LTD-322KD-31 LED Display Datasheet - 0.3-inch Digit Height - Hyper Red - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTD-322KD-31 is a dual-digit, seven-segment LED display module designed for numeric readout applications. It features a digit height of 0.3 inches (7.62 mm), providing clear and legible characters suitable for a variety of electronic equipment. The device utilizes AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology to produce a Hyper Red emission, characterized by high brightness and excellent color purity. The display has a black face with white segments, creating a high-contrast appearance that enhances readability under various lighting conditions. It is constructed with a special reflector material capable of withstanding high-temperature soldering processes, making it robust for standard assembly lines. The package is lead-free and compliant with RoHS directives.

1.1 Key Features

• 0.3 inch (7.62 mm) digit height for clear visibility.
• Utilizes AlInGaP Hyper Red LED chips for high brightness and efficiency.
• Continuous uniform segments ensure consistent character appearance.
• Low power requirement, suitable for battery-powered devices.
• Excellent character appearance with high contrast (black face, white segments).
• Wide viewing angle for flexible mounting and user positioning.
• High reliability due to solid-state construction.
• Luminous intensity is categorized (binned) for consistent performance matching.
• Lead-free package compliant with environmental regulations.

1.2 Device Description

The part number LTD-322KD-31 specifically denotes a duplex (dual-digit), common cathode display with a right-hand decimal point. The common cathode configuration simplifies driving circuitry, as all segment LEDs for a given digit share a common ground connection. The right-hand decimal point is integrated for displaying fractional values.

2. Mechanical and Packaging Information

2.1 Package Dimensions

The display's mechanical outline is defined in the datasheet with all dimensions provided in millimeters. Key dimensional notes include:

• General dimensional tolerance is ±0.25 mm unless otherwise specified.
• Pin tip shift tolerance is ±0.4 mm.
• Specific quality criteria are defined for the segment area: foreign material ≤10 mil, ink contamination ≤20 mil, and bubbles ≤10 mil.
• Bending of the reflector is limited to 1% of its length.
• A printed circuit board (PCB) hole diameter of 1.0 mm is recommended for optimal assembly.

2.2 Physical Appearance and Polarity Identification

The display features a black face. Four sides of the package are painted black using ink, while one specific side is painted using a black pen, resulting in a slight visual difference. This side serves as a physical marker for polarity or orientation during assembly. The pin connections are clearly defined to prevent incorrect insertion.

3. Electrical and Optical Characteristics

3.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. They are specified at an ambient temperature (Ta) of 25°C.

• Power Dissipation per Segment: 70 mW
• Peak Forward Current per Segment: 90 mA (at 1/10 duty cycle, 0.1ms pulse width)
• Continuous Forward Current per Segment: 25 mA (derating linearly by 0.33 mA/°C above 25°C)
• Operating Temperature Range: -35°C to +85°C
• Storage Temperature Range: -35°C to +85°C
• Solder Condition: 265 ±5°C for 5 seconds, with the soldering iron tip positioned 1/16 inch below the seating plane.

3.2 Electrical/Optical Characteristics

These are the typical operating parameters measured at Ta=25°C.

• Average Luminous Intensity per Segment (IV):
  • MIN: 320 µcd, TYP: 900 µcd at IF=1mA
  • TYP: 11700 µcd at IF=10mA
• Peak Emission Wavelength (λp): 650 nm (at IF=20mA)
• Spectral Line Half-Width (Δλ): 20 nm (at IF=20mA)
• Dominant Wavelength (λd): 639 nm (tolerance ±1 nm) (at IF=20mA)
• Forward Voltage per Chip (VF): TYP 2.6V, range 2.1V to 2.6V (tolerance ±0.1V) (at IF=20mA)
• Reverse Current per Segment (IR): MAX 100 µA (at VR=5V) - Note: This is for test only, not for continuous operation.
• Luminous Intensity Matching Ratio: MAX 2:1 (between segments in similar light area at IF=1mA)
• Cross Talk Specification: ≤ 2.5%

3.3 Bin Range Distribution (Grading System)

The luminous intensity of the LEDs is categorized into bins to ensure consistency within a production batch. The bin codes (F, G, H, J, K) correspond to specific minimum and maximum luminous intensity values in microcandelas (µcd), each with a tolerance of ±15%. This allows designers to select displays with matched brightness levels.

