LTC-2687CKS-P LED Display Datasheet - 0.28-inch Digit Height - AlInGaP Yellow - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTC-2687CKS-P is a surface-mount device (SMD) featuring a triple-digit, seven-segment display. Its primary application is in electronic equipment requiring clear, bright numeric readouts, such as instrumentation panels, consumer electronics interfaces, and industrial control systems. The core advantage of this display lies in its use of Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor technology for the yellow LED chips, which offers superior brightness and efficiency compared to older technologies. The device is categorized for luminous intensity, ensuring consistent brightness levels across production batches, and is constructed with a lead-free package compliant with RoHS directives.

1.1 Key Features and Target Market

The display is designed for integration into space-constrained applications where reliability and readability are paramount. Its 0.28-inch (7.0 mm) digit height provides a good balance between size and visibility. Key features include continuous uniform segments for a clean appearance, low power requirement, high brightness and contrast, and a wide viewing angle. These characteristics make it suitable for office equipment, communication devices, household appliances, and other general electronic equipment where exceptional reliability for life-critical systems is not the primary requirement.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. They are not intended for normal operation.

• Power Dissipation per Segment: 70 mW. This is the maximum power that can be safely dissipated as heat by a single segment.
• Peak Forward Current per Segment: 60 mA. This current is permissible 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 (Ta) increases above 25°C. For example, at 85°C, the maximum continuous current would be approximately: 25 mA - (0.28 mA/°C * (85°C - 25°C)) = 8.2 mA.
• Operating & Storage Temperature Range: -35°C to +105°C.
• Soldering Temperature: 260°C for 3 seconds, measured 1/16 inch (≈1.6mm) below the seating plane.

2.2 Electrical & Optical Characteristics

These parameters are measured under typical conditions (Ta=25°C) and define the device's performance.

• Average Luminous Intensity (Iv): This is the key brightness parameter. At a forward current (IF) of 1 mA, the typical value is 400 µcd (microcandelas). At 10 mA, it rises to 2750 µcd. The minimum specified value at 1 mA is 126 µcd.
• Forward Voltage per Chip (VF): Typically 2.6V with a maximum of 2.6V at IF=20 mA. The minimum is 2.05V. This range is critical for designing the driving circuitry's voltage supply.
• Peak Emission Wavelength (λp): 588 nm (typical). This is the wavelength at which the emitted light intensity is highest.
• Dominant Wavelength (λd): 587 nm (typical). This is the single wavelength perceived by the human eye to match the color of the source.
• Spectral Line Half-Width (Δλ): 15 nm (typical). This indicates the spectral purity; a smaller value means a more monochromatic color.
• Reverse Current (IR): Maximum 100 µA at a reverse voltage (VR) of 5V. This parameter is for test purposes only; continuous reverse bias operation is prohibited.
• Luminous Intensity Matching Ratio: Maximum 2:1 for segments within a similar light area at IF=1mA. This ensures visual uniformity across the display.
• Cross Talk: Specified as ≤ 2.5%, indicating minimal unwanted illumination between adjacent segments.

3. Binning System Explanation

The datasheet indicates the device is "Categorized for Luminous Intensity." This implies a binning process where displays are sorted based on measured luminous intensity (Iv) at a standard test current (likely 1mA or 10mA). This ensures customers receive products with consistent brightness levels. While specific bin codes are not detailed in this excerpt, typical bins would group devices with Iv values within a certain range (e.g., 300-450 µcd). Designers must account for this potential variation if absolute brightness matching is critical across multiple units or production runs.

4. Performance Curve Analysis

While the specific graphs are not detailed in the provided text, typical curves for such a device would include:

• Forward Current (IF) vs. Forward Voltage (VF) Curve: Shows the exponential relationship. The curve helps determine the necessary drive voltage for a desired current.
• Luminous Intensity (Iv) vs. Forward Current (IF) Curve: Demonstrates how brightness increases with current, typically in a near-linear fashion within the operating range before efficiency drops at very high currents.
• Luminous Intensity (Iv) vs. Ambient Temperature (Ta) Curve: Shows how brightness decreases as temperature increases. This is crucial for applications with high ambient temperatures.
• Spectral Distribution Curve: A plot of relative intensity vs. wavelength, centered around 587-588 nm, showing the narrow yellow emission band.

5. Mechanical & Package Information

5.1 Package Dimensions

The device has a standard SMD footprint. All dimensions are in millimeters with a general tolerance of ±0.25 mm. Key mechanical notes include limits on foreign material (≤10 mil), ink contamination (≤20 mils), bubbles in segments (≤10 mil), bending (≤1% of reflector length), and plastic pin burr (max 0.1 mm). These ensure proper appearance and solderability.

5.2 Pin Connection and Polarity

The display has a 12-pin configuration. It uses a multiplex common anode design. This means the anodes of the LEDs for each digit (DIG1, DIG2, DIG3) are connected together internally and brought out to separate pins (pins 11, 10, and 8 respectively). The cathodes for each segment (A-G and DP) are shared across all digits and connected to their respective pins. This design allows control of a multi-digit display with fewer I/O pins by rapidly cycling (multiplexing) which digit is powered at any given time. Pin 4 is marked as "No Connection." The right-hand decimal point (DP) cathode is on pin 5.

5.3 Internal Circuit Diagram

The internal diagram visually represents the multiplexed common anode architecture, showing how the three digit anodes and the seven segment (+DP) cathodes are interconnected.

6. Soldering & Assembly Guidelines

6.1 SMT Soldering Instructions

The device is rated for a maximum of two reflow soldering cycles. A cooling period to normal temperature is required between cycles.

