LTE-4208M Infrared Emitter Diode Datasheet - 940nm Wavelength - T-1 3/4 Package (5mm) - 1.6V Forward Voltage - 100mW Power Dissipation

1. Product Overview

LTE-4208M is a high-performance infrared emitting diode, specifically designed for applications requiring reliable and efficient non-visible light emission. Its core function is to convert electrical energy into infrared radiation with a peak wavelength of 940 nanometers (nm). This wavelength is ideal for applications that require minimizing visible light interference, as it is essentially invisible to the human eye while being efficiently detected by silicon-based photodetectors such as phototransistors and photodiodes.

The device employs a standard T-1 3/4 (approximately 5mm diameter) package with a transparent lens. This miniature plastic package offers a cost-effective solution while providing mechanical robustness. A key design feature is its spectral and mechanical compatibility with corresponding phototransistor series (e.g., LTR-3208), which simplifies optical system design by ensuring optimal alignment and signal coupling between the emitter and detector pair.

1.1 Core Advantages and Target Market

The primary advantages of the LTE-4208M include its high radiant intensity output, consistent performance guaranteed through a rigorous binning process, and its compact, low-cost form factor. It is pre-screened into specific radiant intensity ranges (binned), allowing designers to select components that precisely meet their system sensitivity requirements without the need for external calibration or trimming circuits. This predictability enhances manufacturing yield and system reliability.

The target market for this component primarily includes industrial and consumer electronic products requiring proximity sensing, object detection, or optical encoding. Its most prominent application is in smoke detectors, which detect smoke particles by measuring light scattering or attenuation. Other potential applications encompass non-contact switches, short-range data transmission (e.g., remote control systems), industrial automation sensors, and object counters.

2. In-depth Technical Parameter Analysis

Understanding electrical and optical parameters is crucial for reliable circuit design and ensuring the LED operates within its Safe Operating Area (SOA).

2.1 Absolute Maximum Ratings

These ratings define the stress limits that could cause permanent damage to the device. It is not recommended to operate under conditions close to or at these limits for extended periods.

• Power Dissipation (Pd):100 mW. This is the maximum power the device can dissipate as heat when the ambient temperature (TA) is 25°C. Exceeding this limit risks thermal runaway and failure.
• Peak Forward Current (I_FP):3 A. This is the maximum instantaneous current allowed under pulse conditions (300 pulses per second, 10μs pulse width). It is significantly higher than the continuous current rating, highlighting the device's ability to handle short-duration, high-intensity pulses.
• Continuous Forward Current (I_F):50 mA. This is the maximum DC current that can be continuously applied without exceeding the power dissipation rating, assuming a typical forward voltage.
• Reverse Voltage (V_R):5 V. The device has very low tolerance to reverse bias. Applying a reverse voltage exceeding 5V may cause immediate breakdown. The datasheet explicitly states that the device is not designed for reverse operation.
• Operating and Storage Temperature:are -40°C to +85°C and -55°C to +100°C, respectively. These ranges define the environmental conditions for reliable operation and non-operational storage.
• Pin soldering temperature:260°C for 5 seconds at a distance of 4.0mm from the package body. This is critical for wave soldering or reflow soldering processes to prevent damage to the internal semiconductor chip or plastic package.

2.2 Electrical and Optical Characteristics

These parameters are measured under standard test conditions (TA=25°C, I_F=20mA, unless otherwise specified), defining the typical performance of the device.

• Radiant Intensity (I_E):This is the core optical output parameter, expressed in milliwatts per steradian (mW/sr). It represents the optical power emitted per unit solid angle. The device is binned (grades A through G) based on its measured output at the standard test current of 20mA, with minimum and typical values ranging from 3.6/13.2 mW/sr (Grade A) to 28.8 mW/sr (Grade G). This binning allows for selection based on the required signal strength.
• Peak Emission Wavelength (λ_Peak):940 nm. This is the wavelength at which the emitted optical power reaches its maximum value. It belongs to the near-infrared spectral range.
• Spectral line half-width (Δλ):50 nm. This parameter, also known as the Full Width at Half Maximum (FWHM), defines the spectral bandwidth. A width of 50nm means the emitted light covers a wavelength range of approximately 915nm to 965nm at half of its peak intensity.
• Forward Voltage (V_F):1.2V (min), 1.6V (typ). This is the voltage drop across the diode when conducting a current of 20mA. It is crucial for calculating the value of the series resistor in the drive circuit: R = (V_supply- V_F) / I_F.
• Reverse current (I_R):At V_R=5V, maximum 100 μA. This is the small leakage current that flows when the diode is reverse-biased at its maximum rated value.
• Viewing Angle (2θ_1/2):20 degrees. This is the full angle at which the radiation intensity drops to half of its maximum (axial) value. A viewing angle of 20° indicates a relatively narrow, focused beam, which is advantageous for directional sensing applications.