4. Internal Circuit and Pin Configuration

4.1 Internal Circuit Diagram

The display has an internal circuit where each of the seven segments (A through G) and the decimal point (DP) in each digit is an individual LED. The cathodes of all segments for Digit 1 are connected together to a common pin, and similarly for Digit 2. This forms the common cathode configuration for each digit.

4.2 Pin Connection Table

The device has a 10-pin configuration. The pinout is as follows:

• Pin 1: Anode G (Segment G)
• Pin 2: No Connection (N/C)
• Pin 3: Anode A (Segment A)
• Pin 4: Anode F (Segment F)
• Pin 5: Common Cathode for 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 for Digit 1

This arrangement allows for multiplexed driving, where the two digits are illuminated alternately at a high frequency to create the perception of both being on simultaneously.

5. Application Guidelines and Cautions

5.1 Intended Use and Design Considerations

This display is designed for ordinary electronic equipment including office equipment, communication devices, and household applications. For applications requiring exceptional reliability where failure could jeopardize safety (e.g., aviation, medical systems), consultation is required prior to use. Key design considerations include:

• Drive Circuitry: Constant current driving is strongly recommended to ensure consistent luminous output and longevity. The circuit must be designed to accommodate the full range of forward voltage (VF: 2.1V to 2.6V) to guarantee the target drive current is delivered under all conditions.
• Current and Temperature Management: Operating the display above the recommended current or ambient temperature will lead to accelerated light output degradation and potential premature failure. The drive current must be derated for higher ambient temperatures.
• Protection Circuits: The driving circuit should incorporate protection against reverse voltages and transient voltage spikes that may occur during power-up or shutdown, as these can damage the LED chips.
• Avoiding Reverse Bias: Continuous reverse bias should be avoided as it can cause metal migration within the semiconductor, increasing leakage current or causing short circuits.

5.2 Assembly and Handling Precautions

• Soldering: Adhere strictly to the specified soldering condition (265°C ±5°C for 5 seconds). The temperature of the display body itself must not exceed the maximum ratings during assembly.
• Mechanical Stress: Do not apply abnormal force to the display body during assembly. Use appropriate tools and methods.
• Environmental Conditions: Avoid rapid changes in ambient temperature, especially in high-humidity environments, to prevent condensation from forming on the LED surface, which could affect performance or cause damage.
• Storage: Store within the specified temperature range (-35°C to +85°C). Additional storage condition notes caution against environments that could lead to moisture ingress or mechanical stress.
• Front Panel/Filter Interaction: If a printing film or pattern filter is applied to the display surface using pressure-sensitive adhesive, it is not recommended to let this side be in tight contact with the front panel or cover. Pressure or friction may cause the film to shift from its original position.

6. Performance Analysis and Technical Comparison

6.1 Performance Curve Analysis

While specific graphical curves are referenced in the datasheet, typical performance for AlInGaP Hyper Red LEDs can be inferred:

• IV (Current-Voltage) Curve: Exhibits a standard diode characteristic with a forward voltage typically around 2.6V at 20mA. The curve is relatively steep, indicating good conductivity once the turn-on voltage is reached.
• Luminous Intensity vs. Current (LI-I): Light output increases super-linearly with current at lower levels, becoming more linear at higher currents. Operating at 10mA provides significantly higher brightness than at 1mA, as indicated in the specifications.
• Temperature Dependence: The forward voltage (VF) has a negative temperature coefficient (decreases with increasing temperature). Luminous intensity typically decreases as junction temperature rises, which is why thermal management and current derating are critical.
• Spectral Distribution: The peak wavelength of 650 nm and dominant wavelength of 639 nm place this LED in the deep red/hyper red region of the spectrum. The narrow spectral half-width (20 nm) indicates good color purity.

