Industry Article

Buck Converters Enable Efficient Power Conversion in Automotive Applications

January 14, 2021 by Nick Ikuta, ROHM Semiconductor

In this article, learn about the role of buck converters in automotive power supply design, and explore some requirements to consider when selecting a buck converter.

Power converters are critical for efficient power delivery in today’s automobiles, from gasoline or diesel engine vehicles to hybrids and electric vehicles (EVs). Primary buck converters are highly useful for solving technical challenges and simplifying automotive power system design. 


Figure 1. Power system design for automobiles is more challenging than ever, particularly for hybrids and EVs.


Power Supply Challenges in Automotive Applications

Power system design in automobiles is becoming more complicated due to the ever-increasing number of electronics integrated under the hood. 

Today, most vehicles contain a wide variety of features for improving drivability and the user experience, including GPS systems, hands-free calling, in-car infotainment, advanced driver-assistance systems (ADAS), and more. Although these features are beneficial to end-users, they result in technical challenges, including higher power requirements, more electrical noise (EMI), and higher operating temperatures. 

Power conversion considerations grow increasingly important as cars become more and more like “computers on wheels.”


Power Inefficiencies and Increasing EMI Under The Hood

Typical power supply design is aimed at keeping power supply in a vehicle constant. However, this can result in noise problems. “Always on” design generates more EMI due to the non-linear characteristics of power supplies. Moreover, more electronics integrated into smaller geometries results in “crosstalk,” which can lower power efficiency through capacitive or inductive coupling.

Quiescent or stand-by current is also a critical consideration. It refers to the minimum current required to keep a power converter functional in light load mode (LLM). Lower quiescent current levels improve power efficiency by minimizing power dissipation and extending battery life. 


Higher Operating Temperatures

Operating temperatures are increasing in automotive applications due to heat dissipation from the engines and transmission systems. These higher temperatures may impact the reliability of power supply circuits, making components more prone to failures. 

Essential requirements for thermal management include overcurrent, overvoltage, and overtemperature protection. Many automakers specify that components meet industry standards, such as the AEC-Q100 stress test, for reliability in typical elevated conditions under the hood. 


The Role of Automotive Buck Converters

Multiple voltage levels are required in different sections of modern vehicles. For example, EVs and hybrid vehicles utilize 48VDC power supplies (four times greater than the 12VDC bus used in conventional cars and trucks). A USB port in the dashboard section, however, requires only 5V. 

Similarly, voltages supplied by the batteries or supercapacitors and alternator may be insufficient in engine control units (ECUs) and must be stepped up to an adequate level. As automotive boardnet voltage varies over a wide range, DC-DC power converters are used as crossover solutions to achieve the desired supply voltages. 

Buck converters enable DC-DC conversion in power supplies to step down a high input voltage to a lower output voltage. They work by temporarily storing the input energy in an inductor or transformer’s magnetic field and supplying it to different loads at varying voltage levels. 

Efficient power conversion can reduce EMI, lower power dissipation, and extend battery life. Automotive applications for primary buck converters include voltage regulation in cluster systems, in-vehicle infotainment, LED lighting modules, and telematics. 


Requirements for Buck Converter Selection

For many designers, choosing the right buck converter comes down to the following criteria:

  • Higher switching frequencies: High switching frequencies in buck converters improves load transient response and allows for smaller capacitors and inductors to be used in power supplies. 
  • Low input voltage operation: A wide input voltage range and low-voltage operation is essential where critical loads must remain functional at all times — regardless of the power requirements in other areas. A good example is keeping critical systems online during cold cranking, where the voltage can fall to as low as 3.5V. 
  • Low quiescent current: Extending battery life is desirable in today’s automobiles, despite the increasing power requirements. Ideally, buck converters should have a very low quiescent current, which helps conserve battery life by drawing less power when regulating low or zero loads. The maximum stand-by current recommended for automotive applications is 100μA. 
  • Wide operating temperature range: As earlier discussed, automotive power supplies must be capable of withstanding elevated temperatures under the hood. 


ROHM’s Buck Converters for Automotive Solutions

In an age where technology is increasingly being integrated into vehicles, the right components ensure proper design and execution, especially when it comes to power conversion. 

ROHM's BD9P23X AEC-Q100 qualified primary buck converter achieves efficient power conversion in automotive applications with Nano Pulse Control® technology. Nano Pulse Control® is an ultra-high-speed pulse control technology that combines three advanced ROHM technologies in the circuit design, layout, and process areas. 



Figure 2. The BD9P235EFV-C buck DC-DC converter from ROHM.


ROHM’s primary buck converter offers low quiescent current, low input voltage operation, and adjustable switching frequency and comes in a small-footprint, wettable flank package for optimal board savings. For more information on ROHM’s automotive solutions, visit their website.