In the name of life safety! ADI ultra-low EMI dual-channel step-down regulator greatly simplifies ADAS design

When you see a serious car accident leading to many deaths and injuries, do you also feel anxious: Why is there no effective ADAS (advanced driver assistance system) to protect life? Indeed, ADAS has been proven to prevent casualties caused by accidents, but due to technical maturity, system reliability, and cost issues, the popularization process cannot be accomplished overnight. With the continuous development of upstream and downstream industries in the industry chain, ADAS-related technologies are becoming more abundant and mature, consumers are paying more and more attention to safety and increasing government safety regulations, and automotive ADAS has entered a period of strong growth.Max Consulting reported that the automotive ADAS market was worth 24.24 billion U.S. dollars in 2018

When you see a serious car accident leading to many deaths and injuries, do you also feel anxious: Why is there no effective ADAS (advanced driver assistance system) to protect life? Indeed, ADAS has been proven to prevent casualties caused by accidents, but due to technical maturity, system reliability, and cost issues, the popularization process cannot be accomplished overnight. With the continuous development of upstream and downstream industries in the industry chain, ADAS-related technologies are becoming more abundant and mature, consumers are paying more and more attention to safety and increasing government safety regulations, and automotive ADAS has entered a period of strong growth. Maims Consulting reported that the automotive ADAS market was worth US$24.24 billion in 2018 and is expected to reach US$91.83 billion by 2025. The compound annual growth rate during the forecast period is as high as 20.96%.

In the name of life safety! ADI ultra-low EMI dual-channel step-down regulator greatly simplifies ADAS design

Figure 1: In November 2018, the Lanhai Expressway crash caused 15 deaths and 45 injuries

The rapid growth of the ADAS market is partly due to the enhancement of the EMI performance of the power system, which has greatly strengthened the reliability and stability of ADAS-electromagnetic interference may cause the system to be less sensitive, or even malfunction or crash. High-performance analog chip manufacturer ADI’s dual-channel step-down regulator LT8650S, using Silent Switcher® 2 The architecture minimizes EMI radiation while providing high efficiency at high switching frequencies, which is very suitable for automotive applications that are sensitive to electromagnetic interference, including ADAS.

Design Difficulties of ADAS Power System

ADAS mainly collects environmental data inside and outside the vehicle through various on-board sensors to detect risks from surrounding objects, such as unruly pedestrians, cyclists, other vehicles in unsafe driving directions, etc., and promptly alert the driver; usually It will also provide dynamic functions, such as adaptive cruise, emergency braking, automatic parking, etc., which are active safety technologies that improve driving safety, and are generally considered to be procedural technologies for automatic driving.

In the name of life safety! ADI ultra-low EMI dual-channel step-down regulator greatly simplifies ADAS design

Figure 2: ADAS function realization and technology development trend

As one of the important guarantees for driving safety, what are the special requirements for the power system that provides energy for ADAS? Generally, automotive applications such as ADAS are directly powered by the main battery of the car, with a nominal voltage of 9V to 18V. However, since the voltage transient in the automotive system may be as high as 42V and as low as 3.5V during cold start, any DC/DC At a minimum, the converter must be able to handle a wide input voltage range of 3.5V to 42V.

Previously, many ADAS used 5V and 3.3V rails to power various analog and digital IC products, but the operating requirements of many processor I/O and core voltages were lower than 2V, or even as low as 0.8V. At the same time, limited by the increasingly cramped system space, additional radiators should not be considered as much as possible. In addition, in the current ADAS, the switching regulator must also switch at a frequency of 2MHz or higher, rather than the switching frequency of less than 500kHz in the past. The key driving force behind this transformation is the need for a solution with a smaller board area and staying above the AM frequency band to avoid any potential electromagnetic interference and ensure compliance with various anti-noise standards in automobiles.

Dual DC/DC converter with excellent EMI performance

How to solve the power design problem of ADAS? ADI’s dual-output monolithic synchronous step-down converter LT8650S has excellent EMI performance, small solution size, high efficiency and other advantages, which can meet the stringent requirements related to automotive safety. As shown in Figure 3, the LT8650S consists of two high-voltage 4A channels that provide voltages as low as 0.8V, allowing the device to drive the currently available and lowest-voltage microprocessor cores. Its synchronous rectification topology provides up to 94.4% efficiency at 2MHz switching frequency, while the burst mode (Burst Mode)®) Operate under no-load standby conditions to keep the quiescent current below 6.2µA (both channels are on), making this device ideal for always-on systems.

In the name of life safety! ADI ultra-low EMI dual-channel step-down regulator greatly simplifies ADAS design

Figure 3: LT8650S schematic ─ provide 5V/5A and 3.3V/4A output at 2MHz

The switching frequency of LT8650S can be set in the range of 300kHz to 3MHz, and can be synchronized to this range; the shortest on-time of 40ns allows 16V in the high-voltage channel with a switching frequency of 2MHzINTo 2.0VOUTStep-down conversion; unique Silent Switcher® 2 The architecture uses two internal input capacitors and internal BST and INTVCC Capacitors to minimize the area of ​​the thermal loop.

The design of LT8650S combines well-controlled switching edges and an internal structure with an integral ground plane, and copper pillars are used instead of bonding wires, thus significantly reducing EMI/EMC radiation. This improved EMI/EMC performance is not sensitive to the circuit board layout, which simplifies the design and reduces risk, even when using a two-layer PC board. The LT8650S can easily meet the automotive CISPR 25 Class 5 peak EMI limits when switching at a switching frequency of 2MHz over the entire load range. Spread spectrum frequency modulation can also be used to further reduce EMI levels.

In the name of life safety! ADI ultra-low EMI dual-channel step-down regulator greatly simplifies ADAS design

Figure 4: Radiated EMI diagram of LT8650S

The LT8650S uses internal top and bottom high-efficiency power switches, and the necessary boost diode, oscillator, control and logic circuits are integrated in a single chip. Low-ripple burst mode operation maintains high efficiency at low output currents while keeping the output ripple below 10mV pp. Finally, the LT8650S is packaged in a small thermally enhanced 4mm x 6mm 32-pin LGA package.

in conclusion

Data from Gasgoo Automotive Research Institute shows that as the assembly rate of ADAS technology in new cars continues to increase, China’s ADAS market will enter a period of rapid penetration in the next 2-3 years. This rapid growth is expected to continue to the volume of high-level autonomous vehicles. Produce. In the face of the popularity of ADAS in higher-end models, the “best-in-class” power converters provided by ADI can provide the required high-end performance without complicated layouts or design methods, greatly simplifying the design task, and making ADAS Designers are more comfortable, so as to achieve the goal of paying tribute to life safety with technological development faster.

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