Are we ready for self-driving cars? This is the question I have been asking myself recently, maybe you have the same question! Of course, as far as I am concerned, since my teenage daughter started learning to drive, I have been somewhat out of self-interest. After she finished the first class, I asked her how she was, and her answer surprised me a bit. It seemed that driving didn’t worry her much, but the drivers around her made her uneasy.

Introduction

Are we ready for self-driving cars? This is the question I have been asking myself recently, maybe you have the same question! Of course, as far as I am concerned, since my teenage daughter started learning to drive, I have been somewhat out of self-interest. After she finished the first class, I asked her how she was, and her answer surprised me a bit. It seemed that driving didn’t worry her much, but the drivers around her made her uneasy. She complained that they were always too close to her rear bumper, they never used turn signal lights, and they would unexpectedly cut in in front of her car in order to change lanes. These complaints are reasonable, and I empathize with my own experience on the roads of Northern California.

This reminds me of self-driving cars, which do not require a human driver to sit behind the steering wheel (of course, there may be one, but it is not actually using the control mechanism from a traditional perspective). In contrast, the mainframe of a microcomputer equivalent to a human driver runs a large amount of computer code and is connected to various sensor arrays inside and outside the vehicle. They are connected to the cloud and can simulate the external environment around the vehicle in full real-time, so as to anticipate the actions to be taken based on the current surrounding traffic conditions. Regardless of the range and status of the climate, environment, and traffic conditions, these operations will be performed normally.

Unfortunately, a self-driving road test vehicle crashed and killed a cyclist recently in Arizona. According to local police, the cyclist was crossing the road off the sidewalk. Although the bicycle was at the scene of the accident, the police did not believe that the victim was riding a bicycle when the accident occurred. The victim was rushed to a nearby hospital and was pronounced dead shortly after arriving at the hospital.

At the time of the incident, there was a person behind the steering wheel of the self-driving SUV, but that person did not actually control the vehicle. According to local officials, there were no other passengers in the car at the time of the incident. It is worth noting that Arizona is one of the few states in the United States, and it is legal to determine that the driver’s seat of a self-driving car does not require a human in order to take over the control of the vehicle when necessary. However, such accidents cannot increase the public’s confidence in the autonomous driving capabilities of driverless cars.

Autonomous vehicle schedule

There is no doubt that although autonomous vehicles will encounter some setbacks in the development process, they are still gradually approaching us. Therefore, there are some questions worth pondering: when will we actually enter autonomous driving, and how long will it take?

According to the analysis of the automobile industry, there are two standard terms for the transition path of autonomous driving: one is evolutionary, as many cars are currently being gradually advanced (similar to Tesla’s autonomous driving function); the other is revolutionary , That is, fully autonomous vehicles (such as those being developed by Google). In my opinion, it is still unclear which path alone will achieve success, but the more likely result is a symbiosis and fusion of the two.

So, how will it develop in the next few years? Based on the relevant information I have obtained from experts in some key industries, the following areas will be further developed:

More advanced driver assistance functions can be synchronized with navigation and GPS systems.

Companies like Google will collect and accumulate data about every situation that autonomous vehicles may encounter.

Surveying and mapping companies will need to strengthen the support of 3D surveying and mapping data in major cities.

Car manufacturers and high-tech automotive system suppliers need to work closely with each other to ensure that light detectors, lidars, radar sensors, GPS, and cameras work together.

Cars incorporating the above-mentioned functions must be tested under all terrain and climate conditions.

Looking to the future, by 2020, cars equipped with the above-mentioned semi-automatic functions should be able to drive autonomously to pass traffic conditions such as intersections, traffic lights, and parking yields. Nevertheless, these highly autonomous vehicles still require a human driver to sit in front in an emergency. It is estimated that by 2024, these semi-autonomous vehicles will be able to drive normally under more severe conditions (such as inclement weather and night). By then, Lyft taxi-hailing service providers may be able to start using this type of car without any drivers. Of course, automakers need to ensure that their cars can understand signals from passers-by, such as recruiting when crossing a street. All these developments inevitably require automakers to equip their vehicles with many autonomous functions, so that it is possible to realize fully autonomous vehicles on the road in the mid-2030s.

