IR Emitter LTE-7477LM1-TA Datasheet - High Speed, High Power - 880nm Wavelength - English Technical Document

1. Product Overview

The LTE-7477LM1-TA is a high-performance infrared (IR) emitter designed for applications requiring fast response times and significant radiant output. Its core function is to convert electrical energy into infrared light at a specific wavelength. This device is engineered for pulse operation, making it suitable for data transmission, remote control systems, proximity sensing, and other scenarios where rapid on/off switching is critical. The package features a blue transparent resin, which is typical for IR emitters as it allows the infrared light to pass through while being opaque to visible light, reducing interference.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed.

• Power Dissipation (P_D): 200 mW. This is the maximum total power the device can dissipate as heat under any operating condition. Exceeding this limit risks thermal runaway and failure.
• Peak Forward Current (I_FP): 2 A. This is the maximum allowable current for pulsed operation, specified under very specific conditions: a pulse width of 10 microseconds (μs) and a duty cycle of 0.1% (100 pulses per second). This high current capability enables very high instantaneous optical output.
• Continuous Forward Current (I_F): 100 mA. This is the maximum DC current that can be applied continuously. The significant difference between peak and continuous current highlights the device's optimization for pulsed, not constant, illumination.
• Reverse Voltage (V_R): 5 V. Applying a reverse voltage higher than this can break down the semiconductor junction.
• Operating & Storage Temperature: The device is rated for industrial temperature ranges: -40°C to +85°C for operation, and -55°C to +100°C for storage. This ensures reliability in harsh environments.
• Lead Soldering Temperature: 260°C for 5 seconds, measured 1.6mm from the package body. This is a standard rating for wave or reflow soldering processes.

2.2 Electrical & Optical Characteristics

These parameters are measured under standard test conditions (T_A = 25°C) and define the device's typical performance.

• Radiant Intensity (I_E): 35 mW/sr (Min), 75 mW/sr (Typ) at I_F = 50mA. This measures the optical power emitted per unit solid angle (steradian). The high typical value indicates a powerful output, suitable for long-range or low-receiver-sensitivity applications.
• Peak Emission Wavelength (λ_P): 880 nm (Typ). This is the wavelength at which the emitter outputs the most optical power. It falls within the near-infrared spectrum, which is commonly used in consumer electronics (e.g., TV remotes) and is efficiently detected by silicon photodiodes.
• Spectral Line Half-Width (Δλ): 50 nm (Max). This parameter indicates the spectral bandwidth; a value of 50nm means the emitted light's intensity is at least half its peak value across an 880nm ± 25nm range. A narrower bandwidth would be more monochromatic.
• Forward Voltage (V_F): 1.5V (Min), 1.75V (Typ), 2.1V (Max) at I_F = 350mA (pulsed). This is the voltage drop across the diode when conducting. It is crucial for designing the driving circuit's voltage supply and current-limiting resistor.
• Reverse Current (I_R): 100 μA (Max) at V_R = 5V. This is the small leakage current that flows when the diode is reverse-biased within its maximum rating.
• Rise/Fall Time (T_r/T_f): 40 nS (Typ). This is the time it takes for the optical output to rise from 10% to 90% of its maximum value (rise time) or fall from 90% to 10% (fall time) in response to a step change in current. The 40ns specification confirms its "high speed" capability, enabling data transmission rates into the megahertz range.
• Viewing Angle (2θ_1/2): 16° (Typ). This is the full angle at which the radiant intensity drops to half of its value at the center (0°). A 16° angle is relatively narrow, producing a more focused beam compared to wide-angle emitters, which is beneficial for directed communication or sensing.

3. Performance Curve Analysis

While the PDF references typical characteristic curves, their specific data can be interpreted based on the provided parameters. The curves would typically illustrate the relationship between forward current (I_F) and forward voltage (V_F), which is exponential in nature. They would also show the relative radiant intensity versus forward current, which is generally linear at lower currents but may saturate at higher currents due to thermal effects. The temperature dependence of both V_F (which decreases with temperature) and radiant intensity (which also typically decreases with increasing junction temperature) would be critical for understanding performance under non-ambient conditions. The spectral distribution curve would show a peak at approximately 880nm with a Gaussian-like shape, tapering off to half-power points roughly 25nm on either side of the peak.

