Infrared Emitter LTE-11L2D Datasheet - T1 3mm Package - 940nm Wavelength - 1.8V Forward Voltage - 170mW Power Dissipation - English Technical Document

1. Product Overview

The LTE-11L2D is a high-performance infrared emitting diode designed for applications requiring reliable and efficient non-visible light emission. Its core function is to convert electrical energy into infrared radiation at a peak wavelength of 940 nanometers. This wavelength is ideal for applications where interference from ambient visible light needs to be minimized, as it falls outside the typical human visual spectrum. The device is housed in a standard T-1 package with a 3mm diameter, featuring a dark blue lens that helps in identifying the component and may offer some filtering properties. A key advantage of this emitter is its high radiant intensity, enabling strong signal transmission even at moderate drive currents. Its design targets markets and applications where compact size, cost-effectiveness, and consistent optical performance are critical.

1.1 Core Features and Target Applications

The primary features of the LTE-11L2D include its popular T-1 form factor, which ensures compatibility with standard PCB layouts and automated assembly processes. The dark blue lens is a visual identifier. Its peak emission at 940nm is a standard for infrared communication, offering a good balance between silicon photodetector sensitivity and atmospheric transmission. The device supports pulse operation, which is essential for power-efficient remote control systems and data transmission protocols. Being lead-free and RoHS compliant makes it suitable for global electronics manufacturing. The main application areas are the infrared signaling in consumer remote controls for televisions, audio systems, and other home appliances. It is also suitable for short-range data transmission links and various sensor technologies, such as proximity sensors, object counters, and reflective optical switches, where an invisible light source is preferred.

2. Technical Parameters: In-Depth Objective Interpretation

This section provides a detailed analysis of the electrical, optical, and thermal characteristics specified in the datasheet, explaining their significance for design engineers.

2.1 Absolute Maximum Ratings

The Absolute Maximum Ratings define the stress limits beyond which permanent damage to the device may occur. These are not conditions for normal operation. The power dissipation (P_V) is rated at 170 mW at an ambient temperature (T_A) of 25°C. This value decreases with increasing ambient temperature, as shown in the derating curve. The continuous forward current (I_F) is 100 mA, while a much higher surge current (I_FSM) of 700 mA is allowed for very short pulses (100 µs), which is typical for remote control burst transmission. The low reverse voltage rating (V_R = 5V) indicates the diode's PN junction is not designed to withstand significant reverse bias, so circuit protection (like a series resistor or parallel protection diode) is often necessary. The maximum junction temperature (T_j) is 100°C, and the thermal resistance from junction to ambient (R_thJA) is 300 K/W when the leads are soldered to a PCB with 7mm length. This thermal parameter is crucial for calculating the maximum allowable power dissipation at elevated ambient temperatures to prevent overheating.

2.2 Electrical and Optical Characteristics

These parameters are measured under specific test conditions (typically I_F = 100mA, pulse width = 20ms) at 25°C and represent the device's typical performance. The Radiant Intensity (I_E) has a typical value of 68 mW/sr, with a minimum of 40 mW/sr. This measures the optical power emitted per unit solid angle and is a key figure of merit for the emitter's brightness. The ±10% tolerance should be considered in optical design. The Peak Emission Wavelength (λ_P) is typically 940nm. The Spectral Bandwidth (Δλ) is approximately 50nm, defining the range of wavelengths emitted. The Forward Voltage (V_F) is typically 1.8V with a maximum of 1.5V at the test current, which is important for calculating the required supply voltage and series resistor value. The Reverse Current (I_R) is very low (max 10 µA at 5V). The Rise and Fall Times (t_r, t_f) are 20 ns, indicating the device can be switched very quickly, supporting high-speed pulsed operation. The Half Angle (θ_1/2) is ±22°, meaning the emission angle where the intensity drops to 50% of its peak value. This defines the beam width and radiation pattern.

3. Performance Curve Analysis

The datasheet provides several graphs that illustrate the device's behavior under varying conditions, which are essential for robust system design.

