LTD-323JR LED Display Datasheet - 0.3-inch Digit Height - 2.6V Forward Voltage - Super Red Color - English Technical Documentation

1. Product Overview

The LTD-323JR is a high-performance, seven-segment numeric display module designed for applications requiring clear, bright, and reliable numerical readouts. Its primary function is to visually represent numeric digits (0-9) and some alphanumeric characters using individually addressable LED segments.

This device is engineered with a focus on readability and efficiency. It utilizes advanced AlGaInP (Aluminum Gallium Indium Phosphide) semiconductor technology for its light-emitting elements. This material system is known for producing high-efficiency red and amber light. The display features a black face, which provides excellent contrast by absorbing ambient light, and white segments that diffuse the emitted red light uniformly, resulting in sharp, well-defined characters.

The core advantage of this display lies in its solid-state construction, offering superior reliability and longevity compared to other display technologies like vacuum fluorescent or incandescent types. It is categorized for luminous intensity, ensuring consistent brightness levels across production batches for uniform appearance in multi-digit applications.

1.1 Key Features and Target Applications

The LTD-323JR is characterized by several key features that make it suitable for a wide range of industrial, commercial, and consumer applications.

• 0.3-inch Digit Height (7.62 mm): This compact size offers a good balance between visibility and space-saving design, ideal for instrument panels, test equipment, point-of-sale terminals, and appliance displays.
• Continuous Uniform Segments: The segments are designed without gaps or discontinuities, creating smooth, professional-looking numerals that enhance readability.
• Low Power Requirement: Operating at low forward currents, it is energy-efficient and suitable for battery-powered or low-power devices.
• High Brightness & High Contrast: The combination of bright AlGaInP LEDs and a black face ensures the display is easily readable even under high ambient light conditions.
• Wide Viewing Angle: The optical design allows the display to be read clearly from a broad range of angles, increasing flexibility in device placement and user interaction.
• Solid-State Reliability: With no moving parts or fragile filaments, the LED display offers excellent shock and vibration resistance and a very long operational lifetime.

Typical applications include digital multimeters, clock radios, industrial control panels, medical devices, automotive dashboards (for secondary displays), and household appliances like microwave ovens or washing machines.

2. Technical Specifications Deep Dive

This section provides a detailed, objective analysis of the electrical and optical parameters specified in the datasheet. Understanding these parameters is crucial for proper circuit design and ensuring optimal display performance.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation outside these limits is not advised.

• Power Dissipation per Segment: 70 mW. This is the maximum power that can be safely dissipated as heat by a single LED segment under continuous operation. Exceeding this can lead to overheating and accelerated degradation.
• Peak Forward Current per Segment: 90 mA (at 1/10 duty cycle, 0.1ms pulse width). This rating is for pulsed operation, allowing higher instantaneous current for multiplexed displays to achieve higher peak brightness. The average current must still comply with the continuous rating.
• Continuous Forward Current per Segment: 25 mA at 25°C. This is the maximum DC current recommended for continuous illumination of a segment. The datasheet specifies a derating factor of 0.33 mA/°C above 25°C, meaning the maximum allowable current decreases as ambient temperature increases to prevent thermal runaway.
• Reverse Voltage per Segment: 5 V. Applying a reverse voltage higher than this can cause breakdown and failure of the LED junction.
• Operating & Storage Temperature Range: -35°C to +85°C. The device is rated for operation and storage within this industrial temperature range.
• Solder Temperature: Maximum 260°C for 3 seconds at 1.6mm below the seating plane. This defines the reflow soldering profile to avoid damaging the plastic package or the internal wire bonds.

2.2 Electrical & Optical Characteristics (at Ta=25°C)

These are the typical operating parameters under specified test conditions.

