IR Emitter LED LTE-4206C Datasheet - Package Dimensions - Forward Voltage 1.6V - Radiant Intensity 7.67mW/sr - Peak Wavelength 940nm - English Technical Document

1. Product Overview

The LTE-4206C is a miniature, low-cost 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, which is invisible to the human eye but can be detected by matching photodetectors. The device is housed in a compact, end-looking plastic package with a transparent color, making it suitable for space-constrained designs.

The primary advantage of this component is its mechanical and spectral matching to the LTR-4206 series of phototransistors. This pre-matched pairing simplifies design-in, ensures optimal performance in emitter-detector pairs, and reduces development time for applications like object detection, proximity sensing, and optical switches. Its selected intensity ranges allow for binning, providing designers with consistent performance parameters.

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 under these conditions is not guaranteed.

• Power Dissipation (Pd): 90 mW. This is the maximum allowable power the device can dissipate as heat under continuous operation at 25°C ambient temperature.
• Continuous Forward Current (IF): 60 mA. The maximum DC current that can be passed through the LED indefinitely.
• Peak Forward Current: 1 A. This high current is permissible only under pulsed conditions (300 pulses per second, 10 μs pulse width) and should not be exceeded.
• Reverse Voltage (VR): 5 V. Exceeding this voltage in reverse bias can cause junction breakdown.
• Operating Temperature Range: -40°C to +85°C. The ambient temperature range for reliable operation.
• Storage Temperature Range: -55°C to +100°C.
• Lead Soldering Temperature: 260°C for 5 seconds, measured 1.6mm from the package body. This is critical for wave or reflow soldering processes.

2.2 Electrical & Optical Characteristics

These parameters are measured at an ambient temperature (TA) of 25°C and define the device's typical performance.

• Forward Voltage (VF): Typically 1.6V at a test current (IF) of 20mA, with a maximum of 1.2V. This is the voltage drop across the LED when operating.
• Reverse Current (IR): Maximum 100 μA at a reverse voltage (VR) of 5V. This indicates the leakage current when the device is reverse-biased.
• Peak Emission Wavelength (λPeak): 940 nm. This is the wavelength at which the IR emitter outputs its maximum radiant intensity.
• Spectral Line Half-Width (Δλ): 50 nm. This parameter describes the bandwidth of the emitted light, indicating how narrowly or broadly the wavelengths are distributed around the peak.
• Viewing Angle (2θ1/2): 20 degrees. This defines the angular spread of the emitted radiation where the intensity is half of the peak value (Full Width at Half Maximum).

3. Binning System Explanation

The LTE-4206C is sorted into different performance bins based on its radiant intensity and aperture radiant incidence. This allows designers to select components that meet specific sensitivity requirements for their application.

• BIN A: Aperture Radiant Incidence (Ee): 0.184 - 0.54 mW/cm²; Radiant Intensity (Ie): 1.383 - 4.06 mW/sr.
• BIN B: Aperture Radiant Incidence (Ee): 0.36 - 0.78 mW/cm²; Radiant Intensity (Ie): 2.71 - 5.87 mW/sr.
• BIN C: Aperture Radiant Incidence (Ee): 0.52 - 1.02 mW/cm²; Radiant Intensity (Ie): 3.91 - 7.67 mW/sr.
• BIN D: Aperture Radiant Incidence (Ee): 0.68 mW/cm² (Min); Radiant Intensity (Ie): 5.11 mW/sr (Min).

All measurements are taken at a forward current (IF) of 20mA. Higher bin letters (C, D) generally indicate higher output power devices.

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 940nm and the 50nm spectral half-width, illustrating the band of infrared light emitted.

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

This is the standard IV (Current-Voltage) curve for a diode. It shows the exponential relationship between current and voltage. The typical forward voltage of 1.6V at 20mA can be verified from this graph. The curve is essential for designing the current-limiting circuitry for the LED.

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

This graph demonstrates that the optical output power (radiant intensity) is approximately linear with the forward current over a significant range. It helps designers determine the required drive current to achieve a desired optical output.

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

This curve is critical for understanding thermal effects. It shows that the radiant intensity decreases as the ambient temperature increases. This derating must be accounted for in applications operating at high temperatures to ensure sufficient signal strength at the detector.

4.5 Radiation Diagram (Fig. 6)

This polar plot visually represents the viewing angle (2θ1/2 = 20°). It shows the spatial distribution of the emitted infrared light, which is important for aligning the emitter with its corresponding detector.

5. Mechanical & Package Information

5.1 Package Dimensions

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

• All dimensions are in millimeters (inches provided in parentheses).
• Standard tolerance is ±0.25mm (±0.010") unless specified otherwise.
• 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 described as "smoking transparent color," which typically means a tinted, translucent plastic that allows the IR light to pass while providing some diffusion and physical protection for the semiconductor die.

5.2 Polarity Identification

While not explicitly detailed in the provided text, standard IR LED packages like this typically have a flat side or a longer lead to denote the cathode. The datasheet diagram would show this marking. Correct polarity is essential to prevent reverse bias damage.

6. Soldering & Assembly Guidelines

The key specification for assembly is the lead soldering temperature: 260°C for a maximum of 5 seconds, measured 1.6mm (0.063") from the package body. This rating is crucial for preventing thermal damage during wave soldering or reflow processes.

Design Considerations:

• Heat Sinking: While not typically required for low-power LEDs, ensuring the PCB layout does not trap excessive heat around the component is good practice, especially if operating near maximum ratings.
• ESD Protection: Like all semiconductor devices, IR emitters can be sensitive to electrostatic discharge. Standard ESD handling precautions should be observed during assembly.

