LTD-322JR LED Display Datasheet - 0.3-inch Digit Height - 2.6V Forward Voltage - Super Red Color - English Technical Document

1. Product Overview

The LTD-322JR is a single-digit, seven-segment LED display module designed for applications requiring clear, bright numeric readouts. Its primary function is to visually represent numeric characters (0-9) and some limited alphanumeric symbols through the selective illumination of its individual LED segments. The device is constructed using AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material, which is grown on a non-transparent GaAs (Gallium Arsenide) substrate. This material technology is specifically chosen for its efficiency in producing high-brightness red light. The display features a black face, which significantly enhances contrast by absorbing ambient light, and white segments that become illuminated in a vibrant super red color when powered. The physical digit height is 0.3 inches (7.62 mm), making it suitable for medium-sized panels where readability from a moderate distance is important.

1.1 Core Advantages and Target Market

The key advantages of this display stem from its AlInGaP LED technology and design. It offers high luminous intensity, excellent character appearance with continuous uniform segments, and a wide viewing angle, ensuring legibility from various positions. It operates with low power requirements, contributing to energy efficiency in the end application. The solid-state construction provides inherent reliability and long operational life with no moving parts. This combination of features makes the LTD-322JR ideal for target markets including industrial instrumentation (e.g., panel meters, process controllers), consumer appliances (e.g., microwave ovens, washing machine timers), test and measurement equipment, and any embedded system requiring a durable, bright, and clear numeric display interface.

2. Technical Parameter Deep-Dive

This section provides an objective and detailed analysis of the device's specifications as defined in the datasheet.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed.

• Power Dissipation per Segment: 70 mW. This is the maximum power that can be safely dissipated as heat by a single illuminated segment under continuous DC operation.
• Peak Forward Current per Segment: 90 mA. This current is permissible only under pulsed conditions with a 1/10 duty cycle and a 0.1 ms pulse width. It allows for brief periods of overdrive to achieve higher instantaneous brightness, such as in multiplexed displays.
• Continuous Forward Current per Segment: 25 mA at 25°C. This is the recommended maximum current for steady-state (DC) operation of a single segment at room temperature. The rating derates linearly by 0.33 mA/°C as the ambient temperature (Ta) increases above 25°C, meaning the allowable continuous current decreases to prevent overheating.
• Reverse Voltage per Segment: 5 V. Applying a reverse bias voltage higher than this can break down the LED's PN junction.
• Operating & Storage Temperature Range: -35°C to +85°C. The device is rated to function and be stored within this ambient temperature range.
• Solder Temperature: Maximum 260°C for a maximum of 3 seconds, measured 1.6mm below the seating plane. This is a critical parameter for wave or reflow soldering processes to prevent thermal damage to the LED chips or package.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters measured at an ambient temperature (Ta) of 25°C.

• Average Luminous Intensity (I_V): 200 μcd (min), 600 μcd (typ) at a forward current (I_F) of 1 mA. This quantifies the perceived brightness of the light output. The wide range indicates a binning system for intensity.
• Peak Emission Wavelength (λ_p): 639 nm (typ) at I_F=20mA. This is the wavelength at which the spectral power output is maximum, placing it in the "super red" or "red-orange" region of the visible spectrum.
• Spectral Line Half-Width (Δλ): 20 nm (typ). This measures the bandwidth of the emitted light, indicating a relatively pure, monochromatic red color.
• Dominant Wavelength (λ_d): 631 nm (typ). This is the wavelength perceived by the human eye, closely related to the color point.
• Forward Voltage per Segment (V_F): 2.0 V (min), 2.6 V (typ) at I_F=20mA. This is the voltage drop across an LED segment when conducting the specified current. It is crucial for designing the current-limiting circuitry.
• Reverse Current per Segment (I_R): 100 μA (max) at a reverse voltage (V_R) of 5V. This is the small leakage current when the LED is reverse-biased.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 (max). This specifies the maximum allowable ratio between the brightest and dimmest segment within a single digit, ensuring uniform appearance.

3. Binning System Explanation

The datasheet indicates the device is "categorized for luminous intensity." This implies a binning or sorting process post-manufacturing.

3.1 Luminous Intensity Binning

Due to inherent variations in the semiconductor manufacturing process, individual LED chips exhibit slight differences in light output efficiency. To ensure consistency for the end-user, LEDs are tested and sorted into different intensity bins based on their measured luminous intensity at a standard test current (e.g., 1mA). The specified range of 200 to 600 μcd suggests multiple bins exist. Designers can select bins appropriate for their application's brightness uniformity requirements. The 2:1 intensity matching ratio for segments within one device is a tighter tolerance applied after binning.

