HSDL-4261 IR Emitter Datasheet - 870nm Wavelength - 1.4V Forward Voltage - 190mW Power Dissipation - English Technical Document

1. Product Overview

The HSDL-4261 is a discrete infrared emitter component designed for applications requiring high-speed optical data transmission. It utilizes AlGaAs (Aluminum Gallium Arsenide) LED technology to produce infrared light at a peak wavelength of 870 nanometers. This device is characterized by its fast switching capabilities, making it suitable for digital communication interfaces.

1.1 Core Advantages

• High-Speed Operation: Features a typical optical rise and fall time of 15 nanoseconds, enabling data transmission in high-bandwidth applications.
• High Optical Power: Delivers high radiant intensity, providing a strong signal for reliable infrared communication.
• RoHS Compliant: Manufactured as a lead-free product, complying with environmental regulations.
• Clear Package: Housed in a transparent color package that does not filter the emitted infrared light.

1.2 Target Applications

• Industrial Infrared Equipment
• Infrared Portable Instruments
• Consumer Electronics (e.g., optical mice)
• High-Speed Infrared Communications (e.g., IR LANs, modems, dongles)

2. In-Depth Technical Parameter Analysis

All specifications are defined at an ambient temperature (TA) of 25°C unless otherwise stated.

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.

• Continuous Forward Current (IFDC): 100 mA maximum.
• Peak Forward Current (IFPK): 500 mA maximum, under pulsed conditions (Duty Factor=20%, Pulse Width=100µs).
• Power Dissipation (PDISS): 190 mW maximum. Must be derated with increasing ambient temperature as shown in the characteristic curves.
• Reverse Voltage (VR): 5 V maximum.
• Storage Temperature Range (TS): -40°C to +100°C.
• Operating Temperature Range (TO): -40°C to +85°C.
• Junction Temperature (TJ): 110°C maximum.
• Lead Soldering Temperature: 260°C for a maximum of 5 seconds, with the iron tip no closer than 1.6mm from the package body.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters under specified test conditions.

• Radiant Optical Power (Po): Typically 9 mW at IF=20mA and 45 mW at IF=100mA.
• Radiant On-Axis Intensity (IE): Typically 36 mW/sr at IF=20mA and 180 mW/sr at IF=100mA.
• Peak Emission Wavelength (λPeak): 870 nm typical (range: 850 nm to 890 nm) at IF=20mA.
• Spectral Line Half-Width (Δλ): Approximately 47 nm at IF=20mA.
• Forward Voltage (Vf): Typically 1.4 V at IF=20mA and 1.7 V at IF=100mA.
• Forward Voltage Temperature Coefficient (△V/△T): Approximately -1.5 mV/°C at IF=20mA.
• Viewing Angle (2θ1/2): 26 degrees typical, defining the angular spread of the emitted radiation.
• Intensity Temperature Coefficient (△IE/△T): Approximately -0.22 %/°C at IF=100mA, indicating a decrease in output with rising temperature.
• Wavelength Temperature Coefficient (△λ/△T): Approximately +0.18 nm/°C at IF=20mA.
• Optical Rise/Fall Time (Tr/Tf): 15 ns typical, measured from 10% to 90% of the optical output.
• Series Resistance (RS): Typically 4.1 Ohms at IF=100mA.
• Diode Capacitance (CO): Typically 80 pF at 0V bias and 1 MHz.
• Thermal Resistance (RθJA): Typically 280 °C/W from the junction to the ambient via the pins.

3. Performance Curve Analysis

The datasheet provides several graphs illustrating key relationships.

3.1 Forward Current vs. Relative Radiant Intensity

This curve shows that the optical output intensity increases super-linearly with forward current, especially at higher currents. It highlights the importance of current drive for achieving desired brightness.

3.2 Forward Voltage vs. Forward Current

The IV characteristic curve demonstrates the typical exponential relationship for a diode. The forward voltage increases with current and is also temperature-dependent.

3.3 Forward Voltage vs. Ambient Temperature

This graph shows the negative temperature coefficient of the forward voltage. At a constant current, Vf decreases as temperature increases, which is a critical consideration for constant-voltage drive circuits.

