LTF-3605KR-01 LED Display Datasheet - 0.3-inch Digit Height - AlInGaP Super Red - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTF-3605KR-01 is a six-digit, seven-segment LED display module designed for numeric readout applications. It features a digit height of 0.3 inches (7.68 mm), providing a clear and legible display suitable for various electronic equipment interfaces. The device utilizes AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology on a GaAs substrate to produce a super red emission. The display has a black face for high contrast and white segments for optimal light diffusion and appearance. Its core advantages include low power consumption, excellent character uniformity, high brightness, and a wide viewing angle, making it ideal for consumer electronics, instrumentation, and industrial control panels where reliable numeric indication is required.

1.1 Key Features

• 0.3 inch (7.68 mm) Digit Height
• Continuous Uniform Segments for consistent appearance
• Low Power Requirement
• Excellent Character Appearance
• High Brightness & High Contrast
• Wide Viewing Angle
• Solid-State Reliability
• Categorized for Luminous Intensity (Binning)
• Lead-Free Package (RoHS Compliant)

1.2 Device Description

This is a multiplex common cathode display. Each of the six digits shares its cathode connection, while the anodes for each segment (A-G and DP) are connected across digits, requiring a multiplexed driving scheme. It includes a right-hand decimal point (DP) per digit.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 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. This is the maximum power that can be safely dissipated by a single LED segment.
• Peak Forward Current per Segment: 90 mA. This is allowed only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) to prevent overheating.
• Continuous Forward Current per Segment: 25 mA at 25°C. This current derates linearly at 0.28 mA/°C as ambient temperature increases above 25°C. The driver circuit must ensure the current does not exceed this derated value at the maximum operating temperature.
• Operating & Storage Temperature Range: -35°C to +105°C. The device is rated for industrial temperature ranges.
• Solder Condition: Reflow soldering should be performed with the temperature at 1/16 inch below the seating plane not exceeding 260°C for 3 seconds.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters measured at Ta=25°C under specified test conditions.

• Average Luminous Intensity (Iv): Ranges from 320 µcd (min) to 900 µcd (typ) at IF=1mA. At IF=10mA, the typical intensity is 11,700 µcd. This high efficiency is characteristic of AlInGaP technology.
• Peak Emission Wavelength (λp): 639 nm (typical). This defines the primary color point of the super red emission.
• Spectral Line Half-Width (Δλ): 20 nm. This indicates the spectral purity of the emitted light.
• Dominant Wavelength (λd): 631 nm. This is the single-wavelength perception of the color by the human eye.
• Forward Voltage per Chip (VF): 2.6V (max) at IF=20mA. The driver circuit must be designed to accommodate this maximum voltage drop.
• Reverse Current (IR): 100 µA (max) at VR=5V. This parameter is for test purposes only; continuous reverse bias operation is prohibited.
• Luminous Intensity Matching Ratio: 2:1 (max). This specifies the maximum allowable variation in brightness between segments under the same drive conditions, ensuring visual uniformity.
• Cross Talk: ≤ 2.5%. This defines the maximum amount of unintended light emission from a non-driven segment when an adjacent segment is illuminated.

3. Binning System Explanation

The datasheet states the product is \"Categorized for Luminous Intensity.\" This implies a binning process where displays are sorted based on measured light output at a standard test current (likely 1mA or 10mA as per the characteristics table). Using displays from the same intensity bin within a single application is critical to avoid noticeable brightness differences between units, which is explicitly recommended in the application cautions. While the PDF does not detail specific bin code ranges, designers should consult the manufacturer for binning information when consistency across multiple displays is required.

4. Performance Curve Analysis

The PDF references \"Typical Electrical / Optical Characteristics Curves\" on page 7/10. While the specific graphs are not provided in the text, standard curves for such LEDs would typically include:

• IV Curve (Current vs. Voltage): Shows the exponential relationship, helping to determine the necessary drive voltage for a target current.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with current, essential for brightness calibration and understanding efficiency.
• Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as temperature rises, crucial for thermal management in the application.
• Forward Voltage vs. Ambient Temperature: Indicates how the VF changes with temperature, which can affect constant-current driver design.
• Spectral Distribution: A plot of relative intensity vs. wavelength, centered around the 639nm peak, confirming the super red color.

