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Research on Development Trend of Automobile Power Management

In the automotive field, electronic systems have become denser and more interconnected. These complex systems require power converters to be placed in smaller and smaller spaces, causing sensitive systems to be close to each other, and EMI (electromagnetic interference) problems are inevitable.

However, reducing EMI in power supplies is a growing design challenge for power management. For example, SMPS (Switch Mode Power Supply) as a power converter is a typical source of electromagnetic interference. Therefore, optimizing the power converter and suppressing the impact of EMI has become a key consideration for every automotive system design engineer.

Frontier Trends in Power Management

Cecelia Smith, vice president and general manager of boost and multi-channel DC/DC at Texas Instruments (TI), said that with the increase of electronic components in advanced driver assistance systems (ADAS), automotive infotainment systems and instrument clusters, reducing EMI is imminent. Some trends in power management deserve engineers' attention:

Low electromagnetic interference: Minimize interference with other system components and simplify power supply design and qualification process; High power density: Reduce system cost while increasing power density and achieve more system functions; Low IQ (quiescent current) : Extend battery life and storage time, achieve more functions, and reduce system cost; Low noise and high precision: Reducing or diverting noise can simplify the power chain and improve the reliability of precision analog applications; Isolation: In high voltage and safety-critical applications In order to achieve higher operating voltage and higher reliability.

What are EMIs?

EMI is a type of electromagnetic energy, an undesirable by-product of switching currents and voltages, that arises from a variety of physical phenomena that can manifest itself in rigorous EMI testing.

Take the SMPS, which is commonly used in most applications, as an example. Although its efficiency is higher than that of linear regulators, the efficiency improvement comes at a price, because the MOSFET switching in it will generate a lot of EMI, which will affect the reliability of the circuit. EMI mainly comes from input voltage ripple due to discontinuous input current, fast slew rates on switching nodes, and extra ringing at switching edges caused by parasitic inductance in the power loop. Without proper mitigation, the above phenomena can affect the operation of the power supply, load, or adjacent systems.

EMI Sources in SMPS In automotive systems that require electromagnetic compatibility (EMC), the design should minimize the interference of the source components and the susceptibility of the susceptible components. When end equipment manufacturers integrate components from different suppliers, they must ensure that interfering components and susceptible circuits do not affect each other. The only way is to establish a common set of rules to limit the interference of the former to a certain range. within, reducing the impact on circuits susceptible to interference.

These rules are based on industry-wide norms such as CISPR 25 for the automotive industry and CISPR 32 for multimedia equipment. Therefore, reducing EMI according to CISPR standards is critical for design compliance.

Conventional methods to reduce EMI meet challenges

Reducing EMI is a tricky business requiring various trade-offs. Conventional methods to reduce EMI include using large and expensive filters or reducing switch slew rates, but this directly impacts conversion efficiency.

Passive inductor-capacitor (LC) based EMI filters are often used to reduce input ripple. While an LC filter achieves the attenuation necessary to meet EMI specifications, it comes at the expense of increased system size and cost and reduced overall power density.

In addition, bulky inductors used in input EMI filter designs cannot achieve attenuation in the frequency range above 30MHz due to their low self-resonant frequency, and additional components such as ferrite beads are required to handle high-frequency attenuation, further Increased component count, volume and cost.

Another traditional approach to solving EMI problems is spread spectrum (or clock jittering) to modulate the switching frequency of the SMPS to reduce the spectral peaks associated with the fundamental switching frequency and its harmonics, at the expense of increasing the noise floor.

SMPS Spectrum Before and After Using Spread Spectrum Technology In any case, EMI must be considered at the beginning of the design, since EMI may seriously hinder the design progress in the later stage, wasting a lot of time and money. However, the EMI problem has become more serious as the pressure on designs to improve power supply efficiency increases to reduce size and cost by increasing switching frequency, or to increase efficiency by increasing slew rate. Therefore, it is necessary to find an EMI mitigation technique that does not affect the power supply design, but is also cost-effective and easy to integrate.

Innovative Technology Balancing Efficiency, EMI, Size and Cost

Ganesh Srinivasan, manager of TI's wide input voltage and step-down switching power supply product line, said that in order to meet the EMI challenge, innovative solutions and accurate modeling techniques that help reduce low-frequency and high-frequency EMI must be adopted. These include innovative spread spectrum techniques that help reduce filter size and cost; integrated bypass capacitors that reduce design time and complexity, integrated active EMI filters, and more. Products embodying TI's leading EMI innovations include buck controller LM25149-Q1, synchronous buck converter LMQ61460, charge port controller TPS25850-Q1, non-synchronous boost converter LM5157-Q1 and isolated DC/DC power supply UCC12050.

