Introduction for High-side Power Switch

From Principle, Structure to Scheme Design, Introduction for High-side Power Switch


Semiconductor devices in automobiles are mainly in three categories: 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. Moreover, with the trend of automotive electrification, intelligence, and comfort, the value of single-unit power semiconductors in automobiles will increase, and the demand for power semiconductors will be driven by the same vehicle. The growth rate will be about 8% in the next three to five years.


Automotive power semiconductors cover a wide range of high and low voltage MOSFETs, high-side, low-side and bridge switches with integrated protection circuitry and diagnostics, power conditioning ICs, and safety systems for ABS and airbags. Highly integrated ASIC.


Automakers hope that in-vehicle electronic systems can dramatically increase energy efficiency in as small a space as possible. The high-side switch is an efficient integration of analog circuits and powerful load/output drivers that increase system efficiency and save costs. They together provide the necessary protection for various loads such as motors, lighting, actuators, etc. control.


About 25 years ago, the first PROFET products (PROtected MOS FETs) on the market, meaning relays and fuses for various automotive body applications, finally emerged as an alternative.


Infineon's intelligent high-side switch family product, PROFETTM, is widely used in car manufacturers around the world. Let's take it as an example to analyze the characteristics, application, internal structure and working mode of the intelligent high-side switch.


  1. What is a PROFET?


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


  1. What applications can PROFET be used for?


It is designed to control all load types including resistive, inductive and capacitive loads in harsh automotive environments. These switches offer a wide range of protection, such as overload, over temperature, and short-circuit conditions in all types of automotive and industrial applications.


  1. How do you decide if you need a high-side switch in your application?

 five possible automotive switch configurations

In a typical automotive system, a single power supply voltage Vbb (also known as VBATTERY or VBAT) is used to form the power network. As shown, there are five possible automotive switch configurations that can turn electrical loads on or off.


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


  1. the internal structure of the PROFET high-side switch

 highly patterned PROFET high-side switch.



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


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


The IS pin on the high-side switch is an analog current sense signal that can be monitored by a microprocessor in the electronic control unit (ECU). The current sense signal value is proportional to the load current IL. Current sensing is performed inside the high-side switch to diagnose and protect against faults, high-side current sensing to protect the load and harness, diagnostic load to ensure proper operation, and output current to control output power.


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


operating modes of the high side switch


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


  1. a. Normal mode

normal operation mode



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


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


  1. b. Reverse flow mode

Reverse flow mode



In some cases, depending on the type of load being controlled and the particular application, 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 reverse current mode condition is characterized by a positive supply voltage +Vbb being lower than the output load voltage VOUT resulting in a load current -IL flow that is opposite to the normal load current flow.


A simple resistive load does not cause a reverse flow mode condition. This can only be caused by capacitive or inductive loads. At the same time, note that the reverse flow mode is instantaneous.


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


  1. c. Reverse mode

Reverse mode



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


Although today's car battery terminals are marked and color coded, the reverse mode condition still exists. One condition that can cause a reverse mode condition is that when trying to boost the start of the car, the wrong connection jumps across the two poles of the cable. Reverse battery conditions are likely to damage automotive electronic systems. This means that electronic control units (ECUs) must be prevented from reacting to reverse mode conditions. A very typical industrial application requirement is that the ECU can withstand a -14V reverse mode condition for one minute at 25 degrees Celsius.


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