Infineon BCR35PN: A Comprehensive Technical Overview and Application Note
The Infineon BCR35PN is a monolithic integrated linear constant current sink housed in a compact SOT-223 package. Designed primarily for driving high-power LEDs, it provides a robust and efficient solution for applications requiring stable and reliable current regulation. By integrating the current setting resistor and other protective features on a single chip, it significantly reduces external component count, saves board space, and enhances overall system reliability.
Technical Deep Dive
At its core, the BCR35PN is a three-terminal device (Input, Output, and Reference) that functions as a precise current regulator. Its key electrical characteristics define its performance:
Adjustable Output Current: The output current is easily set using a single external resistor ($R_{SET}$) connected between the Reference and Output pins. The current can be adjusted from a few milliamps up to a typical maximum of 35 mA, making it suitable for a wide range of LED currents.
Wide Operating Voltage Range: It operates with a supply voltage ($V_{CE}$) ranging from 8 V to 40 V. This wide range allows it to handle significant voltage fluctuations, such as those found in automotive applications, and enables the driving of long LED strings.
Low Drop-Out Voltage: The device features a low typical saturation voltage of 0.5 V at 20 mA. This low drop-out voltage minimizes power dissipation within the regulator itself, leading to higher efficiency and reduced heat generation.
Integrated Protections: The BCR35PN is engineered for durability. It includes built-in over-temperature protection, which shuts down the output current if the junction temperature exceeds a safe threshold (~160 °C), automatically restarting once the device cools. It also offers high ESD protection (4 kV HBM), safeguarding it against electrostatic discharge during handling and operation.
Key Application Circuits
1. Basic Constant Current LED Driver: The most straightforward application involves connecting the anode of an LED string to the positive supply rail ($V_{Supply}$). The cathode of the string is connected to the Input pin. The external set resistor ($R_{SET}$) is connected between the Reference and Output pins, with the Output pin tied to ground. The value of $R_{SET}$ (in kΩ) determines the current: $I_{OUT} \approx \frac{0.55V}{R_{SET}}$. This simple setup is perfect for backlighting and architectural lighting.
2. Parallel Configurations for Higher Current: For applications requiring more than 35 mA, multiple BCR35PN devices can be connected in parallel. Each regulator maintains its own defined current, ensuring an even and stable distribution of current across several LED strings without the risk of current hogging by a single LED. This is a significant advantage over simple resistor-based driving.
3. PWM Dimming Control: The BCR35PN is highly compatible with PWM dimming for brightness control. A PWM signal can be applied to the Reference pin via a transistor or logic gate. Pulling this pin to ground effectively turns the current sink off, allowing for a wide dimming range and negligible color shift in the LEDs, which is critical for high-quality lighting.
Design Considerations and Advantages
Thermal Management: Despite its efficiency, power dissipation ($P_D = V_{CE} \times I_{OUT}$) must be calculated. The SOT-223 package offers a low thermal resistance junction-to-ambient ($R_{thJA}$) of ~100 K/W when mounted on a standard FR4 PCB with a small copper area. Ensuring adequate PCB copper pour for heat sinking is crucial for maintaining performance and longevity.
Advantages over Alternatives: Compared to a simple current-limiting resistor, the BCR35PN provides immunity to supply voltage variations and stable current over a wide temperature range, ensuring consistent LED brightness. Compared to a discrete BJT/MOSFET solution, it offers a more compact, simplified, and reliable design with integrated protection.
Conclusion
The Infineon BCR35PN is an exceptionally versatile and robust constant current sink that simplifies the design of reliable LED driving circuits. Its integration of critical functions, wide operating range, and built-in protections make it an ideal choice for industrial, automotive, and consumer lighting applications where performance and stability are paramount. Its ability to be easily adjusted, paralleled, and dimmed provides designers with a powerful component for creating advanced lighting systems.
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Keywords:
1. Constant Current Sink
2. LED Driver
3. PWM Dimming
4. Thermal Management
5. Integrated Circuit Protection
