

7. Internal Circuit and Pin Connection

The "Internal Circuit Diagram" and "Pin Connection" table are fundamental for understanding how to drive the display. The LTP-3862JS uses a multiplexed common anode configuration. This means that all the anodes of the segments for Digit 1 are connected together to pin 4, and all the anodes for Digit 2 are connected to pin 10. The cathode for each individual segment (e.g., segment A, B, C) is brought out to a separate pin and is shared between both digits. To illuminate a specific segment on a specific digit, the designer must:
1. Apply a positive voltage (through a current-limiting resistor) to the common anode pin of the desired digit (4 or 10).
2. Sink current to ground through the cathode pin corresponding to the desired segment.
This multiplexing technique allows control of 34 segments (17 per digit) with only 20 pins, significantly reducing the I/O pin count required from the driving microcontroller. The timing for switching between the two digits must be fast enough to avoid visible flicker, typically above 60 Hz.

8. Application Suggestions and Design Considerations

8.1 Typical Application Scenarios

This display is ideal for any embedded system requiring a compact, two-character readout. Common applications include: digital multimeters and clamp meters, frequency counters, process controllers (showing setpoints or values), power supply units, communication equipment status displays, automotive diagnostic tools, and laboratory instrumentation.

8.2 Critical Design Considerations

• Current Limiting: External current-limiting resistors are mandatory for each cathode line or common anode line to prevent exceeding the maximum continuous forward current and to set the desired brightness. The resistor value is calculated using R = (V_supply - V_F) / I_F.
• Multiplex Drive Circuitry: A microcontroller with sufficient I/O pins or an external driver IC (like a dedicated LED display driver or a shift register with high-current outputs) is needed to handle the multiplexing.
• Thermal Management: In high-temperature environments or when driving at higher currents, ensure the power dissipation per segment does not exceed 70mW. Consider the derating curve for forward current.
• Viewing Angle: The "Wide Viewing Angle" feature is beneficial, but the PCB should be mounted to align the display's optimal viewing direction with the end user's typical line of sight.

9. Technical Comparison and Differentiation

The LTP-3862JS differentiates itself through several key features. Compared to older technology like standard GaAsP or GaP LEDs, the AlInGaP material system offers significantly higher luminous efficiency, resulting in brighter displays at lower currents. The 17-segment architecture provides true alphanumeric capability, unlike 7-segment displays which are limited in the characters they can represent legibly. The black face with white segments enhances contrast ratio, improving readability in bright ambient light compared to displays with a gray or clear face. The multiplexed common anode design offers a good balance between pin count reduction and driver complexity, making it more efficient than a static (non-multiplexed) drive scheme which would require many more I/O pins.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: How do I calculate the resistor value for a segment?
A: Use Ohm's Law: R = (V_CC - V_F) / I_F. For a 5V supply, a typical V_F of 2.3V, and a desired I_F of 10mA: R = (5 - 2.3) / 0.01 = 270 Ohms. Always use the maximum V_F from the datasheet (2.6V) for a conservative design to ensure current doesn't exceed limits.

Q: Can I drive this display with a constant current source instead of a resistor?
A: Yes, a constant current source is an excellent method for driving LEDs as it ensures consistent brightness regardless of minor variations in V_F between segments or with temperature. It is often used in more sophisticated designs.

Q: What does "multiplex common anode" mean for my software?
A: Your software must rapidly alternate between enabling Digit 1 and Digit 2. While Digit 1's anode is active, you set the cathode patterns for the segments you want lit on Digit 1. Then, you switch to Digit 2's anode and set the cathode patterns for Digit 2. This cycle must repeat fast enough to create a persistent image (>>60Hz).

Q: The luminous intensity is given at 1mA, but I want to drive it at 20mA. How much brighter will it be?
A: LED brightness is approximately linear with current over a range. Driving at 20mA could yield roughly 20 times the luminous intensity of the 1mA test condition, but you must consult the I_V vs. I_F curve for accuracy and ensure you do not exceed the absolute maximum ratings.

11. Practical Design and Usage Example

Consider designing a simple two-digit voltmeter display. A microcontroller with an analog-to-digital converter (ADC) reads a voltage. The software converts this value to two decimal digits (e.g., "12"). It uses a look-up table to translate each digit (0-9) into the correct cathode pattern for the 17 segments to form that digit. The microcontroller then employs two of its I/O pins as the digit select lines (connected to the common anodes via transistors, as the MCU pins likely cannot source enough current) and uses up to 17 other I/O pins (or a smaller number with external shift registers) to control the segment cathodes. The code enters a loop that: enables the transistor for the tens digit anode, outputs the cathode pattern for the digit "1\