IR Emitter LTE-302 Datasheet - Side-Looking Package - Peak Wavelength 940nm - Forward Voltage 1.6V - English Technical Document

1. Product Overview

The LTE-302 is a low-cost, miniature infrared (IR) emitter designed for applications requiring reliable optical sensing. Its core advantage lies in its side-looking plastic package, which allows for a compact form factor suitable for space-constrained designs. The device is mechanically and spectrally matched to the LTR-301 series of phototransistors, simplifying the design of optical interrupters, object detection sensors, and proximity sensing systems. The target market includes consumer electronics, industrial automation, security systems, and various embedded sensing applications where cost-effective and reliable IR emission is required.

2. In-Depth Technical Parameter Analysis

2.1 Electrical and Optical Characteristics

The electrical and optical performance is specified at an ambient temperature (T_A) of 25°C. Key parameters include:

• Forward Voltage (V_F): Typically 1.6V at a forward current (I_F) of 20mA, with a maximum of 1.6V. This parameter is crucial for driver circuit design.
• Peak Emission Wavelength (λ_Peak): 940 nanometers (nm). This wavelength is ideal for applications using silicon-based photodetectors, which have good sensitivity in the near-infrared region, and it is less visible to the human eye compared to shorter wavelengths.
• Spectral Line Half-Width (Δλ): 50 nm. This indicates the spectral bandwidth of the emitted light, centered around the peak wavelength.
• Viewing Angle (2θ_1/2): 40 degrees. This defines the angular spread of the emitted radiation where the intensity is at least half of the peak intensity.
• Reverse Current (I_R): Maximum 100 µA at a reverse voltage (V_R) of 5V. This parameter indicates the leakage current when the device is reverse-biased.

2.2 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. They are not for continuous operation.

• Power Dissipation (P_D): 75 mW.
• Continuous Forward Current (I_F): 50 mA.
• Peak Forward Current: 1 A under pulsed conditions (300 pulses per second, 10 µs pulse width).
• Reverse Voltage: 5 V.
• Operating Temperature Range: -40°C to +85°C.
• Storage Temperature Range: -55°C to +100°C.
• Lead Soldering Temperature: 260°C for 5 seconds, measured 1.6mm from the package body.

3. Binning System Explanation

The LTE-302 utilizes a binning system based on its radiant intensity and aperture radiant incidence. This system groups devices with similar optical output power to ensure consistency in application performance. The bins are tested at a forward current of 20mA.

• Radiant Intensity (I_E): Measured in milliwatts per steradian (mW/sr), it represents the optical power emitted per unit solid angle. Bins range from B (0.662-1.263 mW/sr) to F (minimum 1.444 mW/sr).
• Aperture Radiant Incidence (E_e): Measured in milliwatts per square centimeter (mW/cm²), it represents the power density at the emitter's aperture. Bins correspond to the radiant intensity bins, from B (0.088-0.168 mW/cm²) to F (minimum 0.192 mW/cm²).

This binning allows designers to select devices with the required optical output for their specific sensing distance and receiver sensitivity, ensuring reliable system operation.

4. Performance Curve Analysis

The datasheet provides several characteristic curves that illustrate device 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 spectral half-width of approximately 50nm. The shape is typical for an AlGaAs IR LED.

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

This IV (Current-Voltage) characteristic curve is essential for designing the current-limiting circuit. It shows the exponential relationship typical of a diode. The curve allows estimation of the voltage drop at currents other than the test condition of 20mA.

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

This graph demonstrates that the optical output power is approximately linear with forward current within the recommended operating range. Driving the LED beyond its maximum ratings will not yield proportional increases in output and risks damage.

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

This curve shows the temperature dependence of the optical output. The radiant intensity decreases as the ambient temperature increases. This derating must be accounted for in applications operating at high temperatures to ensure the sensing system maintains sufficient signal strength.

4.5 Radiation Diagram (Fig. 6)

This polar plot visually represents the viewing angle (2θ_1/2 = 40°). It shows the angular distribution of the emitted radiation, which is important for aligning the emitter with a detector and understanding the sensing field.

5. Mechanical and Package Information

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

• All dimensions are provided in millimeters with inches in parentheses.
• A general tolerance of ±0.25mm (±0.010\") applies unless otherwise specified.
• Lead spacing is measured at the point where the leads exit the package body.
• The side-looking orientation means the primary optical axis is parallel to the PCB surface, which is ideal for reflective or interruptive sensing across a board.

Consult the detailed package drawing in the original datasheet for exact dimensions, including body size, lead length, and aperture location.

6. Soldering and Assembly Guidelines

Proper handling is critical to reliability.

• Soldering: The leads can withstand a soldering temperature of 260°C for 5 seconds, provided the heat is applied at least 1.6mm (0.063\") away from the plastic package body. This prevents thermal damage to the epoxy encapsulant and the semiconductor die.
• ESD Precautions: Although not explicitly stated for this device, infrared LEDs are generally sensitive to electrostatic discharge (ESD). Standard ESD handling procedures (using grounded wrist straps, conductive foam) are recommended during assembly.
• Cleaning: If cleaning is required after soldering, use methods and solvents compatible with plastic-encapsulated electronic components to avoid stress cracking or material degradation.