4. Performance Curve Analysis

While the provided datasheet excerpt mentions "Typical Electrical / Optical Characteristic Curves," the specific graphs are not included in the text. Based on standard LED behavior, these curves would typically illustrate the following relationships, which are critical for circuit design:

4.1 Forward Current vs. Forward Voltage (I-V Curve)

This graph shows the exponential relationship between the current flowing through an LED and the voltage across it. The "knee" voltage, around the typical 2.6V, is where current begins to increase significantly. Drivers must regulate current, not voltage, for stable operation.

4.2 Luminous Intensity vs. Forward Current

This curve demonstrates how light output increases with forward current. It is generally linear over a wide range but will saturate at very high currents due to thermal effects and efficiency droop.

4.3 Luminous Intensity vs. Ambient Temperature

LED light output decreases as the junction temperature rises. This curve is essential for applications operating over a wide temperature range to understand brightness compensation needs.

4.4 Spectral Distribution

A plot of relative intensity versus wavelength, showing the peak at ~639 nm and the spectral width of ~20 nm, confirming the color purity.

5. Mechanical & Package Information

5.1 Package Dimensions

The device has a standard 10-pin single-in-line (SIL) package. All dimensions are provided in millimeters with a general tolerance of ±0.25 mm unless otherwise specified. Key dimensions include the overall height, width, depth, digit window size, and the spacing between pins (pitch), which is critical for PCB layout.

5.2 Pin Connection and Polarity Identification

The LTD-322JR is a duplex common cathode display. This means it contains two independent digits (Digit 1 and Digit 2) within one package, each with its own common cathode pin. The pinout is as follows:

• Pin 1: Anode G (Segment G)
• Pin 2: No Connection
• Pin 3: Anode A (Segment A)
• Pin 4: Anode F (Segment F)
• Pin 5: Common Cathode (Digit 2)
• Pin 6: Anode D (Segment D)
• Pin 7: Anode E (Segment E)
• Pin 8: Anode C (Segment C)
• Pin 9: Anode B (Segment B)
• Pin 10: Common Cathode (Digit 1)

The "common cathode" configuration means all the cathodes (negative terminals) of the LEDs for a given digit are connected together internally. To illuminate a segment, its corresponding anode pin must be driven high (or connected to a current source through a resistor), while the common cathode for that digit must be connected to ground (low). This configuration is very common and simplifies multiplexing.

5.3 Internal Circuit Diagram

The internal diagram visually represents the electrical connections described above. It shows two sets of seven LEDs (segments A-G), each set sharing a common cathode connection for Digit 1 and Digit 2, respectively. The anode for each corresponding segment (e.g., Segment A of Digit 1 and Segment A of Digit 2) are separate pins, allowing independent control.

6. Soldering & Assembly Guidelines

Adherence to the specified soldering profile is critical to prevent damage.

6.1 Reflow Soldering Parameters

The absolute maximum rating specifies a peak temperature of 260°C for a maximum duration of 3 seconds, measured 1.6mm below the seating plane (typically the PCB surface). This aligns with standard lead-free reflow profiles (e.g., IPC/JEDEC J-STD-020). The preheat, soak, reflow, and cooling rates should be controlled according to the PCB assembly specifications. Thermal shock should be avoided.

6.2 Handling and Storage

Devices should be stored in their original moisture-barrier bags with desiccant in a controlled environment (within the -35°C to +85°C storage range). Standard ESD (Electrostatic Discharge) precautions should be observed during handling to protect the sensitive LED junctions.

7. Application Suggestions

7.1 Typical Application Circuits

The most common drive method is multiplexing. Since the display has two digits with separate common cathodes, a microcontroller can rapidly alternate between illuminating Digit 1 and Digit 2. For each digit cycle, it sets the appropriate common cathode low and applies the correct pattern of high signals to the segment anode pins (through current-limiting resistors). The human eye's persistence of vision blends these rapid pulses into a stable, two-digit number. This method drastically reduces the required number of microcontroller I/O pins compared to static (DC) driving.