4. Mechanical & Packaging Information

4.1 Package Dimensions

The device uses a standard through-hole package, commonly known as a T-1¾ (5mm) package. Key dimensional notes include:

• All dimensions are in millimeters, with a general tolerance of ±0.25mm unless specified otherwise.
• A maximum resin protrusion of 1.5mm under the flange is allowed.
• Lead spacing is measured at the point where the leads exit the package body, which is critical for PCB layout.
• The blue transparent package material is epoxy resin, which is molded to provide mechanical strength and environmental protection.

4.2 Polarity Identification

For this package type, the cathode (negative lead) is typically identified by a flat spot on the rim of the package or by the shorter lead. The anode (positive lead) is the longer lead. Correct polarity must be observed during circuit assembly to prevent damage.

5. Soldering & Assembly Guidelines

The absolute maximum rating for lead soldering is 260°C for 5 seconds, measured 1.6mm from the package body. This is compatible with standard wave soldering and reflow profiles. It is crucial to avoid excessive thermal stress. Prolonged exposure to high temperature or heating the package body directly can crack the epoxy resin or damage the semiconductor die. When hand soldering, use a temperature-controlled iron and minimize contact time. Follow standard ESD (Electrostatic Discharge) precautions during handling and assembly, as the semiconductor junction is sensitive to static electricity.

6. Packaging & Ordering Information

The datasheet indicates the device is supplied on a reel for automated assembly, with a separate diagram provided for the reel package dimensions. The part number LTE-7477LM1-TA follows a manufacturer-specific coding system. The "TA" suffix often denotes tape-and-reel packaging. Designers should confirm the exact reel specifications (e.g., quantity per reel, reel diameter, tape width) with the distributor or manufacturer for production planning.

7. Application Suggestions

7.1 Typical Application Scenarios

• Infrared Data Transmission: Ideal for IrDA-compliant or proprietary serial data links (e.g., remote controls, short-range device-to-device communication) due to its high speed (40ns rise/fall) and high pulsed current capability.
• Proximity & Object Sensing: Used in pairs with an IR detector for object detection, counting, or level sensing in appliances, industrial equipment, and consumer electronics.
• Optical Switches & Encoders: Suitable for interruptive or reflective optical encoders where a pulsed IR beam is modulated.
• Security Systems: Can be used in infrared beam barriers for intrusion detection.

7.2 Design Considerations

• Drive Circuit: A current-limiting resistor is mandatory when driving with a voltage source. For pulsed operation, calculate the resistor value based on the supply voltage (V_CC), the desired pulse current (I_FP ≤ 2A), and the forward voltage (V_F ≈ 1.75V). Use the formula: R = (V_CC - V_F) / I_F. For high-speed switching, a transistor (BJT or MOSFET) driver is necessary to achieve fast current rise times.
• Thermal Management: Although rated for pulsed operation, the average power dissipation must not exceed 200mW. For high-duty-cycle pulses, consider the average current and resulting power. The device's radiant output decreases with increasing junction temperature.
• Optical Design: The narrow 16° viewing angle provides directionality. Lenses or reflectors can be used to further collimate or shape the beam for specific applications. Ensure the receiver (photodiode or phototransistor) is sensitive to the 880nm wavelength.
• Ambient Light Immunity: In sensing applications, modulation of the IR signal (e.g., with a specific frequency) and synchronous detection at the receiver are essential to reject interference from ambient light sources like sunlight or incandescent bulbs, which also contain IR components.

8. Technical Comparison & Differentiation

The LTE-7477LM1-TA differentiates itself primarily through its combination of high speed and high power in a standard package. Many IR emitters optimize for one characteristic at the expense of the other. A standard remote-control LED might have a similar viewing angle and wavelength but a much lower permissible pulsed current (e.g., 100mA) and slower rise time. Conversely, a high-power IR LED for illumination might handle higher continuous current but have much slower response times. This device sits in a niche suitable for high-speed, medium-range data links or pulsed sensing systems requiring strong signal strength.

