LTE-3273DL IR Emitter and Detector Datasheet - 940nm Wavelength - 5mm Package - 1.6V Forward Voltage - 150mW Power Dissipation - English Technical Document

1. Product Overview

The LTE-3273DL is a discrete infrared component integrating an emitter and detector. It is designed for applications requiring reliable infrared signal transmission and reception. The core of the device is based on Gallium Arsenide (GaAs) technology, which is standard for producing efficient infrared light emission at the 940nm wavelength. This wavelength is ideal for consumer electronics as it is invisible to the human eye yet easily detectable by silicon-based photodetectors, minimizing ambient light interference.

The component's primary function is to serve as a transceiver in simple IR data links. Its design emphasizes a balance between performance and cost-effectiveness, making it suitable for high-volume, cost-sensitive applications. The blue transparent package aids in identifying the component type and allows the 940nm IR light to pass through with minimal attenuation.

1.1 Features

• Optimized for High Current, Low Forward Voltage: Engineered to operate efficiently at higher drive currents while maintaining a relatively low voltage drop, which helps in reducing power consumption in battery-operated devices.
• Pulse Operation Capability: Can handle high peak forward currents (up to 2A) in pulsed mode, enabling the creation of strong, short-duration IR bursts ideal for remote control commands or data transmission.
• Wide Viewing Angle (45° half-angle): Provides a broad emission and detection pattern, making alignment between transmitter and receiver less critical and increasing system robustness.
• Blue Transparent Package: The housing is tinted blue, which acts as a visible light filter, reducing sensitivity to ambient visible light and improving signal-to-noise ratio for the IR detector.

1.2 Applications

• Infrared Sensors: Used in proximity sensors, object detection, and line-following robots.
• Remote Controls: The standard component in TV, audio system, and set-top box remote controls for command transmission.
• Simple IR Data Links: For short-range, low-speed wireless communication between devices.
• Security Systems: Can be used in beam-break intrusion detectors.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation at or near these limits is not recommended for extended periods.

• Power Dissipation (Pd): 150 mW: The maximum total power (from both the emitter and detector circuits) that can be safely dissipated as heat by the package at an ambient temperature (TA) of 25°C. Exceeding this can lead to overheating and failure.
• Peak Forward Current (I_FP): 2 A: The maximum allowable current through the IR emitter diode under pulsed conditions (300 pulses per second, 10μs pulse width). This enables high-intensity IR flashes.
• Continuous Forward Current (I_F): 100 mA: The maximum DC current that can flow through the emitter continuously. For typical operation, driving at 20-50mA is common.
• Reverse Voltage (V_R): 5 V: The maximum reverse-bias voltage that can be applied across the emitter diode before breakdown occurs. This is relatively low, so care must be taken to avoid reverse polarity connection.
• Operating & Storage Temperature: Rated from -40°C to +85°C and -55°C to +100°C respectively, indicating suitability for industrial and consumer environments.
• Lead Soldering Temperature: 260°C for 5 seconds: Specifies the reflow soldering profile tolerance, crucial for PCB assembly without damaging the component.

2.2 Electrical & Optical Characteristics

These are the guaranteed performance parameters under specified test conditions at 25°C.

• Radiant Intensity (I_E): Measures the optical power output per solid angle (mW/sr). At I_F=20mA, it's typically 8.0 mW/sr (min 5.6). At I_F=100mA, it jumps to 40.0 mW/sr (min 28.0). This non-linear increase shows higher efficiency at higher currents within limits.
• Peak Emission Wavelength (λ_P): 940 nm: The wavelength at which the emitter outputs the most optical power. This matches the peak sensitivity of silicon photodiodes and is outside the visible spectrum.
• Spectral Line Half-Width (Δλ): 50 nm: The bandwidth of the emitted light. A value of 50nm indicates the light is not monochromatic but spans from roughly 915nm to 965nm at half the peak intensity.
• Forward Voltage (V_F): The voltage drop across the emitter diode when conducting. It is typically 1.6V at 50mA and 2.3V at 500mA. This parameter is vital for designing the current-limiting driver circuit.
• Reverse Current (I_R): 100 μA max: The small leakage current that flows when the diode is reverse-biased at 5V. A low value is desirable.
• Viewing Angle (2θ_1/2): 45°: The full angle at which the radiant intensity drops to half of its peak value. This defines the emission/detection cone.

