Infrared Emitter LED LTE-7377LM1-TA Datasheet - High Speed, High Power, Blue Package - English Technical Document

1. Product Overview

This document details the specifications for a high-performance infrared (IR) emitter component. The device is engineered for applications requiring rapid response times and significant optical output power. Its core design philosophy centers on reliability and efficiency in pulsed operation environments, making it suitable for a range of sensing and communication systems. The component is housed in a distinctive blue transparent package, which can aid in visual identification during assembly and may offer specific filtering or transmission properties for the emitted wavelength.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the stress limits beyond which permanent damage to the device may occur. These values are not for continuous operation but represent thresholds that must not be exceeded under any condition.

• Power Dissipation (P_D): 200 mW. This is the maximum amount of power the device can dissipate as heat. Exceeding this limit risks thermal runaway and failure.
• Peak Forward Current (I_FP): 2 A. This rating applies under specific pulsed conditions (100 pulses per second, 10 µs pulse width). It indicates the device's capability to handle very high instantaneous currents for short durations, which is critical for generating high-intensity optical pulses.
• Continuous Forward Current (I_F): 100 mA. The maximum DC current that can be passed through the device continuously without degrading its performance or lifespan.
• Reverse Voltage (V_R): 5 V. The maximum voltage that can be applied in the reverse bias direction. Exceeding this can cause junction breakdown.
• Operating Temperature Range (T_A): -40°C to +85°C. The ambient temperature range over which the device is guaranteed to meet its published specifications.
• Storage Temperature Range (T_stg): -55°C to +100°C. The temperature range for non-operational storage without degradation.
• Lead Soldering Temperature: 260°C for 5 seconds, measured 1.6mm from the package body. This defines the thermal profile tolerance for wave or hand soldering processes.

2.2 Electrical & Optical Characteristics

These parameters are measured at a standard ambient temperature of 25°C and define the typical performance of the device under specified test conditions.

• Radiant Intensity (I_E): 35 mW/sr (Minimum). Measured with a forward current (I_F) of 50mA. Radiant intensity describes the optical power emitted per unit solid angle (steradian), indicating the brightness of the source from a specific direction.
• Peak Emission Wavelength (λ_P): 880 nm (Typical). This is the wavelength at which the optical output power is maximum. 880nm is in the near-infrared spectrum, invisible to the human eye but detectable by silicon photodiodes and many sensors.
• Spectral Line Half-Width (Δλ): 50 nm (Maximum). This parameter, also known as Full Width at Half Maximum (FWHM), indicates the spectral bandwidth of the emitted light. A value of 50nm shows it is not a monochromatic source but emits over a range of wavelengths centered around 880nm.
• Forward Voltage (V_F): 1.5V (Min), 1.75V (Typ), 2.1V (Max). Measured at a high pulsed current of 350mA (100pps, 10µs pulse). This is the voltage drop across the diode when forward-biased and conducting. It is crucial for designing the driving circuitry and calculating power dissipation.
• Reverse Current (I_R): 100 µA (Maximum). The leakage current when a reverse bias of 5V is applied. A low value is desirable.
• Rise/Fall Time (T_r/T_f): 40 nS (Maximum). This defines the switching speed of the device, measured as the time for the optical output to transition from 10% to 90% of its final value (rise) and vice-versa (fall). The 40ns specification confirms its suitability for high-speed modulation and pulsed applications.
• Viewing Angle (2θ_1/2): 16 degrees (Typical). This is the full angle at which the radiant intensity drops to half of its maximum value (on-axis). A 16° angle indicates a relatively narrow beam, useful for directed illumination or sensing over a specific path.

3. Performance Curve Analysis

The datasheet references typical characteristic curves which are essential for detailed design analysis. While the specific graphs are not reproduced in the provided text, their typical content and significance are explained below.

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

This graph shows the relationship between the current flowing through the diode and the voltage across it. It is non-linear, exhibiting a turn-on/threshold voltage (around 1.2-1.4V for GaAs IR LEDs) after which current increases rapidly with a small increase in voltage. Designers use this curve to select appropriate current-limiting resistors or design constant-current drivers.

3.2 Radiant Intensity vs. Forward Current

This plot illustrates how the optical output power increases with drive current. It is typically linear over a wide range but may saturate at very high currents due to thermal effects and internal efficiency droop. The slope of this line relates to the device's external quantum efficiency.