• Reflow Soldering: Pre-heat: 120-150°C. Pre-heat time: 120 seconds maximum. Peak temperature: 260°C maximum. Time above liquidus: 5 seconds maximum.
• Hand Soldering (Iron): Temperature: 300°C maximum. Soldering time: 3 seconds maximum per joint.

6.2 Recommended Soldering Pattern

A land pattern (footprint) is provided to ensure proper solder joint formation and mechanical stability. Adhering to this pattern is essential for reliable assembly.

6.3 Moisture Sensitivity & Storage

The device is shipped in moisture-proof packaging. Once opened, it begins absorbing moisture from the environment. If not stored in dry conditions (≤30°C, ≤60% RH), it must be baked before reflow to prevent "popcorning" or delamination during the high-temperature soldering process.

• Baking Conditions (once only):
  • In Reel: 60°C for ≥48 hours.
  • In Bulk: 100°C for ≥4 hours or 125°C for ≥2 hours.

7. Packaging & Ordering Information

7.1 Packing Specifications

The devices are supplied on tape-and-reel for automated assembly.

• Reel Dimensions: Standard 13-inch reel.
• Quantity per Reel: 600 pieces.
• Minimum Order Quantity (MOQ) for Remainders: 200 pieces.
• Carrier Tape: Dimensions are specified to ensure component retention and feeding.
• Leader/Trailer Tape: A minimum 400mm leader and 40mm trailer are included to facilitate machine loading.

7.2 Part Number Interpretation

The part number LTC-2687CKS-P likely follows an internal coding system where: - LTC: Product family/prefix. - 2687: Specific model identifier. - CKS: May indicate package type, color, or other attributes. - P: May indicate packing style (e.g., tape and reel).

8. Application Notes & Design Considerations

8.1 Design Recommendations

• Drive Method: Constant current driving is strongly recommended over constant voltage to ensure consistent luminous intensity and longevity, as the forward voltage (VF) has a range (2.05V to 2.6V).
• Circuit Protection: The driving circuit must protect against reverse voltages and transient spikes during power-up/shutdown to prevent damage.
• Current Limiting: The safe operating current must be chosen considering the maximum ambient temperature, factoring in the current derating specified in the absolute maximum ratings.
• Thermal Management: Avoid operating at currents or temperatures higher than recommended to prevent severe light output degradation or premature failure.
• Reverse Bias: Must be avoided as it can cause metal migration, increasing leakage current or causing short circuits.

8.2 Typical Application Scenarios

This display is ideal for: - Digital multimeters and test equipment. - Appliance control panels (microwaves, ovens). - Audio/video equipment displays. - Industrial timer and counter readouts. - Point-of-sale terminal displays.

9. Technical Comparison & Differentiation

Compared to older technologies like standard GaAsP or GaP LEDs, the AlInGaP technology in this display offers significantly higher luminous efficiency, resulting in brighter output at lower currents. The black face with white segments provides high contrast, enhancing readability in various lighting conditions. The multiplexed common anode design is a standard for multi-digit displays, offering a good balance between pin count and control complexity compared to static drive designs which require many more I/O lines.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Why is the maximum continuous current derated with temperature? A: LED efficiency decreases and internal heat generation increases at higher temperatures. Derating prevents the junction temperature from exceeding safe limits, which would accelerate light output decay and reduce lifespan.

Q: What does "Luminous Intensity Matching Ratio ≤ 2:1" mean for my design? A: It means the brightest segment in a defined area will be no more than twice as bright as the dimmest segment in that same area under identical drive conditions. This ensures visual uniformity. For critical applications, selecting devices from the same intensity bin is advised.

Q: Can I drive this display with a 5V microcontroller pin directly? A: No. The typical forward voltage is 2.6V, but a current-limiting resistor or, preferably, a constant-current driver circuit is mandatory. Connecting directly to a 5V pin would likely destroy the LED segment due to excessive current.

11. Practical Design & Usage Case

Case: Designing a 3-digit voltmeter readout. A microcontroller would be used to control the display. Three I/O pins would be configured as outputs to sink current to the common anodes (DIG1, DIG2, DIG3). Seven (or eight, including DP) other I/O pins would be configured as current sources (via transistors or a dedicated driver IC) for the segment cathodes (A-G, DP). The firmware would implement multiplexing: turn on DIG1, set the segment pattern for the first digit, wait a short time (e.g., 2ms), turn off DIG1, turn on DIG2, set the pattern for the second digit, and so on, cycling rapidly. The persistence of vision makes all digits appear continuously lit. The drive current must be calculated based on the desired brightness and the duty cycle of the multiplexing.

12. Operating Principle Introduction

An LED (Light Emitting Diode) is a semiconductor p-n junction diode. When a forward voltage exceeding the junction's built-in potential is applied, electrons from the n-region and holes from the p-region are injected into the junction region. When these charge carriers recombine, energy is released in the form of photons (light). The specific wavelength (color) of the light is determined by the energy bandgap of the semiconductor material. AlInGaP (Aluminum Indium Gallium Phosphide) has a bandgap that corresponds to light in the yellow/amber/orange/red spectrum, offering high efficiency. The multiplexed drive scheme takes advantage of the LED's fast switching speed and the human eye's persistence of vision to control multiple digits with a reduced number of control lines.

13. Technology Trends

The trend in display technology continues towards higher efficiency, lower power consumption, and greater integration. While discrete segment displays like this one remain vital for specific applications, there is a broader shift towards fully integrated dot-matrix displays and OLEDs that offer greater flexibility in displaying alphanumeric characters and graphics. However, for simple, high-brightness, low-cost numeric readouts, SMD segment displays using efficient materials like AlInGaP and InGaN (for blue/green/white) will continue to be relevant in industrial, automotive, and consumer applications for the foreseeable future, particularly where extreme reliability and long life are required under a wide range of environmental conditions.