5. Mechanical & Package Information

5.1 Package Dimensions

The display's mechanical outline is defined in the datasheet. Key notes include:

• All dimensions are in millimeters.
• General tolerance is ±0.25 mm unless otherwise specified.
• Pin tip shift tolerance is ±0.4 mm.
• The recommended PCB hole diameter for the pins is 0.9 mm.
• Quality criteria are specified for foreign material (≤10mil), ink contamination (≤20mils), bubbles in segments (≤10mil), and reflector bending (≤1% of length).

5.2 Pin Connection & Polarity Identification

The device has 14 pins in a single row. The pinout is as follows:

• Pin 1: Common Cathode for Digit 2
• Pin 2: Common Cathode for Digit 3
• Pin 3: Anode for Segment D
• Pin 4: Anode for Decimal Point (DP)
• Pin 5: Common Cathode for Digit 4
• Pin 6: Anode for Segment C
• Pin 7: Common Cathode for Digit 5
• Pin 8: Common Cathode for Digit 6
• Pin 9: Anode for Segment E
• Pin 10: Anode for Segment F
• Pin 11: Anode for Segment G
• Pin 12: Anode for Segment A
• Pin 13: Anode for Segment B
• Pin 14: Common Cathode for Digit 1

Pin 1 is marked as \"No Connection\" in the table, which appears to be a documentation inconsistency as it is also listed as Cathode for Digit 2. The internal circuit diagram should be consulted for clarification. The device uses a common cathode configuration.

6. Soldering & Assembly Guidelines

The absolute maximum ratings specify the soldering profile: the temperature at a point 1/16 inch (approximately 1.6 mm) below the seating plane of the display must not exceed 260°C for more than 3 seconds during assembly. This is a standard reflow soldering condition. Designers must ensure the PCB layout and reflow oven profile comply with this to prevent thermal damage to the LED chips or plastic package.

7. Application Recommendations

7.1 Typical Application Scenarios

This display is intended for ordinary electronic equipment including office equipment, communication devices, and household applications. Its clear red digits make it suitable for:

• Digital multimeters and test equipment
• Industrial timer and counter displays
• Consumer appliance control panels (e.g., ovens, microwaves)
• Audio equipment frequency/level displays
• Point-of-sale terminal readouts

7.2 Design Considerations & Cautions

The datasheet includes extensive application cautions which form critical design rules:

• Drive Circuit Design: Constant current driving is strongly recommended to ensure consistent brightness and longevity. The circuit must be designed to accommodate the full range of forward voltage (VF, up to 2.6V) to guarantee the intended drive current is delivered under all conditions.
• Current & Thermal Management: The operating current must be chosen considering the maximum ambient temperature, applying the specified derating factor (0.28 mA/°C above 25°C). Exceeding ratings causes severe light degradation or failure.
• Protection Circuits: The driving circuit must protect the LEDs from reverse voltages and transient voltage spikes during power-up/shutdown. Continuous reverse bias can cause metal migration, increasing leakage or causing shorts.
• Environmental Considerations: Avoid rapid ambient temperature changes in high humidity to prevent condensation on the display. Do not apply abnormal mechanical force during assembly.
• Optical Films/Overlays: If using a pressure-sensitive film or overlay, avoid letting it press directly against the display surface, as it may shift and cause viewing issues.
• Multi-Display Consistency: For applications using two or more displays, select units from the same luminous intensity bin to avoid uneven brightness (hue) across the set.

8. Storage Conditions

For long-term reliability, specific storage conditions are mandated:

• Standard Storage (in original packaging): Temperature: 5°C to 30°C. Humidity: Below 60% RH.
• Storage outside these conditions may lead to pin oxidation, requiring replating before use.
• It is advised to consume inventory promptly and avoid large long-term stocks.
• If an unsealed package has been stored for over 6 months, it is recommended to bake the displays at 60°C for 48 hours and complete assembly within one week to remove moisture and prevent \"popcorning\" during soldering.

