Point 1：What is Smart power switch?
The power device can protect itself in various abnormal conditions and report errors will greatly improve the reliability of the power device itself and the safety of the whole system. Infineon's smart high-edge classic PROFET family, shown below, is an integrated diagnostic and Protect power device (MOSFETs) that responds to abnormal conditions and reports back to the control unit. Especially in automotive applications, the complex electrical architecture of automobiles greatly improves the difficulty of electronic fault detection. We need to know the working state of circuits and devices, so as to quickly locate faults.
Intelligent high edge switch PROFET series
Intelligent power switches are suitable for driving different types of loads, such as resistive loads (PTC), inductive loads (motor), capacitive loads and headlights. And can replace many components of the car system, such as relays and fuses. It contains a number of protection functions to deal with various common circuit failure problems.
It also has current detection capabilities, allowing additional savings on shunt resistors and discrete difference comparators in applications where circuit detection accuracy is not critical. Certain product families also come with switching speed adjustment, which is useful for optimizing current spikes and EMI. In the layout of PCB board, because of Infineon's intelligent power switch device has a high degree of integration, it does not even need much more Pin than the vertical MOSFET.
Point 2：How can intelligent power switches avoid failure
To protect the power device from failure, we need to analyze the common failure causes and solve them one by one.
Common failure causes for conventional discrete MOSFET devices are:
1. Overvoltage caused by sharp fluctuations of supply voltage (for example, the 12V electrical system of an automobile, the voltage may fluctuate from 5.5V to 24V during ignition and tripping)
2. Device overvoltage caused by voltage spikes V_ds=V_bat+V_L at both ends of the MOSFET when the inductive load is turned off
3. The short-circuit current generated by a short circuit in the load or circuit makes the device overcurrent/overtemperature failure
Therefore, the use of MosFeTs in automotive 12V or 24V electrical systems requires consideration of whether the breakdown voltage of the device can withstand dramatic voltage fluctuations. The voltage peak of inductive load can be optimized by adjusting the switching speed of the device. In case of failure caused by overcurrent/overtemperature, the MOSFET can be disconnected in time to protect the device and circuit.
In addition to the above failure problems, there are also some abnormal conditions such as sudden load disconnection or battery undervoltage. Although components may not be damaged, the circuit cannot work normally at this time. We need to know the state of the circuit in time and adjust it.
It is worth mentioning that the problem of battery reverse polarity is also a failure model to be considered in the automobile system. Careless drivers can switch the battery upside down when changing a car battery or powering it on. However, when the battery is reversed, the MOSFET body diode will be directly switched on and produce a large amount of loss, resulting in rapid temperature rise of the chip.
Point 3：Intelligent power switch selection
Intelligent power switches are divided into intelligent high-side switches and low-side switches. As the name suggests, a High side switch indicates that the power switch is on the side of the load with high potential, that is, between the battery and the load. The Low side switch is on the low potential side of the load, usually between the load and the ground.
As shown in the figure above, both can turn the circuit on or off in normal operation. For both short spots in the high side circuit shown here, disconnecting the MOSFETs will protect both the circuit and the load. However, for the two short circuit points in the low-side circuit, after disconnecting the low-side MOSFET, the circuit is still in the problem of power to ground short circuit or load can not be disconnected. Turning off the MOSFET will disconnect the circuit only if the circuit behind the low-side switch shorts to ground. In contrast, the use of high-side switches in the circuit will have better protection. However, it should be noted that if you want to use an N-channel MOSFET on the high side, it will require an extra Charge pump or Bootstrap circuit to drive the switch tube because of its variable source voltage.
The smart high-edge switch PROFET series provides protection for different types of loads. For example, when the voltage on the capacitive load is higher than the battery voltage, the problem is similar to the battery reverse polarity. In this case, the smart high-edge switch will report an error and turn on the MOSFET, allowing the current to flow through the channel, thereby reducing the overall calorific value of the chip. Infineon's intelligent clamp function protects the power component by suppressing voltage spikes when the inductive load is turned off.
In addition to the PROFET line, Infineon Smart High Edge family includes the Load Guard line for ADAS applications, which features adjustable current limiting protection.
And low side intelligent switch because of the protection ability of the entire circuit is limited (in the battery short circuit to the ground and load open circuit can not influence the circuit), more need to consider over temperature/over current protection. For this reason, Infineon Highly Integrated Temperature protected FET is called HITFET. In addition to Slew rate adjustment, Infineon HITFET's low-edge smart switch will also feature a slew rate adjustment feature to boost EMI performance.