3. Performance Curve Analysis

The datasheet provides several graphs illustrating key relationships. These are essential for understanding behavior under non-standard conditions.

3.1 Spectral Distribution (Fig.1)

This curve plots relative radiant intensity against wavelength. It confirms the peak at 940nm and the approximately 50nm spectral half-width. The shape is characteristic of a GaAs IRED.

3.2 Forward Current vs. Ambient Temperature (Fig.2)

This graph shows the derating of the maximum allowable continuous forward current as ambient temperature increases. Above 25°C, the maximum current must be reduced to prevent exceeding the 150mW power dissipation limit, as the component's ability to shed heat diminishes.

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

The IV characteristic curve of the emitter diode. It is exponential in nature, like a standard diode. The curve allows designers to determine the required drive voltage for a desired operating current, especially important for low-voltage battery systems.

3.4 Relative Radiant Intensity vs. Ambient Temperature (Fig.4) & vs. Forward Current (Fig.5)

Figure 4 shows that optical output power decreases as temperature increases (a negative temperature coefficient), which must be compensated for in designs requiring stable performance over a wide temperature range. Figure 5 shows the non-linear relationship between drive current and light output, indicating increasing efficiency up to a point before potential saturation or thermal effects.

3.5 Radiation Diagram (Fig.6)

A polar plot illustrating the spatial distribution of the emitted IR light. The diagram visually confirms the wide 45° half-angle, showing intensity normalized to the peak at 0°.

4. Mechanical and Packaging Information

4.1 Outline Dimensions

The component features a standard 5mm radial leaded package. Key dimensions include a body diameter of approximately 5mm, a typical lead spacing of 2.54mm (0.1\") where leads emerge from the body, and an overall height. The flange at the base aids in placement during PCB assembly. Protruded resin under the flange is specified to be a maximum of 0.5mm. The flat spot on the rim of the lens typically indicates the cathode (negative) lead for the emitter section.

4.2 Polarity Identification

For the emitter section, the longer lead is usually the anode (positive). The detector (photodiode) section within the same package will have its own anode and cathode. The datasheet's pinout diagram is critical for correct connection. Incorrect polarity can damage the emitter diode if reverse voltage exceeds 5V.

5. Soldering and Assembly Guidelines

• Reflow Soldering: The absolute maximum rating for lead soldering is 260°C for 5 seconds, measured 1.6mm from the package body. This aligns with typical lead-free reflow profiles (peak temp ~250°C).
• Hand Soldering: If hand soldering is necessary, use a temperature-controlled iron and minimize the contact time to less than 3 seconds per lead to prevent heat damage to the internal semiconductor die and the plastic package.
• Cleaning: Use appropriate cleaning solvents that are compatible with the blue transparent epoxy resin of the package.
• Storage Conditions: Store in a dry, anti-static environment within the specified temperature range (-55°C to +100°C) to prevent moisture absorption (which can cause \"popcorning\" during reflow) and electrostatic discharge damage.

6. Application Suggestions and Design Considerations

6.1 Typical Circuit Configuration

For the emitter: A simple series resistor is commonly used to limit the forward current. The resistor value is calculated as R = (V_CC - V_F) / I_F. For example, with a 5V supply, V_F=1.6V, and desired I_F=20mA, R = (5 - 1.6) / 0.02 = 170Ω. A transistor (NPN or N-channel MOSFET) is often placed in series to switch the current on/off via a microcontroller.

For the detector (photodiode): It is typically operated in photovoltaic (zero bias) or photoconductive (reverse bias) mode. For simple digital detection, the photodiode can be connected in series with a load resistor. The voltage across this resistor changes with incident IR light, which can be fed into a comparator or amplifier.

