LTS-5701AKF LED Display Datasheet - 0.56-inch Digit Height - Yellow-Orange Color - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTS-5701AKF is a single-digit, seven-segment alphanumeric display designed for applications requiring clear, bright numeric or limited alphanumeric indication. Its core function is to provide visual output by selectively illuminating its segments (A through G and a decimal point) to form characters. The device is built using Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor technology, which is grown on a Gallium Arsenide (GaAs) substrate. This material system is specifically chosen for its efficiency in producing high-brightness yellow-orange light. The display features a gray faceplate, which enhances contrast by reducing ambient light reflection, and white segment outlines for clear character definition when unlit. It is categorized as a common anode type, meaning the anodes of all LED segments are connected internally, simplifying current sourcing in typical microcontroller-driven circuits.

1.1 Core Advantages and Target Market

The primary advantages of this display stem from its AlInGaP construction and design. It offers high luminous intensity and excellent contrast, ensuring readability even in well-lit environments. The wide viewing angle is a critical feature for applications where the display may be viewed from various positions. Its solid-state reliability, with no moving parts and a robust semiconductor construction, leads to long operational life and resistance to shock and vibration. The low power requirement makes it suitable for battery-powered or energy-conscious devices. This combination of features targets markets including industrial instrumentation (e.g., panel meters, timers, counters), consumer appliances (e.g., microwave ovens, coffee makers), automotive dashboards (for auxiliary displays), test and measurement equipment, and any embedded system requiring a simple, reliable numeric readout.

2. In-Depth Technical Parameter Analysis

This section provides a detailed, objective interpretation of the key electrical and optical parameters specified in the datasheet, explaining their significance for design engineers.

2.1 Absolute Maximum Ratings

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

• Power Dissipation per Segment (70 mW): This is the maximum amount of electrical power that can be converted into heat (and light) by a single segment without risk of damage. Exceeding this limit, typically by applying too high a current or forward voltage, can lead to overheating, accelerated aging (lumen depreciation), or catastrophic failure.
• Peak Forward Current per Segment (60 mA at 1/10 duty cycle, 0.1ms pulse): This rating allows for brief pulses of current higher than the continuous rating. It is useful for multiplexing schemes or for achieving momentary higher brightness. The specified duty cycle and pulse width are critical; operating outside these pulse conditions at 60mA is not safe.
• Continuous Forward Current per Segment (25 mA): The maximum DC current that can be applied to a segment indefinitely under specified ambient temperature conditions. The datasheet provides a derating factor of 0.33 mA/°C above 25°C. For example, at an ambient temperature (Ta) of 85°C, the maximum allowable continuous current would be: 25 mA - [(85°C - 25°C) * 0.33 mA/°C] = 25 mA - 19.8 mA = 5.2 mA. This derating is essential for thermal management.
• Reverse Voltage per Segment (5 V): The maximum voltage that can be applied in the reverse direction (cathode positive relative to anode) without causing breakdown. Exceeding this can damage the LED's PN junction.
• Operating & Storage Temperature Range (-35°C to +85°C): Defines the environmental limits for reliable operation and non-operational storage.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters measured under specific test conditions (Ta=25°C unless noted).

• Average Luminous Intensity (I_V): Min: 800 µcd, Typ: 1667 µcd at I_F=1mA. This is a measure of the perceived brightness of the lit segment. The wide range indicates a binning system (see Section 3). Designers must use the minimum value for worst-case brightness calculations.
• Forward Voltage per Segment (V_F): Typ: 2.05V, Max: 2.6V at I_F=20mA. This is the voltage drop across the LED when conducting the specified current. It is crucial for calculating the required current-limiting resistor value: R = (V_supply - V_F) / I_F. Using the maximum V_F ensures sufficient voltage headroom.
• Peak Emission Wavelength (λ_p): 661 nm. This is the wavelength at which the spectral output of the LED is at its maximum. For AlInGaP yellow-orange LEDs, this typically falls in the amber/red-orange part of the spectrum.
• Dominant Wavelength (λ_d): 605 nm. This is the single wavelength perceived by the human eye that matches the color of the LED's light. It is a more relevant parameter for color specification than peak wavelength.
• Spectral Line Half-Width (Δλ): 17 nm. This indicates the spectral purity or bandwidth of the emitted light. A smaller value means a more monochromatic (pure color) output.
• Reverse Current per Segment (I_R): Max: 100 µA 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: 2:1 (max). This specifies the maximum allowable ratio between the brightest and dimmest segment within a single digit or between digits in a multi-digit system. A ratio of 2:1 means the brightest segment can be no more than twice as bright as the dimmest, ensuring uniform appearance.

