The trend toward advanced driver assistance systems (ADAS) and automated driving requires an intelligent and safe supply of the constantly growing number of control units. This demands the protection of the electrical system from defective consumers that cause overcurrent or even short circuits.
This protection can be provided in several ways: On the one hand, by taking measures to limit the current of individual consumers, and, on the other hand, by quickly disconnecting defective power consumers or faulty electrical system sections from the rest of the system before prolonged voltage drops occur in the electrical system. Prolonged voltage drops can otherwise force ECUs for vital ADAS functions into an undervoltage reset, temporarily disabling safety-relevant functions.
Conventional fuses and relays are unsuitable for this task as their switching speed is 100 times lower than that of intelligent semiconductor modules. This puts sensitive loads and power supplies at risk of overload. Further, melted fuses must be replaced and cannot be reset like semiconductor modules. This is not an option, especially in future zone architectures.
Infineon’s new PROFET Load Guard family offers an excellent combination of protection and diagnostic functionalities for designing future ADAS systems. The flexible high-side power switch covers various functions, such as power supply protection, load control and protection, self-protection, and wire protection. Since the PROFET Load Guards limit the inrush surges, they are also suitable for switching capacitive loads. Capacitive load switching mode (CLS mode) also allows large capacitors to be switched on quickly without thermally overloading the module. Due to the adjustable current limitation, the component also protects sensitive filter components in the supply line of sensors (keyword: power over coax). The close tolerance ratio (kILIS) of the actual current value also allows precise diagnosis of the load conditions.
Fig. 1 shows an example application: Two ADAS ECUs (in this case for cameras) are supplied via power over coax. The signal (in the figure: data) and the voltage supply are separated by filters. If a camera causes a short circuit, the PROFET Load Guard (blue in the figure) limits the load current to a preset value. On the one hand, this current limitation protects the filter coils (PoC) from overheating on the load side. On the other hand, the DC/DC power supply also remains within the specified load range and can continue to supply the other camera without any problems. The current limitation thus ensures freedom from interference between the load circuits.
Latest development with adjustable current limitation
Fig. 2 shows the block diagram of the BTG7090-2EPL member of the PROFET Load Guard family with its internal function blocks. The overcurrent limitation block is new. Compared to its predecessors, the PROFET Load Guard does not simply switch off in the event of overcurrent but continues to operate and limits the output current to a preset limit.
To do so, it is equipped with adjustable current limitation. An external resistor is used to configure the maximum current. In the event of an overload, the output current is limited to the limit current programmed with the resistor, and the output transistor of the PROFET Load Guard goes into linear operation. The resulting power loss in the transistor heats up the component. The component only switches off the affected channel to protect itself when the chip temperature or the temperature gradient reaches a certain maximum value. Then the retry strategy comes into play, a combination of auto-restart and latch-off: After switching off, the chip temperature drops again and the PROFET Load Guard is switched back on automatically (assuming a continuous high signal at the control input). After six unsuccessful restart attempts, the output stage switches off permanently (latch-off). A low-high sequence at the control input resets the internal retry counter and switches the output back on.
Due to the adjustable current limitation, the module offers high flexibility in the application, as the functionality can be adapted to changing requirements through the choice of the resistor.
For self-protection, the switch relies on its temperature monitor with switch-off due to overtemperature. Needless to say, the controlling microcontroller can also switch off the PROFET Load Guard. The diagnostic feedback signals on the sense pin are used as the basis for its decisions. The module thus also provides precise feedback (±5%) on the current power consumption of the load.
Dealing with return current reduces power loss
PROFET Load Guards can only switch off the current in one direction. In the other direction, the intrinsic body diode of the MOSFET conducts even if the channel itself does not. Return current exists, for example, in regenerative motors as a load. High power losses can occur in the body diode and heat up the chip and possibly also adjacent channels, causing them to switch off.
The InverseOn product feature allows the internal MOSFET to be switched on as long as the return current is within certain limits. The advantage: The power loss that occurs in the channel of the MOSFET is smaller than that which would occur in the body diode.
Thanks to the capacitive load switching (CLS) function block, the PROFET Load Guard is also suitable for fast charging and switching on large capacitive loads. For this purpose, the input is controlled with specific PWM. This PWM signal puts the module into CLS mode with the continuous auto-restart switch-off strategy. The switching cycles “Switch on and supply with limit current” and “Switch off due to protection against steep temperature rise” are repeated until the voltage drop at the output transistor, in ON state, falls below a certain value. In this case, the capacitive load is considered to be sufficiently charged. After that the PWM is permanently switched through and can be replaced by a high level at the control input. Advantage: The module remains in the specified safe operating area (SOA) during this period.
Availability, simulation capabilities, and evaluation boards
PROFET Load Guards are ISO-26262-ready. Infineon, therefore, provides information in a safety application note (SAN) that helps to integrate the component into a functionally safe system. The first derivative is the dual-channel BTG7090-2EPL; samples are available from Rutronik upon request. Large-scale production is set to start in late 2022. Interested parties can find the data sheet, simulation models, and other tools at www.infineon.com/profetloadguard.
For evaluation purposes, Infineon offers two boards for assembling a kit: the motherboard PROFET ONE4ALL MB V1 (Fig. 4) and the daughterboard BTG7090-2EPL DAUGH BRD.
Together with Infineon’s µIO-Stick and the Config Wizard GUI, the module can be configured, controlled, and tested.
ADAS require a reliable power supply within the vehicle electrical system. To achieve this, the electrical system must be protected from other defective consumers with excessive current requirements. With its current-limiting function that can be adapted to system requirements, the PROFET Load Guard does not allow hazardous short-circuit currents and peak currents at its outputs in the first place, thus protecting the load and the 12 V power supply against overload.
For more information and a direct ordering option, please visit our e-commerce platform at www.rutronik24.com.
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