3.4 DC Forward Current Derating vs. Ambient Temperature

This is a crucial graph for reliability. It defines the maximum permissible continuous forward current as a function of the ambient temperature. As temperature rises, the maximum allowed current must be reduced to prevent the junction temperature from exceeding its 110°C limit. For example, at 85°C, the maximum DC current is significantly lower than at 25°C.

3.5 Radiation Pattern

The polar diagram illustrates the spatial distribution of the emitted infrared light. The HSDL-4261 has a typical viewing angle of 26 degrees (full width at half maximum), resulting in a moderately focused beam suitable for directed communication links.

4. Mechanical & Packaging Information

4.1 Outline Dimensions

The device is a standard through-hole LED package. Key dimensions include the lead spacing, body diameter, and overall height. The leads are designed to be formed at a point at least 3mm from the base of the lens. A minimum protrusion of resin under the flange is specified. All dimensional tolerances are typically ±0.25mm unless otherwise noted.

4.2 Polarity Identification

The component uses standard LED polarity marking. The longer lead typically denotes the anode (positive connection), while the shorter lead is the cathode (negative connection). This must be verified during assembly to ensure correct operation.

5. Soldering & Assembly Guidelines

5.1 Storage Conditions

For long-term storage, the ambient should not exceed 30°C or 70% relative humidity. If removed from the original moisture-barrier bag, components should be used within three months. For extended storage outside the original packaging, use a sealed container with desiccant or a nitrogen-filled desiccator.

5.2 Cleaning

If cleaning is necessary, use only alcohol-based solvents such as isopropyl alcohol. Harsh chemicals should be avoided.

5.3 Lead Forming

Bending must be performed at room temperature and before soldering. The bend should be made at least 3mm from the base of the LED lens. The package body should not be used as a fulcrum during bending to avoid damaging the internal die attach or wire bonds.

5.4 Soldering Parameters

Hand Soldering (Iron): Maximum temperature 260°C for a maximum of 5 seconds per lead. The iron tip must be no closer than 1.6mm from the base of the epoxy lens.
Wave Soldering: Pre-heat to a maximum of 100°C for up to 60 seconds. The solder wave temperature should be a maximum of 260°C with a contact time of 5 seconds. The device should be dipped no lower than 2mm from the base of the epoxy bulb.
Important: Dipping the lens into solder must be avoided. IR reflow soldering is not suitable for this through-hole package type. Excessive temperature or time can cause lens deformation or catastrophic failure.

6. Application Design Considerations

6.1 Drive Circuit Design

LEDs are current-operated devices. To ensure uniform brightness when driving multiple LEDs in parallel, it is strongly recommended to use an individual current-limiting resistor in series with each LED. Connecting LEDs directly in parallel without individual resistors is not advised due to variations in their forward voltage (Vf) characteristics, which can lead to significant current imbalance and uneven brightness.

6.2 Thermal Management

Given the thermal resistance (RθJA) of 280°C/W, power dissipation must be carefully managed. Operating at the maximum continuous current (100mA) with a typical Vf of 1.7V results in 170mW of power dissipation. This would cause a junction temperature rise of approximately 47.6°C above ambient (170mW * 280°C/W). At an ambient of 85°C, the junction would reach 132.6°C, exceeding the maximum rating of 110°C. Therefore, the derating curve in Figure 6 must be strictly followed.

6.3 Electrostatic Discharge (ESD) Protection

This component is susceptible to damage from electrostatic discharge. Recommended handling precautions include:
- Using a grounded wrist strap or anti-static gloves.
- Ensuring all equipment, workstations, and storage racks are properly grounded.
- Using an ionizer to neutralize static charge that may build up on the plastic lens during handling.

6.4 Optical Design

The 26-degree viewing angle and 870nm wavelength should be matched with an appropriate photodetector (e.g., a PIN photodiode with a matching spectral response). For optimal range and signal integrity, consider using lenses or apertures to collimate or focus the beam, especially in directed communication links. The clear package allows for external optical elements without intrinsic filtering.