3. Binning System Explanation

The datasheet states the device is "Categorized for Luminous Intensity." This implies a binning or sorting process post-manufacturing. Due to inherent variations in the semiconductor epitaxial growth and chip fabrication, LEDs exhibit variations in key parameters. To ensure consistency for the end-user, manufacturers test and sort (bin) LEDs into groups with closely matched characteristics.

Luminous Intensity Binning: The wide range given for Average Luminous Intensity (800 to 1667 µcd) suggests that devices are sorted into different intensity bins. A purchase order for the LTS-5701AKF may specify a particular intensity bin code (e.g., a minimum intensity level) to guarantee a certain brightness level for the application. Designers should consult the manufacturer's detailed binning documentation for available codes.

Wavelength/Color Binning: While not explicitly detailed with min/typ/max ranges for dominant wavelength beyond the 605 nm typical, AlInGaP devices are also commonly binned for color (dominant wavelength or chromaticity coordinates) to ensure a consistent hue across all segments and digits in a display. Variations outside a specified bin would be visually noticeable as different shades of yellow-orange.

4. Performance Curve Analysis

The datasheet references "Typical Electrical / Optical Characteristic Curves." While the specific graphs are not provided in the text, we can infer their standard content and importance.

Forward Current vs. Forward Voltage (I_F-V_F Curve): This non-linear curve shows how V_F increases with I_F. It demonstrates the exponential relationship typical of a diode. The "knee" of this curve is around the typical V_F (2.05V-2.6V). This graph is vital for understanding the dynamic resistance of the LED and for designing efficient drive circuits, especially when using PWM for dimming.

Luminous Intensity vs. Forward Current (I_V-I_F Curve): This curve shows that light output is approximately proportional to forward current in the normal operating range. However, efficiency (lumens per watt) often peaks at a current lower than the maximum rating. Driving the LED at very high currents leads to thermal saturation and reduced efficiency.

Luminous Intensity vs. Ambient Temperature (I_V-T_a Curve): For AlInGaP LEDs, luminous intensity typically decreases as junction temperature increases. This curve quantifies that derating, which is critical for applications operating at high ambient temperatures. It directly relates to the current derating factor specified in the Absolute Maximum Ratings.

Relative Intensity vs. Wavelength (Spectral Distribution Curve): This bell-shaped curve would show the intensity of light emitted across the spectrum, centered around the peak wavelength (661 nm) with a width defined by the half-width (17 nm). It confirms the color characteristics of the LED.

5. Mechanical and Packaging Information

5.1 Package Dimensions and Drawing

The device uses a standard 10-pin, single-digit, seven-segment LED package. Key dimensional notes from the datasheet include: all dimensions are in millimeters, with general tolerances of ±0.25mm unless otherwise specified. A specific tolerance is given for pin tip shift: +/- 0.4 mm, which is important for PCB footprint design to ensure proper alignment and solderability. The exact dimensions for height, width, digit height (14.22mm), segment size, and pin spacing are defined in the package drawing (referenced but not detailed in text). Engineers must obtain the full mechanical drawing for accurate PCB layout.

5.2 Pin Connection and Polarity Identification

The pinout is clearly defined:

• Pins 3 and 8: Common Anode (CA). These are internally connected and must be connected to the positive supply voltage.
• Pins 1, 2, 4, 5, 6, 7, 9, 10: Cathodes for segments E, D, C, DP (Decimal Point), B, A, F, G respectively. These pins are connected to ground (or a current sink) via a current-limiting resistor to illuminate the corresponding segment.

The "Rt. Hand Decimal" description in the part number suggests the decimal point is located on the right-hand side of the digit. Polarity is clearly indicated by the Common Anode designation. Applying reverse polarity (connecting CA to ground and a cathode to V+) will not illuminate the segment and, if the reverse voltage exceeds 5V, may damage the device.

