IR Emitter LTE-2871 Datasheet - T-1 3/4 Package - Forward Voltage 1.6V - Peak Wavelength 940nm - English Technical Document

1. Product Overview

This document provides the complete technical specifications for a high-performance infrared (IR) emitter component. The device is engineered to deliver high radiant intensity within a narrow viewing angle, making it suitable for applications requiring directed infrared illumination. Its core advantages include a cost-effective design combined with specialized performance characteristics for high-intensity output. The primary target markets include industrial automation, sensing systems, proximity detection, and optical communication links where reliable, focused infrared light is essential.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

All ratings are specified at an ambient temperature (T_A) of 25°C. Exceeding these limits may cause permanent damage to the device.

• Power Dissipation: 90 mW
• Peak Forward Current: 1 A (under pulsed conditions: 300 pps, 10 μs pulse width)
• Continuous Forward Current (I_F): 60 mA
• Reverse Voltage (V_R): 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)

2.2 Electrical & Optical Characteristics

Key performance parameters are measured at T_A=25°C with a standard test current of I_F = 20 mA, unless otherwise noted.

• Forward Voltage (V_F): Typical 1.6 V, Maximum 1.6 V at I_F=20mA. This parameter defines the voltage drop across the emitter when operating.
• Reverse Current (I_R): Maximum 100 μA at V_R=5V. This indicates the leakage current when the device is reverse-biased.
• Peak Emission Wavelength (λ_Peak): 940 nm. This is the wavelength at which the emitter radiates its maximum optical power, placing it in the near-infrared spectrum.
• Spectral Line Half-Width (Δλ): 50 nm. This specifies the bandwidth of the emitted light, measured as the full width at half maximum (FWHM) of the spectral distribution curve.
• Viewing Angle (2θ_1/2): 16 degrees. This narrow beam angle confirms the device's focused output, defined as the full angle where radiant intensity drops to half of its peak value.

3. Binning System Explanation

The component is categorized into performance bins based on its radiant output. This allows for selection based on required intensity levels. The key binned parameters are Aperture Radiant Incidence (E_e in mW/cm²) and Radiant Intensity (I_E in mW/sr), both measured at I_F=20mA.

• Bin A: E_e: 0.44 - 0.96 mW/cm²; I_E: 3.31 - 7.22 mW/sr.
• Bin B: E_e: 0.64 - 1.20 mW/cm²; I_E: 4.81 - 9.02 mW/sr.
• Bin C: E_e: 0.80 - 1.68 mW/cm²; I_E: 6.02 - 12.63 mW/sr.
• Bin D: E_e: 1.12 mW/cm² (Min); I_E: 8.42 mW/sr (Min). This represents the highest output bin.

Designers must specify the required bin code to ensure the optical power meets the application's sensitivity requirements for the detector system.

4. Performance Curve Analysis

The datasheet includes several graphical representations of device behavior under varying conditions.

4.1 Spectral Distribution

The spectral output curve (Fig.1) centers sharply around the 940nm peak wavelength with a defined 50nm half-width. This characteristic is crucial for matching with silicon photodetectors, which have peak sensitivity in this region, and for ensuring compatibility with optical filters to reject ambient light.

4.2 Forward Current vs. Forward Voltage (I-V Curve)

The I-V characteristic curve (Fig.3) shows the typical exponential relationship for a semiconductor diode. The specified forward voltage of 1.6V (max) at 20mA provides the necessary data for designing the current-limiting driver circuit. The curve helps in calculating power dissipation (V_F * I_F) under different operating currents.

4.3 Relative Radiant Intensity vs. Forward Current

This curve (Fig.5) illustrates how the optical output power scales with the drive current. It is typically linear over a significant range but may exhibit saturation or efficiency roll-off at very high currents. This data is essential for determining the operating point to achieve the desired optical output without exceeding absolute maximum ratings.

4.4 Temperature Dependence

Two curves detail thermal performance. Figure 2 shows how the maximum allowable forward current derates as ambient temperature increases above 25°C, a critical consideration for reliability. Figure 4 depicts the relative radiant intensity as a function of ambient temperature, showing the typical decrease in output efficiency as temperature rises, which must be compensated for in precision sensing applications.

4.5 Radiation Pattern

The polar radiation diagram (Fig.6) visually confirms the narrow 16-degree viewing angle. The pattern shows the spatial distribution of the emitted infrared light, which is vital for designing optical alignment and ensuring the illuminated spot size meets the application's needs.

5. Mechanical & Package Information

5.1 Package Type and Dimensions

The device uses a modified T-1 3/4 (5mm) through-hole package. Key dimensional notes from the drawing include:

• All dimensions are in millimeters (inches provided in parentheses).
• Standard tolerance is ±0.25mm (±0.010") unless a specific feature calls for a different tolerance.
• The maximum protrusion of resin under the package flange is 1.0mm (0.039").
• Lead spacing is measured at the point where the leads exit the package body, which is important for PCB footprint design.

The package is designed for standard wave soldering or hand-soldering processes.

5.2 Polarity Identification

For through-hole packages, polarity is typically indicated by a flat spot on the package rim or by leads of different lengths (the longer lead usually being the anode). The datasheet's dimensional drawing should be consulted for the exact marking scheme. Correct polarity is essential to prevent reverse bias application exceeding the 5V limit.

6. Soldering & Assembly Guidelines

Strict adherence to soldering profiles is necessary to prevent thermal damage to the semiconductor die and the epoxy lens.

