LTE-3371T IR Emitter Datasheet - High Power 940nm - Forward Voltage 1.6V - 150mW - Clear Package - English Technical Document

1. Product Overview

The LTE-3371T is a high-performance infrared (IR) emitter designed for applications requiring robust optical output and reliable operation under demanding electrical conditions. Its core design philosophy centers on delivering high radiant power while maintaining a low forward voltage drop, making it efficient for both continuous and pulsed driving schemes. The device emits light at a peak wavelength of 940 nanometers, which is ideal for applications where visibility to the human eye is undesirable, such as in night-vision systems, remote controls, and optical sensors.

The emitter is housed in a clear, transparent package that maximizes light extraction and provides a wide viewing angle, ensuring uniform radiation patterns. This product is particularly suited for industrial, automotive, and consumer electronics applications where consistent performance over a range of temperatures and currents is critical.

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 intended for normal operation.

• Power Dissipation (150 mW): This is the maximum amount of power the device can dissipate as heat at an ambient temperature (T_A) of 25°C. Exceeding this limit risks overheating the semiconductor junction, leading to accelerated degradation or catastrophic failure. Designers must ensure the thermal management of the PCB and surrounding environment keeps the junction temperature within safe limits, especially when operating at high continuous currents.
• Peak Forward Current (2 A @ 300pps, 10μs pulse): The device can handle very high instantaneous currents, but only under specific pulsed conditions (300 pulses per second, each 10 microseconds wide). This rating is crucial for applications like infrared communication, where data is transmitted in short, high-power bursts. The average current during pulsed operation must still be managed to stay within the continuous current and power dissipation limits.
• Continuous Forward Current (100 mA): The maximum DC current that can be passed through the device indefinitely under specified conditions. Operating near this limit requires excellent heat sinking.
• Reverse Voltage (5 V): The maximum voltage that can be applied in the reverse-biased direction. Exceeding this can cause breakdown and immediate failure. Circuit protection, such as a series resistor or a parallel protection diode, is often necessary.
• Operating & Storage Temperature Ranges: The device is rated for industrial-grade temperature ranges (-40°C to +85°C operating, -55°C to +100°C storage), indicating robustness for harsh environments.
• Lead Soldering Temperature (260°C for 5 seconds): Provides guidelines for wave or hand soldering, specifying the maximum temperature and time the leads can be exposed 1.6mm from the package body.

2.2 Electrical & Optical Characteristics

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

• Aperture Radiant Incidence (E_e) & Radiant Intensity (I_E): These are the core optical output parameters. E_e measures power density (mW/cm²), while I_E measures the power emitted per solid angle (mW/sr). Both are tested at a forward current (I_F) of 20mA. The values are binned (see Section 3), with typical ranges from 0.64-1.20 mW/cm² (Bin B) up to 4.0 mW/cm² (Bin G). Higher bins deliver significantly more optical power.
• Peak Emission Wavelength (λ_Peak): Nominally 940 nm. This wavelength is efficiently detected by silicon photodiodes and is largely invisible, making it perfect for covert illumination.
• Spectral Line Half-Width (Δλ): Approximately 50 nm. This specifies the spectral bandwidth; a narrower width indicates a more monochromatic source, which can be important for filtering out ambient light in sensing applications.
• Forward Voltage (V_F): A key electrical efficiency parameter. Typical V_F is 1.6V at 50mA and 2.1V at 250mA. The relatively low V_F at high current (1.65V min, 2.1V max @ 250mA) is a highlighted feature, reducing power loss and heat generation in the LED itself.
• Reverse Current (I_R): Maximum 100 μA at a reverse voltage (V_R) of 5V. A low leakage current is desirable.
• Viewing Angle (2θ_1/2): 40 degrees (minimum). This is the full angle at which the radiant intensity drops to half of its maximum value (on-axis). A wide viewing angle of 40° provides broad, even illumination, suitable for applications like proximity sensors or area illumination.

3. Binning System Explanation

The LTE-3371T employs a rigorous binning system for its radiant output, categorized from Bin B to Bin G. This system ensures consistency within a production batch and allows designers to select devices matching their specific optical power requirements.

• Optical Power Binning: The primary binning parameter is radiant intensity (I_E) and aperture radiant incidence (E_e). For example, Bin D devices have a typical I_E range of 8.42-16.84 mW/sr, while Bin G devices are rated at 30 mW/sr (minimum). There is no upper limit specified for Bin G, indicating it represents the highest-performing units from production.
• Design Impact: When designing a system, specifying the bin code is essential for predictable performance. Using a lower bin may require higher drive current to achieve the same optical output as a higher bin, affecting system efficiency and thermal design. For cost-sensitive applications, a lower bin may be sufficient, while high-performance systems will require Bin E, F, or G.
• Wavelength Consistency: The datasheet specifies a single peak wavelength (940nm) without binning, suggesting tight control over the epitaxial growth process, resulting in consistent spectral characteristics across all bins.

4. Performance Curve Analysis

The provided graphs offer crucial insights into the device's behavior under non-standard conditions.

