Introduction Conflicting design requirements such as high reliability, low cost, and extremely short development cycles have forced power supply designers to adopt new and groundbreaking technological solutions—technologies never before explored in traditional automotive power supply design. Basic Principles of Automotive Power Supply Design Most automotive power supply architectures must adhere to six basic principles: 1) Input voltage range VIN: The instantaneous fluctuation range of the 12V battery voltage determines the input voltage range of the power conversion IC. The ISO 7637-1 industry standard defines the voltage fluctuation range for automotive batteries. Figures 1 and 2 show the waveforms specified in the ISO 7637 standard, illustrating the critical conditions that high-voltage automotive power converters must meet. [img=500,278]http://image.mcuol.com/News/081020165909960.jpg[/img] [img=500,220]http://image.mcuol.com/News/081020165910451.jpg[/img] 2) Heat dissipation considerations: Heat dissipation needs to be designed based on the minimum efficiency of the DC-DC converter. Well-designed switching power converters are typically more efficient than linear regulators, and this higher efficiency eliminates the need for large heatsinks and bulky packages in power supply designs. Most inexpensive, small-size bare-pad packages can dissipate 2W of power at 85°C and 1W at 125°C. High-power designs above 20W have stricter thermal management requirements and necessitate synchronous rectification architectures. High-efficiency external MOSFET controllers help improve the power supply's heat dissipation capabilities. 3) Quiescent Current (IQ) and Shutdown Current (ISD): With the rapid increase in the number of electronic control units (ECUs) in automobiles, the total current consumed by the car battery is also constantly increasing. Even when the engine is running and the battery is depleted, some ECU units continue to operate. To ensure that the quiescent current (IQ) is within a controllable range, most OEMs have begun to limit the IQ of each ECU. For example, the EU requirement is 100 μA/ECU. 4) Cost Control: OEMs need to compromise on module costs, development/certification costs, product launch time, and specifications. Ensuring optimal design within cost constraints is crucial, and the bill of materials (BOM) for the power supply section can significantly impact cost. Module cost is related to PCB type, heatsink, component layout, and other design factors. For example, replacing a CM-3 single-layer board with an FR-4 4-layer board will result in a significant difference in PCB heat dissipation. 5) Location/Layout: In power supply design, the layout of the PCB and components will limit the overall performance of the power supply. Structural design, PCB layout, noise sensitivity, interconnection issues in multilayer boards, and other board placement constraints all limit the design of highly integrated power supplies. Utilizing point-of-load power to generate all necessary power also leads to high costs, and integrating numerous components onto a single chip is not ideal. Power supply designers need to balance overall system performance, mechanical limitations, and cost based on specific project requirements. 6) Electromagnetic radiation: Electromagnetic interference generated by one circuit may cause another circuit to malfunction. For example, interference from radio channels may cause airbags to malfunction. To avoid these negative effects, OEMs set maximum electromagnetic radiation limits for ECU units. To keep electromagnetic interference (EMI) within controlled limits, the type, topology, peripheral component selection, board layout, and shielding of the DC-DC converter are all crucial. Over the years, power IC designers have developed various techniques to limit EMI. External clock synchronization, operating frequencies above the AM modulation band, integrated MOSFETs, soft-switching technology, and spread spectrum technology are all EMI suppression solutions introduced in recent years. Applications and Power Requirements The basic architecture selection for most system power supplies should begin with power requirements and the battery voltage transient waveforms defined by automotive manufacturers. Current requirements should be reflected in the board's thermal design. Table 1 summarizes the circuit and voltage requirements for most designs. General-Purpose Power Supply Topologies Four commonly used power supply architectures are listed here , summarizing typical design architectures in the automotive field over the past three years. Of course, users can achieve specific design requirements in different ways; most solutions can be summarized into one of these four structures. Solution 1 This architecture offers a flexible design for optimizing the efficiency, layout, PCB heat dissipation, and noise levels of DC-DC converters. The main advantages of Solution 1 are: • Increase the flexibility of core design. Even if it is not the lowest cost/highest efficiency solution, adding a separate converter helps to reuse the original design. It helps to make better use of switching power supplies and linear regulators. For example, generating 1.8V 300mA from 3.3V is more efficient and less expensive than directly stepping down from a car battery to 1.8V. • Distributes heat from the PCB, which provides flexibility in selecting the converter's location and heat dissipation. • Allows the use of high-performance, cost-effective low-voltage analog ICs, offering a wider range of choices compared to high-voltage ICs. The disadvantages of Option 1 are: larger circuit board area, relatively higher cost, and excessive complexity for designs with multiple power supply requirements. Option 2 This solution represents a trade-off between high integration and design flexibility, offering advantages in cost, size, and complexity compared to Solution 1. It is particularly suitable for applications requiring two buck outputs with independent control. For example, it may be necessary to provide uninterrupted 3.3V power while allowing the 5V power supply to be shut off when needed to conserve IQ current. Another application is generating 5V and 8V power supplies, eliminating the need for a boost converter that boosts the 5V voltage. [img=500,273]http://image.mcuol.com/News/081020165910893.jpg[/img] A dual-output controller using external MOSFETs offers the same PCB layout flexibility and facilitates heat dissipation as the previous solution. For converters with built-in MOSFETs, designers should be careful not to dissipate excessive heat in a single location on the PCB. Solution 3 This architecture transforms the multi-output high-voltage conversion problem into a single high-voltage conversion and a highly integrated low-voltage conversion IC. Compared to multi-output high-voltage conversion ICs, the highly integrated low-voltage conversion IC is less expensive and readily available on the market. If the low-voltage PMIC in Scheme 3 has more than two outputs, then Scheme 3 will suffer from the same drawbacks as Scheme 4. The main disadvantage of Option 3 is that multiple voltages are concentrated on the same chip, requiring careful consideration of PCB heat dissipation during board layout. [img=500,226]http://image.mcuol.com/News/081020165911004.jpg[/img] Option 4 The newly released highly integrated PMIC can integrate all the necessary power conversion and management functions on a single chip, breaking through many limitations in power supply design. However, high integration also has some negative impacts. In highly integrated PMICs, integration and drive capability are often contradictory. For example, during product upgrades, the regulator with built-in MOSFETs in the original design may not meet the load drive requirements of the new design. Cascading a low-voltage converter to a high-voltage converter can help reduce costs, but this approach is limited by the regulator's on/off control. For example, if the 3.3V power supply must be turned on when the 5V power supply is turned off, the 3.3V input cannot be connected to the 5V power supply output; otherwise, the 5V power supply cannot be turned off, resulting in a high quiescent current IQ. Maxim's automotive power solutions... Maxim's automotive power ICs overcome many power management challenges, providing unique high-performance solutions. Power products include highly integrated, multi-functional PMICs (as shown in Figure 4) with overvoltage protection, microprocessor monitoring, switching converters, and linear regulators. The power ICs meet automotive-grade quality certifications and manufacturing requirements, such as AECQ100 certification, DFMEA, various temperature ratings (including 85°C, 105°C, 125°C, and 135°C), and specific packaging requirements.