LTS-315AJD LED Display Datasheet - 0.3-inch Digit Height - Hyper Red Color - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTS-315AJD is a compact, high-performance single-digit seven-segment display designed for applications requiring clear numeric readouts. Its primary function is to provide a highly legible, bright numeric character in a small form factor. The core advantage of this device lies in its use of advanced AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for the LED chips, which offers superior efficiency and color purity compared to older technologies like standard GaAsP LEDs. This makes it particularly suitable for portable instruments, consumer electronics, industrial control panels, and test equipment where power consumption, readability, and reliability are critical. The device is categorized for luminous intensity, ensuring consistent brightness levels across production batches.

2. Technical Specifications Deep Dive

2.1 Optical Characteristics

The optical performance is defined by several key parameters measured at a standard ambient temperature of 25°C. The Average Luminous Intensity (Iv) has a typical value of 600 µcd at a forward current (IF) of 1mA, with a specified range from 200 µcd (min) upwards. This parameter indicates the perceived brightness of the lit segments. The light emitted is characterized as hyper red. The Peak Emission Wavelength (λp) is typically 650 nm, while the Dominant Wavelength (λd) is specified as 639 nm at IF=20mA. The difference between peak and dominant wavelength relates to the shape of the emission spectrum. The Spectral Line Half-Width (Δλ) is 20 nm, indicating a relatively narrow band of emitted light, which contributes to the saturated red color. Luminous intensity is measured using a sensor and filter that approximates the CIE photopic eye-response curve, ensuring the values correlate with human vision.

2.2 Electrical Characteristics

The electrical parameters define the operating conditions and limits. The Forward Voltage per Segment (VF) ranges from 2.1V to 2.6V at a test current of 20mA. This is the voltage drop across the LED when it is conducting. The Reverse Current per Segment (IR) is a maximum of 100 µA when a reverse voltage (VR) of 5V is applied, indicating the device's leakage in the off-state. A Luminous Intensity Matching Ratio (Iv-m) of 2:1 is specified, meaning the brightness of the dimmest segment relative to the brightest segment in a single device will not exceed this ratio at IF=1mA, ensuring uniform appearance.

2.3 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage may occur. The Continuous Forward Current per Segment is 25 mA at 25°C, derating linearly at 0.33 mA/°C as temperature increases. The Peak Forward Current per Segment is 90 mA, but only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The Power Dissipation per Segment must not exceed 70 mW. The maximum Reverse Voltage is 5V. The device can operate and be stored within a Temperature Range of -35°C to +85°C. The solder temperature must not exceed 260°C for a maximum of 3 seconds at a distance of 1.6mm below the seating plane during assembly.

3. Binning System Explanation

The datasheet states the device is "Categorized for Luminous Intensity." This implies a binning or sorting process based on measured light output. While specific bin codes are not detailed in this document, typical practice involves testing each unit at a standard current (e.g., 1mA or 20mA) and grouping them into bins with defined minimum and maximum luminous intensity ranges. This ensures customers receive displays with consistent brightness levels for a given drive current, which is crucial for multi-digit displays or products where multiple units are used side-by-side. Designers should consult the manufacturer for the specific binning structure and available intensity grades.

4. Performance Curve Analysis

The datasheet references "Typical Electrical / Optical Characteristic Curves" which are essential for detailed design. While the specific graphs are not provided in the text excerpt, typical curves for such devices would include: Forward Current vs. Forward Voltage (I-V Curve): This shows the nonlinear relationship, helping to determine the required series resistor for a given supply voltage. Luminous Intensity vs. Forward Current (I-Iv Curve): This indicates how brightness increases with current, often showing a near-linear relationship within the operating range before efficiency drops at very high currents. Luminous Intensity vs. Ambient Temperature: This curve shows the derating of light output as the junction temperature rises, which is critical for high-temperature or high-current applications. Spectral Distribution: A plot of relative intensity versus wavelength, confirming the peak and dominant wavelength values and the shape of the emission spectrum.

5. Mechanical and Package Information

The LTS-315AJD features a gray face with white segments, which enhances contrast and readability. The package is a standard 14-pin dual in-line package (DIP). The digit height is 0.3 inches (7.62 mm). A detailed dimensioned drawing is referenced in the datasheet (PAGE 2 of 5), with all dimensions provided in millimeters and standard tolerances of ±0.25 mm unless otherwise noted. This drawing is critical for PCB footprint design, ensuring proper fit and alignment of the display on the circuit board.

6. Pin Connection and Internal Circuit

The device has a common cathode configuration. The pinout is as follows: Pin 1: Anode F, Pin 2: Anode G, Pin 3: No Pin, Pin 4: Common Cathode, Pin 5: No Pin, Pin 6: Anode E, Pin 7: Anode D, Pin 8: Anode C, Pin 9: Anode RDP (Right-Hand Decimal Point), Pin 10: No Pin, Pin 11: No Pin, Pin 12: Common Cathode, Pin 13: Anode B, Pin 14: Anode A. Pins 4 and 12 are internally connected as the common cathode. The internal circuit diagram shows each segment LED (A-G and DP) with its anode connected to the respective pin and all cathodes tied together to the common cathode pins. This configuration simplifies multiplexing when driving multiple digits.