7. Technical Comparison & Differentiation

The HSDL-4261 positions itself within the infrared emitter market through specific combinations of parameters:
Speed vs. Power: It offers a balance between high-speed switching (15ns) and relatively high optical power output (45mW typ. at 100mA). Some emitters may be faster with lower power, or higher power with slower response.
Wavelength: The 870nm peak wavelength is a common standard for many infrared data links and remote control systems, offering a good balance between silicon photodetector sensitivity and lower ambient light noise compared to visible or near-visible wavelengths.
Package: The standard through-hole package makes it suitable for both prototyping and applications where wave soldering is used, differentiating it from surface-mount alternatives which require reflow processes.

8. Frequently Asked Questions (FAQs)

8.1 Can I drive this LED with a constant voltage source?

It is not recommended. The exponential I-V characteristic of an LED means that a small change in voltage causes a large change in current, which can easily exceed the maximum rating if driven directly from a voltage source. Always use a series resistor or a constant current driver to set the operating point.

8.2 Why does the output intensity decrease with temperature?

The negative temperature coefficient of radiant intensity (-0.22%/°C) is a fundamental property of the semiconductor material. As temperature increases, non-radiative recombination processes within the semiconductor become more dominant, reducing the efficiency of light generation.

8.3 What is the purpose of the derating curve?

The derating curve (Fig. 6) is essential for ensuring long-term reliability. It prevents the LED junction temperature from exceeding its maximum rated value (110°C) by limiting the power dissipation (and thus the forward current) as the ambient temperature increases. Ignoring this curve can lead to rapid degradation and failure.

8.4 Is this LED suitable for continuous operation?

Yes, but within the limits defined by the Absolute Maximum Ratings and the derating curve. For continuous DC operation, the forward current must not exceed 100mA at 25°C ambient and must be reduced at higher ambient temperatures as per Fig. 6. For pulsed operation with high peak currents, the duty cycle and pulse width specifications must be adhered to.

9. Practical Application Example

Scenario: Designing a simple IR data transmitter for short-range serial communication.
1. Circuit Design: Use a microcontroller GPIO pin to drive the LED. Place a current-limiting resistor in series with the LED's anode. Calculate the resistor value using R = (Vcc - Vf_LED) / I_desired. For a 3.3V supply, a desired current of 50mA, and a typical Vf of 1.5V: R = (3.3V - 1.5V) / 0.05A = 36 Ohms. Use the next standard value (e.g., 39 Ohms).
2. Thermal Check: Power dissipation in the LED: P = Vf * I = 1.5V * 0.05A = 75mW. Junction temp rise: ΔTj = P * RθJA = 0.075W * 280°C/W = 21°C. At a maximum ambient of 85°C, Tj = 106°C, which is below the 110°C limit.
3. Software: Configure the microcontroller to generate the desired digital modulation (e.g., On-Off Keying) on the GPIO pin. The 15ns rise/fall time of the LED allows for high data rates.
4. Layout: Keep the LED and its series resistor close to the driving pin to minimize parasitic inductance. Ensure the receiver (photodiode) is aligned within the 26-degree viewing angle of the emitter.

10. Operating Principle

The HSDL-4261 is a semiconductor p-n junction diode based on AlGaAs materials. When a forward bias voltage is applied, electrons from the n-region and holes from the p-region are injected across the junction into the opposite regions. These injected minority carriers recombine with majority carriers. In a direct bandgap semiconductor like AlGaAs, a significant portion of these recombinations are radiative, meaning they release energy in the form of photons. The specific energy bandgap of the AlGaAs alloy used determines the wavelength of the emitted photons, which in this case is centered around 870nm in the infrared spectrum. The clear epoxy package encapsulates the semiconductor chip, provides mechanical protection, and acts as a lens to shape the output beam.

11. Industry Trends

Infrared emitters continue to evolve in several key areas relevant to components like the HSDL-4261:
Increased Speed: Demand for higher data rates in optical wireless communication (Li-Fi, high-speed IRDA) drives development of emitters with even faster rise/fall times.
Enhanced Efficiency: Improvements in epitaxial growth and chip design aim to produce more optical power (lumens or radiant flux) per unit of electrical input power (watts), reducing heat generation and improving system efficiency.
Integration: There is a trend towards integrating the emitter with driver circuitry or even with a photodetector in a single package to create complete optical transceiver modules, simplifying end-user design.
New Wavelengths: While 870-940nm remains standard for silicon-based receivers, there is research into other wavelengths for specific applications like gas sensing or eye-safe LiDAR.