3.1 Relative Spectral Distribution

Figure 1 shows the relative radiant intensity versus wavelength. The curve is centered around 940nm with the defined 50nm bandwidth. This graph is vital for ensuring compatibility with the receiving photodetector's spectral sensitivity, which is typically also peaked in the near-infrared region. Designers must confirm that the emitter's output spectrum adequately overlaps with the detector's response curve for optimal signal strength.

3.2 Thermal and Current Derating

Figure 2 depicts the forward current limit versus ambient temperature. It shows how the maximum allowable continuous current decreases as the ambient temperature rises above 25°C to keep the junction temperature below its 100°C maximum. This derating is a direct consequence of the device's thermal resistance and power dissipation. For reliable operation in high-temperature environments, the drive current must be reduced accordingly.

3.3 Forward Current vs. Voltage and Relative Output

Figure 3 is the standard I-V (current-voltage) characteristic curve. It shows the exponential relationship, confirming the typical V_F of around 1.8V at 100mA. Figure 4 and Figure 5 show how the relative radiant intensity changes with forward current and ambient temperature. The output is not perfectly linear with current and decreases with increasing temperature due to reduced internal quantum efficiency. These curves help in selecting the optimal operating point to achieve the desired optical output while managing power consumption and thermal load.

3.4 Radiation Diagram

Figure 6 is a polar radiation pattern diagram. It visually represents the half-angle of ±22°, showing how the intensity distributes spatially. This is critical for designing the optical path, whether for a wide-angle broadcast (like a remote control) or a more focused beam. The pattern is generally Lambertian-like for this type of package, meaning intensity is approximately proportional to the cosine of the viewing angle.

4. Mechanical and Package Information

4.1 Outline Dimensions

The mechanical drawing provides all critical dimensions. The package is a standard T-1 with a body diameter of 3.2mm ±0.15mm and a typical lens height. The lead diameter is 0.5mm. The lead spacing, measured where leads emerge from the package, is 2.54mm nominal, which is the standard 0.1-inch pitch for through-hole components. The minimum lead length is 25.4mm. A notable feature is the potential for up to 0.7mm of protruded resin under the flange, which must be considered for PCB standoff and cleaning. The anode and cathode are clearly marked on the diagram; the longer lead is typically the anode, but the diagram is the definitive reference.

4.2 Polarity Identification

Polarity is clearly indicated in the outline drawing. Incorrect polarity connection will prevent the device from emitting light and may subject it to reverse voltage stress. The flat spot on the package rim often aligns with the cathode side, which is the shorter lead. Always verify against the datasheet diagram during assembly.

5. Soldering and Assembly Guidelines

5.1 Recommended Solder Pad Layout

Figure 8 shows the recommended solder pad footprint for PCB design. The pad for the cathode and anode are shown, along with dimensions for the copper area and solder resist. A well-designed pad ensures a reliable solder joint, proper mechanical stability, and aids in heat dissipation during soldering. Following these recommendations helps prevent tombstoning and poor solder fillets.

5.2 Soldering Profile and Precautions

The datasheet specifies a lead soldering temperature of 260°C maximum for 5 seconds, measured 2.0mm from the body. This is a critical parameter for wave soldering or hand soldering processes. Exceeding this time-temperature profile can damage the internal die, wire bonds, or the epoxy package, leading to premature failure or degraded optical performance. Figure 9 illustrates a recommended wave soldering temperature profile, showing the preheat, soak, reflow, and cooling stages. It is essential to follow this profile to minimize thermal shock. General storage conditions are within the specified storage temperature range of -40°C to +100°C, in a dry environment to prevent moisture absorption which can cause \"popcorning\" during reflow (though this is more critical for SMD parts).

6. Application Suggestions and Design Considerations

6.1 Typical Application Circuits

The most common application is in an infrared remote control transmitter. A basic circuit involves a microcontroller GPIO pin driving the emitter through a current-limiting resistor. The resistor value is calculated as R = (V_CC - V_F) / I_F. For example, with a 3.3V supply, V_F=1.8V, and desired I_F=100mA, R = (3.3 - 1.8) / 0.1 = 15Ω. The resistor's power rating must be sufficient (P = I_F² * R = 0.15W). For pulsed operation, ensure the microcontroller can source/sink the required peak current. A transistor (BJT or MOSFET) driver is often used for higher currents or when the MCU pin cannot source enough current.