4.1 Spectral Distribution (Fig. 1)

This curve confirms the peak emission at 940nm and the approximately 50nm spectral half-width. The shape is typical of an AlGaAs-based IR emitter. The curve shows minimal emission in the visible spectrum, confirming its covert nature.

4.2 Forward Current vs. Ambient Temperature (Fig. 2)

This derating curve is critical for thermal management. It shows the maximum allowable continuous forward current decreasing as ambient temperature increases. At 85°C, the maximum allowable current is significantly lower than the 100mA rating at 25°C. Designers must use this graph to determine the safe operating current for their application's worst-case ambient temperature.

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

This is the standard I-V curve, showing the exponential relationship. The curve allows designers to estimate the voltage drop and power dissipation (V_F * I_F) for any given operating current, which is vital for selecting an appropriate current-limiting resistor or driver circuit.

4.4 Relative Radiant Intensity vs. Ambient Temperature (Fig. 4) & Forward Current (Fig. 5)

Figure 4 shows that optical output decreases as temperature increases (a negative temperature coefficient), a common trait in LEDs. Figure 5 shows the super-linear increase in output with current. While output rises with current, efficiency often drops at very high currents due to increased heat. These curves help balance the trade-off between output power, efficiency, and device lifetime.

4.5 Radiation Diagram (Fig. 6)

This polar plot visually represents the viewing angle. The concentric circles represent relative intensity (from 0 to 1.0). The plot confirms the wide, roughly Lambertian (cosine-like) emission pattern, with intensity falling to half its peak value at approximately ±20° from the center axis (40° total).

5. Mechanical & Packaging Information

The device uses a standard through-hole package with a clear resin lens. Key dimensional notes from the datasheet include:

• All dimensions are in millimeters, with a standard tolerance of ±0.25mm unless otherwise specified.
• A maximum resin protrusion of 1.5mm under the flange is allowed, which must be considered for PCB stand-off and cleaning.
• Lead spacing is measured at the point where leads exit the package body, which is critical for PCB footprint design.
• The package includes a flange, which aids in mechanical stability during soldering and provides a visual and physical reference for orientation.

Polarity Identification: The datasheet implies standard LED polarity (typically, the longer lead is the anode). However, designers should always verify the specific package drawing for the anode/cathode marking, often indicated by a flat spot on the package flange or a notch.

6. Soldering & Assembly Guidelines

Adherence to these guidelines is essential for reliability.

• Soldering: The absolute maximum rating specifies lead soldering at 260°C for a maximum of 5 seconds, measured 1.6mm from the package body. This is compatible with standard wave or hand soldering processes. For reflow soldering, a profile with a peak temperature below 260°C and limited time above liquidus should be used to prevent thermal damage to the plastic package or the internal die bond.
• Handling: Standard ESD (Electrostatic Discharge) precautions should be observed, as the semiconductor junction can be damaged by static electricity.
• Cleaning: The clear resin package may be sensitive to certain aggressive solvents. Compatibility should be checked if post-solder cleaning is required.
• Storage: Devices should be stored within the specified temperature range (-55°C to +100°C) in a low-humidity, non-corrosive environment. Moisture-sensitive devices should be kept in sealed bags with desiccant if they are not baked prior to use.

7. Application Suggestions

7.1 Typical Application Scenarios

• Infrared Illumination for CCTV/Night Vision: Arrays of these emitters can be used to provide covert illumination for security cameras with IR-sensitive sensors.
• Proximity and Presence Sensing: Paired with a photodetector, the emitter can be used in touchless switches, object detection, and liquid level sensing.
• Optical Data Transmission: Suitable for short-range, low-data-rate IR communication links (e.g., remote controls, industrial telemetry) due to its high pulsed current capability.
• Industrial Automation: Used in optical encoders, object counting on production lines, and break-beam sensors.

7.2 Design Considerations

• Current Driving: An LED is a current-driven device. Always use a constant current source or a current-limiting resistor in series with a voltage source. The resistor value is calculated as R = (V_supply - V_F) / I_F. Use the maximum V_F from the datasheet to ensure the current does not exceed the desired value under all conditions.
• Thermal Management: For continuous operation at high currents (e.g., >50mA), consider the power dissipation (P_D = V_F * I_F). Ensure the PCB has adequate copper area (thermal pads) to conduct heat away from the leads. Refer to the derating curve (Fig. 2).
• Optical Design: The wide viewing angle may require lenses or reflectors to collimate the light for long-range applications. For diffuse illumination, the wide angle is beneficial.
• Electrical Protection: Consider adding a small-value resistor in series with the LED to limit inrush current and a reverse-biased protection diode across the LED if the driving circuit could induce a reverse voltage.

