Supplying Stabilized Power Supplies for Automotive Systems in the CASE Era: DC-DC Converters with Enhanced Load Response Performance through Proprietary Technology

Next-Generation Vehicles Evolving through CASE

Today a concept known as CASE (Connected, Autonomous, Shared, and Electric) is bringing about a revolution in the automotive industry. CASE has led to a redefinition of mobility, and progress is being made on a large-scale renovation of internal system configurations (Figure 1). Automobiles in the near future will be equipped with various high-performance electronic systems far more advanced than anything seen today.

Figure 1

Braking functions to avoid or reduce collisions, using sensors to detect the state of travel and automatically apply the brakes when danger is detected, are already becoming standard features. And cars are now evolving toward Advanced Driver Assistance Systems (ADAS), in which various types of information are collected by numerous sensors, cameras, and radar devices, and sophisticated information processing technology such as AI (artificial intelligence) is utilized to support safe and pleasant travel in a variety of travel scenarios. Hereafter automobiles will progress toward fully automated driving, in which electronic systems automate all decisions and operations involved in vehicle piloting.

Through advances in ADAS and automated driving system technology, drivers will be freed from driving operations and will gain more free time. A vehicle in motion will become, for the passengers, a private space isolated from the surrounding area, something not always easily obtained in today’s society. Automobiles offering interior space that can be utilized effectively, enabling passengers to make meaningful use of their transit time, are now being developed with a view to market launches in the near term. There will likely be redoubled momentum to outfit cars with more sophisticated entertainment systems, with ICT equipment that can be used for work and for information collection, and with displays offering even more power and features.

Power Supplies to Stably Run High-Performance Onboard Systems will be Essential

As the functions and performance of onboard electronic systems evolve, semiconductor chips to execute information processing and control within systems will probably trend toward even higher-performance SoCs and microcontrollers, equipped with even large amounts of memory. Semiconductors installed in vehicles have in the past been designed and manufactured with emphasis on safety, and numerous very well-tested and mature products have been used. Today, however, in order to implement in software the sophisticated functions and safety assurance that are requirements in this CASE era, the most advanced semiconductor chips are being installed. At the same time, the ever-burgeoning processing power of semiconductors has meant the occurrence of sharper and larger load fluctuations in the power supply circuitry that run such systems. No matter how advanced the performance of semiconductor chips may be, if the power supply that drives them is not stable, proper functioning cannot be expected. The power supplies for next-generation onboard electronic systems must be able to suppress fluctuations in output voltage to a minuscule level even when large load changes suddenly occur.

As the number of electronic devices mounted in cars increases, the capacitance of output capacitors used with power supply ICs can be increased to deal with increased load fluctuations resulting from advanced performance. However, if this method is used, individual onboard electronic systems must be dealt with separately, so that time and man-hours are required for power supply circuit design. This tends to be a factor impeding the early launch of new car products and frustrating efforts to cut development costs. Hence there has been a need for power supply ICs that do not require additional output capacitance and that can achieve excellent response performance in the event of load fluctuations.

In general, power supply ICs stabilize the output voltage even when load fluctuations occur; for this purpose, what is called a feedback circuit is provided to constantly monitor the output voltage, comparing it with an IC internal reference voltage in order to perform fine adjustments to the output voltage. If the feedback circuit responds quickly, fluctuations in the output voltage caused by changes in the input voltage or the load current or something else can be eliminated in a short length of time. However, if the circuit is designed to respond extremely rapidly, the circuit operation may become unstable and the desired response performance may be difficult to achieve. In order to obtain stabilized output without adding output capacitance, this issue must be resolved.

Improvement of Load Response Performance of Power Supply ICs through Proprietary ROHM Technology

ROHM has added the BD9S402MUF-C with improved load response performance to its BD9Sxxx series of buck DC-DC converters, which are power supply ICs for microcontrollers, SoCs, and memory in automotive applications (Figure 2). In numerous onboard power supply systems, two-level power supply circuits are used in which the 12 V that is the output voltage of lead storage batteries is dropped to 5.0 V or some other voltage by a primary (first-stage) buck DC-DC converter, and then this is further dropped by a secondary (second-stage) buck DC-DC converter to a low power supply voltage such as 1.0 V required to drive the latest semiconductors. The BD9Sxxx series are power supply ICs that are used in this secondary circuit.

Figure 2

The BD9S402MUF-C achieves extremely stable operation (excellent load response characteristics) through the introduction of ROHM’s proprietary QuiCur^™ high-speed load response technology. QuiCur^™ separates the error amplifier in the feedback path of the DC-DC converter into two stages. As a result, signal processing for voltage control with fast response, and signal processing for voltage correction to obtain a stabilized output voltage, can be allocated effectively, so that response performance can be elevated to the highest possible level while maintaining stability. Compared with power supply ICs with comparable functions, output voltage fluctuations are reduced by 25% to achieve 30 mV stable operation (under conditions of a 1.2 V output voltage, output capacitance 44 µF, load current change 0 → 2 A/2 µsec), enabling applications in advanced ADAS requiring power supplies with stabilized outputs within ±5% voltage fluctuation even for low-voltage outputs.

Moreover, by applying QuiCur^™ features, it is possible, simply through high and low settings of the GAIN pin, to switch between three operation modes: voltage fluctuation priority (for stable operation that is top class in the industry), capacitance reduction priority (for stable operation with small 22 µF capacitance), and phase margin priority. The BD9S402MUF-C can be used selectively, for example by employing voltage fluctuation priority mode when using it with high-performance SoCs to improve the quality of the power supplied, and opting for capacitance reduction priority mode for use with microcontrollers in order to reduce the number of components and decrease board mounting space so as to cut total costs. The desired stable operation can be achieved not only upon initial circuit design but also when there are changes in specifications or models, contributing to dramatic reductions in design man-hours.

Also for Use in 0.6 V Power Supplies Needed to Drive Next-Generation Semiconductors

By introducing Nano Pulse Control^™, ROHM’s own ultra-high-speed pulse control technology, the BD9S402MUF-C can execute stable control even for short switch-on times under 50 ns, which have heretofore been difficult to accommodate. While maintaining a fast 2.2 MHz switching frequency, a low voltage of 0.8 V can be output directly, with a high ±1.0% precision including temperature characteristics, from a 5 V power supply input. Today’s most advanced SoCs and microcontrollers use extremely low power supply voltages near 1.0 V, but as chip integration advances and circuits become ever finer, it is anticipated that next-generation power supply voltages of 0.6 V will be used. The BD9S402MUF-C is capable of 0.6 V output as well.

The BD9S402MUF-C is optimal for various onboard applications in which high-performance SoCs or microcontrollers and DDR memory are installed, such as ADAS with sensors, cameras, radar and the like, wireless communication modules or gateways and other communication systems, and infotainment systems such as clusters and head-up displays (HUDs). It is certainly a power supply IC that will be indispensable for onboard electronic system development in the CASE era.