• Average Luminous Intensity (I_V): 200 (Min), 600 (Typ) µcd at I_F=1mA. This is the measure of perceived brightness. The wide range indicates a binning system; designers must account for this variation or select binned parts for uniform appearance.
• Peak Emission Wavelength (λ_p): 639 nm (Typ) at I_F=20mA. This is the wavelength at which the optical power output is maximum. It falls in the red region of the visible spectrum.
• Spectral Line Half-Width (Δλ): 20 nm (Typ). This indicates the spectral purity or bandwidth of the emitted light. A value of 20 nm is typical for a standard red LED, resulting in a saturated red color.
• Dominant Wavelength (λ_d): 631 nm (Typ). This is the single wavelength perceived by the human eye that best matches the color of the LED. It is slightly shorter than the peak wavelength.
• Forward Voltage per Segment (V_F): 2.0 (Min), 2.6 (Typ) V at I_F=20mA. This is the voltage drop across the LED when conducting the specified current. It is crucial for designing the current-limiting resistor value: R = (V_supply - V_F) / I_F.
• Reverse Current per Segment (I_R): 100 µA (Max) at V_R=5V. This is the small leakage current that flows when the LED is reverse-biased within its maximum rating.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 (Max). This specifies the maximum allowable brightness variation between different segments of the same digit or between digits, ensuring visual uniformity.

3. Binning System Explanation

The datasheet indicates the device is "categorized for luminous intensity." This refers to a binning or sorting process performed during manufacturing.

Luminous Intensity Binning: Due to inherent variations in the semiconductor epitaxial growth and chip fabrication processes, LEDs from the same production batch can have different brightness outputs. Manufacturers test and sort (bin) these LEDs into groups based on their measured luminous intensity at a standard test current (e.g., 1mA, as specified). The LTD-323JR's typical intensity range of 200-600 µcd suggests multiple bins may exist. For applications requiring consistent brightness across multiple displays (like a multi-digit panel), specifying parts from the same intensity bin is essential. The 2:1 intensity matching ratio is a related parameter guaranteed within a device.

While the datasheet does not explicitly mention voltage or wavelength binning for this part, it is common practice. Designers should consult the manufacturer for detailed binning information if critical for their application.

4. Performance Curve Analysis

The datasheet references "Typical Electrical / Optical Characteristic Curves." While the specific graphs are not provided in the text, we can discuss the standard relationships they typically depict, which are vital for understanding device behavior.

• Forward Current vs. Forward Voltage (I-V Curve): This curve shows the exponential relationship between current and voltage for a diode. For the LTD-323JR, the typical V_F is 2.6V at 20mA. The curve helps designers understand the voltage threshold and how V_F changes slightly with temperature and current.
• Luminous Intensity vs. Forward Current (I-L Curve): This graph shows that light output is approximately proportional to forward current in the normal operating range. It is not perfectly linear, especially at very high currents where efficiency drops due to heating.
• Luminous Intensity vs. Ambient Temperature: The light output of LEDs generally decreases as the junction temperature increases. This curve is critical for applications operating over a wide temperature range to ensure sufficient brightness is maintained at high temperatures.
• Spectral Distribution: A graph showing the relative optical power across wavelengths. It would confirm the peak (639 nm) and dominant (631 nm) wavelengths and show the shape of the emission spectrum, characterized by the 20 nm half-width.

5. Mechanical & Packaging Information

5.1 Package Dimensions and Pinout

The device features a standard dual-in-line package (DIP) format suitable for through-hole PCB mounting. The exact dimensions are provided in a drawing (referenced but not detailed in text), with tolerances of ±0.25 mm.

Pin Connection:

1. Pin 1: Cathode G (Segment G, typically the middle segment)
2. Pin 2: No Connection
3. Pin 3: Cathode A (Segment A, top segment)
4. Pin 4: Cathode F (Segment F, upper left segment)
5. Pin 5: Common Anode (Digit 2)
6. Pin 6: Cathode D (Segment D, lower middle segment)
7. Pin 7: Cathode E (Segment E, lower left segment)
8. Pin 8: Cathode C (Segment C, upper right segment)
9. Pin 9: Cathode B (Segment B, top right segment)
10. Pin 10: Common Anode (Digit 1)

Internal Circuit Diagram: The display has a "Duplex Common Anode" configuration. This means it contains two independent digits (Digit 1 and Digit 2). Each digit has its own common anode pin (Pins 10 and 5). All corresponding segment cathodes (A, B, C, D, E, F, G) for both digits are connected internally and brought out to common cathode pins (Pins 3, 9, 8, 6, 7, 4, 1). This architecture allows multiplexing: by sequentially enabling one anode (digit) at a time and driving the appropriate cathode pins for that digit, multiple digits can be controlled with a reduced number of I/O pins.