7. Application Suggestions

7.1 Typical Application Scenarios

• Object Detection & Proximity Sensing: Paired with the LTR-4206 phototransistor, it can detect the presence or absence of an object by interrupting the IR beam.
• Optical Switches & Encoders: Used in rotary or linear encoders to sense position or movement through a patterned disk or strip.
• IR Data Transmission: Can be used for short-range, low-data-rate wireless communication (e.g., remote control signals, sensor telemetry) when modulated.
• Smoke Detection: In some optical smoke detector designs, an IR LED and detector pair can sense scattered light from smoke particles.

7.2 Design Considerations

• Current Limiting: An LED is a current-driven device. A series resistor or constant current driver is mandatory to set the operating current and prevent thermal runaway. Calculate the resistor value using R = (Vsupply - VF) / IF.
• Optical Alignment: The narrow 20° viewing angle requires precise mechanical alignment between the emitter and detector for optimal coupling efficiency.
• Ambient Light Immunity: Since it emits at 940nm, it is less susceptible to interference from visible ambient light. However, sunlight and other strong IR sources (like incandescent bulbs) can contain significant energy at 940nm and may cause interference. Optical filtering on the detector or modulation of the emitter signal can mitigate this.
• Thermal Derating: Account for the decrease in output power with increasing temperature (as shown in Fig. 4) by providing sufficient drive current margin or selecting a higher bin part.

8. Technical Comparison & Differentiation

The primary differentiating feature of the LTE-4206C is its explicit mechanical and spectral matching to the LTR-4206 phototransistor series. This offers several advantages over selecting emitter and detector components separately:

• Guaranteed Performance: The pair is characterized together, ensuring the spectral response of the detector aligns well with the emission spectrum of the LED for maximum sensitivity.
• Mechanical Compatibility: The packages are designed to fit together in standard mounting configurations, simplifying mechanical design.
• Cost-Effective Solution: Provides a reliable, pre-validated optocoupler building block at a low cost due to its miniature plastic package and high-volume manufacturing.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the difference between Radiant Intensity (Ie) and Aperture Radiant Incidence (Ee)?

A: Radiant Intensity (mW/sr) measures the optical power emitted per unit solid angle (steradian), describing the directional concentration of light. Aperture Radiant Incidence (mW/cm²) is the power density incident on a surface (like a detector) at a specified distance, which depends on both the intensity and the distance/geometry.

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

A: No. You must use a current-limiting resistor. For example, with a 5V supply, a VF of 1.6V, and a desired IF of 20mA: R = (5V - 1.6V) / 0.02A = 170 Ohms. A standard 180 Ohm resistor would be suitable.

Q: Why is the viewing angle only 20 degrees?

A> A narrow viewing angle concentrates the emitted light into a tighter beam. This increases the intensity on-axis, allowing for longer sensing distances or lower drive currents, and improves signal-to-noise ratio by reducing scattered light. It is ideal for aligned emitter-detector pairs.

Q: How do I choose the right bin (A, B, C, D)?

A> The choice depends on your system's sensitivity requirements and operating margins. If your detector needs a strong signal or if the system operates over a wide temperature range (where output drops), choose a higher bin (C or D) for more output power. For less critical or short-range applications, a lower bin may be sufficient and cost-effective.

10. Practical Design Case

Scenario: Designing a Paper Presence Sensor in a Printer.

A common use is to detect when paper is present in a tray. An LTE-4206C IR emitter and its matched LTR-4206 phototransistor are placed on opposite sides of the paper path. When no paper is present, the IR light reaches the detector, causing it to conduct. When a sheet of paper passes between them, it blocks the IR beam, the detector stops conducting, and the microcontroller senses this change, registering the presence of paper.

Design Steps:

1. Circuit Design: Drive the LED with 20mA using a transistor switch controlled by the MCU, with a series resistor for current limiting. Connect the phototransistor in a common-emitter configuration with a pull-up resistor to create a digital output signal that toggles based on received light.
2. Mechanical Design: Precisely align the emitter and detector using the package dimensions, ensuring the 20° beam is directed at the detector's active area. Provide a clean optical path.
3. Component Selection: Select a BIN C or D emitter to ensure a strong signal reaches the detector even if dust accumulates on the lenses over time.
4. Software: Implement debouncing logic to distinguish a genuine paper edge from vibration or dust.

11. Operational Principle

An Infrared Light Emitting Diode (IR LED) operates on the principle of electroluminescence in a semiconductor p-n junction. When a forward voltage is applied, electrons from the n-type region and holes from the p-type region are injected across the junction. When these charge carriers recombine, they release energy. In an IR LED, the semiconductor material (typically based on Gallium Arsenide - GaAs) is chosen so that this released energy corresponds to a photon in the infrared spectrum (around 940nm). The intensity of the emitted light is directly proportional to the rate of carrier recombination, which is controlled by the forward current (IF). The transparent package encapsulates and protects the semiconductor die while allowing the infrared photons to escape.

12. Technology Trends

Infrared emitter technology continues to evolve alongside broader optoelectronics trends. There is a constant drive towards higher efficiency, allowing for greater optical output power at lower drive currents, which reduces system power consumption and heat generation. Package miniaturization is another key trend, enabling integration into ever-smaller consumer electronics and IoT devices. Furthermore, there is development towards more precise wavelength control and narrower spectral bandwidths for applications requiring specific spectral filtering, such as in gas sensing or high-ambient-light-noise environments. The integration of emitters and detectors into single, smart sensor modules with built-in signal processing is also a growing area, simplifying system design for end-users.