IR Emitter LED LTE-4238 Datasheet - Wavelength 880nm - Forward Current 100mA - Power Dissipation 150mW - English Technical Document

1. Product Overview

The LTE-4238 is a high-power infrared (IR) light-emitting diode (LED) designed for applications requiring reliable and intense infrared illumination. Its primary function is to emit non-visible light at a peak wavelength of 880 nanometers, making it suitable for sensing, remote control, and optical switching systems. A key feature is its mechanical and spectral matching to specific series of phototransistors, ensuring optimal performance in receiver-emitter pairs for precise signal transmission.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The device is rated for operation within strict environmental and electrical limits to ensure longevity and reliability. The maximum continuous forward current is 100 mA, with a peak forward current capability of 2 A under pulsed conditions (300 pps, 10 µs pulse width). The maximum power dissipation is 150 mW at an ambient temperature (T_A) of 25°C. The operating temperature range is from -40°C to +85°C, while the storage range extends from -55°C to +100°C. The device can withstand a reverse voltage of up to 5 V. For assembly, the leads can be soldered at 260°C for a maximum duration of 5 seconds, measured 1.6mm from the package body.

2.2 Electrical & Optical Characteristics

Key performance parameters are specified at T_A=25°C and a forward current (I_F) of 20 mA. The radiant intensity (I_E) is typically 4.81 mW/sr, indicating the optical power output per solid angle. The aperture radiant incidence (E_e) is 0.64 mW/cm². The forward voltage (V_F) typically ranges from 1.3V to 1.8V. The spectral characteristics are defined by a peak emission wavelength (λ_Peak) of 880 nm and a spectral half-width (Δλ) of 50 nm, defining the narrowness of the emitted light band. The reverse current (I_R) is a maximum of 100 µA at a reverse voltage (V_R) of 5V. The viewing angle (2θ_1/2) is 20 degrees, describing the angular spread of the emitted radiation where intensity falls to half its peak value.

3. Performance Curve Analysis

The datasheet provides several graphs illustrating device behavior under varying conditions.

3.1 Spectral Distribution

Figure 1 shows the relative radiant intensity as a function of wavelength. The curve is centered at 880 nm with a typical half-width of 50 nm, confirming the monochromatic nature of the IR output suitable for filtering and precise detection.

3.2 Forward Current vs. Ambient Temperature

Figure 2 depicts the derating of the maximum allowable forward current as ambient temperature increases. This graph is critical for thermal management design, ensuring the device operates within its safe operating area (SOA) under all environmental conditions.

3.3 Forward Current vs. Forward Voltage

Figure 3 illustrates the IV (current-voltage) characteristic of the diode. This non-linear relationship is essential for designing the driving circuitry, determining the required voltage to achieve a specific operating current.

3.4 Relative Radiant Intensity vs. Ambient Temperature & Forward Current

Figures 4 and 5 show how the optical output power changes with temperature and drive current. Output typically decreases with rising temperature (Figure 4) and increases super-linearly with forward current (Figure 5), highlighting the trade-offs between output, efficiency, and thermal load.

3.5 Radiation Pattern

Figure 6 is a polar diagram showing the spatial distribution of emitted light. The 20-degree viewing angle is confirmed, showing a beam profile that is relatively focused, which is advantageous for directed illumination applications.

4. Mechanical & Package Information

4.1 Package Dimensions

The device uses a standard LED package with a flange. Key dimensions include the body size, lead spacing, and protrusion limits. All dimensions are provided in millimeters with a standard tolerance of ±0.25mm unless otherwise specified. The lead spacing is measured at the point where the leads exit the package body. A maximum resin protrusion under the flange of 1.0mm is allowed. Engineers must refer to the detailed mechanical drawing (implied in the PDF) for precise placement and footprint design on printed circuit boards (PCBs).

4.2 Polarity Identification

Standard LED polarity conventions apply, typically indicated by a flat side on the package or by leads of different lengths (anode longer than cathode). The specific marking must be verified from the package drawing to ensure correct orientation during assembly, preventing reverse bias damage.

5. Soldering & Assembly Guidelines

The absolute maximum rating for lead soldering temperature is 260°C for 5 seconds, measured 1.6mm (0.063") from the package body. This rating is compatible with standard lead-free reflow soldering profiles (e.g., IPC/JEDEC J-STD-020). It is crucial to adhere to this limit to prevent thermal damage to the internal semiconductor die, wire bonds, or the epoxy lens material. Preheating is recommended to minimize thermal shock. Devices should be stored in a dry, controlled environment as per moisture sensitivity level (MSL) guidelines, which should be obtained from the manufacturer's handling instructions.

