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Maxim > Design Support > Technical Documents > Application Notes > ASICs > APP 3893
Keywords: High switching frequency and high voltage operation
APPLICATION NOTE 3893
High-Frequency Automotive Power Supplies
Jul 17, 2007
Abstract: The combination of high switching frequency and high-voltage capability is difficult to achieve in
IC design. You can, however, design an automotive power supply that operates with high frequency if
you protect it from temporary high-voltage conditions. High-frequency operation is becoming important as
more and more electronic functions are integrated into the modern automobile. This article discusses
several ways to protect low-voltage electronic circuits from the harsh effects of the automotive electrical
environment. Also included are the results of laboratory tests for noise immunity.
Introduction
The increasing density of electronics in automobiles presents unique challenges and opportunities to the
power-system designer. Most automotive modules require low voltages such as 5V or 3.3V, but the use
of linear voltage regulators to step down the battery voltage dissipates considerable power. Excessive
power dissipation makes thermal management difficult and expensive. As a result, the increasing power
requirements of faster processors and ASICs have steered the preferred method of power conversion
from simple, low-cost, but inefficient linear regulation to the more complex but efficient switching
converter.
Advantages of a Switching Converter
Passive components such as the power inductor and power capacitor can be physically smaller at higher
switching frequencies, so the size of a switching converter depends on the switching frequency. By
reducing power dissipation, high-efficiency converters also eliminate bulky and expensive heat sinks.
Thus, the use of switching converters can shrink the overall size of the power supply. These advantages
make the switching converter an increasingly attractive choice for power management in automotive
applications such as body electronics, infotainment systems, and engine-control modules.
Considerations for Choosing a Switching Converter
The choice of switching frequency is critical, because a switching converter poses its own set of
problems. The electromagnetic noise generated by its fundamental switching frequency and higher
harmonics can interfere with other electronics. AM radio receivers, for example, are sensitive to
interference in the range 530kHz to 1710kHz. A switching frequency greater than 1710kHz, therefore,
eliminates fundamental and harmonic interference from the AM frequency band. Test data will show that
the moderate voltage, high-frequency processes used with a simple protector, as in Maxim devices, are
excellent solutions for addressing automotive power management needs. Ultimately, it is quite clear that
designers no longer need high-voltage controllers to design these switching converters.
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