HSDL-4260 Infrared LED Datasheet - T-1 3/4 Package - 875nm Wavelength - 100mA Forward Current - English Technical Document

1. Product Overview

The HSDL-4260 is a high-performance infrared light-emitting diode (LED) designed for applications requiring fast response times and reliable optical output. It utilizes AlGaAs (Aluminum Gallium Arsenide) technology, which is known for its efficiency and stability in the infrared spectrum. The primary function of this component is to emit infrared light at a peak wavelength of 875 nanometers (nm), which is invisible to the human eye but highly effective for various sensing and communication systems.

The core advantages of this LED include its high-speed capability, with rise and fall times as low as 40 nanoseconds (ns), enabling it to be used in data transmission and fast-switching applications. Its compact T-1 3/4 package makes it suitable for space-constrained designs. The target markets for this device are diverse, encompassing industrial infrared equipment, portable infrared instruments, consumer electronics such as optical mice and remote controllers, and high-speed infrared communication systems like IR LANs, modems, and dongles.

2. In-Depth Technical Parameter Analysis

2.1 Electrical Characteristics

The electrical parameters define the operating boundaries and performance under specific conditions, measured at an ambient temperature of 25°C. The forward voltage (VF) is a critical parameter, typically ranging from 1.4V to 1.9V at a forward current (IF) of 20mA, and from 1.7V to 2.3V at 100mA. This indicates the voltage drop across the LED when it is conducting. The series resistance (RS) is specified at 4 ohms (typical) at 100mA, which influences the current-voltage relationship and power dissipation. The diode capacitance (CO) is 70 picofarads (pF) maximum at 0V and 1 MHz, a factor important for high-frequency switching applications. The reverse voltage (VR) rating is 4V maximum, beyond which the LED junction may break down.

2.2 Optical Characteristics

The optical performance is central to the LED's function. The radiant on-axis intensity (IE) is between 150 and 200 milliwatts per steradian (mW/Sr) at 100mA, quantifying the optical power emitted within a specific solid angle along the central axis. The viewing angle (2θ1/2) is 15 degrees, defining the angular spread where the radiant intensity drops to half of its peak value. The peak wavelength (λpk) is 875nm, with a spectral width (full width at half maximum, FWHM) of 45nm, describing the range of wavelengths emitted. The temperature coefficient for radiant intensity is -0.36% per °C, indicating a decrease in output with increasing temperature.

2.3 Thermal and Absolute Maximum Ratings

These ratings specify the limits beyond which permanent damage may occur. The absolute maximum forward current (IFDC) is 100mA continuously. A peak forward current (IFPK) of 500mA is allowed under pulsed conditions (20% duty cycle, 100µs pulse width). The maximum power dissipation (PDISS) is 230mW. The storage temperature range is from -40°C to 100°C. Crucially, the maximum LED junction temperature (TJ) is 110°C. The thermal resistance from junction to ambient (RθJA) is 300°C/W, a key parameter for calculating the junction temperature rise based on power dissipation. The recommended operating temperature range is from -40°C to 85°C.

3. Performance Curve Analysis

3.1 V-I (Voltage-Current) Characteristic

Figure 2 in the datasheet illustrates the relationship between forward voltage (Vf) and forward current (If). This curve is non-linear, typical for diodes. At low currents, the voltage increases gradually. As the current approaches the typical operating range (e.g., 20mA to 100mA), the curve becomes steeper, reflecting the series resistance. This graph is essential for designing the current-limiting circuitry to ensure the LED operates within its specified voltage range.

3.2 Spectral Distribution

Figure 1 shows the relative radiant intensity versus wavelength. The curve peaks at 875nm. The spectral width (Δλ) of 45nm (FWHM) is visible as the width of this peak at half its maximum height. This information is vital for applications sensitive to specific wavelengths, such as matching with photodetector sensitivity or avoiding interference from ambient light sources.

