1. Product Overview
The LTC-5689KD is a high-performance, triple-digit, seven-segment LED display module designed for applications requiring clear numeric readouts. It features a digit height of 0.56 inches (14.2 mm), providing excellent visibility. The display utilizes advanced AlInGaP (Aluminum Indium Gallium Phosphide) HYPER RED LED chips grown on a GaAs substrate. This technology is chosen for its high efficiency and superior color purity in the red spectrum. The device presents a high-contrast appearance with black face and white segments, enhancing readability under various lighting conditions. It is categorized for luminous intensity and is offered in a lead-free package compliant with RoHS directives, making it suitable for modern electronic designs with environmental considerations.
1.1 Key Features and Advantages
The LTC-5689KD offers several distinct advantages that make it a reliable choice for designers:
- Optical Performance: Delivers high brightness and high contrast, ensuring the display is easily readable. It boasts a wide viewing angle, making it suitable for applications where the viewer may not be directly in front of the display.
- Power Efficiency: Has a low power requirement, which is beneficial for battery-powered or energy-conscious devices.
- Aesthetic and Build Quality: Features continuous uniform segments, contributing to an excellent character appearance without visual breaks or gaps in the lit segments. The solid-state construction ensures high reliability and long operational life.
- Design Flexibility: The multiplex common anode configuration simplifies driving circuitry for multi-digit displays, reducing the number of required microcontroller I/O pins.
- Quality Assurance: Devices are categorized (binned) for luminous intensity, allowing for consistent brightness matching when multiple displays are used in a single assembly.
2. Technical Specifications Deep Dive
2.1 Absolute Maximum Ratings
These ratings define the limits beyond which permanent damage to the device may occur. Operating the display under these conditions is not recommended.
- Power Dissipation per Segment: 70 mW maximum.
- Peak Forward Current per Segment: 90 mA (under pulsed conditions: 1/10 duty cycle, 0.1ms pulse width).
- Continuous Forward Current per Segment: 25 mA at 25°C. This rating derates linearly at 0.28 mA/°C as ambient temperature increases above 25°C.
- Operating & Storage Temperature Range: -35°C to +105°C.
- Soldering Conditions: The device can withstand soldering at 260°C for 3 seconds, measured 1/16 inch (approximately 1.6mm) below the seating plane.
2.2 Electrical & Optical Characteristics
These are the typical operating parameters measured at an ambient temperature (Ta) of 25°C.
- Average Luminous Intensity (Iv): Ranges from 320 μcd (minimum) to 1250 μcd (maximum), with a typical value provided, when driven at a forward current (IF) of 1 mA.
- Peak Emission Wavelength (λp): 650 nm (at IF=20mA). This defines the color point of the HYPER RED emission.
- Spectral Line Half-Width (Δλ): 20 nm (at IF=20mA), indicating the spectral purity.
- Dominant Wavelength (λd): 639 nm (at IF=20mA).
- Forward Voltage per Chip (VF): Typically 2.60V, with a range from 2.10V to 2.60V at IF=20mA. Circuit design must account for this variation.
- Reverse Current per Segment (IR): Maximum of 100 μA when a reverse voltage (VR) of 5V is applied. This parameter is for test purposes only; continuous reverse bias operation is prohibited.
- Luminous Intensity Matching Ratio: 2:1 maximum for segments within a similar light area at IF=1mA, ensuring uniformity.
- Cross Talk: Specification is less than 1.0%, minimizing unwanted illumination of adjacent segments.
3. Mechanical and Package Information
3.1 Package Dimensions and Tolerances
The mechanical drawing provides critical dimensions for PCB layout and enclosure design. All primary dimensions are in millimeters with a standard tolerance of ±0.25mm unless otherwise specified. Key notes for assembly include: foreign material or bubbles on a segment must not exceed 10 mils; bending of the reflector must be less than 1% of its length; surface ink contamination must be under 20 mils. The pin tip shift tolerance is ±0.4 mm. For reliable soldering, a PCB hole diameter of 1.0 mm is recommended.
