LTE-R38381L-S IR Emitter and Detector Datasheet - 940nm Wavelength - 1A Forward Current - 1.8W Power - English Technical Document

1. Product Overview

This document provides the complete technical specifications for a discrete infrared emitter component. The device is designed for applications requiring a high-power, reliable infrared light source. It utilizes a Gallium Arsenide (GaAs) chip to emit light at a peak wavelength of 940 nanometers, which is in the near-infrared spectrum and invisible to the human eye. The primary function of this component is to serve as a controlled infrared emitter in various electronic systems.

1.1 Core Advantages and Target Market

The component offers several key advantages for infrared applications. It features a high radiant intensity, enabling strong signal transmission. It is designed for a high driving current, which contributes to its output power. The device is also characterized by its long operational life and high performance reliability. It is compliant with environmental regulations such as RoHS, classifying it as a green product. The target applications for this infrared emitter are diverse, primarily focusing on areas like infrared emitters for remote control systems and PCB-mounted infrared sensors for proximity detection, object sensing, or data transmission.

2. Technical Parameters: In-Depth Objective Interpretation

The following sections provide a detailed, objective analysis of the device's key technical parameters as defined in its specification limits.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed and should be avoided in reliable design.

• Power Dissipation (Pd): 1.8 Watts. This is the maximum amount of power the device can dissipate as heat at an ambient temperature (TA) of 25°C. Exceeding this will cause the junction temperature to rise excessively.
• Peak Forward Current (IFP): 5 Amperes. This is the maximum allowable current under pulsed conditions (300 pulses per second, 10-microsecond pulse width). It is significantly higher than the DC rating, leveraging the device's thermal inertia.
• DC Forward Current (IF): 1 Ampere. This is the maximum continuous forward current the device can handle.
• Reverse Voltage (VR): 5 Volts. Applying a reverse voltage higher than this can break down the semiconductor junction.
• Thermal Resistance (RθJ): 10 K/W. This parameter indicates how effectively heat travels from the semiconductor junction to the ambient. A lower value means better heat dissipation.
• Operating Temperature Range: -40°C to +85°C. The device is guaranteed to function within this ambient temperature range.
• Storage Temperature Range: -55°C to +100°C.

2.2 Electrical and Optical Characteristics

These are the typical and guaranteed performance parameters measured under specified test conditions (TA=25°C, unless noted).

• Radiant Intensity (I_E): 160 mW/sr (Min). This measures the optical power emitted per unit solid angle (steradian) along the axis. It defines the beam's strength in a specific direction.
• Total Radiant Flux (Φ_e): 590 mW (Typ). This is the total optical power emitted by the device into all directions (4π steradians).
• Peak Emission Wavelength (λ_P): 940 nm (Typ). The wavelength at which the emitted optical power is maximum.
• Spectral Line Half-Width (Δλ): 50 nm (Typ). This is the spectral bandwidth where the radiant intensity is at least half of its peak value. It describes the purity of the emitted color (wavelength).
• Forward Voltage (V_F): 1.8V (Typ), 2.3V (Max) at I_F=1A. The voltage drop across the device when conducting the specified forward current.
• Reverse Current (I_R): 10 μA (Max) at V_R=5V. The small leakage current that flows when the device is reverse-biased.
• Rise/Fall Time (t_r/t_f): 30 ns (Typ). The time required for the optical output to rise from 10% to 90% (or fall from 90% to 10%) of its final value in response to a step current. This determines the maximum modulation speed.
• Viewing Angle (2θ_1/2): 90 degrees (Typ). The full angle at which the radiant intensity is half the value at the center (0°). A 90° angle indicates a wide beam pattern.

3. Performance Curve Analysis

The datasheet includes several graphs illustrating the device's behavior under varying conditions. These curves are essential for understanding non-linearities and temperature dependencies.

3.1 Spectral Distribution

A graph (Fig.1) shows the relative radiant intensity versus wavelength. The curve is centered around 940 nm with a typical half-width of 50 nm. This confirms the device emits in the near-infrared region, which is optimal for many sensors and remote controls that filter out visible light.

3.2 Forward Current vs. Forward Voltage (I-V Curve)

The I-V curve (Fig.3) demonstrates the exponential relationship typical of a diode. At the rated current of 1A, the forward voltage is typically 1.8V. Designers must ensure the drive circuit can provide this voltage at the required current.

3.3 Temperature Dependence

Key graphs illustrate the impact of temperature:

• Forward Current vs. Ambient Temperature (Fig.2): Shows how the maximum allowable forward current derates as ambient temperature increases, due to the fixed power dissipation limit.
• Relative Radiant Intensity vs. Ambient Temperature (Fig.4): Indicates that the optical output power decreases as the junction temperature rises. This is a critical factor for maintaining consistent performance.
• Relative Radiant Intensity vs. Forward Current (Fig.5): Shows the sub-linear relationship between drive current and light output, especially at higher currents where efficiency may drop and heating increases.

