What are the operating modes of the high-side switch? Pay attention to what?

There are three main categories of semiconductor devices in automobiles: sensors, MCUs and power semiconductors. Among them, power semiconductors are mainly used in power control systems, lighting systems, fuel injection, chassis safety and other systems. In addition, as the trend of vehicle electrification, intelligence, and comfort has brought about an increase in the value of stand-alone power semiconductors in automobiles, and jointly drive the demand for power semiconductors in automobiles, the growth rate will be about 8% in the next 3 to 5 years.

There are three main categories of semiconductor devices in automobiles: sensors, MCUs and power semiconductors. Among them, power semiconductors are mainly used in power control systems, lighting systems, fuel injection, chassis safety and other systems. In addition, as the trend of vehicle electrification, intelligence, and comfort has brought about an increase in the value of stand-alone power semiconductors in automobiles, and jointly drive the demand for power semiconductors in automobiles, the growth rate will be about 8% in the next 3 to 5 years.

Automotive power semiconductors cover a wide range, from high- and low-voltage MOSFETs, to high-side, low-side and bridge switches with integrated protection circuits and diagnostic functions, and power supply adjustment ICs, all the way to safety systems such as ABS and airbags Highly integrated ASIC.

Automobile manufacturers hope that in-vehicle Electronic systems can greatly improve energy efficiency in the smallest possible space. The high-side switch is an efficient integration of analog circuits and powerful load/output drivers, which can improve system efficiency and save costs. Together with the microcontroller, they provide the necessary protection and protection for various loads such as motors, lighting, actuators, etc. control.

About 25 years ago, the first PROFET product (PROtected mosFET, protected MOSFET) appeared on the market, which meant that relays and fuses for various automotive body applications finally appeared as alternatives.

Infineon’s intelligent high-side switch family product-PROFET?, has been widely used in quan cart factory. Let us take it as an example to analyze the characteristics, applications, internal structure and working mode of the smart high-side switch.

1. What is PROFET?

PROFET? = PROtected mosFET, MOS tube with protection function. It is Infineon’s highly integrated high-side switch family, with a wide range of intelligent features, including complex diagnostics and protection capabilities. The high-current PROFET power switch contains a DMOS power MOSFET and CMOS logic circuit.

2. What applications can PROFET be used for?

It is designed for controlling all types of loads including resistive loads, inductive loads and capacitive loads in harsh automotive environments. The protection range of these switches is extremely wide, such as overload, over temperature, short circuit conditions in all types of automotive and industrial applications.

3. How to decide whether a high-side switch is needed in the application?

What are the operating modes of the high-side switch? Pay attention to what?

In a typical automotive system, a single power supply voltage Vbb (also called VBATTERY or VBAT) forms a power supply network. As shown in the figure, there are five possible automotive switch configuration schemes that can turn on or off electrical loads.

High-side switches play an important role in many of the automotive switch configurations. These high-side switches are used worldwide in the automotive field for various reasons: load drive, diagnostic performance, ability to mitigate the impact of short-circuit faults on the system, and relatively low system costs.

4. The internal structure of the PROFET high-side switch

What are the operating modes of the high-side switch? Pay attention to what?

How does the PROFET high-side switch complete the load driving and diagnostic functions?

Let’s take a look at the internal structure of the highly graphical PROFET high-side switch.

The IS pin on the high-side switch is an analog current detection signal, which can be monitored by the microprocessor in the electronic control unit (ECU). The current detection signal value is proportional to the load current IL. Current detection is performed inside the high-side switch to diagnose and protect when a fault occurs. High-side current detection is used to protect the load and wiring harness, diagnose the load to ensure reasonable operation, and measure the output current to control the output power.

5. What are the operating modes of the high-side switch? Pay attention to what?

What are the operating modes of the high-side switch? Pay attention to what?

In the automotive field, when the power supply voltage Vbb is higher than the output load voltage VOUT, it is the normal operation mode. Certain temporary conditions may cause the power supply voltage to be lower than the output load voltage. This is a reverse current mode or reverse current condition. In addition (such as when replacing the battery or boosting the start), the polarity of the battery may be reversed. This is the reverse connection mode or the reverse connection of the battery electrode status.

a. Normal mode

What are the operating modes of the high-side switch? Pay attention to what?

In the normal operation mode, the battery electrode direction is connected correctly, and the battery voltage Vbb is higher than or equal to the output load voltage VOUT.

Because Vbb ≥ VOUT, the intrinsic diode of the MOSFET is reverse biased and therefore does not conduct. At this time, if the microprocessor turns off the high-side switch, no current flows in any direction through the MOSFET. If the microprocessor closes the high-side switch, current flows from the battery (in the traditional sense) through the MOSFET, and then to the load.

b. Reflux mode

In some cases, depending on the type of load being controlled and specific applications, transient conditions may cause the battery voltage Vbb to be lower than the output load voltage VOUT, which is the reverse current mode or reverse current condition.

The characteristic of the reverse current mode condition is that the positive supply voltage Vbb is lower than the output load voltage VOUT, which causes the load current CIL to flow in the opposite direction to the normal load current.

A purely resistive load will not cause a reverse flow mode condition. Only capacitive load or inductive load can cause this situation. Also note that the reflux mode situation is instantaneous.

The following can cause reverse flow mode conditions: The load being controlled by the high-side switch can be operated as a generator. A typical load of this type is an induction motor. When Vbb drops instantaneously, the motor acts as a generator during this instant, thus providing a higher voltage than the battery voltage.

c. Reverse connection mode

To replace the car battery or maintain the car electronic system, you need to disconnect and reconnect the battery. When the battery is reconnected, the two poles of the battery may be reversed, which is called reverse connection mode or reverse connection of the battery poles.

Although today’s car battery terminals are marked and color-coded, the reverse connection mode still exists. One situation that may cause the reverse mode condition to occur is when trying to boost the start of the car, wrongly connecting the poles of the jumper cable. The reverse connection of the battery is likely to damage the car’s electronic system. This means that electronic control units (ECUs) must be prevented from occurring in reverse mode conditions. A very typical industrial application requirement is that at a temperature of 25 degrees, the ECU can withstand the reverse connection mode condition of -14V for one minute.

In summary, we introduced the intelligent characteristics, application scenarios, internal structure and working mode of the intelligent high-side switch family PROFET. I hope the above content can help everyone understand the high-side switch.