3. Explanation of the Grading System

LTE-4208M employs a single key binning parameter: radiant intensity. Devices are tested and grouped (Bins A through G) based on their measured output at the standard 20mA test current. This system offers several benefits:

1. Design Consistency:Engineers can select specific bins to ensure consistent optical signal levels across all units in a production batch, thereby improving product uniformity.
2. Performance Matching:When used with a matched photodetector, selecting an emitter bin allows for more precise control of the overall sensitivity and dynamic range of the optical sensor system.
3. Cost Optimization:For applications with less stringent sensitivity requirements, using devices from lower bins (e.g., A, B bins) may be more cost-effective.

The datasheet does not indicate binning for forward voltage or wavelength for this model, suggesting strict process control over these parameters, or that they are not key differentiators for its target applications.

4. Performance Curve Analysis

Typical characteristic curves visually demonstrate the behavior of the device under various conditions, which is crucial for robust system design beyond the nominal 25°C point.

4.1 Spectral Distribution (Figure 1)

The curve shows a Gaussian-like distribution centered at 940nm with a full width at half maximum of approximately 50nm. This confirms the monochromaticity of the LED output, which is crucial for filtering out ambient light interference in sensing applications. The shape of this curve is typical for AlGaAs-based infrared LEDs.

4.2 Forward Current vs. Ambient Temperature (Figure 2)

This derating curve is crucial for thermal management. It shows the maximum allowable continuous forward current decreasing as the ambient temperature increases. At 85°C (the maximum operating temperature), the allowable current is significantly lower than the 50mA rating at 25°C. Designers must use this graph to ensure the operating current does not exceed the curve value at the system's expected maximum ambient temperature.

4.3 Forward Current vs. Forward Voltage (Figure 3)

This is the standard I-V curve for a diode. It shows the exponential relationship between current and voltage. This curve allows designers to estimate V_F, which is important for power supply design and efficiency calculations.

4.4 Relative Radiation Intensity vs. Ambient Temperature (Figure 4)

This figure illustrates the temperature dependence of the optical output. The relative radiant intensity decreases as the temperature increases. For example, at 85°C, the output may be only 60-70% of its value at 25°C. This negative temperature coefficient must be considered when designing systems intended to operate over a wide temperature range, to avoid signal loss at high temperatures.

4.5 Relative Radiation Intensity vs. Forward Current (Figure 5)

This curve indicates that within the typical operating range (e.g., up to 50mA), the optical output is approximately proportional to the forward current. However, this relationship is not perfectly linear; at very high currents, the efficiency (radiant intensity per mA) may slightly decrease due to increased thermal effects and other non-idealities within the semiconductor.

4.6 Radiation Pattern (Figure 6)

This polar plot visually defines the viewing angle. Normalized intensity is plotted against the angle from the central axis (0°). The plot confirms a half-angle of 20°, showing a rapid drop in intensity beyond approximately ±10° from the center. This pattern is characteristic of an LED with a simple dome lens, providing a focused beam suitable for directional applications.

5. Mechanical and Packaging Information

5.1 Outline Dimensions

Na'urar tana bin daidaitaccen girman T-1 3/4 na rami. Muhimman girma sun haɗa da diamita na jiki kusan 5mm, tazarar fil ɗin da aka saba da ita a wurin da fil ɗin ke fitowa daga harsashi shine 2.54mm (0.1"), da kuma jimlar tsayi. Lura cewa matsakaicin tsawo na resin a ƙarƙashin flange shine 1.0mm. Fil ɗin yawanci ana yin su da gawa na tagulla mai lulluɓe. Harsashi yana amfani da ruwan tabarau na epoxy mai gaskiya, mara launi.