8. Technical Comparison & Differentiation

Based on its specifications, the LTE-3371T differentiates itself in several key areas:

• High Current Capability: The 2A peak pulsed current rating is notably high for a device in this package style, enabling very bright, short-duration pulses ideal for long-range sensing or communication.
• Low Forward Voltage: The typical V_F of 1.6V at 50mA is relatively low for a high-power IR emitter. This translates directly into higher electrical efficiency and less wasted heat for a given optical output compared to devices with higher V_F.
• Wide Viewing Angle & Clear Package: The combination provides uniform, high-efficiency light output without the diffusing effect of a tinted package, maximizing the total flux delivered.
• Industrial Temperature Rating: The -40°C to +85°C operating range makes it suitable for automotive and outdoor applications where standard commercial-grade components might fail.

9. Frequently Asked Questions (Based on Technical Parameters)

9.1 Can I drive this LED directly from a 5V microcontroller pin?

No, not directly. A microcontroller GPIO pin typically sources a limited current (e.g., 20-40mA) and would be unable to provide the voltage headroom needed. You must use a driver circuit. The simplest method is a series resistor: For a 5V supply and a target I_F of 50mA, using the maximum V_F of 1.6V, R = (5V - 1.6V) / 0.05A = 68Ω. The resistor power rating should be P = I²R = (0.05)² * 68 = 0.17W, so a 1/4W resistor is sufficient.

9.2 What is the difference between Radiant Intensity (mW/sr) and Aperture Radiant Incidence (mW/cm²)?

Radiant Intensity (I_E) is a measure of how much optical power the source emits per unit solid angle in a specific direction (usually on-axis). It describes the "concentration" of the beam. Aperture Radiant Incidence (E_e) is the power density (power per unit area) measured at a specific distance, typically over the active area of a detector placed perpendicular to the beam. For a given LED, they are related, but I_E is more fundamental for characterizing the source itself, while E_e is more practical for calculating the signal on a specific detector.

9.3 Why does the optical output decrease with increasing temperature (Fig. 4)?

This is due to several semiconductor physics phenomena. Primarily, increased temperature raises the probability of non-radiative recombination events within the active region of the LED. Instead of producing a photon (light), the energy from the recombining electron-hole pair is converted into lattice vibrations (heat). This reduces the internal quantum efficiency of the device. Additionally, the peak emission wavelength may shift slightly with temperature.

10. Practical Design Case Study

Scenario: Designing a short-range (1-meter) IR proximity sensor to detect the presence of an object.

• Emitter Drive: Use the LTE-3371T (Bin D for good output). Drive it with a 100mA, 1ms pulse every 100ms (1% duty cycle) from a 5V supply via a MOSFET switch. Average current is 1mA, well within limits. A series resistor of (5V - 2.1V_max)/0.1A ≈ 30Ω is needed.
• Detector: Use a silicon phototransistor or photodiode with a spectral response peak near 940nm. Place it a few centimeters away from the emitter to avoid direct coupling.
• Optics: The wide 40° viewing angle of the LTE-3371T is perfect for creating a diffuse "light curtain" in front of the sensor pair. No additional lenses are required for this short-range, diffuse application.
• Signal Processing: The detector's output will show a baseline level (ambient light) and a spike when the emitted pulse reflects off a nearby object. A synchronous detection circuit (looking for the signal only during the 1ms pulse) can greatly improve immunity to ambient light noise.

11. Operational Principle

The LTE-3371T is a semiconductor light-emitting diode (LED). Its operation is based on electroluminescence in a direct bandgap semiconductor material, likely Aluminum Gallium Arsenide (AlGaAs). When a forward voltage is applied, electrons are injected from the n-type region and holes from the p-type region into the active region (the p-n junction). These charge carriers recombine, releasing energy. In a direct bandgap material like AlGaAs, this energy is primarily released as photons (light). The specific wavelength of 940nm is determined by the bandgap energy of the semiconductor material used in the active layer, which is engineered during the epitaxial growth process. The clear epoxy package serves to protect the semiconductor die, provide mechanical support for the leads, and act as a lens to shape the emitted light output.

12. Technology Trends

Infrared emitter technology continues to evolve alongside broader optoelectronics trends. Key areas of development include:

• Increased Power Density & Efficiency: Ongoing improvements in epitaxial growth and chip design aim to extract more optical power from a given chip size while minimizing forward voltage, directly improving lumens-per-watt (or watts-electrical to watts-optical) efficiency.
• Advanced Packaging: Trends include surface-mount device (SMD) packages with improved thermal performance (e.g., chip-on-board or COB designs), allowing for higher continuous operating currents and better reliability. There is also development in packages with integrated lenses or diffusers for specific beam patterns.
• Multi-Wavelength & VCSELs: For sensing applications like time-of-flight (ToF) and LiDAR, there is significant growth in Vertical-Cavity Surface-Emitting Lasers (VCSELs), which offer narrower spectral width, faster modulation speeds, and lower divergence than traditional LED emitters like the LTE-3371T. However, LEDs remain highly cost-effective and reliable for many applications.
• Integration with Drivers: There is a trend towards smarter components, with some emitters integrating simple drive circuitry or protection features (like ESD diodes) within the package.

The LTE-3371T, with its focus on high-current pulse capability, low V_F, and robust construction, represents a mature and reliable solution within this evolving landscape, particularly suited for applications where cost-effective, high-output IR illumination is required.