3.3 Temperature Dependence

Figure 4 depicts the forward voltage change with ambient temperature for two current levels (20mA and 100mA). The forward voltage has a negative temperature coefficient, meaning it decreases as temperature increases (approximately -1.3 mV/°C at 100mA). Figure 6 shows the derating curve for maximum permissible DC forward current versus ambient temperature. To keep the junction temperature below 110°C, the maximum allowed continuous current must be reduced as the ambient temperature rises. For example, at 85°C, the maximum current is significantly lower than at 25°C.

3.4 Radiant Intensity vs. Current and Radiation Pattern

Figure 5 plots relative radiant intensity against DC forward current. The output is generally proportional to current but may exhibit some non-linearity at very high currents due to heating effects. Figure 7 is the radiation (polar) diagram, graphically representing the spatial distribution of emitted light. The 15-degree viewing angle is clearly shown, with intensity dropping to 50% of the on-axis value at approximately ±7.5 degrees from the center.

4. Mechanical and Packaging Information

The device is housed in a standard T-1 3/4 (5mm) radial leaded package. The package dimensions are provided in the datasheet with all measurements in millimeters. Key notes include: a tolerance of ±0.25mm unless specified otherwise, a maximum protrusion of resin under the flange of 1.5mm, and lead spacing measured at the point where leads exit the package body. The package provides mechanical protection and aids in heat dissipation. The leads are typically made of a solderable material like tin-plated copper.

5. Soldering and Assembly Guidelines

The datasheet specifies a critical soldering parameter: the lead soldering temperature must not exceed 260°C for a duration of 5 seconds, measured at a distance of 1.6mm (0.063 inches) from the package body. This is to prevent thermal damage to the internal semiconductor die and wire bonds. For wave or reflow soldering, standard profiles for through-hole components should be followed, ensuring the peak temperature and time above liquidus do not exceed the specified limit. Proper handling to avoid electrostatic discharge (ESD) is recommended, although not explicitly stated, as it is a good practice for semiconductor devices.

6. Application Suggestions

6.1 Typical Application Scenarios

• Infrared Remote Controls: The 875nm wavelength is commonly used in consumer IR protocols. The high speed allows for efficient data encoding.
• Optical Mice: Used as the light source to illuminate the surface. The fast response time helps in tracking rapid movements.
• Infrared Data Links (IR LANs, Dongles): The 40ns rise/fall time enables high data rate transmission for short-range wireless communication.
• Industrial Sensors: Used in proximity sensors, object detection, and encoders where reliable infrared emission is required.
• Portable Instruments: Suitable for battery-powered devices due to its relatively low forward voltage.

6.2 Design Considerations

• Current Driving: Always use a series current-limiting resistor or a constant current driver to prevent exceeding the maximum forward current, especially considering the negative temperature coefficient of Vf.
• Heat Management: For continuous operation at high currents or elevated ambient temperatures, consider the thermal derating curve (Fig. 6). Adequate PCB copper area or a heatsink may be necessary to keep the junction temperature below 110°C.
• Optical Design: The 15-degree viewing angle is relatively narrow. Lenses or diffusers may be needed to shape the beam for specific applications. Ensure the receiver (photodiode/phototransistor) is sensitive to the 875nm wavelength.
• Circuit Layout: For high-speed communication applications, minimize parasitic capacitance and inductance in the drive circuit to preserve the fast switching characteristics.

7. Technical Comparison and Differentiation

While many infrared LEDs exist, the HSDL-4260 differentiates itself through its combination of parameters. Compared to standard low-speed IR LEDs used in simple remote controls, it offers significantly faster switching (40ns vs. hundreds of ns), making it unsuitable only for simple on/off signaling but for pulsed data transmission. Its AlGaAs technology typically offers better efficiency and temperature stability than older GaAs technologies. The T-1 3/4 package is a common industry standard, ensuring easy sourcing and compatibility with existing optical assemblies, compared to surface-mount alternatives which might offer smaller size but different thermal and assembly challenges.

8. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED directly from a 5V or 3.3V microcontroller pin?