3.2 Pin Configuration and Internal Circuit
The display has a 14-pin configuration. It is a multiplexed common anode type. The pinout is as follows: Pins 1-7 are the cathodes for segments A through G, respectively. Pin 8 is the common cathode for decimal points DP1, DP2, and DP3. Pins 9, 10, and 11 are the common anodes for digits 3, 2, and 1, respectively. Pin 12 is the common anode for decimal points DP4 and DP5. Pins 13 and 14 are the cathodes for DP5 and DP4, respectively. The internal circuit diagram clearly shows how the three digits and five decimal points are interconnected, which is essential for designing the correct multiplexing driver sequence.
4. Application Guidelines and Design Considerations
4.1 Critical Application Cautions
Adherence to these guidelines is crucial for reliable operation:
- Operating Limits: Never exceed the absolute maximum ratings for current, power, or temperature, as this will cause severe light output degradation or catastrophic failure.
- Drive Circuit Design: Constant current driving is strongly recommended to maintain consistent brightness and longevity. The circuit must be designed to accommodate the full range of forward voltage (VF) specified. Protection against reverse voltages and transient spikes during power cycling is mandatory to prevent damage.
- Thermal Management: The drive current must be derated based on the maximum ambient temperature in the application environment to prevent overheating.
- Environmental Factors: Avoid rapid temperature changes in humid environments to prevent condensation on the display. Do not apply mechanical force to the display body during assembly.
- Use with Overlays: If a printing/pattern film is applied with pressure-sensitive adhesive, avoid letting it press directly against a front panel, as external force may cause it to shift.
- Multi-Display Matching: For assemblies using two or more displays, select units from the same luminous intensity bin to ensure uniform appearance.
- Mechanical Stress Testing: If the end product requires drop or vibration testing, the conditions must be evaluated in advance to ensure display compatibility.
4.2 Storage Conditions
Proper storage preserves the display's solderability and performance. The recommended storage conditions, while the product is in its original moisture-barrier packaging, are a temperature between 5°C and 30°C with relative humidity below 60% RH. If these conditions are not met, or if the barrier bag is opened for more than six months, the pins may oxidize. In such cases, re-plating and re-sorting may be necessary before use. It is advised to manage inventory to avoid long-term storage and consume products promptly.
5. Performance Curves and Characteristics Analysis
The datasheet references typical performance curves which are essential for detailed design analysis. While the specific graphs are not reproduced in the text, they typically include:
- Forward Current vs. Forward Voltage (I-V Curve): Shows the relationship between drive current and the voltage drop across the LED chip, crucial for designing the current-limiting circuitry.
- Luminous Intensity vs. Forward Current: Illustrates how light output increases with drive current, helping to select the appropriate operating point for desired brightness.
- Luminous Intensity vs. Ambient Temperature: Demonstrates the derating of light output as temperature rises, informing thermal design decisions.
- Spectral Distribution: A graph of relative intensity versus wavelength, confirming the peak and dominant wavelengths and the spectral half-width.
- Test and measurement equipment (multimeters, power supplies).
- Industrial control panels and timers.
- Consumer appliances like microwave ovens, audio receivers, or climate control systems.
- Point-of-sale terminals and informational displays.
These curves allow engineers to predict performance under non-standard conditions (different currents or temperatures) and to optimize the design for efficiency and reliability.
6. Typical Application Scenarios and Design Notes
The LTC-5689KD is intended for ordinary electronic equipment including office automation devices, communication equipment, and household appliances. Its clear numeric display makes it suitable for:
Design Note: For applications requiring exceptional reliability where failure could impact safety (e.g., aviation, medical devices, transportation controls), a pre-application consultation is necessary to evaluate suitability. The driving microcontroller firmware must implement a correct multiplexing routine that sequentially energizes the common anodes (pins 9, 10, 11, 12) while pulling the corresponding segment cathodes low to illuminate the desired segments for each digit. The persistence of vision effect creates the illusion of all digits being continuously lit.
