LTE-4238R IR Emitter Datasheet - Clear Package - Peak Wavelength 880nm - Forward Voltage 1.8V - English Technical Document

1. Product Overview

The LTE-4238R is a miniature, low-cost infrared (IR) emitter designed for optoelectronic applications. Its core function is to emit infrared light at a specific wavelength, typically for use in sensing, detection, and communication systems where an invisible light source is required. The device is housed in a clear, transparent plastic end-looking package, allowing for efficient light transmission. A key advantage of this component is its mechanical and spectral matching to specific series of phototransistors (like the LTR-3208 series), which simplifies design-in for receiver-emitter pairs and ensures optimal performance in sensing applications. This makes it suitable for markets involving object detection, proximity sensing, touchless switches, and basic optical data links.

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. The LTE-4238R can dissipate up to 150 mW of power. It handles a peak forward current of 2 Amperes under pulsed conditions (300 pulses per second, 10 microsecond pulse width), while the maximum continuous forward current is 100 mA. The device can withstand a reverse voltage of up to 5 Volts. The operational temperature range is from -40°C to +85°C, and it can be stored in environments from -55°C to +100°C. For assembly, the leads can be soldered at 260°C for a maximum of 5 seconds, provided the soldering point is at least 1.6mm from the package body.

2.2 Electro-Optical Characteristics

These parameters are specified at an ambient temperature (T_A) of 25°C and a test forward current (I_F) of 20mA, which serves as a standard operating point. The radiant intensity (I_E), a measure of optical power emitted per solid angle, has a typical value of 4.81 mW/sr. The aperture radiant incidence (E_e), representing power density, is typically 0.64 mW/cm². The device emits light at a peak wavelength (λ_Peak) of 880 nanometers, which is in the near-infrared spectrum. The spectral bandwidth, defined as the half-width (Δλ), is 50 nm, indicating the spread of wavelengths around the peak. The forward voltage (V_F) typically ranges from 1.3V to 1.8V at 20mA. The reverse current (I_R) is a maximum of 100 µA when a 5V reverse bias is applied. The viewing angle (2θ_1/2), where radiant intensity drops to half its maximum value, is 20 degrees, defining a relatively narrow beam.

3. Binning System Explanation

The datasheet indicates that devices are "SELECTED TO SPECIFIC ON-LINE INTENSITY AND RADIANT INTENSITY RANGES." This implies a binning or sorting process based on measured optical output parameters. While specific bin codes are not listed in this excerpt, typical binning for such emitters involves grouping components according to their radiant intensity (I_E) and sometimes forward voltage (V_F) to ensure consistency in application performance. Designers should consult the manufacturer for detailed binning specifications to select parts that meet precise intensity requirements for their application.

4. Performance Curve Analysis

The datasheet includes several typical characteristic curves. Figure 1 shows the Spectral Distribution, plotting relative radiant intensity against wavelength. It confirms the peak at 880nm and the 50nm half-width. Figure 2 illustrates the relationship between Forward Current and Ambient Temperature, showing how the maximum allowable continuous current decreases as temperature increases to stay within the power dissipation limit. Figure 3 is the Forward Current vs. Forward Voltage (I-V) curve, demonstrating the diode's exponential characteristic. Figure 4 shows how Relative Radiant Intensity varies with Ambient Temperature, typically showing a decrease in output as temperature rises. Figure 5 plots Relative Radiant Intensity against Forward Current, showing the near-linear relationship between drive current and light output within the operating range. Finally, Figure 6 is the Radiation Diagram, a polar plot depicting the spatial distribution of emitted light, confirming the 20-degree viewing angle.

5. Mechanical and Package Information

5.1 Package Dimensions

The device uses a miniature plastic end-looking package. Key dimensional notes include: all dimensions are in millimeters (with inches in parentheses), standard tolerance is ±0.25mm unless specified otherwise, the maximum resin protrusion under the flange is 1.0mm, and lead spacing is measured at the point where leads exit the package. The exact dimensional drawing is referenced but not fully detailed in the provided text.

5.2 Polarity Identification

For an infrared LED, the longer lead is typically the anode (positive), and the shorter lead is the cathode (negative). The package may also have a flat side or other marking near the cathode. Correct polarity must be observed during circuit assembly to prevent damage.

6. Soldering and Assembly Guidelines

The absolute maximum rating specifies lead soldering temperature: 260°C for a maximum of 5 seconds, with the condition that this is applied at least 1.6mm (0.063") from the package body. This is critical to prevent thermal damage to the semiconductor die and the plastic encapsulation. For reflow soldering, a standard profile with a peak temperature not exceeding 260°C and careful control of time above liquidus is recommended. The device should be stored in a dry, anti-static environment prior to use. Moisture sensitivity level (MSL) information, if applicable, should be obtained from the manufacturer.

7. Packaging and Ordering Information

The part number is LTE-4238R. The datasheet references a specification number (DS-50-98-0043) and a revision (C). Specific packaging details (e.g., tape and reel dimensions, quantity per reel) are not provided in this excerpt. The "BNS-OD-C131/A4" and "BNS-OD-FC001/A4" codes likely refer to internal document control numbers. For ordering, the base part number LTE-4238R is used, and any binning or special selection codes would be appended as per the manufacturer's system.