7. Soldering and Assembly Guidelines

Adherence to the specified soldering profile is crucial to prevent thermal damage. The maximum allowable solder temperature is 260°C, and the component should be subjected to this temperature for no more than 3 seconds. The measurement point is 1.6mm below the seating plane (typically the PCB surface). This aligns with standard lead-free reflow soldering profiles. It is recommended to follow standard IPC guidelines for cleaning and handling moisture-sensitive devices, although the datasheet does not specify a moisture sensitivity level (MSL). Proper ESD (Electrostatic Discharge) precautions should always be observed when handling LED components.

8. Application Suggestions

8.1 Typical Application Scenarios

This display is ideal for any device requiring a single, highly visible numeric digit. Common applications include: panel meters for voltage, current, or temperature; digital clocks and timers; scoreboards; instrumentation readouts on consumer appliances (e.g., microwave ovens, coffee makers); status indicators on industrial equipment; and portable electronic devices.

8.2 Design Considerations

Current Limiting: A series resistor must be used with each segment anode (or in the common cathode path) to limit the forward current to a safe value, typically between 5mA and 20mA depending on the required brightness and power budget. The resistor value is calculated using R = (Vcc - Vf) / If, where Vcc is the supply voltage, Vf is the forward voltage of the segment (use max value for reliability), and If is the desired forward current. Multiplexing: For multi-digit displays, a multiplexing scheme is used where digits are illuminated one at a time rapidly. The LTS-315AJD's common cathode design is well-suited for this. The peak current rating allows for higher pulsed currents during multiplexing to achieve higher perceived brightness. Viewing Angle: The datasheet mentions a wide viewing angle, which should be considered for the mechanical placement of the display relative to the user.

9. Technical Comparison and Differentiation

The key differentiator of the LTS-315AJD is its use of AlInGaP on a non-transparent GaAs substrate. Compared to traditional GaAsP (Gallium Arsenide Phosphide) red LEDs, AlInGaP technology offers significantly higher luminous efficiency, meaning more light output for the same electrical input power. This results in the "high brightness" and "low power requirement" features listed. The hyper red color (dominant wavelength ~639nm) is also more saturated and visually distinct than standard red LEDs. The gray face/white segment design enhances contrast, contributing to "excellent character appearance." The categorization for luminous intensity provides an additional level of quality control not always present in basic displays.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: What resistor value should I use to drive a segment with a 5V supply?
A: Using the maximum Vf of 2.6V and a target If of 15mA: R = (5V - 2.6V) / 0.015A = 160 ohms. A standard 150 or 180 ohm resistor would be suitable. Always verify brightness at the chosen current.

Q: Can I connect the two common cathode pins together on the PCB?
A: Yes, pins 4 and 12 are internally connected. Connecting them both on the PCB is recommended to reduce resistance and improve current distribution, especially when driving all segments simultaneously.

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength is the wavelength at which the emission spectrum has its maximum intensity. Dominant wavelength is the single wavelength of monochromatic light that would appear to have the same color as the LED's output to the human eye. Dominant wavelength is more relevant for color specification.

Q: How does temperature affect performance?
A: As temperature increases, the forward voltage (Vf) typically decreases slightly, while the luminous intensity decreases more significantly. The continuous current rating also derates above 25°C. Design for the maximum expected operating temperature.

11. Practical Design and Usage Example

Consider designing a simple single-digit voltmeter reading 0-9. A microcontroller's I/O pins can be used to drive the segment anodes (A-G) through current-limiting resistors (e.g., 180 ohms for a 5V system). The common cathode pin(s) would be connected to a microcontroller pin configured as an open-drain output or through an NPN transistor to sink the combined segment current. The microcontroller would decode the measured voltage to a 7-segment pattern and output it. The decimal point (RDP) can be used optionally. The low power requirement makes this suitable for battery-powered prototypes. The high contrast and brightness ensure readability in various lighting conditions.

12. Technology Principle Introduction

The LTS-315AJD is based on AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material. When a forward voltage is applied across the p-n junction of this material, electrons and holes recombine, releasing energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, in the hyper red region. The use of a non-transparent GaAs substrate helps absorb stray light, improving contrast by preventing internal reflection that could make unlit segments appear faintly illuminated. The light is emitted from the top surface of the chip, through an epoxy lens which shapes the viewing angle.

13. Industry Trends and Developments

While discrete seven-segment displays remain vital for specific applications, the broader trend in display technology is towards integration and miniaturization. This includes the proliferation of dot-matrix OLED and LCD displays that offer alphanumeric and graphic capabilities. However, for applications requiring extreme simplicity, robustness, high brightness in sunlight, wide temperature range, and low cost, LED seven-segment displays like the LTS-315AJD continue to be the optimal choice. Advances in LED materials, such as the move from GaAsP to AlInGaP documented here, constantly improve their efficiency and reliability. Future developments may include even higher efficiency materials and direct integration of drive electronics into the display package.