Infrared Emitter LTE-3276 Datasheet - 850nm Wavelength - 50mA Forward Current - 1.8V Forward Voltage - High Power & Speed - English Technical Document

1. Product Overview

The LTE-3276 is a high-performance infrared (IR) emitter designed for applications requiring fast response times and significant radiant output. Its core advantages lie in its combination of high speed and high power capabilities, making it suitable for pulse operation in demanding environments. The device is housed in a clear transparent package, which is typical for IR emitters to allow maximum transmission of the infrared light. The target market includes industrial automation, communication systems (like IrDA), remote controls, optical switches, and sensor systems where reliable, high-intensity infrared signaling is required.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation at or near these limits is not recommended for extended periods.

• Power Dissipation (P_D): 200 mW. This is the maximum total power the device can dissipate as heat under any operating condition.
• Peak Forward Current (I_FP): 1 A. This high current is permissible only under pulsed conditions (300 pulses per second, 10 μs pulse width). It highlights the device's capability for short, intense bursts of light.
• Continuous Forward Current (I_F): 100 mA. This is the maximum DC current that can be applied continuously.
• Reverse Voltage (V_R): 5 V. Exceeding this voltage in reverse bias can break down the semiconductor junction.
• Operating & Storage Temperature Range: -40°C to +85°C. This wide range ensures reliability in harsh environmental conditions.
• Lead Soldering Temperature: 260°C for 6 seconds at 1.6mm from the body. This is critical for wave or reflow soldering processes to prevent thermal damage.

2.2 Electrical & Optical Characteristics

These parameters are specified at an ambient temperature (T_A) of 25°C and define the typical performance of the device.

• Radiant Intensity (I_E): A key measure of optical output power per solid angle. At I_F = 20mA, it is 12.75 mW/sr (typical). At I_F = 50mA, it increases significantly to 32 mW/sr (typical), demonstrating a non-linear, efficient increase with current.
• Peak Emission Wavelength (λ_P): 850 nm (typical). This is in the near-infrared spectrum, invisible to the human eye but easily detected by silicon photodiodes and cameras with IR sensitivity.
• Spectral Line Half-Width (Δλ): 40 nm (typical). This indicates the spectral bandwidth; a narrower width would indicate a more monochromatic source.
• Forward Voltage (V_F): At I_F = 50mA, V_F is 1.49V (typical), with a maximum of 1.80V. At I_F = 200mA, V_F rises to 1.83V (typical), max 2.3V. This positive temperature coefficient must be considered in driver design.
• Viewing Angle (2θ_1/2): 50 degrees (typical). This is the full angle at which the radiant intensity drops to half of its peak value. A 50° angle provides a good balance between beam concentration and coverage.

3. Performance Curve Analysis

The datasheet provides several typical characteristic curves that are essential for circuit design and understanding device behavior under varying conditions.

3.1 Spectral Distribution (Fig. 1)

This curve plots relative radiant intensity against wavelength. It confirms the peak wavelength around 850 nm and shows the shape and width (40 nm half-width) of the emission spectrum. This is crucial for matching the emitter with a detector's spectral sensitivity.

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

This IV curve shows the exponential relationship typical of a diode. The curve allows designers to determine the necessary drive voltage for a desired operating current, which is critical for designing constant-current drivers.

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

This graph shows how light output increases with drive current. It is generally linear at lower currents but may show saturation effects at very high currents due to thermal and efficiency limitations. This data is vital for setting the operating point to achieve the required optical power.

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

This curve demonstrates the negative temperature coefficient of the LED's output. As ambient temperature rises, the radiant intensity decreases. This thermal derating must be factored into designs intended for high-temperature environments to ensure sufficient signal margin.

3.5 Radiation Diagram (Fig. 6)

This polar plot visually represents the spatial distribution of the emitted light, clearly illustrating the 50-degree viewing angle. It helps in designing optical systems for focusing or collimating the IR beam.

4. Mechanical & Packaging Information

4.1 Package Dimensions

The device uses a standard through-hole package, likely a T-1 3/4 (5mm) style common for IR emitters. Key dimensional notes from the datasheet include:

• All dimensions are in millimeters (inches).
• Tolerance is ±0.25mm(.010") unless otherwise noted.
• Protruded resin under the flange is 1.5mm(.059") maximum.
• Lead spacing is measured where the leads emerge from the package.

The clear transparent package material is typically epoxy, optimized for high transmittance at 850 nm.

4.2 Polarity Identification

For a standard LED package, the longer lead is typically the anode (positive), and the shorter lead is the cathode (negative). The package may also have a flat side near the cathode. Observing correct polarity is essential to prevent reverse bias damage.

5. Soldering & Assembly Guidelines

The absolute maximum rating for lead soldering is explicitly stated: 260°C for 6 seconds, measured 1.6mm (.063") from the body. This is a critical parameter for assembly.

• Wave/Hand Soldering: Adhere strictly to the 260°C/6s limit. Preheating is recommended to minimize thermal shock.
• Reflow Soldering: While not explicitly mentioned for SMD, the temperature profile should ensure the package body temperature does not exceed the storage maximum of 85°C for extended periods, and the lead temperature at the specified point must not exceed 260°C.
• Storage Conditions: Store in a dry, anti-static environment within the specified temperature range (-40°C to +85°C) to prevent moisture absorption and degradation.