3.3 Radiant Intensity vs. Ambient Temperature

This curve demonstrates the temperature dependence of the optical output. For LEDs, radiant intensity generally decreases as junction temperature increases. This derating factor is critical for designing systems that operate over the full temperature range (-40°C to +85°C) to ensure consistent performance.

3.4 Spectral Distribution

A graph showing the relative optical power emitted as a function of wavelength. It would peak at the typical 880nm and have a width defined by the 50nm FWHM specification. This is important for matching the emitter to the spectral sensitivity of the detector being used.

4. Mechanical & Package Information

4.1 Package Dimensions

The device uses a standard LED package format with a flange for mechanical stability and potentially for heat sinking. Key dimensional notes from the datasheet include:

• All dimensions are in millimeters, with inches in parentheses.
• A general tolerance of ±0.25mm (±0.010") applies unless a specific feature has a different callout.
• The resin under the flange may protrude by a maximum of 1.5mm (0.059").
• Lead spacing is measured at the point where the leads exit the package body, which is critical for PCB footprint design.

The specific dimensional drawing would provide exact values for body length, width, height, lead diameter, and spacing.

4.2 Polarity Identification

Infrared LEDs are polarized components. The package typically has a flat side or a notch on the rim to indicate the cathode (negative) lead. The longer lead may also indicate the anode (positive), but the package marking is the definitive reference. Correct polarity is essential for operation.

5. Soldering & Assembly Guidelines

Adherence to soldering specifications is vital to prevent mechanical or thermal damage.

• Soldering Temperature: The leads can withstand 260°C for up to 5 seconds, provided the heat is applied at least 1.6mm (0.063") away from the plastic package body. This prevents the resin from melting or being thermally stressed.
• Process Recommendation: For reflow soldering, a standard lead-free profile with a peak temperature not exceeding 260°C is suitable. The time above liquidus should be controlled to minimize total thermal input.
• Cleaning: If cleaning is required, use processes compatible with the blue transparent epoxy resin. Harsh solvents should be avoided.
• Storage Conditions: Store in a dry, anti-static environment within the specified storage temperature range (-55°C to +100°C). Moisture Sensitivity Level (MSL) information, if applicable, would be found in a separate packing specification.

6. Packaging & Ordering Information

The final page of the datasheet is dedicated to packing details. This typically includes:

• Packaging Format: The devices are likely supplied on tape and reel for automated placement, standard for surface-mount components. The reel size, tape width, pocket dimensions, and orientation are defined here.
• Quantity per Reel: The standard number of pieces per reel (e.g., 1000, 2000, 4000).
• Model Number: The part number LTE-7377LM1-TA is the complete ordering code. Suffixes like "-TA" may indicate tape-and-reel packaging or specific binning options.

7. Application Suggestions

7.1 Typical Application Scenarios

• Infrared Sensing: Proximity sensors, object detection, line-following robots, and interruptive optical switches (e.g., paper detection in printers). The narrow viewing angle and high speed are beneficial.
• Optical Communication: Short-range data links, remote control transmitters (for TVs, etc.), and industrial IR data transmission where immunity to EMI is needed. The 40ns rise/fall time supports moderate data rates.
• Machine Vision & Illumination: Providing invisible illumination for CCTV cameras with night vision capability or for specialized machine vision systems.

7.2 Design Considerations

• Drive Circuitry: Due to the high permissible pulsed current (2A), a dedicated driver transistor (BJT or MOSFET) is almost always required. A simple series resistor is insufficient for such high-current pulses and would waste excessive power.
• Current Limiting: For DC or pulsed operation, the current must be actively limited to prevent exceeding the Absolute Maximum Ratings. Use a constant-current driver for stable optical output.
• Heat Management: While the package has a flange, for continuous operation at high currents (approaching 100mA), consideration should be given to the PCB layout to act as a heat sink, especially if operating at high ambient temperatures.
• Optical Design: The 16-degree viewing angle may require lenses or diffusers if a different beam pattern is needed. The 880nm wavelength requires a detector sensitive in that range (e.g., silicon photodiode, phototransistor).
• Electrical Protection: A small series resistor or transient voltage suppressor (TVS) may be advisable to protect against voltage spikes, especially in industrial environments, despite the 5V reverse voltage rating.

