Infrared LED Emitter LTE-3271B Datasheet - 940nm Wavelength - High Current & Low Forward Voltage - 150mW Power Dissipation - English Technical Document

1. Product Overview

The LTE-3271B is a high-performance infrared (IR) light-emitting diode (LED) designed for applications requiring robust and efficient infrared illumination. Its core design philosophy centers on delivering high optical power output while maintaining a relatively low forward voltage, which contributes to improved energy efficiency in the system. The device is engineered to handle high pulse currents, making it suitable for demanding applications like remote controls, proximity sensors, optical switches, and industrial automation systems where brief, intense bursts of IR light are necessary. The emitter operates at a peak wavelength of 940nm, which is in the near-infrared spectrum and is less visible to the human eye compared to shorter wavelengths, reducing perceived light pollution in sensitive environments.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation at or near these limits is not recommended for extended periods. Key limits include a continuous forward current (I_F) of 100mA and a peak forward current of 2A under pulsed conditions (300 pulses per second, 10μs pulse width). The maximum power dissipation is 150mW, which is critical for thermal management. The device can operate within an ambient temperature range of -40°C to +85°C and be stored from -55°C to +100°C.

2.2 Electro-Optical Characteristics

These parameters are measured at a standard test condition of 25°C ambient temperature and a forward current of 20mA, unless otherwise specified. The performance is categorized into different bin grades (A through E), which is a common practice for sorting LEDs based on their output characteristics.

• Radiant Intensity (I_E): This measures the optical power emitted per unit solid angle (steradian). For Bin A, the typical value is 11.32 mW/sr, while Bin E offers a higher typical output of 12.37 mW/sr. This parameter is crucial for determining the intensity of the IR beam.
• Aperture Radiant Incidence (E_e): This measures the radiant power incident on a surface per unit area. Values range from 0.8 mW/cm² (Min, Bin A) to 1.65 mW/cm² (Typ, Bin E).
• Peak Emission Wavelength (λ_P): The nominal peak wavelength is 940nm, with a spectral half-width (Δλ) of 50nm, defining the bandwidth of the emitted IR light.
• Forward Voltage (V_F): The voltage drop across the LED at a given current. At 50mA, V_F is typically 1.6V (max 1.85V). At a higher drive current of 500mA, V_F increases to a typical 2.3V (max 2.3V). The low forward voltage at moderate currents is a key feature contributing to system efficiency.
• Viewing Angle (2θ_1/2): Defined as the full angle at which the radiant intensity is half of the maximum intensity (on-axis). This device has a wide viewing angle of 50 degrees, providing broad, diffuse illumination rather than a narrow beam.

3. Binning System Explanation

The LTE-3271B utilizes a binning system primarily based on Radiant Intensity (I_E) and Aperture Radiant Incidence (E_e). Bins range from A to E, with higher-letter bins generally indicating higher optical output power. For instance, Bin A has a typical I_E of 11.32 mW/sr, while Bin E has 12.37 mW/sr. This allows designers to select components that meet specific brightness requirements for their application, ensuring consistency in production batches. It is important to specify the required bin grade when ordering to guarantee the desired performance level.

4. Performance Curve Analysis

The datasheet includes several characteristic graphs that illustrate device behavior under varying conditions.

4.1 Spectral Distribution (Fig. 1)

This curve shows the relative radiant intensity as a function of wavelength. It confirms the peak emission at 940nm and the approximately 50nm spectral half-width, indicating the LED emits light across a band of infrared wavelengths centered at 940nm.

4.2 Forward Current vs. Forward Voltage (Fig. 3)

This IV curve is non-linear, typical for diodes. It shows how the forward voltage increases with increasing forward current. The curve is essential for designing the current-limiting circuitry to ensure stable operation without exceeding maximum ratings.

4.3 Relative Radiant Intensity vs. Forward Current (Fig. 5)

This graph demonstrates that the light output (relative radiant intensity) increases with drive current. However, the relationship is not perfectly linear, especially at higher currents, due to efficiency droop and thermal effects.

4.4 Relative Radiant Intensity vs. Ambient Temperature (Fig. 4)

This curve illustrates the negative temperature coefficient of the LED's output. As the ambient temperature rises, the radiant intensity decreases. This thermal derating is a critical factor for applications operating in elevated temperature environments.

4.5 Radiation Diagram (Fig. 6)

This polar plot visually represents the spatial distribution of light, confirming the 50-degree viewing angle. The intensity is highest at 0 degrees (on-axis) and decreases symmetrically to half-power at ±25 degrees.

5. Mechanical and Package Information

The device uses a standard through-hole package. Key dimensional notes include: all dimensions are in millimeters, with a general tolerance of ±0.25mm. The leads are spaced where they emerge from the package body. A small protrusion of resin under the flange is allowed, with a maximum height of 1.5mm. The physical dimensions are crucial for PCB layout, ensuring proper fit and alignment in the target application.

6. Soldering and Assembly Guidelines

The absolute maximum ratings specify that the leads can be soldered at a temperature of 260°C for a duration of 5 seconds, measured at a distance of 1.6mm from the package body. This is a standard rating for wave or hand soldering processes. It is imperative to adhere to this limit to prevent thermal damage to the internal semiconductor die and the epoxy lens material. During reflow soldering (if applicable for a surface-mount variant, though this is a through-hole part), a profile that avoids exceeding this temperature at the lead junction is necessary. Proper ESD (Electrostatic Discharge) handling procedures should always be followed during assembly.