6.2 Differentiation from Other Technologies

Compared to older GaAsP or standard red GaP LEDs, AlInGaP technology offers several advantages:

• Higher Efficiency and Brightness: AlInGaP provides superior luminous efficacy, resulting in higher light output for the same drive current.
• Better Temperature Stability: While still temperature-sensitive, AlInGaP generally maintains performance better at elevated temperatures than older technologies.
• Superior Color: The hyper red color is often perceived as more vibrant and saturated.
• The use of a non-transparent GaAs substrate helps in directing light forward, improving overall efficiency compared to some transparent-substrate designs.

7. Typical Application Scenarios and Design Case

7.1 Application Scenarios

The LTD-322KD-31 is ideal for any device requiring a compact, bright, and reliable numeric display. Common applications include:

• Test and measurement equipment (multimeters, power supplies).
• Consumer electronics (audio amplifiers, clock radios, kitchen appliances).
• Industrial control panels and timers.
• Point-of-sale terminals and calculators.
• Automotive aftermarket accessories (e.g., voltage monitors).

7.2 Design Case: Multiplexed Drive Circuit

A typical design uses a microcontroller to drive this display in a multiplexed configuration. The microcontroller would have two sets of 8 outputs (7 segments + decimal) connected to the segment anodes (pins 1,3,4,6,7,8,9 and the decimal point anode if used). Two additional microcontroller pins, configured as open-drain or connected through transistors, would control the common cathode pins (5 and 10). The software routine would:

1. Turn off both common cathode drivers.
2. Output the segment pattern for Digit 1 to the segment lines.
3. Briefly enable (ground) the common cathode for Digit 1.
4. After a short delay (e.g., 5-10ms), turn off Digit 1's cathode.
5. Output the segment pattern for Digit 2.
6. Briefly enable the common cathode for Digit 2.
7. Repeat the cycle at a frequency high enough to avoid visible flicker (typically >60Hz).

Current-limiting resistors are required in series with each segment anode line. Their value is calculated based on the supply voltage (Vcc), the LED forward voltage (VF ~2.6V), and the desired segment current (e.g., 10mA for high brightness): R = (Vcc - VF) / I_segment. A constant current driver IC can be used instead of resistors for more precise and stable brightness control.

8. Frequently Asked Questions (FAQ)

8.1 What is the purpose of the binned luminous intensity?

Binning ensures consistency within a production run. When using multiple displays in a single product (like a multi-digit panel), specifying the same bin code guarantees all digits will have closely matched brightness, preventing some digits from appearing dimmer or brighter than others.

8.2 Can I drive this display with a constant voltage source?

It is not recommended. LEDs are current-driven devices. Their forward voltage has a tolerance and varies with temperature. A constant voltage source with a series resistor is a common approximation, but for optimal performance and longevity, especially over a wide temperature range, a true constant current driver is superior.

8.3 Why is there a "No Connection" pin?

The 10-pin package is likely a standard footprint. Pin 2 is left as No Connection (N/C) in this specific device variant. It should not be connected to any circuit trace.

8.4 How do I interpret the "Cross talk specification ≤ 2.5%"?

Cross talk refers to unwanted illumination of a segment that is meant to be off, caused by leakage current or capacitive coupling from adjacent driven segments. A value of ≤2.5% means the luminous intensity of an "off" segment should be no more than 2.5% of the intensity of a fully "on" segment under specified conditions, ensuring good contrast between active and inactive segments.

8.5 What does "Hyper Red" mean compared to standard red?

Hyper Red typically denotes an LED with a dominant wavelength longer than that of standard red LEDs, often in the range of 630-660 nm. It appears as a deeper, more saturated red color. The LTD-322KD-31's dominant wavelength of 639 nm falls into this category, offering high visual impact and good performance in applications where color distinction is important.