7.2 Design Considerations

• Current Limiting Resistors: Essential for every anode line. The resistor value (R) is calculated using Ohm's Law: R = (V_supply - V_F) / I_F. Using the typical V_F of 2.6V at 20mA and a 5V supply, R = (5 - 2.6) / 0.02 = 120 Ω. A slightly higher value (e.g., 150 Ω) is often used to increase longevity and account for V_supply variations.
• Multiplexing Frequency: Should be high enough to avoid visible flicker, typically above 60-100 Hz. The duty cycle for each digit in a 2-digit multiplex is 1/2, so the peak current can be higher than the DC rating to maintain average brightness (as allowed by the 90mA peak rating).
• Viewing Angle: The wide viewing angle is beneficial but consider the primary viewing direction during mechanical enclosure design.
• Contrast Enhancement: The black face provides inherent contrast. Ensure the display window or overlay does not introduce reflections or glare that could reduce readability.

8. Technical Comparison & Differentiation

Compared to older LED technologies like standard GaAsP (Gallium Arsenide Phosphide) red LEDs, the AlInGaP technology used in the LTD-322JR offers significantly higher luminous efficiency, resulting in greater brightness for the same drive current. It also provides better color purity and stability over temperature and lifetime. Compared to contemporary alternatives, its key differentiators are the specific 0.3-inch digit height in a common-cathode duplex configuration, the super red color point (~639 nm), and the categorization for luminous intensity which aids in achieving uniform displays when using multiple units.

9. Frequently Asked Questions (FAQ)

9.1 Can I drive this display with a 3.3V microcontroller?

Yes, but careful calculation is needed. With a V_F of 2.6V, the voltage headroom (3.3V - 2.6V = 0.7V) is low. Using the formula R = 0.7V / I_F, for a 10mA current you would need a 70 Ω resistor. At 20mA, the required 35 Ω resistor leaves almost no margin for V_supply or V_F variation, potentially dimming the display. It is more reliable to use a 5V supply for the LED segments, controlled via transistors or a driver IC from the 3.3V microcontroller.

9.2 What is the difference between "peak" and "dominant" wavelength?

Peak Wavelength (λ_p): The single wavelength where the optical power output is physically the highest. Dominant Wavelength (λ_d): The wavelength of monochromatic light that would appear to have the same color as the LED's output to a standard human observer. It is calculated from the LED's full spectrum and the CIE color matching functions. For a narrow-spectrum LED like this one, they are often close in value.

9.3 How do I achieve uniform brightness when multiplexing?

Ensure the multiplexing routine has equal on-time for each digit. Since brightness is proportional to average current, you can adjust the segment current (via resistor values or driver settings) to compensate for the duty cycle. For a 2-digit multiplex at 1/2 duty cycle, you might drive each segment at 40mA peak (within the 90mA rating) to achieve an average of 20mA, matching the DC test condition for brightness.

10. Design-in Case Study

Scenario: Designing a simple two-digit temperature readout for an industrial oven controller. The microcontroller has limited I/O pins.
Implementation: The LTD-322JR is ideal. Its duplex common cathode design requires only 8 I/O pins to control (7 segment anodes + 1 pin to toggle the two common cathodes, using a transistor if needed). The high brightness and wide viewing angle ensure the temperature is readable on a factory floor. The AlInGaP technology ensures stable performance at the elevated ambient temperatures near the oven. The designer selects LEDs from the same luminous intensity bin to guarantee both digits appear equally bright. Current-limiting resistors are calculated for a 5V supply and a multiplexed peak current of 30mA per segment, providing a bright, flicker-free display.

11. Technology Principle Introduction

AlInGaP is a III-V compound semiconductor. When forward-biased, electrons and holes are injected into the active region where they recombine, releasing energy in the form of photons (light). The specific bandgap energy of the AlInGaP alloy determines the wavelength of the emitted light, which in this case is in the red region (~639 nm). The use of a non-transparent GaAs substrate helps contain light within the structure, directing more of it upwards through the top of the chip for higher extraction efficiency compared to older transparent-substrate designs. The black epoxy package absorbs stray light, improving contrast.

12. Technology Trends

While AlInGaP remains a dominant technology for high-efficiency red, orange, and yellow LEDs, ongoing research focuses on improving efficiency at higher drive currents (reducing "efficiency droop") and enhancing reliability. For displays, the trend is towards higher pixel densities (smaller digits/discrete LEDs) and the integration of driver electronics directly into the package ("intelligent displays"). However, for standard segmented numeric displays like the LTD-322JR, the technology is mature, with emphasis on cost reduction, tighter binning for uniformity, and improved thermal management for high-reliability applications.