5.3 Internal Circuit Diagram

The referenced diagram would show the internal electrical connections: eight individual LED chips (seven segments plus decimal point), each with its anode connected to the common anode pins (3 & 8) and its cathode connected to its respective dedicated pin. This confirms the common anode topology.

6. Soldering and Assembly Guidelines

The datasheet provides a specific soldering condition: "1/16 inch Below Seating Plane for 3 Seconds at 260°C." This is a wave soldering specification. It means the leads can be immersed in a solder wave to a depth of approximately 1.6mm (1/16") below the plastic body of the display for a maximum of 3 seconds, with the solder pot at 260°C. This prevents excessive heat from traveling up the leads and damaging the internal LED chips or the plastic package.

Important Considerations:

• Reflow Soldering: If using reflow soldering (common for SMT, but this is a through-hole part), the profile must be carefully controlled. The maximum temperature rating of the unit during assembly must not be exceeded. The peak body temperature should typically be kept below the maximum storage temperature (85°C) or as per a more specific reflow profile if provided by the manufacturer.
• Cleaning: After soldering, use only cleaning agents compatible with the display's plastic material to avoid cracking or clouding.
• Handling: Avoid mechanical stress on the pins. Use proper ESD (Electrostatic Discharge) precautions during handling and assembly.
• Storage: Store in the specified temperature range (-35°C to +85°C) in a low-humidity, anti-static environment.

7. Application Suggestions and Design Considerations

7.1 Typical Application Circuits

The most common drive method is multiplexing, especially for multi-digit displays. Since it's a common anode display, the anodes (pins 3 & 8) would be connected to a microcontroller's I/O pins configured as outputs set HIGH (or to a transistor used as a high-side switch). The cathodes for all segments (A-G, DP) would be connected to current sink drivers, which could be discrete transistors, dedicated LED driver ICs (like 74HC595 shift registers with constant current, or MAX7219), or microcontroller pins with sufficient sink capability. A current-limiting resistor is required in series with each cathode path (or a single resistor per common anode if current is regulated per digit). The resistor value is calculated as: R = (V_supply - V_F - V_CE(sat) or V_drop) / I_F. Use the maximum V_F for a safe design.

7.2 Design Considerations

• Current Limiting: Always use a current-limiting resistor or a constant-current driver. Never connect an LED directly to a voltage source.
• Multiplexing Frequency: For multiplexed displays, use a refresh rate high enough to avoid visible flicker (typically >60 Hz per digit). The duty cycle determines the average current. For N digits, the peak current per segment can be up to N times the desired average current, but must not exceed the peak current rating (60mA under specified conditions).
• Viewing Angle: Position the display considering its wide viewing angle to ensure visibility for the end-user.
• Contrast Enhancement: The gray face helps, but for high-ambient-light conditions, consider adding a contrast filter or a hood.
• Thermal Management: Adhere to current derating rules at high ambient temperatures. Ensure adequate ventilation if multiple displays are used in a confined space.

8. Technical Comparison and Differentiation

Compared to other seven-segment display technologies:

• vs. Standard GaAsP or GaP LEDs (Red, Green): AlInGaP offers significantly higher luminous efficiency (more light output per mA) and better temperature stability, resulting in brighter displays with more consistent performance.
• vs. LCDs: LEDs are emissive (produce their own light), making them clearly visible in darkness without a backlight, whereas reflective LCDs require ambient light. LEDs also have a much faster response time and a wider operating temperature range. However, LCDs typically consume far less power for static displays.
• vs. VFDs (Vacuum Fluorescent Displays): VFDs can offer high brightness and wide viewing angles but require relatively high driving voltages and are more fragile. LEDs are more rugged, require lower voltages, and have a longer lifetime.
• Within AlInGaP Displays: The LTS-5701AKF differentiates itself with its specific 0.56" digit height, yellow-orange color, common anode configuration, right-hand decimal point, and its categorized (binned) luminous intensity, ensuring a level of quality and consistency for professional applications.