6. Application Suggestions

6.1 Typical Application Scenarios

• Infrared Data Transmission (IrDA): Its high speed makes it suitable for serial data links.
• Remote Controls: High power ensures long range and reliable operation.
• Optical Switches & Object Detection: Used in conjunction with a photodetector to sense presence, position, or counting.
• Industrial Safety Curtains: Creating an invisible beam barrier for machine guarding.
• Night Vision Illumination: For CCTV cameras with IR sensitivity.

6.2 Design Considerations

• Driver Circuit: Always use a series current-limiting resistor or a constant-current driver. Calculate based on the forward voltage (V_F) at the desired operating current (I_F).
• Heat Management: For continuous operation near the maximum current, consider the power dissipation (P_D = V_F * I_F) and ensure adequate heatsinking if necessary to keep the junction temperature within limits.
• Pulsed Operation: For the 1A peak pulse current, ensure the driver can deliver the required high current pulse with a fast rise/fall time to leverage the high-speed capability.
• Optical Design: Use lenses or reflectors to shape the 50° beam according to the application need (e.g., narrow for long range, wide for area coverage).
• Detector Matching: Pair with a photodetector (e.g., phototransistor, photodiode) whose peak spectral sensitivity is around 850 nm for optimal performance.

7. Technical Comparison & Differentiation

The LTE-3276 differentiates itself in the market through its specific combination of parameters:

• High Power at Moderate Current: 32 mW/sr at 50mA is a strong output, beneficial for applications requiring good signal-to-noise ratio.
• High-Speed Capability: The specification for pulse operation implies a fast intrinsic response time, suitable for modulated signals.
• Robust Construction: The wide operating temperature range and clear package indicate design for reliability.
• Compared to standard low-power IR LEDs, this device offers significantly higher radiant intensity. Compared to laser diodes, it is safer (eye-safe in this power class), has a wider beam, and is generally more robust and easier to drive.

8. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED directly from a 5V microcontroller pin?
A: No. You must use a current-limiting resistor. For example, to drive at I_F=50mA with a V_F of ~1.5V from a 5V supply: R = (5V - 1.5V) / 0.05A = 70 Ohms. Use a 68 or 75 Ohm resistor and check the power rating (P = I²R = 0.175W, so a 1/4W resistor is sufficient).

Q: What is the difference between Radiant Intensity (mW/sr) and Aperture Radiant Incidence (mW/cm²)?
A: Radiant Intensity is the power emitted per unit solid angle (steradian), describing the source's directional strength. Aperture Radiant Incidence is the power density (mW per cm²) arriving at a detector's surface at a specified distance and alignment. The latter depends on the former and the distance/inverse-square law.

Q: How do I use it in pulsed mode?
A: Use a transistor (BJT or MOSFET) switch controlled by your logic signal to pulse the LED. Ensure the driver can source the high peak current (up to 1A) with fast switching. The average current must still respect the continuous current rating (100mA) when considering duty cycle.

Q: Why does the output decrease with temperature?
A> This is a fundamental characteristic of semiconductor LEDs. Increased temperature increases non-radiative recombination processes within the semiconductor material, reducing the internal quantum efficiency and thus the light output.

9. Practical Design Case

Case: Designing a Long-Range Infrared Object Detection Sensor.
Goal: Detect an object at 5 meters.
Design Steps:
1. Emitter Drive: Operate the LTE-3276 at I_F=50mA (pulsed at 1kHz, 50% duty cycle) to achieve high peak intensity (32 mW/sr) while keeping average power manageable.
2. Optics: Add a simple collimating lens in front of the emitter to narrow the 50° beam to a more focused ~10° beam, significantly increasing intensity at a distance.
3. Detector: Use a matched silicon phototransistor with a peak response at 850nm. Place a narrow-bandpass optical filter (centered at 850nm) in front of it to reject ambient light.
4. Circuit: The receiver circuit amplifies the small photocurrent. Use synchronous detection (modulating the emitter and tuning the receiver to the same frequency) to reject DC ambient light and low-frequency noise, greatly improving range and reliability.
This setup leverages the LTE-3276's high power and speed for a robust, interference-immune detection system.

10. Operating Principle Introduction

An infrared emitter like the LTE-3276 is a light-emitting diode (LED) based on semiconductor physics. When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region. When these charge carriers recombine, they release energy. In this specific device, the semiconductor material (typically based on Aluminum Gallium Arsenide - AlGaAs) is engineered so that this energy is released as photons in the infrared spectrum, with a peak wavelength of 850 nanometers. The "clear transparent" epoxy package is doped to be transparent to this wavelength, allowing the photons to escape efficiently. The "high speed" characteristic refers to the fast turn-on and turn-off times of this recombination process, enabling the LED to be modulated at high frequencies for data transmission.

11. Technology Trends

Infrared emitter technology continues to evolve alongside broader optoelectronic trends. Key developments include:
Increased Power Efficiency: Research focuses on improving the internal quantum efficiency (more photons per electron) and the light extraction efficiency from the package, leading to higher radiant intensity for the same electrical input power.
Smaller Form Factors: The drive towards miniaturization pushes for surface-mount device (SMD) packages with similar or better performance than traditional through-hole types.
Enhanced Speed: For communication applications, devices are being developed with even faster modulation bandwidths to support higher data rates.
Wavelength Diversification: While 850nm and 940nm are common, other wavelengths are being optimized for specific applications, such as eye-safe longer wavelengths or specific absorption lines for gas sensing.
Integration: There is a trend towards integrating the emitter with a driver IC or even with a detector in a single module, simplifying system design for end-users.