Of course, all the development progress required to achieve this timetable will create great opportunities for the IC semiconductor industry, because putting it into practice will require many systems to add a lot of silicon technology content. These silicon technology content will be composed of digital and analog integrated circuits (ICs).

Self-driving cars-can the power system be competent?
Figure 1.2 provides a simplified schematic diagram of the LT8650S with 5 V, 4 A and 3.3 V, 4 A outputs at 1.2 MHz.

Analog IC

Fully autonomous vehicles will obviously be equipped with numerous Electronic systems composed of different digital and analog ICs. They will include advanced driver assistance systems (ADAS), autonomous driving computers, automatic parking assistance, blind spot monitoring, intelligent cruise control, night vision, lidar, etc., to name a few. All these systems require a variety of different voltage rails and current levels to ensure their normal operation. They can be powered directly from the car battery and/or alternator, or in some cases, from power rails that have been post-regulated via these voltage rails. The latter usually occurs in the case of the core voltage of VLSI digital ICs (such as FPG and GPU). At this time, an operating voltage of less than 1 V and a current of several to tens of amperes may be required.

The system designer must ensure that the ADAS meets the various noise immunity standards in the car. In the automotive environment, switching regulators are replacing linear regulators in areas where low heat dissipation and high efficiency are important. Moreover, the switching regulator is usually the first active component on the input power bus, so it has an important impact on the EMI performance of the entire converter circuit.

There are two types of EMI emissions: conduction and radiation. Conducted emission is connected to the product through wires and traces. Since the noise is limited to specific terminals or connectors in the design, as mentioned above, with the help of a good layout or filter design in the early development process, it is usually relatively easy to ensure compliance with the conducted radiation requirements.

However, radiation emission is another matter entirely. Anything on the circuit board that carries current will radiate electromagnetic fields. Each trace on the circuit board is an antenna, and each copper layer is a resonator. In addition to pure sine waves or DC voltage, anything else will generate noise in the entire signal spectrum. Even with careful design, before the system is tested, the power supply designer does not really know how bad the radiated emission will be, and the radiated emission test can only be officially carried out after the design is basically completed.

Filters are often used to attenuate the signal strength of a specific frequency or a certain frequency range, thereby reducing EMI. This part of the energy that travels through space (radiation) can be attenuated by adding metal and magnetic shielding. The part of the energy in the PCB trace (conduction) can be suppressed by adding ferrite beads and other filters. EMI cannot be eliminated, but it can be attenuated to a level acceptable to other communications and digital devices. In addition, many regulatory agencies have implemented relevant standards to ensure compliance.

High voltage converter solution with low EMI/EMC radiation

In view of the application limitations described in this article, ADI’s Power by Linear? Division has developed the LT8650S-a synchronous step-down converter that supports high input voltage, single chip, and low EMI radiation. The device’s 3 V to 42 V input voltage range makes it an ideal choice for automotive applications (including ADAS), because automotive applications must be competent for regulation in cold start and start-stop scenarios, with a minimum input voltage as low as 3 V and transient power cut-off More than 40 V. As shown in Figure 1, the device adopts a dual-channel design, composed of two high-voltage 4 A channels, and provides an output voltage as low as 0.8 V, which can drive the microprocessor core with the lowest voltage on the market. When the switching frequency is 2 MHz, its synchronous rectification topology can achieve efficiency as high as 94.4%, and under no-load standby conditions, Burst Mode? keeps the quiescent current below 6.2 ?A (both channels are open) ), so it is very suitable for always-on system use.