9. Frequently Asked Questions (Based on Technical Parameters)

Q1: Can I drive this display with a 5V microcontroller without a current-limiting resistor if I use the I/O pin's current limit?
A: No. Relying solely on the microcontroller's internal pin current limit is not safe or reliable for the LED. The pin limit is for protection, not for setting a precise operating point. The LED's forward voltage is ~2.1-2.6V. Connecting it directly to a 5V pin would attempt to force a very high current, potentially damaging both the microcontroller pin and the LED. An external current-limiting resistor is mandatory.

Q2: Why are there two common anode pins (3 and 8)?
A: This is a common design practice to improve current distribution and reliability. The total current for all lit segments flows into the common anode. Having two pins in parallel reduces the current load and thermal stress on each individual pin and the internal bond wires, enhancing longevity and allowing for higher overall brightness.

Q3: The luminous intensity is given at 1mA, but the forward voltage is given at 20mA. Which should I use for design?
A: Use both, but for different calculations. Use the V_F @ 20mA (or your chosen operating current) to calculate the series resistor value. Use the I_V vs. I_F relationship (from the characteristic curve) to estimate the brightness at your chosen operating current. The 1mA I_V value is a standardized test point for comparison and binning.

Q4: What does "Lead-Free Package (according to RoHS)" mean?
A: It means the materials used in the construction of the device, including the solder plating on the leads, comply with the Restriction of Hazardous Substances (RoHS) directive. Specifically, it indicates the absence of lead (Pb), mercury, cadmium, hexavalent chromium, and certain flame retardants (PBB, PBDE) above permitted levels. This is important for environmental compliance in most global markets.

10. Practical Design and Usage Examples

Example 1: Simple 4-Digit Voltmeter Display. Four LTS-5701AKF digits could be used to display voltage from 0.000 to 19.99V. A microcontroller with an ADC would measure the voltage. The display would be multiplexed: the microcontroller would calculate which segments to light for each digit and cycle through the four common anodes rapidly while driving the shared cathode lines for the active digit's segments. Care must be taken to limit the peak current per segment based on the multiplexing duty cycle (e.g., 1/4 duty = peak current can be 4x the desired average brightness current).

Example 2: Industrial Timer/Counter. In a factory setting, a device might count items on a production line. The LTS-5701AKF's high brightness and wide viewing angle make it suitable for operators to see the count from a distance. Its rugged solid-state construction withstands vibration. The design would need to ensure the display is readable in the factory's lighting conditions, possibly requiring a sunshield.

11. Technology Principle Introduction

The LTS-5701AKF is based on Aluminum Indium Gallium Phosphide (Al_xIn_yGa_1-x-yP) semiconductor technology. This is a III-V compound semiconductor where the relative proportions of Aluminum (Al), Indium (In), and Gallium (Ga) determine the bandgap energy of the material. The bandgap energy directly dictates the wavelength (color) of light emitted when electrons recombine with holes across the junction. AlInGaP is particularly efficient for producing light in the yellow, orange, amber, and red regions of the spectrum. The epitaxial layers are grown on a Gallium Arsenide (GaAs) substrate. When a forward voltage exceeding the junction's built-in potential is applied, electrons are injected into the P-region and holes into the N-region. Their recombination in the active region releases energy in the form of photons (light). The gray faceplate absorbs ambient light to improve contrast, while the white segment outlines provide a reference for unlit segments.

12. Technology Trends and Developments

While traditional seven-segment LED displays like the LTS-5701AKF remain highly relevant for specific applications due to their simplicity, reliability, and cost-effectiveness, broader trends in display technology are evident. There is a general shift towards higher integration and addressability. This includes the proliferation of dot-matrix LED displays and OLEDs that offer full alphanumeric and graphic capabilities. Integrated driver solutions (like I2C or SPI-controlled LED driver chips) are becoming standard, simplifying microcontroller interfacing. In terms of materials, while AlInGaP is mature and efficient for its color range, research continues into improving efficiency (lumens per watt), color rendering, and stability over temperature and lifetime. For niche applications requiring extreme simplicity, robustness, and specific numeric output, discrete seven-segment displays will continue to be a viable and often optimal solution. The trend for such components is towards even lower power consumption, higher brightness efficiency, and potentially smaller form factors while maintaining readability.