7. Packaging and Ordering Information

The devices are packaged in bags. Each bag contains 1000 pieces (pcs/Bag). These bags are then packed into inner cartons, with 8 bags per inner carton. Finally, 8 inner cartons are packed into one outer carton. Therefore, the total quantity per outer shipping carton is 64,000 pieces (1000 pcs/bag * 8 bags/carton * 8 cartons/outer = 64,000 pcs). The part number is LTE-3271B. The specific bin grade (A, B, C, D, or E) must be specified as part of the ordering code to receive the desired performance level.

8. Application Suggestions

8.1 Typical Application Scenarios

• Infrared Remote Controls: The high pulse current capability and 940nm wavelength make it ideal for transmitting coded signals to TVs, audio systems, and other appliances.
• Proximity and Presence Sensing: Paired with a photodetector, it can be used in automatic faucets, hand dryers, security systems, and object detection.
• Optical Switches and Encoders: Used to create interruptive or reflective sensors for counting, position sensing, and speed measurement.
• Industrial Automation: For machine vision lighting, barcode scanning, and alignment systems in manufacturing.
• Night Vision Illumination: Providing covert lighting for security cameras equipped with IR-sensitive sensors.

8.2 Design Considerations

• Current Driving: Always use a series current-limiting resistor or a constant-current driver circuit. The value should be calculated based on the supply voltage, the desired forward current (I_F), and the forward voltage (V_F) from the datasheet, considering its variation with current and temperature.
• Thermal Management: Although power dissipation is 150mW max, ensuring adequate heat sinking or airflow is important, especially when operating at high continuous currents or in high ambient temperatures, to maintain performance and longevity.
• Optical Design: The wide 50-degree viewing angle provides diffuse light. For applications requiring a more focused beam, secondary optics (lenses) may be necessary.
• Bin Selection: Choose the appropriate intensity bin to meet the optical power requirements of your receiver circuit, allowing for margin due to temperature effects and aging.

9. Technical Comparison and Differentiation

The LTE-3271B differentiates itself in the market through its combination of high current capability (2A pulse, 100mA continuous) and low forward voltage characteristics. This combination allows it to deliver high optical power pulses while minimizing power loss and heat generation in the driving circuitry compared to emitters with higher V_F. The wide viewing angle is another key differentiator, making it suitable for applications requiring area illumination rather than a spot beam. Its 940nm wavelength is a standard for consumer electronics, offering a good balance between silicon detector sensitivity and low visibility.

10. Frequently Asked Questions (FAQ)

Q: What is the difference between Radiant Intensity and Aperture Radiant Incidence?
A: Radiant Intensity (I_E) measures power per solid angle (directionality). Aperture Radiant Incidence (E_e) measures power per unit area at a specific distance/position. I_E is more relevant for characterizing the source itself, while E_e is useful for calculating irradiance on a target surface.

Q: Can I drive this LED directly from a 5V logic output?
A: No. You must use a current-limiting resistor. For example, with a 5V supply, a typical V_F of 1.6V at 20mA, the required resistor would be R = (5V - 1.6V) / 0.02A = 170 Ohms. A standard 180 Ohm resistor would be suitable.

Q: Why does the output power decrease with temperature?
A> This is due to several semiconductor physics effects, including increased non-radiative recombination and changes in internal quantum efficiency. Proper thermal design is essential to maintain consistent performance.

Q: What does the \"Binning\" system mean for my design?
A> Binning ensures you get LEDs with consistent optical power. If your circuit is calibrated for a specific light level, specifying a bin (e.g., Bin C) ensures every LED you use will have output within the min/max range for that bin, reducing unit-to-unit variation in your final product.

11. Practical Design and Usage Case

Case: Designing a Long-Range Infrared Remote Control. The goal is to achieve a reliable operating distance of 15 meters. The designer selects the LTE-3271B in Bin E for maximum radiant intensity. The driving circuit uses a microcontroller to generate modulated data pulses. To achieve high instantaneous brightness for long range, the LED is driven with short, high-current pulses (e.g., 1A pulses at 10μs width, within the 2A rating), rather than a lower continuous current. A transistor switch is used to handle the high pulse current. The wide viewing angle of the LED helps compensate for slight misalignment between the remote and the receiver. The low forward voltage characteristic helps conserve battery life in the handheld remote unit.

12. Principle of Operation

An Infrared LED is a semiconductor p-n junction diode. When a forward voltage 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 this specific device, the semiconductor material (typically based on Aluminum Gallium Arsenide - AlGaAs) is engineered so that this energy is released primarily as photons of light in the infrared spectrum, with a peak wavelength of 940 nanometers. The intensity of the emitted light is directly proportional to the rate of carrier recombination, which is controlled by the forward current flowing through the diode.

13. Technology Trends

The general trend in IR emitter technology is toward higher efficiency (more optical power output per electrical watt input), higher power density, and increased reliability. This is driven by advancements in epitaxial growth techniques, improved internal quantum efficiency, and better thermal management within the package. There is also ongoing development in multi-wavelength and broad-spectrum IR sources for advanced sensing applications like spectroscopy and gas detection. Furthermore, integration of drivers and control logic directly with the emitter chip (smart LEDs) is an emerging trend for simplifying system design. The LTE-3271B, with its focus on high current and low voltage, aligns with the efficiency trend for battery-powered and energy-conscious applications.