BTS428L2 Power Switch: Features, Application Circuit, and Design Considerations
The BTS428L2 from Infineon Technologies is a versatile and robust PROFET™ (Protected MOSFET) high-side power switch, designed to control a wide range of resistive and inductive loads in automotive and industrial applications. Integrating a protective feature set with a powerful N-channel MOSFET, it simplifies design, enhances reliability, and reduces board space.
Key Features of the BTS428L2
The device's appeal lies in its comprehensive integration of power switching and protection. Its standout features include:
High Current Capability: It can handle a continuous current of up to 7.5 A, making it suitable for driving demanding loads like motors, heaters, and lamps.
Low Standby Current: With a typical quiescent current of just 5 µA, it is ideal for automotive applications where low power consumption in sleep or standby mode is critical for meeting overall system energy demands.
Advanced Protection Functions: The BTS428L2 is renowned for its robust integrated protection. This includes overload protection, short-circuit protection, over-voltage protection (including load-dump), over-temperature protection, and reverse battery protection (with the use of an external series diode).
Diagnostic Feedback: It provides a current sense (IS) pin that delivers a proportional current mirroring the load current. This enables precise load diagnostics, including detection of open-load, short-to-ground, and overtemperature conditions, which is vital for system health monitoring and debugging.
Optimized Electromagnetic Compatibility (EMC): The built-in active slew rate control minimizes voltage transients (dV/dt) during switching, significantly reducing electromagnetic emissions and simplifying EMC compliance.
Typical Application Circuit
Implementing the BTS428L2 is straightforward. A typical application circuit for driving a DC motor or lamp is shown below:
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1. Load Connection: The controlled load (e.g., a motor) is connected between the OUTPUT pin and ground.
2. Power Supply: The vehicle's battery supply (VBAT, typically 12V) is connected to the INPUT pin.
3. Control Input: A microcontroller (MCU) GPIO pin controls the switch via the IN pin. A logic-high signal (typically > 3.5V) turns the MOSFET on, energizing the load.
4. Diagnostics: The IS pin is connected to the MCU's analog-to-digital converter (ADC) through a precision sense resistor (RS) to ground. The voltage across this resistor (VIS = IIS RS) is proportional to the load current.
5. Reverse Battery Protection: An external Schottky diode is placed in series with the INPUT pin to protect the IC if the battery connections are reversed.
Critical Design Considerations
To ensure reliable and long-term operation, several factors must be considered during the design-in phase:
Thermal Management: The power dissipation (PD = ILOAD2 RDS(on)) generates heat. The RDS(on) is very low (max. 30 mΩ), but at high currents, heating is significant. Proper PCB layout is crucial: the exposed die pad (Source pin) must be soldered to a large copper area (PCB ground plane) to act as a heatsink. Thermal vias can be used to transfer heat to inner layers.
Inductive Load Handling: When switching off inductive loads like motors, the rapid change in current causes a negative voltage spike at the OUTPUT pin. The BTS428L2's internal clamping circuit safely handles this energy. However, understanding the maximum energy of the load is essential to ensure it stays within the device's safe operating area (SOA).
Current Sense Resistor Calculation: The value of RS must be chosen carefully. It should be large enough to generate a measurable voltage at the MCU's ADC for small currents but not so large that the voltage at the IS pin exceeds its maximum specification (typically 5V) at maximum load current. A value between 500Ω and 2kΩ is common.
Wiring and Layout: High-current paths (from INPUT to OUTPUT to load) should be kept as short and wide as possible to minimize parasitic resistance and inductance. Decoupling capacitors placed close to the INPUT pin are mandatory to suppress voltage spikes and ensure stable operation.
The BTS428L2 represents an excellent solution for designers seeking a highly integrated, protected, and diagnostic-rich power switch. Its combination of high current handling, ultra-low quiescent current, and robust built-in protection makes it a top choice for enhancing reliability and simplifying design in 12V and 24V systems, particularly in the demanding automotive environment.
Keywords: BTS428L2, PROFET, High-Side Switch, Automotive Applications, Diagnostic Feedback
