IR Emitter LED LTE-4206 Datasheet - 940nm Wavelength - 20mA Forward Current - 1.6V Forward Voltage - 20° Viewing Angle - English Technical Document

1. Product Overview

The LTE-4206 is a low-cost, miniature infrared (IR) emitter designed for use in optoelectronic sensing and communication applications. Its core function is to emit infrared light at a peak wavelength of 940 nanometers (nm). The device is housed in a clear, transparent plastic end-looking package, allowing for efficient light emission. A key feature is its mechanical and spectral matching to corresponding series of phototransistors, which simplifies the design of receiver circuits by ensuring compatibility in physical dimensions and spectral response.

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. They are specified at an ambient temperature (T_A) of 25°C.

• Power Dissipation (P_D): 90 mW. This is the maximum allowable power the device can dissipate as heat.
• Peak Forward Current (I_FP): 1 A. This is the maximum permissible pulsed current, specified under conditions of 300 pulses per second (pps) with a 10 μs pulse width.
• Continuous Forward Current (I_F): 60 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 damage the LED junction.
• 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.
• Lead Soldering Temperature: 260°C for 5 seconds, measured 1.6mm from the package body.

2.2 Electrical & Optical Characteristics

These parameters are measured at T_A=25°C and define the device's performance under normal operating conditions. The forward current (I_F) for testing optical parameters is typically 20mA.

• Aperture Radiant Incidence (E_e): Measured in mW/cm², this is the radiant power per unit area incident on a surface. The value varies by bin (see section 3).
• Radiant Intensity (I_E): Measured in mW/sr, this is the radiant power emitted per unit solid angle. It is a key parameter for characterizing the brightness of the IR source. Values are binned.
• Peak Emission Wavelength (λ_Peak): 940 nm (typical). This is the wavelength at which the emitted optical power is maximum. It falls within the near-infrared spectrum.
• Spectral Line Half-Width (Δλ): 50 nm (typical). This parameter, also known as Full Width at Half Maximum (FWHM), indicates the spectral bandwidth. A value of 50 nm means the emitted light covers a range of wavelengths approximately 50 nm wide centered around the peak.
• Forward Voltage (V_F): 1.2 V (min), 1.6 V (typ) at I_F=20mA. This is the voltage drop across the LED when conducting the specified current.
• Reverse Current (I_R): 100 μA (max) at V_R=5V. This is the small leakage current that flows when the device is reverse-biased.
• Viewing Angle (2θ_1/2): 20 degrees. This is the full angle at which the radiant intensity drops to half of its maximum value (on-axis). A 20° angle indicates a relatively focused beam.

3. Binning System Explanation

The LTE-4206 utilizes a binning system for its key optical output parameters, Aperture Radiant Incidence (E_e) and Radiant Intensity (I_E). Binning is a manufacturing process that sorts components into performance groups to ensure consistency within a defined range. The device is categorized into four bins: A, B, C, and D.

• Bin A: E_e = 0.184 - 0.54 mW/cm²; I_E = 1.383 - 4.06 mW/sr.
• Bin B: E_e = 0.36 - 0.78 mW/cm²; I_E = 2.71 - 5.87 mW/sr.
• Bin C: E_e = 0.52 - 1.02 mW/cm²; I_E = 3.91 - 7.67 mW/sr.
• Bin D: E_e = 0.68 mW/cm² (min); I_E = 5.11 mW/sr (min). This bin represents the highest output group.

This system allows designers to select a bin that meets their specific sensitivity or range requirements for a given application.

4. Performance Curve Analysis

The datasheet provides several characteristic curves that illustrate the device's 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 940 nm and the approximately 50 nm spectral half-width. The curve shape is typical for a GaAlAs infrared LED.

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

This graph plots I_F against V_F. It demonstrates the exponential relationship characteristic of a diode. The curve is essential for designing the current-limiting driver circuit. The typical V_F of 1.6V at 20mA can be verified here.

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

This plot shows that the optical output (radiant intensity) is nearly linear with forward current over a significant range. This linearity simplifies control; increasing drive current directly and predictably increases light output.

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

This crucial curve illustrates the temperature dependence of the LED's output. Radiant intensity decreases as ambient temperature increases. This derating must be accounted for in designs intended to operate over the full temperature range (-40°C to +85°C) to ensure sufficient signal strength at high temperatures.

4.5 Radiation Diagram (Fig. 6)

This is a polar plot depicting the spatial distribution of emitted light. It visually confirms the 20° viewing angle, showing how intensity falls off at angles away from the central axis (0°).

5. Mechanical & Package Information

The device uses a miniature plastic end-looking package. Key dimensional notes from the datasheet include:

• All dimensions are in millimeters (inches provided in parentheses).
• General tolerance is ±0.25mm (±0.010") unless otherwise specified.
• The maximum protrusion of resin under the flange is 1.0mm (0.039").
• Lead spacing is measured at the point where the leads emerge from the package body.
• The package is clear and transparent.

(Note: Specific numerical dimensions from a drawing are not provided in the text excerpt, but would typically include body diameter, length, lead diameter, and spacing).

6. Soldering & Assembly Guidelines

The primary guideline provided is for hand soldering: the leads can be soldered at 260°C for a maximum duration of 5 seconds, with the heat applied at least 1.6mm (0.063") away from the plastic package body. This is to prevent thermal damage to the epoxy resin. For wave or reflow soldering, standard infrared LED profiles should be followed, paying attention to peak temperature and time above liquidus to stay within the package's thermal limits.