6. Soldering & Assembly Guidelines

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

• Reflow Soldering: The maximum recommended temperature is 260°C, measured 1.6mm below the package body, for a maximum duration of 3 seconds. This profile is typical for lead-free soldering processes. The plastic package material has a specific glass transition temperature; exceeding the thermal limits can cause package cracking, deformation, or internal bond wire failure.
• Hand Soldering: If hand soldering is necessary, use a temperature-controlled iron. Apply heat to the pin and PCB pad, not directly to the plastic body. Limit soldering time per pin to less than 3-5 seconds to minimize heat transfer to the package.
• Cleaning: Use only cleaning agents compatible with the display's plastic material. Avoid ultrasonic cleaning unless explicitly approved, as it can cause mechanical stress.
• Storage Conditions: Store in a dry, anti-static environment within the specified temperature range (-35°C to +85°C) to prevent moisture absorption (which can cause "popcorning" during reflow) and electrostatic discharge damage.

7. Application Design Considerations

7.1 Driving Circuit Design

To drive the LTD-323JR effectively and safely, a current-limiting scheme is mandatory. A simple resistor in series with each segment is the most common method.

Example Calculation: For a 5V supply (V_CC), driving a segment at the typical forward current of 20mA with a typical V_F of 2.6V:
R_limit = (V_CC - V_F) / I_F = (5V - 2.6V) / 0.020A = 120 Ω.
A standard 120Ω resistor would be used. The power dissipation in the resistor is I²R = (0.02)² * 120 = 0.048W, so a standard 1/8W or 1/4W resistor is sufficient.

Considerations:

• Use the maximum V_F from the datasheet (2.6V) for this calculation to ensure the current does not exceed the limit even with a low-V_F part.
• For multiplexed operation, the instantaneous current during the brief ON time can be higher to achieve the desired average brightness. For example, with a 1/4 duty cycle, the peak current could be 80mA to achieve an average of 20mA, but it must not exceed the 90mA peak rating.
• Use transistors (BJTs or MOSFETs) or dedicated driver ICs (like 74HC595 shift registers with constant-current outputs or MAX7219 display drivers) to sink/sink the segment and digit currents, especially for multiplexing more than a few digits.

7.2 Thermal Management

While individual segments dissipate little power (max 70mW), a multi-digit display driven at high currents can generate significant heat. Ensure adequate airflow around the display and consider the following:

• Adhere to the current derating curve above 25°C ambient temperature.
• Avoid placing the display near other heat-generating components.
• For high-brightness requirements, consider using pulsed operation (PWM) at a higher peak current but lower duty cycle instead of a high continuous current, as this can improve efficiency and reduce average heating.

8. Technical Comparison & Differentiation

The LTD-323JR, based on AlGaInP technology, offers distinct advantages over older LED technologies like GaAsP (Gallium Arsenide Phosphide) and GaP (Gallium Phosphide):

• vs. GaAsP/GaP Red LEDs: AlGaInP LEDs are significantly brighter and more efficient. They produce a more saturated, "true" red light (around 630-640 nm) compared to the orange-red hue of older technologies. This results in the "High Brightness & High Contrast" claim.
• vs. Larger Displays: The 0.3-inch size offers a good compromise. Smaller displays save space but may be harder to read at a distance; larger displays are more visible but consume more board area and power.
• vs. Common Cathode Displays: The common anode configuration is often preferred when interfacing with microcontroller GPIO pins configured as current sinks (pulling to ground), which is a common and robust driving method.

9. Frequently Asked Questions (FAQ)

Q1: What is the purpose of the "No Connection" pin (Pin 2)?
A1: This pin is mechanically present to maintain the standard 10-pin DIP package spacing and physical stability but is not electrically connected internally. It should be left unconnected or connected to a PCB pad for mechanical support only.

Q2: Can I drive this display directly from a microcontroller pin?
A2: It is not recommended to drive an LED segment directly from a standard GPIO pin. Most MCU pins have limited current sourcing/sinking capability (often 20-25mA absolute max per pin and less for the total port). Exceeding this can damage the MCU. Always use a current-limiting resistor and consider using a transistor or driver IC to handle the current.