3.4 Radiation Pattern

The radiation diagram (Fig.6) is a polar plot showing the angular distribution of emitted light. The 90° viewing angle is visually confirmed, showing intensity dropping to half at ±45° from the center axis. This pattern is important for aligning the emitter with a detector or ensuring adequate coverage in a sensing application.

4. Mechanical and Package Information

4.1 Outline Dimensions

The device has a standard through-hole package form factor. The dimensional drawing specifies the body size, lead spacing, and lead diameter. All dimensions are provided in millimeters with a typical tolerance of ±0.1 mm unless otherwise stated. The cathode is identified on the package, which is crucial for correct orientation during PCB assembly.

4.2 Suggested Soldering Pad Dimensions

A diagram provides recommended land pattern (footprint) dimensions for PCB design. Following these recommendations helps ensure a reliable solder joint and proper mechanical stability after wave or reflow soldering.

5. Welding and Assembly Guide

5.1 Soldering Conditions

The datasheet provides clear guidelines for two soldering methods:

• Reflow Soldering: Recommended for surface-mount assembly. The profile must have a pre-heat stage (150-200°C), a peak temperature not exceeding 260°C, and a time above 260°C limited to a maximum of 10 seconds. The device can withstand this profile a maximum of two times.
• Hand Soldering (Iron): The soldering iron tip temperature should not exceed 300°C, and contact time should be limited to 3 seconds per lead. This should be performed only once.

A reference to a JEDEC-compliant reflow temperature profile is provided as a generic target, emphasizing the need to adhere to both JEDEC limits and solder paste manufacturer specifications.

5.2 Storage and Handling

• Storage (Sealed Bag): Devices should be stored at ≤30°C and ≤90% Relative Humidity (RH). The shelf life in the moisture-proof bag with desiccant is one year.
• Storage (Opened Bag): After opening, the ambient should not exceed 30°C / 60% RH. Components should be used within one week. For longer storage outside the original bag, they must be kept in a sealed container with desiccant or in a nitrogen desiccator.
• Baking: If devices are exposed to ambient air for more than one week, a bake at 60°C for at least 20 hours is recommended before soldering to remove absorbed moisture and prevent "popcorning" during reflow.

5.3 Cleaning

If cleaning is necessary after soldering, only alcohol-based solvents like isopropyl alcohol should be used to avoid damaging the package or lens material.

5.4 Drive Method

A critical design note emphasizes that an LED is a current-operated device. To ensure uniform brightness when driving multiple LEDs in parallel, a individual current-limiting resistor must be placed in series with each LED. This compensates for minor variations in the forward voltage (V_F) of individual devices, preventing current hogging and uneven illumination or output power.

6. Packaging and Ordering Information

6.1 Tape and Reel Package Dimensions

Detailed mechanical drawings specify the dimensions of the carrier tape, the pocket that holds the component, and the overall reel (7-inch diameter is mentioned). The tape is sealed with a cover tape to protect components during shipping and automated assembly.

6.2 Packaging Specifications

Key packaging details include:

• Reel size: 7 inches.
• Quantity: 600 pieces per reel.
• Quality: The maximum number of consecutive missing components in the tape is two.
• Standard: Packaging conforms to ANSI/EIA 481-1-A-1994 specifications.

7. Application Suggestions and Design Considerations

7.1 Typical Application Scenarios

Based on its specifications, this infrared emitter is well-suited for:

• Infrared Remote Controls: For TVs, audio systems, and other consumer electronics. The 940nm wavelength is standard for most IR receivers.
• Proximity and Object Sensing: Paired with a photodiode or phototransistor to detect the presence, absence, or distance of an object by reflecting its IR light.
• Optical Switches and Encoders: Interrupting the beam between the emitter and detector to create a non-contact switch or measure rotation/position.
• Short-Range Data Transmission: For IrDA-like applications or simple wireless data links, modulated by its fast rise/fall time.

7.2 Design Considerations

• Heat Management: With a power dissipation of 1.8W and thermal resistance of 10 K/W, driving the device at its maximum DC current will generate significant heat. Adequate PCB copper area (thermal relief) or a heatsink may be necessary for continuous operation, especially in high ambient temperatures.
• Current Drive Circuitry: Use a constant current driver or a voltage source with a series resistor to set the current. Avoid driving directly from a logic pin or unregulated voltage source.
• Optical Design: Consider the 90° viewing angle. For long-range or directed beams, a lens may be required to collimate the light. For wide-area illumination, the native angle may be sufficient.
• Pairing with Detector: Ensure the selected photodetector (PIN photodiode, phototransistor) is sensitive in the 940nm region. Using a detector with a daylight blocking filter will improve the signal-to-noise ratio in ambient light conditions.