5.2 Polarity Identification

For through-hole packages like T-1 3/4, polarity is typically indicated by lead length (the longer lead is usually the anode or positive) and/or a flat marking on the plastic flange near the cathode (negative) lead. Consult the specification sheet drawing for the specific marking used on this component.

6. Welding and Assembly Guide

Adhering to soldering specifications is crucial to prevent thermal shock and potential failures.

• Manual soldering:Use a temperature-controlled soldering iron. Limit soldering time per pin to 3-5 seconds, with temperature not exceeding 350°C. Apply heat to the pin, not the package body.
• Wave soldering/Reflow soldering:The specified condition is 260°C for 5 seconds at a distance of 4.0mm from the package body. This means the component can withstand typical infrared or convection reflow profiles, but the thermal capacity of the leads must be considered to ensure the package itself does not overheat.
• Cleaning:If cleaning is required after soldering, use solvents compatible with the epoxy molding compound. Avoid ultrasonic cleaning unless its safety for the component has been verified.
• Storage:Store in a dry, anti-static environment within the specified temperature range (-55°C to +100°C). Moisture-sensitive devices should be kept in sealed bags with desiccant if not baked before use.

7. Application Suggestions and Design Considerations

7.1 Typical Application: Smoke Detector

In a photoelectric smoke detector, the LTE-4208M is positioned within a chamber such that, under clear air conditions, its beam does not directly strike the paired phototransistor. When smoke particles enter the chamber, they scatter the infrared light, causing a portion of the light to deflect onto the phototransistor. The resulting increase in detector current triggers the alarm. For this application:

• Select a radiant intensity bin that provides sufficient signal for reliable smoke detection while minimizing power consumption.
• Drive the LED with pulsed current (e.g., short high pulses like 100mA for 10μs) instead of DC to increase peak signal, achieve better signal-to-noise ratio, reduce average power consumption, and extend battery life.
• Consider temperature derating for radiation intensity and maximum current, as the detector may be installed in an attic or other environments with significant temperature fluctuations.

7.2 General Design Considerations

• Current Limiting:Always use a series resistor or constant current driver to limit the forward current. Never connect an LED directly to a voltage source.
• Reverse Voltage Protection:In circuits where reverse voltage transients may occur (e.g., inductive loads, hot-plugging), consider connecting a protection diode in parallel with the LED (cathode to anode) to clamp any reverse voltage below 0.7V.
• Heat Dissipation:For continuous operation near the maximum current rating, consider the PCB layout. Providing ample copper area around the pins aids in heat dissipation.
• Optical Design:A narrow viewing angle of 20° simplifies the optical design for collimation but requires careful mechanical alignment with the receiver. For wider coverage, a diffuser or lens may be necessary.

8. Technical Comparison and Differentiation

Compared to generic, unbinned infrared LEDs, the key differentiation of the LTE-4208M lies in its guaranteed radiant intensity binning, which provides predictable performance. Compared to Surface-Mount Device (SMD) infrared LEDs, the T-1 3/4 through-hole package may offer higher power dissipation capability due to its larger thermal mass and longer leads, potentially allowing for higher continuous or pulsed drive currents. Its clear package is superior to tinted or diffused packages when maximum forward light output and beam definition are required, although it does not inherently provide shielding against visible light.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Since the peak rating is 3A, can I drive this LED continuously at 3A?
A: No. The 3A rating is for very short pulses (10μs) at a specific duty cycle. The maximum continuous current is 50mA. Exceeding this will quickly damage the device due to overheating.

Q: Why is the reverse voltage rating only 5V?
A: Infrared LEDs are optimized for forward conduction. Their semiconductor structure is not designed to withstand high reverse bias. Ensure the circuit prevents the application of reverse voltage.

Q: How to select the correct bin (A to G)?
A: Choose based on the signal strength required by your system at the receiver. If your detector circuit has high gain and you need to minimize power consumption, lower bins (A, B) may suffice. For longer distances, weaker detectors, or systems requiring high signal-to-noise ratio, select higher bins (E, F, G). Testing with your specific optical path is recommended.