7. Application Recommendations

7.1 Typical Application Scenarios

• Optical Interrupters/Slotted Switches: Paired with a matched phototransistor (like the LTR-301), the emitter creates a beam. An object passing through the gap interrupts the beam, triggering a detection signal. Used in printers, vending machines, and industrial counters.
• Reflective Object Sensing: The emitter and a detector are placed side-by-side. The emitter illuminates a surface, and the detector senses the reflected light. Used for paper detection, liquid level sensing, and proximity detection.
• Industrial Control & Security: Used in safety curtains, door sensors, and tamper detection.

7.2 Design Considerations

• Current Limiting: Always use a series resistor or constant current driver to limit the forward current to the desired value (e.g., 20mA). Calculate the resistor value using R = (V_supply - V_F) / I_F.
• Optical Alignment: Precise mechanical alignment between the emitter and the detector is critical for maximum signal strength, especially with the 40° viewing angle.
• Ambient Light Immunity: For reliable operation in environments with varying ambient light (e.g., sunlight, room lights), consider modulating the emitter drive current and using a synchronized detection circuit in the receiver to filter out DC ambient light signals.
• Thermal Management: Ensure the device operates within its specified temperature range. Derate the maximum forward current if the ambient temperature approaches the upper limit of 85°C.

8. Technical Comparison and Differentiation

The LTE-302's primary differentiation lies in its specific combination of attributes:

• Side-Looking Package vs. Top-View: The side-looking form factor is a key advantage for applications where the sensing path is parallel to the PCB, saving vertical space compared to top-view emitters.
• Matched to LTR-301 Series: This guaranteed mechanical and spectral match simplifies design and procurement for optical interrupter modules, ensuring optimal performance without the need for custom optical alignment or spectral filtering.
• Cost-Effective Miniature Design: It offers a balance of performance and size at a low cost, making it suitable for high-volume consumer applications.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the binning codes (B, C, D, E, F)?
A: They categorize devices based on their optical output power (radiant intensity). You select a bin to ensure your sensor system has consistent and sufficient signal strength. For longer sensing distances or lower sensitivity detectors, a higher bin (e.g., E or F) may be necessary.

Q: Can I drive this IR LED with a 5V supply directly?
A: No. The typical forward voltage is 1.6V. Connecting it directly to 5V would cause excessive current to flow, destroying the device. You must always use a current-limiting resistor.

Q: Why is the peak wavelength 940nm?
A: 940nm is in the near-infrared spectrum. It is a common wavelength because silicon photodetectors (phototransistors, photodiodes) have good sensitivity here, and it is largely invisible, making it suitable for discreet sensing applications.

Q: How does temperature affect performance?
A: As shown in Fig. 4, the radiant intensity decreases with increasing temperature. In a hot environment, the output signal will be weaker. Design your circuit with sufficient margin or consider temperature compensation if operating over a wide range.

10. Practical Design and Usage Case

Case: Designing a Paper Detection Sensor for a Printer.
An engineer needs to detect the presence of paper in a feed tray. They place an LTE-302 IR emitter and an LTR-301 phototransistor on opposite sides of the paper path, creating a beam. When paper is present, it blocks the beam, and the phototransistor's output goes low. The 40° viewing angle requires careful alignment of the components on the PCB to ensure the beam is narrow enough for precise detection but wide enough for tolerance. The engineer selects devices from Bin D to ensure strong signal strength even if dust accumulates over time. A simple circuit with a 150-ohm resistor limits the current to ~20mA from a 5V supply (5V - 1.6V / 20mA ≈ 170Ω, using 150Ω for a slight margin). The phototransistor output is connected to a comparator or microcontroller input to digitize the detection signal.

11. Principle of Operation

An infrared emitter 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 aluminum gallium arsenide - AlGaAs). This recombination process releases energy in the form of photons (light). The specific composition of the semiconductor layers determines the wavelength of the emitted photons, which for the LTE-302 is centered at 940nm. The plastic package includes an epoxy lens that shapes the emitted light into the specified viewing angle pattern.

12. Technology Trends

Infrared emitters like the LTE-302 are mature, reliable components. General trends in the field include:

• Increased Integration: Moving towards modules that combine the emitter, detector, and signal conditioning circuitry (e.g., ICs with built-in modulation/demodulation) to simplify design and improve noise immunity.
• Miniaturization: Continued reduction in package size (e.g., chip-scale packages) to fit into ever-smaller consumer electronics like wearables and ultra-thin smartphones.
• Higher Efficiency: Development of materials and structures to achieve higher radiant intensity for a given drive current, improving battery life in portable devices.
• Multi-Wavelength and VCSELs: For advanced sensing like time-of-flight (ToF) and LiDAR, vertical-cavity surface-emitting lasers (VCSELs) and arrays are becoming more common, offering higher power and faster modulation capabilities than traditional IR LEDs.