8. Technical Comparison and Differentiation

While a direct comparison requires specific competitor data, this device's key differentiating features based on its own datasheet are:

• High Power Capability: A 1A DC forward current and 5A pulsed current rating indicate a robust chip and package design capable of high output.
• Wide Viewing Angle: The 90° angle provides broad coverage, useful for sensing applications where alignment is not critical or area illumination is needed.
• Fast Switching Speed: A typical 30ns rise/fall time allows for high-frequency modulation, enabling faster data transmission rates in communication applications compared to slower devices.
• Established Reliability: References to JEDEC standards and detailed soldering/moisture sensitivity guidelines suggest a component designed for robust manufacturing processes.

9. Frequently Asked Questions (Based on Technical Parameters)

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

No, this is not recommended and likely to damage either the LED or the microcontroller. The LED typically drops 1.8V at 1A. A microcontroller pin cannot source 1A, and connecting it directly to 5V without a current limit would attempt to draw a destructively high current. You must use a driver circuit (transistor/MOSFET) with a series resistor to limit the current to the desired value.

9.2 Why is the output lower at high temperature?

The efficiency of the semiconductor material in converting electrical current to light (internal quantum efficiency) decreases as the junction temperature increases. This is a fundamental physical property. The graph in Fig.4 quantifies this derating, which must be accounted for in designs operating over a wide temperature range to ensure consistent optical performance.

9.3 What is the difference between Radiant Intensity and Total Radiant Flux?

Radiant Intensity (mW/sr) is a directional measure: the power emitted into a specific solid angle (usually along the central axis). It's key for applications where a detector is placed in a specific location. Total Radiant Flux (mW) is the total integrated power emitted into all directions (the entire sphere). It represents the overall "brightness" of the emitter regardless of direction. A device can have high total flux but low axial intensity if the light is spread very wide.

9.4 How critical is the 1-week floor life after opening the bag?

It is very important for reliable soldering. Plastic packages absorb moisture from the air. During the high-temperature reflow soldering process, this trapped moisture can vaporize rapidly, causing internal delamination, cracks, or "popcorning" that destroys the component. The 1-week limit and baking requirement are based on the package's Moisture Sensitivity Level (MSL) to prevent these failures.

10. Practical Design and Usage Case

Case: Designing a Multi-Emitter Object Detection Barrier
A system requires an infrared light curtain to detect objects passing through a 50cm wide gate. Five emitter-detector pairs will be used.

1. Drive Circuit: Each emitter will be driven by a dedicated N-channel MOSFET, controlled by a shared microcontroller PWM signal to modulate the IR light (e.g., at 38kHz). A single current-limiting resistor will be calculated for each LED branch: R = (V_supply - V_{F_LED}) / I_F. Assuming a 5V supply, V_F=1.8V, and I_F=500mA (derated for reliability), R = (5 - 1.8) / 0.5 = 6.4Ω (use 6.2Ω standard value). The resistor power rating must be at least I²R = (0.5)²*6.2 ≈ 1.55W, so a 2W or 3W resistor is needed.
2. Thermal Management: Each LED dissipates P = V_F * I_F = 1.8V * 0.5A = 0.9W. The PCB should have large copper pours connected to the LED's cathode and anode pads to act as a heatsink, keeping the junction temperature within safe limits.
3. Optical Alignment: The 90° viewing angle simplifies alignment with the corresponding detector across the gap. Small tubular shrouds can be placed around the emitter and detector to limit ambient light interference without overly restricting the beam.
4. Modulation: Driving the emitters with a 38kHz square wave allows the detectors to be tuned to the same frequency, effectively filtering out constant ambient IR light (like from sunlight or lamps) and greatly improving detection reliability.

11. Principle of Operation Introduction

This device is a Light Emitting Diode (LED) that operates in the infrared spectrum. Its core is a semiconductor chip made of Gallium Arsenide (GaAs). When a forward voltage is applied across the chip's P-N junction, electrons from the N-type material recombine with holes from the P-type material. This recombination process releases energy. In a standard silicon diode, this energy is primarily released as heat. In materials like GaAs, a significant portion of this energy is released as photons (light particles). The specific energy bandgap of the GaAs material determines the wavelength of these photons, which in this case is centered around 940 nm, placing it in the near-infrared region. The intensity of the emitted light is directly proportional to the rate of recombination, which is controlled by the forward current flowing through the diode.

12. Technology Trends (Objective Perspective)

The field of infrared emitters continues to evolve alongside broader optoelectronics trends. There is a consistent drive towards higher power density and efficiency, allowing for brighter output from smaller packages or with lower power consumption. This enables more compact sensor designs and longer battery life in portable devices. Integration is another key trend, with components combining the emitter, driver circuitry, and sometimes even a basic detector or monitoring photodiode into a single module or IC package, simplifying system design. Furthermore, advancements in materials, such as the development of more efficient epitaxial structures or the use of new semiconductor compounds, aim to improve performance parameters like wall-plug efficiency (light output per electrical input) and temperature stability. The demand for devices supporting higher modulation speeds also persists, driven by applications in faster data communication and LiDAR (Light Detection and Ranging) systems. These trends focus on enhancing performance, reliability, and ease of use for the system designer.