6.2 Design Considerations

• Noise Immunity: The 940nm wavelength and blue filter help, but ambient light from sunlight or fluorescent lamps (which contain IR) can still cause interference. Using a modulated IR signal (e.g., 38kHz carrier) and a demodulating receiver IC is the standard method to achieve high noise immunity.
• Current Driving: For pulsed operation near the 2A peak, ensure the driving transistor can handle the current and that PCB traces are wide enough to avoid excessive voltage drop.
• Optical Path: Keep the lens clean and free from obstructions. The wide viewing angle eases alignment but reduces maximum range compared to a narrower beam. For longer range, consider adding a simple collimating lens.
• Thermal Management: When operating at high continuous currents or in high ambient temperatures, ensure adequate ventilation around the component to stay within power dissipation limits.

7. Technical Comparison and Differentiation

Compared to standard 940nm IR LEDs, the LTE-3273DL integrates a detector, saving board space in transceiver applications. Compared to slower phototransistors, the integrated photodiode offers faster response times, suitable for modulated data transmission. Its high pulse current capability (2A) is a key advantage over many basic IR LEDs, allowing for stronger signals. The combination of features (high current, wide angle, detector included) in a low-cost package positions it well for consumer remote control and sensing markets.

8. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this IR emitter directly from a microcontroller GPIO pin?
A: No. A typical GPIO pin can only source/sink 20-50mA, which might be at the upper limit, and it cannot provide the voltage swing needed for the ~1.6V V_F. Always use a transistor as a switch.

Q: What is the difference between radiant intensity (mW/sr) and total output power (mW)?
A> Radiant intensity is angular density. Total power would require integrating intensity over the entire emission sphere. For a wide-angle emitter like this, the total power is significantly higher than the intensity value.

Q: How do I interface the photodiode output to a digital input?
A: The photodiode's current output is very small. You need a transimpedance amplifier to convert it to a voltage, followed by a comparator to create a digital signal. For simple on/off detection with ambient light present, a dedicated IR receiver module (with built-in amplifier, filter, and demodulator) is strongly recommended instead of using the raw photodiode.

Q: Why is the reverse voltage rating only 5V?
A> This is typical for GaAs IR emitter diodes. The semiconductor material and structure have a relatively low breakdown voltage. Careful circuit design is needed to avoid accidental reverse bias.

9. Practical Use Case Example

Scenario: Building a Simple IR Object/Proximity Sensor.
The LTE-3273DL can be used in a reflective sensor configuration. The emitter is pulsed at a specific frequency (e.g., 1kHz). The detector, placed next to it, looks for the reflected signal from an object in front. A band-pass filter tuned to 1kHz in the detector's amplifier chain rejects ambient light noise. When an object comes within range, the reflected signal increases, triggering the circuit. This is common in automatic towel dispensers, paper detection in printers, and robot edge detection.

10. Principle of Operation

The device operates on well-established semiconductor physics principles. The Emitter is a Gallium Arsenide (GaAs) Light Emitting Diode (LED). When forward biased, electrons and holes recombine in the PN junction, releasing energy in the form of photons. The bandgap of GaAs determines the photon energy, corresponding to the 940nm infrared wavelength. The Detector is a silicon PIN photodiode. When photons with energy greater than silicon's bandgap (including 940nm IR) strike the depletion region, they generate electron-hole pairs. These carriers are swept by the internal electric field (from built-in or applied bias), creating a photocurrent proportional to the incident light intensity.

11. Industry Trends and Developments

The discrete IR component market continues to evolve. Trends include:
Miniaturization: Moving towards surface-mount device (SMD) packages like 0805 or 0603 for smaller consumer electronics.
Higher Integration: Combining the emitter, detector, driver, and amplifier into a single module with digital interfaces (I2C, UART).
Improved Performance: Development of emitters with higher radiant intensity and narrower beam angles for longer-range applications, and detectors with lower dark current and higher speed.
New Wavelengths: Exploration of wavelengths beyond 940nm for specific sensing applications like gas detection, though 940nm remains dominant for general-purpose remote control and sensing due to cost and compatibility.