LTD-322JF LED Display Datasheet - 0.3-inch Digit Height - Yellow-Orange Color - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTD-322JF is a high-performance, seven-segment LED display module designed for applications requiring clear, bright numeric readouts. Its primary function is to provide a highly legible digital display in a compact form factor.

1.1 Core Advantages and Target Market

This device is engineered with several key advantages that make it suitable for a variety of industrial, commercial, and instrumentation applications. Its core strengths include high brightness and excellent contrast, ensuring readability even in well-lit environments. The wide viewing angle allows the display to be seen clearly from various positions. Furthermore, it offers solid-state reliability, meaning no moving parts and a long operational lifespan with minimal maintenance. The low power requirement makes it energy-efficient. The target market includes test and measurement equipment, industrial control panels, medical devices, automotive dashboards, and consumer appliances where reliable numeric indication is critical.

2. Technical Specifications Deep Dive

This section provides a detailed, objective analysis of the device's key technical parameters as defined in the datasheet.

2.1 Photometric and Optical Characteristics

The optical performance is central to the display's functionality. The device utilizes AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material grown on a non-transparent GaAs substrate, which is responsible for its distinctive yellow-orange emission. The typical average luminous intensity (Iv) is 320 to 800 microcandelas (μcd) when driven at a forward current (IF) of 1mA. This parameter defines the perceived brightness. The peak emission wavelength (λp) is typically 611 nanometers (nm), and the dominant wavelength (λd) is 605 nm, precisely defining the yellow-orange color point. The spectral line half-width (Δλ) is 17 nm, indicating a relatively pure, saturated color emission. Luminous intensity matching between segments is specified at a ratio of 2:1 maximum, ensuring uniform appearance across the digit.

2.2 Electrical Parameters

The electrical characteristics define the operating conditions and power requirements. The forward voltage (VF) per segment is typically 2.6 Volts, with a maximum of 2.6V at a test current of 20mA. This is a critical parameter for designing the current-limiting circuitry. The absolute maximum ratings provide the limits for safe operation: the continuous forward current per segment is 25 mA, and the power dissipation per segment must not exceed 70 mW. A derating factor of 0.33 mA/°C applies for the continuous current above 25°C ambient temperature. The device can withstand a reverse voltage (VR) of up to 5 Volts per segment, and the reverse current (IR) is a maximum of 100 μA at this voltage.

2.3 Thermal and Environmental Specifications

Reliability under various environmental conditions is crucial. The device is rated for an operating temperature range of -35°C to +85°C. The storage temperature range is identical. This wide range ensures functionality in harsh environments. A critical assembly parameter is the solder temperature: the device can withstand a maximum of 260°C for a maximum of 3 seconds, measured 1.6mm below the seating plane of the package. This information is vital for defining the reflow soldering profile during PCB assembly.

3. Binning and Categorization System

The datasheet explicitly states that the devices are \"categorized for luminous intensity.\" This indicates a binning process where units are sorted and labeled based on their measured light output at a standard test condition (typically IF=1mA). This allows designers to select parts with consistent brightness levels for their application, preventing noticeable variations in display intensity between different units or production batches. While the specific bin codes are not detailed in this excerpt, the practice ensures product consistency.

4. Performance Curve Analysis

The datasheet references \"Typical Electrical / Optical Characteristic Curves.\" Although the specific graphs are not provided in the text, standard curves for such devices would typically include:

• Forward Current vs. Forward Voltage (I-V Curve): Shows the nonlinear relationship, crucial for determining the required drive voltage for a desired current.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with current, up to the maximum rated limits.
• Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as temperature increases, which is important for high-temperature applications.
• Spectral Distribution: A plot of relative intensity versus wavelength, visually confirming the peak and dominant wavelengths and spectral width.

These curves are essential for detailed circuit design and understanding performance under non-standard conditions.

5. Mechanical and Package Information

5.1 Physical Dimensions and Outline

The device features a 0.3-inch (7.62 mm) digit height. The package dimensions are provided in a drawing (referenced but not shown in text), with all dimensions in millimeters and standard tolerances of ±0.25 mm unless otherwise noted. The physical construction includes a black face with white segments, which significantly enhances the contrast ratio when the LEDs are off, improving overall readability.

5.2 Pin Connection and Internal Circuit

The LTD-322JF is a duplex common-cathode display, meaning it has two digits (Digit 1 and Digit 2) with their cathodes connected separately. The pinout is as follows: Pin 1: Anode G, Pin 3: Anode A, Pin 4: Anode F, Pin 5: Common Cathode (Digit 2), Pin 6: Anode D, Pin 7: Anode E, Pin 8: Anode C, Pin 9: Anode B, Pin 10: Common Cathode (Digit 1). Pins 2 and a position for Pin 11 are noted as \"No Connection\" or \"No Pin.\" An internal circuit diagram shows the standard seven-segment plus decimal point layout, with separate anodes for each segment and common cathodes for each digit, allowing for multiplexed driving.