7. Technical Comparison and Differentiation
Compared to older technologies like standard GaAsP or GaP red LEDs, the AlInGaP HYPER RED chips in the LTC-5689KD offer significantly higher luminous efficiency, resulting in greater brightness for the same drive current. The color is a deeper, more saturated red (650nm peak) compared to the orange-red of standard red LEDs. The multiplexed common anode design is a key differentiator from static drive displays, offering a major reduction in the required driver pins (from 26+ for static drive to 14 for multiplexed), simplifying PCB layout and reducing microcontroller resource requirements, albeit at the cost of requiring a dedicated scanning driver routine.
8. Frequently Asked Questions (Based on Technical Parameters)
Q: What is the purpose of the luminous intensity binning?
A: Binning ensures consistency. When multiple displays are used side-by-side, selecting from the same bin guarantees minimal visible difference in brightness between units, creating a professional, uniform appearance.
Q: Why is constant current drive recommended over constant voltage?
A: LED forward voltage (VF) has a tolerance (e.g., 2.1V to 2.6V). A constant voltage source would cause significant variation in current (and thus brightness) from one segment or display to another. A constant current source ensures identical current flows regardless of VF variation, guaranteeing uniform brightness.
Q: Can I drive this display with a 5V microcontroller pin directly?
A: No. You must use a current-limiting resistor or, preferably, a dedicated constant-current driver IC. Connecting a 5V pin directly to a segment cathode (with the anode powered) would likely exceed the absolute maximum continuous current (25mA) and destroy the LED. The resistor value must be calculated based on the supply voltage, the LED's VF, and the desired forward current (IF).
Q: What does \"derating linear from 25°C\" mean for continuous forward current?
A> It means that for every degree Celsius the ambient temperature rises above 25°C, the maximum allowable continuous current decreases by 0.28 mA. For example, at 50°C (25°C above), the max current would be 25 mA - (25 * 0.28 mA) = 25 mA - 7 mA = 18 mA per segment.
LED Specification Terminology
Complete explanation of LED technical terms
Photoelectric Performance
| Term | Unit/Representation | Simple Explanation | Why Important |
|---|---|---|---|
| Luminous Efficacy | lm/W (lumens per watt) | Light output per watt of electricity, higher means more energy efficient. | Directly determines energy efficiency grade and electricity cost. |
| Luminous Flux | lm (lumens) | Total light emitted by source, commonly called "brightness". | Determines if the light is bright enough. |
| Viewing Angle | ° (degrees), e.g., 120° | Angle where light intensity drops to half, determines beam width. | Affects illumination range and uniformity. |
| CCT (Color Temperature) | K (Kelvin), e.g., 2700K/6500K | Warmth/coolness of light, lower values yellowish/warm, higher whitish/cool. | Determines lighting atmosphere and suitable scenarios. |
| CRI / Ra | Unitless, 0–100 | Ability to render object colors accurately, Ra≥80 is good. | Affects color authenticity, used in high-demand places like malls, museums. |
| SDCM | MacAdam ellipse steps, e.g., "5-step" | Color consistency metric, smaller steps mean more consistent color. | Ensures uniform color across same batch of LEDs. |
| Dominant Wavelength | nm (nanometers), e.g., 620nm (red) | Wavelength corresponding to color of colored LEDs. | Determines hue of red, yellow, green monochrome LEDs. |
| Spectral Distribution | Wavelength vs intensity curve | Shows intensity distribution across wavelengths. | Affects color rendering and quality. |
Electrical Parameters
| Term | Symbol | Simple Explanation | Design Considerations |
|---|---|---|---|
| Forward Voltage | Vf | Minimum voltage to turn on LED, like "starting threshold". | Driver voltage must be ≥Vf, voltages add up for series LEDs. |