DRSS technology plus integrated active EMI filter: The first advanced DC/DC controller LM25149-Q1 with integrated active EMI filter (AEF) can help engineers optimize the size and EMI of power supplies in automotive electronics. The active EMI filter can detect the noise and ripple voltage at the input, and inject a current opposite to it on the DC input bus, thereby eliminating current or voltage interference, reducing EMI noise and ripple voltage, and significantly improving low-frequency spectrum radiation. The LM25149 combines an active EMI filter with another EMI innovation—Dual Random Spread Spectrum (DRSS) technology—combined to deliver industry-leading EMI performance across the entire EMI test frequency band.

The use of LM25149 can avoid interference to the AM and FM frequency bands, so that the driver is not affected by audio noise, and at the same time avoid EMI interference from damaging the electronic devices inside the car, causing the entire body system including the entertainment system to fail.

According to reports, DRSS technology combines low-frequency triangular modulation and high-frequency pseudo-random modulation to optimize low-frequency and high-frequency EMI performance. The DRSS and active filter combination can achieve a 55dB?V reduction up to 400GHz, further improving the EMI performance of the power supply. In addition, the active components in the active EMI filter amplify the sensed signal and significantly reduce the overall interference on the input line by injecting the appropriate reverse polarity signal through the injection capacitor. This offloads the filtering burden on the required passive components, thereby reducing the size, bulk and cost of these components. The area and volume of its external EMI filter can be reduced by nearly 50% and 75%, respectively.

Reduce EMI noise while reducing volume Another product that integrates DRSS EMI technology is the LM5157-Q1 non-synchronous boost converter, which can help engineers meet the CISPR 25 automotive EMI standard. Its switching frequency is 2.2MHz, which can avoid interference with the AM frequency band and realize a solution to reduce the size of the entire power supply. At the same time, the product has a frequency synchronization range of plus or minus 30%, which can simplify EMI filter design. The LM5157 is suitable for various topologies for various applications, including boost, SEPIC or flyback topologies, bringing customers more topological choices. Its 1.5V minimum input voltage supports the harsher automotive cold crank function and can be used in multiple configurations (boost, SEPIC or flyback converters) for various automotive applications. With up to 6A switch current, engineers can use it as a converter in applications that would normally require a controller, reducing BOM and component count.

Integrated Input Bypass Capacitors: Larger input power loops result in higher emissions at high frequency bands due to higher switch node ringing. Integrating high-frequency input decoupling capacitors within the device package helps minimize input loop parasitics, thereby reducing EMI. The automotive version of the LMQ61460 synchronous buck converter changes the bond wire package to a HotRod™ package and integrates a bypass capacitor. EMI interference, suitable for various automotive environments with harsh environments. LMQ61460 provides 3V-36V wide input voltage range, and the simplified input surge protection design can withstand 42V transient input voltage. Thanks to the integrated input bypass capacitor, the product can greatly reduce the baseline inductance in the package, and at the same time reduce the input ripple, thus providing better EMI performance.

Integrated two high-frequency input bypass capacitors According to reports, the so-called HotRod? package is a flip-chip package based on a lead frame, which flips the silicon chip and places it directly on the lead frame, thereby minimizing bonding The parasitic inductance on the pin caused by the line switching current. In addition to improving power loop inductance, the HotRod™ package helps reduce resistance in the power path, increasing efficiency and reducing solution size. In addition to reducing the input power loop inductance, the package integration of the input high frequency capacitor helps make the solution less susceptible to end system board layout variations.

The structure of the HotRod? package is more reliable than the bonded wire package. Highly integrated dual-port USB at the automotive level: TPS25850-Q1 is a new generation of dual-port, 3A DC/DC charging port controller with a switching frequency of 2.2MHz, which can greatly reduce The output filter inductor helps automotive engineers to easily implement a more compact charging solution. For this product, TI provides engineers with 400KHz and 2.2MHz reference designs, which can enable engineers to replicate and accurately achieve 2.2MHz and 400KHz frequencies, pass strict EMI tests and reduce the size of external inductors, thereby reducing switching frequency. frequency interference. Highly integrated devices that use TPS25850-Q1 to detect and control USB Type-C and battery charging 1.2 specification ports can reduce the solution size by 37%; intelligent thermal management can reduce the risk of thermal shutdown in interconnected devices and improve user performance. experience.

Carefully Solving EMI Dilemmas

Cecelia Smith said that the rapid development of automotive electronic applications has brought enormous pressure to the design of power converters. Great care must be taken when designing power converters to comply with the limits set by standards bodies so that critical systems can operate safely in noisy environments.

The above innovations for automotive applications mainly cover ADAS, entertainment systems, hybrid/electric and powertrain systems, as well as body electronics and lighting systems. The innovative solution will help engineers meet EMI standards while increasing the power density of the design, bringing greater convenience to the design.