• Soldering Temperature: The leads can withstand a temperature of 260°C for a maximum of 5 seconds. This measurement is taken 1.6mm (0.063") from the package body.
• Process Recommendation: For wave soldering, a standard profile with preheat, dwell, and cooling stages is applicable. The 260°C/5s limit should not be exceeded at the lead-to-body junction.
• Cleaning: If cleaning is required, use solvents compatible with the package epoxy material to avoid clouding or cracking of the lens.
• Storage Conditions: Devices should be stored in the original moisture-barrier bag at temperatures within the specified storage range (-55°C to +100°C) and in a low-humidity environment to prevent lead oxidation.

7. Application Recommendations

7.1 Typical Application Scenarios

The combination of high intensity and a narrow beam makes this emitter ideal for:

• Proximity and Presence Sensing: Used in automatic faucets, soap dispensers, hand dryers, and occupancy detection.
• Industrial Optical Sensors: Object counting, edge detection, and position sensing in manufacturing lines.
• Optical Barriers and Interrupters: Creating a focused beam for object detection in security systems or machinery safety curtains.
• Short-Range Data Links: Infrared data transmission (IrDA) where directed light reduces interference and power consumption.
• Night Vision Illumination: As an invisible light source for CCTV cameras with IR-sensitive sensors.

7.2 Design Considerations

• Driver Circuit: A constant current source or a current-limiting resistor in series with the LED is mandatory to set I_F. Calculate the resistor value using R = (V_supply - V_F) / I_F, using the maximum V_F for a safe design.
• Heat Management: While power dissipation is low, operating at high ambient temperatures or near the maximum continuous current requires attention to the derating curves. Ensure adequate ventilation on the PCB.
• Optical Alignment: The narrow beam necessitates precise mechanical alignment with the paired photodetector or the target area. Use the radiation pattern diagram for optical design.
• Electrical Protection: Incorporate protection against reverse voltage connection and voltage transients on the supply line, as the maximum reverse voltage is only 5V.
• Bin Selection: Choose the appropriate output bin (A through D) based on the sensitivity of the receiver and the required signal-to-noise ratio for the application. Higher bins provide more optical power but may have cost implications.

8. Technical Comparison & Differentiation

Compared to standard, non-focused IR emitters, this device offers distinct advantages:

• Higher Radiant Intensity in a Narrow Beam: Standard emitters often have viewing angles of 30° or more, dispersing light over a wider area. This component concentrates its output into a 16° beam, delivering higher intensity on-axis, which translates to longer possible sensing distances or lower required drive current for the same received signal.
• Optimized for Sensing: The narrow beam reduces the likelihood of optical crosstalk in multi-sensor arrays and minimizes reflections from unintended surfaces, improving system accuracy and reliability.
• Cost-Effective Performance: It provides a focused beam characteristic often associated with more expensive lensed packages, but in a standard, low-cost T-1 3/4 format.

9. Frequently Asked Questions (Based on Technical Parameters)

Q1: What is the difference between Aperture Radiant Incidence (E_e) and Radiant Intensity (I_E)?
A1: Radiant Intensity (I_E, mW/sr) is a measure of the optical power emitted per unit solid angle, describing the "concentration" of the beam. Aperture Radiant Incidence (E_e, mW/cm²) is the power density incident on a surface (like a detector) at a specific distance, depending on both intensity and distance. I_E is an intrinsic property of the emitter; E_e is dependent on the system geometry.

Q2: Can I drive this emitter with a 3.3V supply?
A2: Yes, typically. With a typical V_F of 1.6V at 20mA, a series resistor can be used to drop the remaining voltage (3.3V - 1.6V = 1.7V). The resistor value would be R = 1.7V / 0.02A = 85 Ohms. A standard 82 or 100 Ohm resistor would be suitable, recalculating the actual current.

Q3: Why is the peak wavelength 940nm and not 850nm?
A3: 940nm is less visible to the human eye (appears dimmer red or invisible) compared to 850nm, making it better for discreet illumination. Both wavelengths are efficiently detected by silicon photodiodes, though sensitivity is slightly higher at 850nm. The choice depends on the need for visibility versus maximum detector response.

Q4: How do I interpret the binning codes (A, B, C, D)?
A4: The bins represent sorted groups based on measured optical output at the factory. Bin D has the highest guaranteed minimum output, while Bin A has the lowest. Select a bin based on the minimum optical power required for your receiver circuit to function reliably under all conditions (including temperature effects and aging).

10. Design and Usage Case Study

Scenario: Designing a Paper Sheet Counter for a Printer.
The emitter and a phototransistor are placed on opposite sides of the paper path. The narrow 16° beam of the LTE-2871 is crucial. It ensures the light is focused directly across the gap to the detector, minimizing scattering and reflections from the printer's internal mechanics, which could cause false counts. A Bin C or D emitter would be selected to provide a strong signal even if paper dust accumulates slightly on the lens. The driver circuit would use a constant current of 20-40mA, and the receiver circuit would be designed to detect the distinct drop in signal when a sheet of paper interrupts the focused beam. The temperature derating curves would be consulted to ensure reliable operation inside the printer, where ambient temperature might reach 50-60°C.

11. Operational Principle Introduction

An infrared emitter is a semiconductor p-n junction 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 aluminum gallium arsenide - AlGaAs). This recombination process releases energy in the form of photons (light particles). The specific composition of the semiconductor layers determines the wavelength of the emitted photons; for this device, it is engineered to be 940nm, which is in the near-infrared range. The modified package incorporates an epoxy lens that shapes the emitted light into the specified narrow beam pattern, collimating the output for directed applications.

12. Technology Trends

In the field of infrared emitters, general trends focus on increasing efficiency (more optical output power per electrical input watt), enabling higher operating speeds for data communication, and developing surface-mount device (SMD) packages for automated assembly. There is also ongoing work to expand wavelength options for specific sensing applications (e.g., gas sensing) and to integrate emitters with drivers and control logic into smart modules. The fundamental principle of electroluminescence in semiconductor materials remains the basis for this technology.