General

DC-DC Converter IC for ADAS achieves best-in-class stable operation

DC-DC Converter IC for ADAS achieves best-in-class stable operation

If you’re concerned about tightening automotive power requirements, you’re in the right place. Technological innovation in accident prevention and autonomous driving is preparing the industry for a major upheaval, with market forces requiring miniaturization, robustness and greater reliability.

Not only will cars and trucks in the near future outperform today’s vehicles, but the high-tech community has gone on the offensive creating Advanced Driver Assistance Systems (ADAS) SoCs and MCUs with increasingly sophisticated built-in sensors, cameras and radars. This requires power supply ICs that work stably even under heavy load current fluctuations.

To tackle this problem, ROHM developed the BD9S402MUF-C buck dc-dc converter IC with built-in MOSFET, which is aimed at automotive applications with these built-in sensors. In addition to meeting the basic requirements of secondary dc-dc converter ICs in ADAS for 2MHz or higher operation and 4-A output current, the component incorporates the company’s Nano Pulse Control high-speed pulse control technology to provide low-voltage output to 0.6 V – much lower than the typical 1.0 V voltage output required by current SoCs and MCUs.

Nano Pulse Control for monolithic (single chip) dc-dc converters reduces the on-time to 9 ns, said to be the smallest in the industry and a significant achievement as the typical on-time is about 120 ns.

At the same time, the BD9S402MUF-C uses ROHM’s QuiCur high-speed load response technology to provide stable operation at what it believes is an industry-leading 30 mV (measurement conditions: 5-V input voltage, 1.2 V output voltage, 44-μF- output capacitance and load current variation 0 to 2 A/2 s This translates into a 25% reduction in output voltage fluctuation over standard products with equivalent functionality, making it suitable for use in the latest ADAS with severe power conditions providing stable operation within 5%, even with a low output voltage.

Delivering stability

In general, power ICs constantly monitor the output voltage to ensure stable power functionality and include a feedback circuit that fine-tunes the output voltage by comparing it to an internal reference voltage. By providing a faster response, it is possible to reverse changes in the output voltage caused by fluctuations in the input voltage and/or load current in a shorter time.

On the other hand, shortening the response time too much can cause the circuit operation to become unstable and the output voltage to oscillate. In addition, because the response speed is also affected by the output capacitance, it has been difficult to achieve the desired response performance until now.

QuiCur

Incorporating QuiCur into power supply ICs reduces design resources by providing stable operation with fewer external components, making it possible to achieve the required performance without causing instability in feedback circuits.

Not only can it reduce the number of external components and mounting area by minimizing the capacitance of the output capacitor required for the power supply IC, but it also allows linear adjustment of the capacitance and fluctuations in the output voltage, ensuring stable operation guaranteed even when capacity increases due to specification changes.

QuiCur is named after ROHM’s original “Quick Current” high-speed load-response circuit that maximizes the load-transient response characteristics without causing instability in the feedback circuits of power ICs. Response performance equivalent to the company’s conventional products can be achieved at less than half the capacity. In the future, there are plans to expand the power supply IC lineup with QuiCur to support a wider range of applications.

Load response

The BD9S402MUF-C is also equipped with a load-response performance selection function that takes advantage of the features of QuiCur technology. Users can switch the priority between voltage fluctuation (for stable operation) and capacitance decrease (to ensure stable operation at 22μF) by setting High/Low of the GAIN pin.

For example, the user can set the GAIN pin to High for a power supply in a high-performance SoC that needs to handle fast load fluctuations. Or the GAIN pin can be set to Low for a balance between performance and capacitor cost when the power supply for an MCU does not have to account for very precise voltage fluctuations. This greatly increases design flexibility for application designers, as stable operation can be easily achieved during initial design and during specification or model changes.

The BD9S402MUF-C includes built-in low resistance MOSFETs in a VQFN16FV3030 package. The switching frequency is 2.2 MHz. The converter costs $2.00/unit (samples, excluding tax). Samples are now available; mass production is scheduled for April 2023.