Q: The typical forward voltage is 1.6V. For a 20mA current, what size resistor should be used with a 5V power supply?
A: R = (V_supply- V_F) / I_F= (5V - 1.6V) / 0.020A = 170 ohms. Use the closest standard value (e.g., 180 ohms) and check the actual current: I_F= (5V - 1.6V) / 180 = ~18.9mA, which is acceptable.

10. Practical Design Case Studies

Scenario:Design a low-power, battery-powered object counter for an industrial conveyor belt. The system uses a through-beam sensor, where the LTE-4208M is placed opposite the LTR-3208 phototransistor across the conveyor belt.

Design Steps:

1. Objective:Maximize battery life while ensuring reliable detection of all objects.
2. Driving method:Yi amfani da aikin bugun jini. Microcontroller yana samar da bugun jini na 100Hz, 10% na aiki (1ms a kunne, 9ms a kashe).
3. Lissafin halin yanzu:Don ci gaba da cikin iyakar matsakaicin ƙarfi, zaɓi bugun jini na halin yanzu. Bisa ga Pd=100mW da V_F~1.6V, matsakaicin I_FUp to ~62.5mA. For a 10% duty cycle, the pulse I_FUp to 625mA. For a strong signal, a conservative 100mA pulse current was selected.
4. Component Selection:Select LTE-4208M grade D or E for good signal strength. Select the matching LTR-3208 phototransistor.
5. Circuit:Use a microcontroller GPIO pin to drive a transistor (e.g., an NPN BJT or an N-channel MOSFET), which switches a 100mA pulse through the LED. A series resistor sets the current: R = (3.3V_GPIO- V_CE(sat)- V_F) / I_FThe phototransistor output is connected to a comparator or microcontroller ADC.
6. Considerations:By synchronizing detection with LED pulses (synchronous detection), the influence of ambient light is taken into account. The impact of temperature on output intensity is considered.

This method reduces the average current consumption to approximately 10mA (100mA * 10%), instead of a continuous 20-50mA, significantly extending battery life while maintaining strong, detectable light pulses.

11. Working Principles

LTE-4208M wani nau'in diode na semiconductor p-n junction ne wanda aka yi da kayan kamar aluminum gallium arsenide (AlGaAs). Lokacin da aka yi amfani da ƙarfin lantarki mai kyau wanda ya wuce ƙarfin bandgap na kayan, electrons daga yankin n da kuma ramuka daga yankin p ana shigar da su cikin yankin junction. Lokacin da waɗannan masu ɗaukar kaya suka haɗu, suna sakin makamashi. A cikin diode mai haskakawa (LED), wannan makamashi yana fitowa da farko a cikin nau'in photons (haske). Tsawon zangon hasken da aka fitar (launi) yana ƙayyade ta ƙarfin bandgap na kayan semiconductor. Ga AlGaAs da aka daidaita zuwa 940nm, ƙarfin bandgap yana kusan 1.32 electron volts (eV). Kullin epoxy mai gani yana aiki azaman ruwan tabarau, yana siffanta tsarin fitarwa da kuma samar da kariyar muhalli.

12. Technology Trends

Fasahar mai fitar da infrared na ci gaba da bunkasa. Trends masu alaƙa da na'urori kamar LTE-4208M sun haɗa da:

• Efficiency Improvement:Ongoing materials science research aims to enhance the wall-plug efficiency (light power output / electrical power input) of infrared LEDs, reducing heat generation and power consumption for the same light output.
• Higher Speed Modulation:Developing LEDs capable of faster switching for optical data communication (e.g., IrDA, Li-Fi) and high-speed sensing applications.
• Integration:Progressing toward integrated optoelectronic components, combining emitters, detectors, and sometimes driver circuits into a single module to simplify design and improve alignment and performance consistency.
• Alternative Wavelength:Extend to other near-infrared wavelengths (e.g., 850nm, 880nm) for specific applications, such as eye tracking (where 940nm is often preferred due to being less visible) or to be compatible with different silicon detector sensitivities.
• Package Miniaturization:Although through-hole packages remain popular in high-power or high-reliability applications, the trend toward surface-mount technology (SMD) is strong to meet the demands of automated assembly and space-constrained designs.

With its proven T-1 3/4 package, high radiant output, and strict binning, the LTE-4208M represents a mature and reliable solution, well-suited for its primary applications, especially where through-hole mounting is preferred or required.