The switching frequency of the LT8650S can be programmed in the range of 300 kHz to 3 MHz, and synchronization is supported in the entire frequency range. The shortest on-time as low as 40 ns can achieve a 16 VIN to 2.0 VOUT step-down conversion on the high-voltage channel when the switching frequency is 2 MHz. Its unique Silent Switcher? 2 architecture uses two internal input capacitors and internal BST and INTVCC capacitors to minimize the thermal loop area. Combining the strictly controlled switch edge and the internal structure of the integrated ground plane, and replacing the bonding wires with copper pillars, the design of the LT8650S greatly reduces EMI/EMC radiation. Figure 2 shows the characteristics of the output radiation. The improved EMI/EMC performance is not sensitive to the circuit board layout, even when using a 2-layer PCB, which can simplify the design and reduce risk. In the entire load range, when the switching frequency is 2 MHz, the LT8650S can easily meet the automotive CISPR 25 and Class 5 peak EMI limits. You can also use spread spectrum (SSFM) to further reduce EMI levels.

Self-driving cars-can the power system be competent?
Figure 2. LT8650S radiated EMI performance graph.

The LT8650S has built-in upper and lower high-power switches, and integrates the necessary boost diode, oscillator, control and logic circuits into a single chip. The low-ripple burst mode of operation can maintain high efficiency at low output current while keeping the output ripple below 10 mV pp. Finally, the LT8650S is available in a small thermally enhanced 4 mm × 6 mm IC pin LGA package.

Similarly, for applications that require a wider input range than the LT8650S, we have also developed the LT8645S-a synchronous buck converter that supports high input voltage, single chip, and low EMI radiation. Its input voltage range is 3.4 V to 65 V, so it is suitable for automotive applications as well as truck applications. These applications must be competent for regulation in cold start and start-stop scenarios. The minimum input voltage is as low as 3.4 V and the power cut-off transient exceeds 60. V. As shown in Figure 3, the device uses a single-channel design to provide 5 V, 8 A output. When the switching frequency is 2 MHz, its synchronous rectification topology can achieve an efficiency of up to 94%, and under no-load standby conditions, the burst operation mode keeps the quiescent current below 2.5 μA, so it is very suitable for always-on systems.

Self-driving cars-can the power system be competent?
Figure 3.2 Simplified schematic diagram of LT8645S with 5 V and 8 A output at 3.2MHz

The switching frequency of the LT8645S can be programmed from 200 kHz to 2.2 MHz, and it supports synchronization in the entire frequency range. Its unique Silent Switcher 2 architecture uses two internal input capacitors and internal BST and INTVCC capacitors to minimize the thermal loop area. Combining the strictly controlled switch edge and the internal structure of the integrated ground plane, and replacing the bonding wires with copper pillars, the design of LT8645S greatly reduces EMI/EMC radiation. Figure 4 shows the characteristics of the output radiation. The improved EMI/EMC performance is not sensitive to the circuit board layout, even when using a 2-layer PCB, which can simplify the design and reduce risk. In the entire load range, LT8645S can easily meet automotive CISPR 25, Class 5 peak EMI limits. You can also use spread spectrum (SSFM) to further reduce EMI levels.

Self-driving cars-can the power system be competent?
Figure 4. LT8645S radiated EMI performance graph.

LT8645S has built-in upper and lower high-power switches, and integrates the necessary boost diode, oscillator, control and logic circuits into a single chip. The low-ripple burst mode of operation can maintain high efficiency at low output current while keeping the output ripple below 10 mV pp. Finally, the LT8645S is packaged in a small thermally enhanced 4 mm × 6 mm IC 32-pin LQFN package.

in conclusion

The automotive electronic systems required for autonomous vehicles (and trucks) are and will continue to grow in popularity. Of course, the voltage and current levels will change. However, the requirements for low EMI/EMC radiation will not change-even in harsh working environments. Fortunately, ADI’s Power by Linear product line provides more and more solutions to help system designers deal with the challenges of the present, the future, as far as the mid-2030s.

Going back to my daughter’s driving studies, today’s cars have made it easier for her to deal with the drivers around her. However, in the not-too-distant future, she will be able to lean on the driver’s seat and enjoy the car taking her for a drive leisurely.

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