Q3: How do I achieve uniform brightness in a multi-digit application?
A3: First, ensure all segments are driven with identical current. Second, specify displays from the same luminous intensity bin from the manufacturer. Third, implement software brightness calibration or use a driver IC with individual segment intensity control if minor variations persist.

Q4: What does "Duplex Common Anode" mean for multiplexing?
A4: It means you have two separate common pins (one per digit). To multiplex, you would turn on Digit 1's anode (set pin 10 high if using PNP transistors, or connect to ground through a switch if the anode is driven low), set the cathode pattern for the desired number on Digit 1, wait a short time, then turn off Digit 1, turn on Digit 2's anode, set the cathode pattern for Digit 2, and repeat rapidly. The human eye perceives both digits as continuously lit.

10. Design-in Case Study

Scenario: Designing a simple two-digit counter for a piece of lab equipment, powered by a 5V rail, controlled by a 3.3V microcontroller.

Implementation:

1. Current Limiting: Place a 120Ω resistor in series with each of the 7 segment cathode lines.
2. Segment Driving: Connect the cathode lines (through their resistors) to the drain pins of 7 N-channel MOSFETs (e.g., 2N7002). Connect the source pins to ground. Connect the MOSFET gates to 7 GPIO pins on the MCU via 10kΩ pull-down resistors.
3. Digit Driving (Anode Switching): Connect the two common anode pins (Pins 5 & 10) to the collectors of two PNP transistors (e.g., 2N3906). Connect the emitters to the 5V supply. Connect the bases to two more MCU GPIO pins via 10kΩ resistors. Place a 100Ω resistor between each base and the MCU pin for current limiting.
4. Logic: The MCU runs a multiplexing routine. To display '1' on Digit 1 and '5' on Digit 2:
   • Set GPIOs for segments B and C (for '1') to logic HIGH to turn on their MOSFETs, grounding those cathodes.
   • Set the GPIO for Digit 1's PNP transistor to LOW (turning it on, connecting 5V to anode).
   • Wait 5-10ms.
   • Set Digit 1's GPIO HIGH (turn it off).
   • Set GPIOs for segments A, F, G, C, D (for '5') to HIGH.
   • Set the GPIO for Digit 2's PNP transistor to LOW.
   • Wait 5-10ms, then repeat.

This design safely isolates the 5V display circuit from the 3.3V MCU and provides proper current control.

11. Technology Principle

The LTD-323JR is based on solid-state light emission from a semiconductor p-n junction. The active material is AlGaInP (Aluminum Gallium Indium Phosphide). When a forward voltage exceeding the junction's built-in potential (approximately 2.0-2.6V) is applied, electrons from the n-type region and holes from the p-type region are injected into the active region. There, they recombine, releasing energy in the form of photons (light). The specific composition of the AlGaInP alloy determines the bandgap energy of the semiconductor, which directly dictates the wavelength (color) of the emitted light. The use of a non-transparent GaAs substrate helps reflect light upward, improving extraction efficiency. The black face plastic package incorporates a light-diffusing material over the segments to create a uniform appearance and a filter to enhance contrast.

12. Industry Trends

While discrete seven-segment LED displays like the LTD-323JR remain vital for many applications due to their simplicity, robustness, and low cost, several trends are evident in the display technology landscape:

• Integration: There is a move towards displays with integrated driver ICs ("intelligent displays") that simplify the host controller interface, often using serial protocols like I2C or SPI.
• Alternative Technologies: For applications requiring more complex graphics or alphanumerics, dot-matrix LED displays, OLEDs (Organic LEDs), and LCDs are increasingly used. However, for simple numeric readouts requiring high brightness and wide viewing angles, seven-segment LEDs like the LTD-323JR are often the optimal choice.
• Miniaturization & Efficiency: Ongoing developments in LED chip technology continue to improve luminous efficacy (lumens per watt), allowing for brighter displays at lower currents or enabling further miniaturization.
• Color Options: While this datasheet specifies Super Red, the same package and drive concept apply to displays using other LED technologies for different colors, such as InGaN for blue and green, or phosphor-converted white LEDs.

The LTD-323JR represents a mature, reliable, and well-understood solution that continues to serve a critical role in electronic design where clear, dependable numeric indication is required.