A New Device Eliminates the Need for Capacitors in Automotive Power Supply DesignsJune 27, 2020 by Jake Hertz
External capacitors can quickly clutter PCB real estate and drive up BOM costs. What if we could do away with them altogether?
The growing desire for more environmentally-friendly vehicles has led to the electrification of many aspects of automobiles. Power supply design in automobiles is particularly challenging for engineers since a car's battery will generally have a nominal voltage—anywhere from 12 V to 13.5 V. Yet, because of load dumps, transients, inductive loads, and start-up conditions, the battery voltage can vary from -75 V to +50 V.
Example of automotive battery voltage fluctuations and causes. Image used courtesy of Diodes Incorporated
As EVs advance, the number of uniquely-biased electrical components in the vehicle also increases. All things considered, the need for high-quality power supply systems has become paramount in automobiles.
The Basics of a Linear Regulator
While there are many types of well-studied power supply architectures, one of the most fundamental is the linear regulator. A linear regulator is a power supply architecture that, at its core, consists of a resistive divider network, pass transistor, error amplifier, and capacitors for stabilization.
A voltage from the divider network gets fed into the error amplifier and compared to a desired reference voltage. This amplifier will then control a pass transistor, which will either pass through a larger voltage or remain closed if needed. In this way, it keeps the output voltage regulated within some degree of fluctuation to a reference voltage. Input and output capacitors are used to stabilize the voltage and reduce ripple.
Example linear regulator circuit diagram. Image used courtesy of Marty Brown
Linear regulators offer some great advantages like simplicity and small area, especially considering large components like inductors are not part of the architecture. On the other hand, linear regulators are not power efficient. Utilizing a resistive divider network wastes a lot of power in the form of heat across the resistors. For these reasons, engineers sometimes prefer to use more energy-efficient architectures such as switching regulators.
ROHM Releases New Power Supply Technology
One of the goals for power supply designers in the automotive industry is to minimize circuit size and design load. ROHM Semiconductor recently released news of its new Nano Cap power supply technology with exactly this goal in mind.
Historically, a circuit consisting of a linear regulator and an MCU requires a 1 uF capacitor at the output of the linear regulator to minimize ripple, and a 100 nF decoupling capacitor at the input of the MCU. ROHM’s newest release claims to remove the need for the 1 uF capacitor at the regulator’s output and still ensure stable operation.
How Well Does it Work?
According to ROHM, utilizing Nano Cap technology keeps the regulator's peak voltage fluctuations to ±3.6% even without the 1 uF capacitor. This is impressively low: specifically, it is ±1.4% below the industry requirement of ±5% fluctuation. These results are achieved with 1/10th the capacitance otherwise required, making these results very noteworthy.
Graphic showing the advantages of Nano Cap technology. Image used courtesy of ROHM Semiconductor
When used in conjunction with the 1 uF capacitor, ROHM boasts voltage fluctuations as low as ±1%.
Implications of Nano Cap Tech in the Automotive Industry
Claiming to remove the need for the relatively large 1 uF capacitor allows for design engineers to create their systems with fewer components. Decreasing the size of PCBs and items on the bill of materials will undoubtedly decrease the cost of electrical systems. In the automotive industry, this could be extremely important as more and more electrical components are being incorporated, but the space for them is finite.
In the future, ROHM hopes to further enhance Nano Cap technology by eliminating the need for capacitors and expanding this technology not only to linear regulators, but op-amps, LED drivers, and other analog ICs as well.
Do you work with power supply systems in the automotive industry? What are some ways you make the most of board space? Share your experiences in the comments below.