6. Soldering and Assembly Guidelines

As mentioned in the Absolute Maximum Ratings, the critical parameter for assembly is the solder heat tolerance. The component can withstand a peak temperature of 260°C for a maximum duration of 3 seconds, measured at a point 1.6mm below the package body. This defines the upper limit for a standard lead-free reflow soldering profile. Designers and assembly technicians must ensure the thermal profile does not exceed this limit to prevent damage to the LED chips or the internal wire bonds. Proper ESD (Electrostatic Discharge) handling procedures should always be followed during assembly.

7. Application Suggestions

7.1 Typical Application Scenarios

The combination of high brightness, contrast, wide viewing angle, and reliability makes the LTD-322JF ideal for:

• Industrial Controls: Panel meters, process indicators, timer displays.
• Test and Measurement Equipment: Multimeters, frequency counters, power supplies.
• Automotive Aftermarket: Gauges, diagnostic tool displays.
• Consumer Appliances: Microwave ovens, washing machines, audio equipment.
• Medical Devices: Portable monitors, diagnostic equipment (where the specific color may be chosen for clarity).

7.2 Design Considerations

• Current Limiting: Always use series current-limiting resistors for each segment anode. The resistor value is calculated based on the supply voltage (Vcc), the LED forward voltage (Vf ~2.6V), and the desired forward current (e.g., 10-20 mA for good brightness). Formula: R = (Vcc - Vf) / If.
• Multiplexing: For multi-digit displays like this one, multiplexing is the standard driving technique. This involves sequentially enabling one digit's common cathode at a time while presenting the segment data for that digit. This reduces the number of required microcontroller I/O pins significantly.
• Power Dissipation: Ensure the calculated power per segment (Vf * If) does not exceed 70 mW, especially at high ambient temperatures where derating applies.
• Viewing Angle: Position the display considering its wide viewing angle to maximize visibility for the end-user.

8. Technical Comparison and Differentiation

Compared to older technologies like standard GaAsP or GaP red LEDs, the AlInGaP material used in the LTD-322JF offers significantly higher luminous efficiency, resulting in greater brightness for the same drive current. The yellow-orange color (605-611 nm) may offer better perceived brightness and contrast to the human eye in certain lighting conditions compared to deep red. Compared to blue or white LEDs with phosphor conversion, AlInGaP devices typically have a narrower spectral output and higher efficacy for their specific color. The 0.3-inch digit height places it in a common size category for panel-mounted displays, offering a good balance between readability and space requirements.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the \"categorized for luminous intensity\" note?
A: It means the LEDs are sorted (binned) based on their light output. You can order parts from a specific brightness bin to ensure consistency across all displays in your product.

Q: Can I drive this display with a 5V microcontroller directly?
A: No. You must use current-limiting resistors. Connecting a 5V source directly to an LED anode would cause excessive current, destroying the segment. Calculate the resistor value as described in the design considerations.

Q: What does \"duplex common cathode\" mean for driving the display?
A: It means the two digits share segment anodes but have separate cathode pins. This allows you to use multiplexing: turn on Digit 1's cathode and light its segments, then turn it off, turn on Digit 2's cathode and light its segments, and repeat rapidly. The human eye perceives both digits as continuously lit.

Q: Is the decimal point included?
A> The internal circuit diagram and pin description (Anode DP) indicate that a decimal point segment is present and can be controlled independently, just like the main segments (A-G).

10. Design and Usage Case Study

Scenario: Designing a simple two-digit temperature meter. A microcontroller reads a temperature sensor. The value (from 0 to 99) needs to be displayed. The LTD-322JF is chosen for its clarity and ease of use. The design uses 8 microcontroller pins: 7 for the segment anodes (A-G, DP optional) and 1 for the digit cathodes (using a transistor to sink the higher combined cathode current). The firmware implements multiplexing, updating the display 50-100 times per second to avoid flicker. Current-limiting resistors are placed on each of the 7 segment lines. The black face of the display provides excellent contrast against the instrument panel when the display is off.

11. Technology Principle Introduction

The core technology is based on the AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material system. When forward-biased, electrons and holes are injected into the active region of the LED chip where they recombine, releasing energy in the form of photons (light). The specific composition of aluminum, indium, gallium, and phosphorus in the crystal lattice determines the bandgap energy, which directly corresponds to the wavelength (color) of the emitted light. For the LTD-322JF, this composition is tuned to produce photons in the 605-611 nm range, perceived as yellow-orange. The use of a non-transparent GaAs substrate helps in directing light out through the top of the device, improving overall light extraction efficiency compared to some older designs.

12. Industry Trends and Context

AlInGaP technology represents a mature and highly optimized solution for high-brightness red, orange, amber, and yellow LEDs. It has been the dominant material for these colors in indicator and display applications for decades due to its high efficiency and reliability. Current trends in display technology for consumer electronics are dominated by full-color, pixelated solutions like OLEDs and micro-LEDs. However, for dedicated, low-complexity numeric and alphanumeric displays requiring high reliability, wide operating temperature ranges, and long lifespan—especially in industrial, automotive, and appliance sectors—devices like the LTD-322JF remain highly relevant. The trend here is towards even higher efficiency and possibly the integration of driver electronics within the display package (\"intelligent displays\"), though the basic seven-segment form factor continues to be widely used.