9. Frequently Asked Questions (FAQs)

Q: Can I drive this LED with a continuous 100mA current?

A: Yes, according to the Absolute Maximum Ratings, 100mA is the maximum continuous forward current. However, for optimal lifetime and stable output, operating at a lower current (e.g., 50-75mA) is recommended unless the high output is necessary.

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

A: Radiant Intensity is angular-dependent—it measures power per solid angle. Total Radiant Flux (power in mW) would be the intensity integrated over the entire emission solid angle. For a narrow-angle emitter like this, the total flux can be estimated but is not directly provided.

Q: How do I achieve the 2A pulse current?

A: You need a driver circuit capable of sourcing this high current for a very short duration (10μs). A simple resistor from a voltage rail may not suffice due to parasitic inductance. A dedicated LED driver IC or a transistor switch with a low-impedance path and a carefully calculated current-limiting resistor or constant-current circuit is required. Ensure the power supply can deliver the peak current without sagging.

Q: Why is the package blue?

A> The blue dye in the epoxy resin acts as a visible light filter. It is transparent to the 880nm infrared light but blocks most visible light. This reduces the amount of visible light emitted, which is often desirable to make the emitter less noticeable and to prevent interference from ambient visible light in the receiver.

10. Practical Design Case

Scenario: Designing a short-range, high-speed serial data link with a range of 2 meters in an indoor environment.

Design Steps:

1. Driver Circuit: Use a microcontroller GPIO pin to control an N-channel MOSFET. The source of the MOSFET connects to ground. The drain connects to the cathode of the LTE-7477LM1-TA. The anode connects to a current-limiting resistor, which then connects to a 5V supply rail.

2. Resistor Calculation: For a target pulse current of 1A (well below the 2A max for safety margin), and assuming a typical V_F of 1.75V at this current (consult typical curves if available), the resistor value is R = (5V - 1.75V) / 1A = 3.25Ω. Use a standard 3.3Ω, 1W resistor (power during pulse: P = I²R = 1² * 3.3 = 3.3W, but average power at 0.1% duty cycle is only 3.3mW).

3. Layout: Keep the drive loop (5V -> resistor -> LED -> MOSFET -> GND) as small as possible to minimize parasitic inductance, which can slow down the rise time and cause voltage spikes.

4. Receiver: Pair with a high-speed silicon photodiode or phototransistor with a matching 880nm peak sensitivity. Use a transimpedance amplifier circuit to convert the photocurrent back into a voltage signal.

5. Modulation: Implement a simple modulation scheme (e.g., 38kHz carrier) to distinguish the signal from background IR noise. The 40ns rise/fall time of the emitter easily supports this frequency.

11. Operational Principle

An infrared emitter is a semiconductor diode. When forward-biased (positive voltage applied to the anode relative to the cathode), electrons from the n-type region and holes from the p-type region are injected into the active region. When these charge carriers recombine, they release energy. In this specific material system (typically based on Aluminum Gallium Arsenide - AlGaAs), this energy is released primarily as photons in the near-infrared spectrum, with a peak wavelength around 880 nanometers. The intensity of the emitted light is directly proportional to the rate of carrier recombination, which is controlled by the forward current. The blue package acts as a wavelength-selective filter.

12. Technology Trends

Infrared emitter technology continues to evolve. Trends include the development of devices with even faster rise/fall times for higher data rate communication (e.g., for Li-Fi or advanced optical sensing). There is also a push for higher wall-plug efficiency (more light output per electrical watt input) to reduce power consumption in battery-operated devices. Integration is another trend, with emitters being combined with drivers, modulators, or even detectors into single modules or ICs to simplify system design. Furthermore, emitters at different wavelengths (e.g., 940nm, which is less visible to some CMOS image sensors, or 850nm for surveillance cameras) are being optimized for specific application ecosystems.