6. Application Suggestions

6.1 Typical Application Scenarios

This IR emitter is ideal for applications including: optical encoders and position sensors, infrared remote control transmitters, object detection and proximity sensing, industrial automation light curtains, and optical data transmission links. Its matching to specific phototransistors makes it particularly valuable in reflective or transmissive optocoupler designs where alignment and spectral response are critical.

6.2 Design Considerations

Drive Circuitry: A current-limiting resistor is mandatory when driving with a voltage source to set the desired I_F and prevent thermal runaway. The resistor value is calculated using R = (V_supply - V_F) / I_F. For pulsed operation at high peak currents (up to 2A), a transistor switch (e.g., MOSFET) driven by a pulse generator is required.
Thermal Management: The 150 mW power dissipation limit must be respected. At high ambient temperatures or high continuous currents, the junction temperature will rise, potentially reducing output intensity and device lifespan. Proper PCB layout with adequate copper area for heat sinking may be necessary.
Optical Design: The 20-degree viewing angle provides a focused beam. For wider coverage, a diffuser lens may be needed. For maximum coupling efficiency with a matched photodetector, ensure proper mechanical alignment and consider potential sources of ambient IR noise (sunlight, incandescent bulbs).

7. Technical Comparison & Differentiation

The LTE-4238's primary differentiation lies in its high radiant intensity (4.81 mW/sr typical) and its specific selection for matched performance with companion phototransistors. Compared to generic IR LEDs, this preselection ensures tighter tolerances in paired optoelectronic systems, leading to more consistent sensitivity, lower cross-talk, and improved signal-to-noise ratio. The 880 nm wavelength is a common standard, offering a good balance between silicon photodetector sensitivity and lower visibility compared to 940 nm sources.

8. Frequently Asked Questions (FAQs)

Q: What is the purpose of the peak forward current rating (2A) if the continuous current is only 100mA?
A: The peak rating allows for very short, high-current pulses. This is essential for applications like remote controls or data transmission where high instantaneous optical power is needed for range or speed, but the average power (and heat) remains low.

Q: How does ambient temperature affect performance?
A: As temperature increases, the forward voltage typically decreases slightly, the radiant output decreases (as shown in Fig. 4), and the maximum allowable continuous current must be derated (Fig. 2). Design must account for these variations.

Q: Can I drive this LED directly from a microcontroller GPIO pin?
A: Possibly, but with caution. A GPIO pin might source 20-50mA. You must use a series resistor to limit the current to the desired I_F (e.g., 20mA) and ensure the total current does not exceed the microcontroller's pin and package limits. For higher currents or pulses, an external driver transistor is required.

Q: What does "spectrally matched" mean?
A: It means the emission spectrum of this IR LED is optimized to align with the peak spectral sensitivity of its paired phototransistor. This maximizes the detected signal strength for a given emitted power.

9. Practical Design Case Study

Scenario: Designing a Proximity Sensor. The goal is to detect an object within 10 cm. The system uses an LTE-4238 IR emitter and a matched phototransistor placed side-by-side, facing the same direction (reflective sensing mode).
Implementation: The LED is driven with 50 mA pulses (within the continuous rating) at a 1 kHz frequency. A current-limiting resistor sets this bias. The phototransistor's collector is connected to a pull-up resistor and an amplifier/filter circuit. When an object is within range, IR light reflects back into the phototransistor, causing its collector voltage to drop. This signal is then conditioned and fed into a comparator or microcontroller ADC to trigger a detection event.
Key Calculations: The drive resistor value is calculated based on a 5V supply and a V_F of ~1.5V: R = (5V - 1.5V) / 0.05A = 70 Ohms (use 68 Ω standard value). Power dissipation in the LED: P = V_F * I_F = 1.5V * 0.05A = 75 mW, which is well below the 150 mW maximum at 25°C.

10. Operating Principle Introduction

An infrared LED is a semiconductor p-n junction diode. When a forward voltage is applied, electrons from the n-region and holes from the p-region are injected into the junction region. When these charge carriers recombine, energy is released in the form of photons (light). The specific wavelength of 880 nm is determined by the bandgap energy of the semiconductor materials used (typically aluminum gallium arsenide, AlGaAs). The emitted light is incoherent and falls within the near-infrared spectrum, invisible to the human eye but easily detectable by silicon-based photodetectors.

11. Technology Trends

The trend in IR emitters for sensing continues toward higher power density and efficiency in smaller packages. This enables longer detection ranges and lower system power consumption. There is also a move toward integrated solutions, combining the emitter, driver, and sometimes the detector into a single module with digital interfaces (I2C, SPI). Furthermore, advancements in wafer-level packaging (WLP) and chip-scale packaging (CSP) are reducing the size and cost of discrete optoelectronic components while improving reliability. The fundamental principle of operation remains, but the integration and performance per unit volume are steadily increasing.