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The wide diversity of automotive motor-drivers, including those used for HVAC (heating, ventilation, and air conditioning), headlamp, seat positioning, window, and mirror applications, requires circuits that do more than just switch the motor on and off. The drivers have to control direction, torque, speed, acceleration, and deceleration to sense position and to detect stall conditions.
In addition, they have to withstand severe environmental conditions, such as system electrostatic discharge (ESD), over- and reverse-voltages, wide temperature ranges, and electromagnetic interference (EMI). Finally, since some applications are safety-critical, they also have to fulfill very high quality and reliability demands.
Integrating the drive-control functions on a single chip (system-on-chip, or SoC) is a difficult task, because the chips have to operate at high temperatures, high voltages (up to 80V), and handle up to multi-amp currents. This article will describe design implementation of H-Bridges in "smart power" technologies for three automotive applications—a stepper motor actuator for positioning headlamps, a ventilator motor controller to control the airflow and temperature of a car's airflow, and also a Class D power amplifier for audio amplification.
Peaceful coexistence
Most automotive applications require the co-existence of analog and digital functionality. Thus the benefits of combining this functionality on a single chip to create an integrated circuit (IC) are significant. Such mixed-signal integration, however, also presents significant challenges, including having to withstand the severe environmental conditions noted previously.
The typical application diagram of such a mixed-signal IC for automotive use is given below.
Basically, as shown in the schematic, the chip is integrating the system functionality from a sensor (left) to an actuator (right) by going through some digital processing. Conventional mixed-signal technology allows analog control and signal processing functions, such as amplifiers, analog-to-digital converters (ADCs), and filters to be combined with digital functionality including microcontrollers, memory, timers, and logic control functions on a single chip.
All signals to process an algorithm or arithmetic calculation are digital, so conversion of analog to digital signals is mandatory when submitting data for comparison or processing by the microcontroller. Conversion from digital output signals to analog high voltage signals is required to drive an actuator or a load.
High voltages
The most recent mixed signal-technology AMIS developed simplifies the implementation of such driver functionality by allowing much higher voltage functionality (up to 80V) to be integrated into an integrated circuit alongside the relatively low voltages required for conventional mixed signal functions. This high-voltage mixed-signal technology is particularly relevant to automotive electronics applications, for instance, where higher voltage outputs—to drive a motor in a ventilation system, move a headlamp, or to fast switch the transistors in a Class D amplifier in an audio application—need to be combined with analog signal conditioning functions and complex digital processing.
The latest mixed-signal semiconductor processes are helping to address some of these issues. This article specifically looks at the driver design side and concentrates on some of the concerns designers need to consider when specifying integrated mixed-signal ICs.
The market for intelligent automotive motor-driver circuits noted earlier, as well as the intelligent and fast-switching Class D audio drivers is hitting the integration "step" after years of discrete implementation. These applications go beyond simply switching the load on and off, and have to function reliably under severe environmental conditions. This mixture of conditions can be fulfilled only when robust state-of-the-art technologies and the right circuit design and application experience are combined.
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