Over the last 15 to 20 years, automotive power MOSFETs have evolved from a rather plain topic into a dynamic business. Power MOSFETs were selected based on their ability to tolerate the high voltage transients such as load dump and field decay experienced in vehicle electrical systems. Packaging was straight forward and utilized mostly TO220 and TO247 leaded packages.
Applications such as electric windows, fuel injection, intermittent wipers, and cruise control were becoming standard on most automobiles and required similar power devices in their design. During this period, automotive power MOSFETs proliferated with the growing use of electric motors, solenoids, and fuel injectors.
Today's automotive systems have ushered in a new age for power devices. This article will explore several of the new applications that are driving a revolution in power devices within the automobile. It will also look at some of the developments in power MOSFETs that enable today's automotive systems. These developments will have an accelerating impact on the progress of automotive electronics, particularly in emerging markets such as China.
Market dynamics
There are four forces in the new automotive applications driving this evolution in Automotive Power devices, including:
Required stand off voltage (VVDSS)
System power requirements
System intelligence/survivability
Product and system cost
Historically, power devices of approximately 60V VVDSS were used in automotive applications. However, new systems use both higher and lower voltages to more cost effectively deliver system performance not previously available.
Two applications gaining popularity are high-pressure piezo and magnetic-electric fuel injection systems and high-intensity lighting. These applications require power MOSFETs with breakdown capability as high as 150 to 300V. The higher potential piezo and magnetic electric fuel injection systems can deliver better performance by providing more accurate injection of the fuel and a finer air/fuel mixture allowing improved combustion with fewer emissions.
The high intensity lighting generates a brighter light with less energy than standard incandescent lights. This improves visibility at night or in poor weather conditions. It also enhances the ability of other drivers to see the vehicle.
In addition to the higher voltage automotive power applications, the explosion of consumer applications moving into the vehicle have pushed the low end of the voltage spectrum. CD/DVD players, satellite radio, cell phones, GPS navigation, and MP3 player interfaces are several of the newer applications requiring power MOSFET devices. The required power used in these applications is typically lower using smaller discrete or possibly integrated power devices with the same characteristics as the consumer products they are based upon.
Size is very important in these applications and newer power devices utilizing smaller PC board package foot prints and surface mount assembly are standard. Packages such as the Power 56 and the Super SOT SSOT 6 are commonly used for these applications offering considerable power handing capability in very small packages.
Proliferating electronics systems
Many of the automotive systems that have been traditionally mechanical or hydraulic are converting to electrical or electrical/ hydraulic systems. One of the first to change over was the radiator fan. Through the use of an electric motor, the fan belt can be eliminated and the control of the fan can be tied to the actual engine or coolant temperature more accurately.
Other similar applications are electric power steering (EPS), integrated starter alternator (IAS), and active suspension systems. Electric power steering and active suspension systems give the automotive system designer the flexibility of using a single hardware system on multiple vehicle platforms while modifying the feel of the vehicle from sporty to luxury through software modifications.
One characteristic of these electro-mechanical systems is the use of extremely high power levels. These high energy systems require high current power switches. In order to provide the highest current switching at lower losses, these applications typically use high performance trench MOSFETs with 30 to 40V ratings.