| Forward Current | If | Current value for normal LED operation. | Usually constant current drive, current determines brightness & lifespan. |
| Max Pulse Current | Ifp | Peak current tolerable for short periods, used for dimming or flashing. | Pulse width & duty cycle must be strictly controlled to avoid damage. |
| Reverse Voltage | Vr | Max reverse voltage LED can withstand, beyond may cause breakdown. | Circuit must prevent reverse connection or voltage spikes. |
| Thermal Resistance | Rth (°C/W) | Resistance to heat transfer from chip to solder, lower is better. | High thermal resistance requires stronger heat dissipation. |
| ESD Immunity | V (HBM), e.g., 1000V | Ability to withstand electrostatic discharge, higher means less vulnerable. | Anti-static measures needed in production, especially for sensitive LEDs. |
Thermal Management & Reliability
| Term | Key Metric | Simple Explanation | Impact |
|---|---|---|---|
| Junction Temperature | Tj (°C) | Actual operating temperature inside LED chip. | Every 10°C reduction may double lifespan; too high causes light decay, color shift. |
| Lumen Depreciation | L70 / L80 (hours) | Time for brightness to drop to 70% or 80% of initial. | Directly defines LED "service life". |
| Lumen Maintenance | % (e.g., 70%) | Percentage of brightness retained after time. | Indicates brightness retention over long-term use. |
| Color Shift | Δu′v′ or MacAdam ellipse | Degree of color change during use. | Affects color consistency in lighting scenes. |
| Thermal Aging | Material degradation | Deterioration due to long-term high temperature. | May cause brightness drop, color change, or open-circuit failure. |
Packaging & Materials
| Term | Common Types | Simple Explanation | Features & Applications |
|---|---|---|---|
| Package Type | EMC, PPA, Ceramic | Housing material protecting chip, providing optical/thermal interface. | EMC: good heat resistance, low cost; Ceramic: better heat dissipation, longer life. |
| Chip Structure | Front, Flip Chip | Chip electrode arrangement. | Flip chip: better heat dissipation, higher efficacy, for high-power. |
| Phosphor Coating | YAG, Silicate, Nitride | Covers blue chip, converts some to yellow/red, mixes to white. | Different phosphors affect efficacy, CCT, and CRI. |
| Lens/Optics | Flat, Microlens, TIR | Optical structure on surface controlling light distribution. | Determines viewing angle and light distribution curve. |
Quality Control & Binning
| Term | Binning Content | Simple Explanation | Purpose |
|---|---|---|---|
| Luminous Flux Bin | Code e.g., 2G, 2H | Grouped by brightness, each group has min/max lumen values. | Ensures uniform brightness in same batch. |
| Voltage Bin | Code e.g., 6W, 6X | Grouped by forward voltage range. | Facilitates driver matching, improves system efficiency. |
| Color Bin | 5-step MacAdam ellipse | Grouped by color coordinates, ensuring tight range. | Guarantees color consistency, avoids uneven color within fixture. |
| CCT Bin | 2700K, 3000K etc. | Grouped by CCT, each has corresponding coordinate range. | Meets different scene CCT requirements. |
Testing & Certification
| Term | Standard/Test | Simple Explanation | Significance |
|---|---|---|---|
| LM-80 | Lumen maintenance test | Long-term lighting at constant temperature, recording brightness decay. | Used to estimate LED life (with TM-21). |
| TM-21 | Life estimation standard | Estimates life under actual conditions based on LM-80 data. | Provides scientific life prediction. |
| IESNA | Illuminating Engineering Society | Covers optical, electrical, thermal test methods. | Industry-recognized test basis. |
| RoHS / REACH | Environmental certification | Ensures no harmful substances (lead, mercury). | Market access requirement internationally. |
| ENERGY STAR / DLC | Energy efficiency certification | Energy efficiency and performance certification for lighting. | Used in government procurement, subsidy programs, enhances competitiveness. |