6.2 Optical Design Considerations

For optimal range and signal integrity, pair the emitter with a photodetector or phototransistor sensitive at 940nm. Consider the radiation pattern: for a wide coverage remote, the ±22° angle is suitable. For a more directional link, a lens may be added to collimate the beam. The dark blue lens may attenuate some visible light, reducing background noise at the receiver. Ensure the emitter and receiver are aligned correctly. Ambient light from sunlight or incandescent bulbs contains IR components and can cause interference; using a modulated signal (e.g., 38kHz carrier) and a corresponding tuned receiver helps reject this DC ambient noise.

6.3 Thermal Management

Although small, the device dissipates heat. At the maximum continuous current of 100mA and V_F=1.8V, the power dissipated is 180mW, which slightly exceeds the 170mW rating at 25°C. Therefore, for continuous operation, the current should be derated, or the ambient temperature must be low. In pulsed applications (like remote controls with low duty cycle), the average power is much lower, so thermal issues are less concerning. Providing adequate copper area on the PCB around the leads helps sink heat away.

7. Frequently Asked Questions Based on Technical Parameters

Q: Can I drive this IR LED directly from a 5V microcontroller pin?

A: No, not without a current-limiting resistor. Connecting it directly would attempt to draw a very high current, likely destroying the LED and possibly damaging the microcontroller pin. Always use a series resistor calculated based on the supply voltage and desired forward current.

Q: What is the difference between Radiant Intensity (mW/sr) and Radiant Power (mW)?

A: Radiant Intensity is angular-dependent—power per solid angle. Radiant Power is the total optical power emitted in all directions. To find total power, you would integrate the intensity over the entire emission solid angle (defined by the radiation pattern). The datasheet provides intensity, which is more useful for calculating irradiance at a specific distance and angle on a receiver.

Q: Why is the reverse voltage rating only 5V?

A> Infrared LEDs are optimized for forward conduction and light emission. Their PN junction is not designed to block high reverse voltages. Accidentally applying a reverse bias above 5V can cause breakdown and permanent damage. In circuits where reverse voltage is possible, add a protection diode in parallel (cathode to cathode, anode to anode) or ensure the driving circuit never applies a reverse bias.

Q: How do I interpret the half-angle for my design?

A: The half-angle of ±22° means the beam has a total width of approximately 44° where the intensity is above 50% of the peak. At angles greater than this, the intensity falls off rapidly. For a remote control that needs to work when pointed somewhat off-axis, this provides a reasonable coverage. For a strictly line-of-sight data link, alignment within this cone is necessary for strong signal reception.

8. Operational Principle and Technology Trends

8.1 Basic Operating Principle

The LTE-11L2D is a semiconductor light-emitting diode. When a forward voltage exceeding its junction potential (around 1.8V) is applied, electrons and holes are injected into the active region of the semiconductor material (typically based on aluminum gallium arsenide - AlGaAs). These charge carriers recombine, releasing energy in the form of photons. The specific composition of the semiconductor layers determines the wavelength of the emitted photons, which is 940nm for this device. This process is called electroluminescence. The dark blue epoxy package serves to encapsulate and protect the delicate semiconductor chip, shape the emitted light beam, and act as a lens.

8.2 Industry Trends

The infrared emitter market continues to evolve. Trends include the development of emitters with higher radiant intensity and efficiency from the same package size, enabling longer range or lower power consumption. There is also ongoing work to improve the speed (rise/fall times) for very high-speed data transmission applications like IrDA. Integration is another trend, with combined emitter-driver modules becoming available. Furthermore, the drive for miniaturization persists, although the T-1 package remains a staple for through-hole applications due to its robustness and ease of handling. The underlying material science focuses on improving internal quantum efficiency and thermal stability to maintain performance over wider temperature ranges.