8. Application Recommendations

8.1 Typical Application Scenarios

The LTE-4238R is ideal for applications requiring a matched IR source. Its primary use is in conjunction with a spectrally matched phototransistor (like the LTR-3208 series) to form an optical interrupter or reflective object sensor. Common applications include paper detection in printers and copiers, slot or edge sensing, object counting, proximity detection in appliances, and simple touchless switches. The clear package makes it suitable for applications where the emitter might be visible, though the 880nm light is largely invisible to the human eye.

8.2 Design Considerations

1. Current Limiting: An IR LED is a current-driven device. Always use a series current-limiting resistor calculated based on the supply voltage (V_CC), the LED's forward voltage (V_F ~1.8V max), and the desired forward current (I_F). Do not exceed the continuous current rating of 100mA. For pulsed operation, ensure pulse width and duty cycle stay within specified limits to avoid overheating.
2. Thermal Management: The power dissipation rating of 150 mW must not be exceeded. At higher ambient temperatures, derate the maximum allowable forward current as shown in the characteristic curves.
3. Optical Alignment: For best performance in a paired sensor system, ensure precise mechanical alignment between the emitter and the detector. The narrow 20-degree viewing angle aids in directionality but requires careful placement.
4. Ambient Light Immunity: While the matched photodetector helps, designing optical baffles or using modulated IR signals can improve immunity to ambient light interference in sensing applications.

9. Technical Comparison and Differentiation

The LTE-4238R's key differentiating feature is its explicit mechanical and spectral matching to a specific phototransistor series. This guarantees optimal coupling efficiency and simplifies the design process for optical sensors, as the pair is characterized to work together. Compared to generic IR emitters, this matching can lead to higher sensitivity, greater range, or more consistent performance in the final application. The clear package offers slightly higher transmission efficiency compared to tinted packages, maximizing light output. Its miniature size makes it suitable for space-constrained designs.

10. Frequently Asked Questions (FAQs)

Q: What is the purpose of the peak wavelength being 880nm?
A: 880nm is in the near-infrared range. It is invisible to the human eye, making it discreet for sensing applications. It also aligns well with the peak sensitivity of silicon photodetectors (like phototransistors), ensuring efficient detection.

Q: Can I drive this LED directly from a microcontroller pin?
A: It depends on the pin's current sourcing capability. A typical MCU pin can source 20-25mA, which is within the operating range. However, you MUST include a current-limiting resistor in series. Never connect an LED directly to a voltage source or a pin without current control.

Q: How do I interpret the "Viewing Angle" of 20 degrees?
A: This is the full angle at which the emitted light's intensity is at least half of its maximum value (on-axis). A 20-degree angle is relatively narrow, producing a more focused beam compared to wide-angle emitters. This is beneficial for long-range or precise alignment applications.

Q: What does "spectrally matched" mean?
A: It means the emission spectrum of the LTE-4238R (centered at 880nm) is designed to overlap optimally with the spectral response curve of the specified phototransistor. This maximizes the amount of emitted light that the detector can actually "see" and convert into an electrical signal.

11. Practical Design and Usage Examples

Example 1: Object Detection Sensor: Place the LTE-4238R and its matched phototransistor facing each other across a gap. When an object passes through the gap, it interrupts the IR beam, causing the phototransistor's output to change. This simple circuit can be used for counting objects on a conveyor belt or detecting the presence of a paper in a printer tray. The current through the LED can be set to 20mA using a resistor: R = (V_CC - V_F) / I_F. For a 5V supply and V_F of 1.6V, R = (5 - 1.6) / 0.02 = 170 Ohms (use a standard 180 Ohm resistor).

Example 2: Reflective Sensor: Mount the emitter and detector side-by-side, aimed at a common point. The IR light from the emitter reflects off a surface (like a white object or a reflective tape) and is detected by the phototransistor. This setup can detect the proximity of an object or read encoded patterns. The narrow viewing angle helps minimize crosstalk between the emitter and detector in this close configuration.

12. Operating Principle Introduction

An infrared emitter like the LTE-4238R is a semiconductor diode. When forward biased (positive voltage applied to the anode relative to the cathode), electrons and holes recombine in the active region of the semiconductor material (typically based on gallium arsenide, GaAs). This recombination process releases energy in the form of photons (light particles). The specific material composition and structure of the semiconductor determine the wavelength of the emitted photons, which in this case is centered at 880nm in the infrared spectrum. The clear epoxy package encapsulates and protects the semiconductor die while allowing the generated light to escape efficiently.

13. Technology Trends and Context

Infrared emitters remain fundamental components in optoelectronics. Trends in this field include the development of emitters with higher radiant intensity and efficiency from smaller packages, enabling more powerful or longer-range sensors. There is also a move towards surface-mount device (SMD) packages for automated assembly, though through-hole packages like this one are still widely used for prototyping and certain applications. Integration is another trend, with combined emitter-detector modules becoming more common, simplifying system design further. The underlying principle of electroluminescence in semiconductors is well-established, but material science advancements continue to improve performance, reliability, and cost-effectiveness.