A: No. The typical forward voltage is around 1.9V at 20mA. Connecting it directly to a 5V source without a current-limiting resistor would cause excessive current flow, potentially destroying the LED. A series resistor must be calculated based on the supply voltage (Vcc), LED forward voltage (Vf), and desired current (If): R = (Vcc - Vf) / If.

Q: What is the difference between radiant intensity (mW/Sr) and luminous intensity?

A> Radiant intensity measures optical power (in watts) per solid angle, applicable to all wavelengths. Luminous intensity weights this power by the human eye's sensitivity (photopic curve) and is measured in candelas (cd). Since this is an infrared LED (invisible light), luminous intensity is not a relevant metric; radiant intensity is used.

Q: How do I interpret the derating graph (Fig. 6)?

A> The graph shows the maximum safe continuous DC current you can use at a given ambient temperature (Ta) to ensure the junction temperature (Tj) does not exceed 110°C. For example, at Ta=25°C, you can use up to 100mA. At Ta=85°C, the graph shows the maximum current is lower (e.g., approximately 60-70mA, depending on exact reading). You must operate below this line.

Q: Why does the forward voltage decrease with temperature?

A> This is a characteristic of the semiconductor bandgap in AlGaAs materials. As temperature increases, the bandgap energy decreases slightly, requiring a lower voltage to achieve the same current through the diode junction.

9. Practical Design and Usage Case

Case: Designing a Simple Infrared Transmitter for Data.

Objective: Transmit a 38kHz modulated signal for a remote control.

Design Steps:

1. Driver Circuit: Use a transistor (e.g., NPN) as a switch. The microcontroller generates the 38kHz digital signal to the transistor's base. The LED is placed in the collector circuit with a current-limiting resistor connected to Vcc (e.g., 5V).

2. Current Calculation: Choose an operating current, say 50mA for good intensity. With Vf ~1.7V (from datasheet at ~50mA, interpolating), and Vcc=5V, the resistor value R = (5V - 1.7V) / 0.05A = 66 ohms. Use a standard 68-ohm resistor.

3. Thermal Check: Power dissipation in LED: Pd = Vf * If = 1.7V * 0.05A = 85mW. For pulsed operation (50% duty cycle for 38kHz carrier), average power is lower. At room temperature, this is well within limits.

4. Layout: Keep the drive transistor and resistor close to the LED to minimize loop area and noise.

10. Principle Introduction

An infrared LED is a semiconductor p-n junction diode. When forward biased (positive voltage applied to the p-side relative to the n-side), electrons from the n-region and holes from the p-region are injected into the junction region. When these charge carriers recombine, they release energy. In materials like AlGaAs, this energy is released primarily as photons (light) rather than heat. The specific wavelength of the emitted light (875nm in this case) is determined by the bandgap energy of the semiconductor material, which is engineered during the crystal growth process. The fast switching speed (40ns) is achieved by minimizing the parasitic capacitance of the package and the semiconductor structure and by using materials that allow rapid carrier recombination.

11. Development Trends

The field of infrared optoelectronics continues to evolve. Trends relevant to devices like the HSDL-4260 include:

Increased Efficiency: Ongoing material research aims to produce LEDs with higher wall-plug efficiency (optical power out / electrical power in), leading to brighter output or lower power consumption for battery-operated devices.

Higher Speed: Demand for faster data transmission in consumer electronics (e.g., Li-Fi, high-speed IR data links) drives the development of LEDs with sub-nanosecond rise times.

Miniaturization: While the T-1 3/4 package remains popular, there is a strong trend toward surface-mount device (SMD) packages (e.g., 0805, 0603, chip-scale) for automated assembly and smaller form factors.

Integration: Combining the LED with a driver IC, photodetector, or lens into a single module simplifies system design for end-users.

Wavelength Specificity: Development of LEDs with narrower spectral bandwidths for applications requiring precise wavelength matching, such as gas sensing or biomedical instrumentation.