9. Technical Comparison & Differentiation

The LTF-3605KR-01 differentiates itself through its use of AlInGaP technology for the super red color. Compared to older technologies like standard GaAsP red LEDs, AlInGaP offers significantly higher luminous efficiency (brightness per unit current), better temperature stability, and longer lifetime. The 0.3-inch digit height offers a balance between readability and compactness. The common cathode multiplex design is standard for multi-digit displays, reducing the required driver pins from 48 (6 digits * 8 segments) to 14, simplifying the interface microcontroller or driver IC.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the difference between peak wavelength (639nm) and dominant wavelength (631nm)?
A: Peak wavelength is the point of maximum power in the spectral output. Dominant wavelength is the single wavelength perceived by the human eye when viewing the color, which can be slightly different due to the shape of the eye's sensitivity curve and the LED's spectrum.

Q: Can I drive this display with a constant voltage source and a resistor?
A: While possible, it is not recommended. A simple resistor limits current but does not compensate for the VF variation between LEDs or with temperature, leading to inconsistent brightness. A constant current driver is the preferred method for professional designs.

Q: How do I implement the multiplexing for the six digits?
A: A microcontroller or dedicated display driver IC sequentially activates (grounds) one common cathode (Digit 1-6) at a time while applying the correct anode pattern (A-G, DP) for that digit. This cycle repeats rapidly (typically >100Hz) to create the illusion of all digits being on simultaneously.

Q: The max continuous current is 25mA per segment. What current should I use for normal operation?
A> For reliable long-term operation, it is common practice to derate further. Operating at 15-20mA per segment provides excellent brightness while significantly reducing thermal stress and extending operational life. Always confirm the chosen current meets your brightness requirement at the application's maximum ambient temperature.

11. Practical Design Case

Scenario: Designing a digital panel meter operating in an environment up to 50°C.
Steps:
1. Current Calculation: Determine the derated maximum continuous current. From 25°C to 50°C is a 25°C increase. Derating = 25°C * 0.28 mA/°C = 7 mA. Therefore, max safe current at 50°C = 25 mA - 7 mA = 18 mA.
2. Driver Selection: Choose a constant-current LED driver IC capable of multiplexing 6 digits with at least 8 segment outputs. Set the driver's current limit to 18 mA (or a lower value like 15 mA for margin).
3. Thermal Design: Ensure the PCB layout provides adequate copper area around the display pins to act as a heat sink, dissipating heat from the LED junctions.
4. Software: Implement multiplexing firmware with a refresh rate high enough to avoid flicker (e.g., 200 Hz). Include display test and brightness adjustment routines.

12. Operating Principle

The device is based on semiconductor electroluminescence. When a forward bias voltage exceeding the diode's turn-on voltage (approximately 2V for AlInGaP) is applied across an LED segment (anode positive, cathode negative), electrons and holes recombine in the active region of the semiconductor chip. This recombination releases energy in the form of photons (light). The specific material composition (AlInGaP) determines the bandgap energy, which defines the wavelength (color) of the emitted light, in this case, in the red spectrum (~639 nm). The seven segments are individual LED chips arranged in a figure-eight pattern, controlled independently to form numeric characters 0-9.

13. Technology Trends

While discrete seven-segment LED displays remain relevant for specific applications, the broader trend in display technology is moving towards integrated solutions. These include:
- Integrated Driver Displays: Modules with built-in controller chips (like TM1637 or MAX7219 drivers) that simplify the microcontroller interface.
- Surface-Mount Device (SMD) Packages: Replacing through-hole types for automated assembly and smaller form factors.
- Alternative Technologies: For applications requiring more complex graphics or alphanumerics, dot-matrix OLED or LCD displays are increasingly common due to their flexibility.
However, for simple, high-brightness, low-cost numeric readouts in harsh environments (wide temperature range), traditional LED seven-segment displays like the LTF-3605KR-01 continue to offer unmatched reliability and simplicity.