8. Technical Comparison & Differentiation

Based on its specifications, this IR emitter differentiates itself in the market through a combination of key attributes:

• High Speed & High Power Combo: The 40ns switching speed combined with a high radiant intensity (35 mW/sr min) and very high pulsed current capability (2A) is a significant advantage for applications requiring both bright pulses and fast data rates or precise timing.
• Optimized for Pulsed Operation: The explicit ratings for peak pulsed current and the forward voltage specified under pulse conditions indicate the device is engineered for this demanding mode, offering better performance and reliability than LEDs simply rated for DC.
• Narrow Viewing Angle: The 16-degree beam is narrower than many standard IR LEDs (which can be 30-60 degrees), providing more directed light and higher intensity on-axis, which improves signal-to-noise ratio in directed sensing applications.

9. Frequently Asked Questions (FAQs)

Q1: Can I drive this LED with a 5V microcontroller pin using only a series resistor?
A: For brief pulses at low current (e.g., 20-50mA), a series resistor calculation is possible (R = (V_CC - V_F) / I_F). However, for the high-current pulsed operation (350mA or 2A) the device is designed for, a microcontroller pin cannot source enough current. A transistor switch (like a MOSFET) controlled by the MCU is mandatory to deliver the required current from a separate power supply.

Q2: What is the purpose of the blue package? Is it just for color?
A: The blue transparent epoxy acts as a short-wavelength pass filter. It is transparent to the emitted 880nm infrared light but blocks or attenuates visible light. This can help reduce interference from ambient visible light in the detector, improving the signal-to-noise ratio of the IR system. It also serves as a visual identifier.

Q3: How do I interpret the "Radiant Intensity" value for my design?
A: Radiant Intensity (mW/sr) is a measure of how much optical power is emitted into a given solid angle. To estimate the irradiance (power per unit area) at a distance (d) on the optical axis, you can use the approximation: E ≈ I_E / d² for small angles, where E is in mW/cm² if d is in cm. This helps determine if enough light will reach your detector.

Q4: The storage temperature max is 100°C, but the soldering temperature is 260°C. Isn't this contradictory?
A: No. The storage temperature is for long-term, non-operational conditions where the entire package is uniformly at that temperature. The soldering rating is for a very short, localized thermal exposure (5 seconds) applied only to the metal leads, which conduct heat away from the sensitive semiconductor junction and package body.

10. Practical Design Case Study

Scenario: Designing a High-Speed Optical Encoder.
An optical rotary encoder requires a light source to pass through a coded disk onto a photodetector array. The encoder must operate at high rotational speeds, requiring fast switching of the light source to avoid blurring and enable precise edge detection.

• Component Selection Rationale: The LTE-7377LM1-TA is chosen because its 40ns rise/fall time allows for very sharp optical pulses, enabling the system to resolve fine positional changes at high speed. The narrow 16-degree viewing angle helps concentrate light through the narrow slots of the encoder disk, improving contrast.
• Circuit Design: A constant-current driver circuit using a high-speed MOSFET is implemented. The MOSFET is switched by a timer or FPGA output. The current is set to 100mA (continuous max) or a pulsed value like 350mA for higher intensity pulses, staying within the datasheet limits. The forward voltage at this current is used to calculate power dissipation in the driver.
• Layout & Thermal: The PCB footprint matches the package drawing's lead spacing. A small thermal relief pad connected to a ground plane is placed under the flange to aid heat dissipation during continuous operation.
• Optical Alignment: The emitter and detector are aligned on opposite sides of the encoder disk. The narrow beam ensures minimal cross-talk between adjacent tracks on the disk.

11. Operational Principle

This device is a light-emitting diode (LED) based on a semiconductor p-n junction, typically using materials like Gallium Arsenide (GaAs) or Aluminum Gallium Arsenide (AlGaAs) to produce infrared light. When a forward voltage exceeding the junction's turn-on voltage is applied, electrons and holes are injected across the junction. As these charge carriers recombine, energy is released in the form of photons. The specific bandgap energy of the semiconductor material determines the wavelength of the emitted photons, which in this case is centered around 880 nanometers. The blue epoxy package encapsulates the semiconductor chip, provides mechanical protection, and acts as a primary lens shaping the output beam while filtering shorter wavelengths.

12. Technology Trends

Infrared emitter technology continues to evolve alongside broader optoelectronic trends. There is a constant drive towards higher efficiency (more light output per electrical watt input) to reduce power consumption and heat generation. This enables brighter sources or longer battery life in portable devices. Another trend is the integration of emitters with drivers and control logic into smart modules, simplifying system design. Furthermore, there is development towards even faster switching speeds to support higher data rates in optical communication (e.g., for Li-Fi) and more precise time-of-flight (ToF) sensing for 3D imaging and LiDAR applications. The push for miniaturization also continues, leading to smaller package footprints while maintaining or improving performance characteristics.