7. Application Suggestions

7.1 Typical Application Scenarios

• Object Detection & Proximity Sensing: Paired with a matched phototransistor (e.g., LTR-4206 series) in reflective or break-beam configurations. Used in printers, copiers, vending machines, and industrial automation.
• Infrared Data Transmission: Suitable for short-range, low-data-rate serial communication links, remote control units, or optical encoders.
• Smoke Detection: Used in optical chamber-based smoke detectors.

7.2 Design Considerations

• Current Limiting: Always use a series resistor or constant current driver to limit I_F to the desired value (e.g., 20mA for spec performance), never connect directly to a voltage source.
• Thermal Management: Account for output derating with temperature (Fig. 4). Ensure the power dissipation (I_F * V_F) does not exceed 90mW, considering ambient conditions.
• Optical Alignment: The 20° viewing angle requires careful alignment with the paired detector for optimal signal coupling, especially in break-beam setups.
• Electrical Noise: In sensing applications, modulate the LED driver current and use synchronous detection in the receiver circuit to reject ambient light (e.g., sunlight, incandescent bulbs) which may contain 940nm IR components.

8. Technical Comparison & Differentiation

The LTE-4206's primary differentiators are its mechanical and spectral matching to a specific phototransistor series. This guarantees that the receiver's active area and spectral sensitivity curve are optimally aligned with the emitter's output pattern and wavelength, maximizing system efficiency and simplifying mechanical design. The clear package offers higher external efficiency compared to tinted or diffused packages. The binning system provides flexibility in selecting the required output level. Its low cost and miniature size make it suitable for high-volume, space-constrained consumer and industrial applications.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the 940nm wavelength?
A: 940nm is in the near-infrared range, invisible to the human eye. It is a common wavelength because it avoids visible light interference, many silicon photodetectors (like phototransistors) have good sensitivity here, and it is less susceptible to interference from ambient incandescent light (which peaks in the ~1000nm range) compared to 850nm LEDs.

Q: Can I drive this LED with a 5V supply?
A: Yes, but you MUST use a current-limiting resistor. For example, to achieve I_F=20mA with a typical V_F of 1.6V from a 5V supply: R = (5V - 1.6V) / 0.02A = 170Ω. Use the nearest standard value (e.g., 180Ω) and check the actual current.

Q: What does "viewing angle" mean for an emitter?
A: It defines the beam width. A 20° full angle means the emitted light is concentrated within a relatively narrow cone. Half the peak intensity is found at ±10° from the central axis. A smaller angle gives a more focused beam for longer range or precise alignment.

Q: Why is the output binned?
A: Manufacturing variations cause slight differences in output power. Binning sorts LEDs into groups with guaranteed minimum and maximum outputs. This allows designers to choose a bin that ensures their system will work reliably, knowing the exact performance range of the component.

10. Practical Design Case

Case: Designing a Paper Detection Sensor for a Printer.
A break-beam sensor is needed to detect the presence of paper. An LTE-4206 (Bin C) is placed on one side of the paper path, and a matched LTR-4206 phototransistor is placed directly opposite.

1. Driver Circuit: The LED is driven by a microcontroller GPIO pin through a 180Ω resistor to set I_F to ~20mA when the pin is high (3.3V or 5V logic).
2. Modulation: The microcontroller pulses the LED at 1kHz (50% duty cycle) to distinguish its signal from ambient light.
3. Receiver Circuit: The phototransistor collector is connected to a pull-up resistor. The voltage at the collector is read by a microcontroller ADC or a comparator.
4. Detection Logic: When no paper is present, the IR light reaches the phototransistor, it conducts, pulling the collector voltage low. When paper blocks the beam, the phototransistor turns off, and the collector voltage goes high. The microcontroller synchronously samples this signal during the LED pulse to detect the state change.
5. Considerations: The 20° viewing angle ensures the beam is narrow enough to be cleanly interrupted by the paper edge. The Bin C selection provides sufficient radiant intensity to generate a strong signal in the receiver, even allowing for dust accumulation over time.

11. Operating Principle Introduction

An Infrared Light Emitting Diode (IR LED) is a semiconductor p-n junction diode. When a forward voltage exceeding its turn-on threshold (approximately 1.2V for this device) is applied, electrons and holes are injected across the junction. These charge carriers recombine, and for this specific material composition (typically Gallium Aluminum Arsenide - GaAlAs), the energy released during recombination is in the form of photons with a wavelength centered around 940 nm, which is infrared light. The intensity of the emitted light is directly proportional to the rate of recombination, which is controlled by the forward current (I_F). The clear epoxy package acts as a lens, shaping the output beam to the specified 20° viewing angle.

12. Technology Trends

Trends in infrared emitter technology include:

• Increased Efficiency: Development of materials and structures (e.g., multi-quantum wells) to achieve higher radiant intensity (mW/sr) for the same drive current, reducing power consumption.
• Miniaturization: Continued reduction in package size (e.g., chip-scale packages) to enable integration into smaller devices like wearables and ultra-compact sensors.
• Enhanced Reliability & Higher Temperature Operation: Improvements in packaging materials and die attach technologies to extend lifetime and allow operation in harsher environments (e.g., automotive, industrial).
• Integrated Solutions: Combining the IR emitter, driver, and sometimes a detector or logic into a single module or IC to simplify system design and reduce footprint.
• Multi-Wavelength & VCSELs: Use of Vertical-Cavity Surface-Emitting Lasers (VCSELs) for applications requiring very precise, high-speed, or structured light patterns, such as in advanced proximity sensing, 3D imaging (Time-of-Flight), and facial recognition.

The LTE-4206 represents a mature, cost-effective solution for standard infrared sensing needs, while newer technologies address demands for higher performance, integration, and specialized applications.