A DC/DC controller solves three major challenges of automotive USB Type-C power system

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Whether it is a new energy vehicle or a traditional vehicle, the electronic and electrical components in the vehicle occupy a large proportion, so whether a solution can achieve a wide voltage range power supply, high power, high efficiency, and low EMI on a very small board, and at the same time be able to achieve good heat dissipation in the vehicle environment is very important for the vehicle Type C system. This article takes ADI's low EMI, 4-switch, buck-boost DC/DC converter LT8390/LT8390A as an example to explore the challenges and solutions faced by the USB Type-C power supply design in the car. At a switching frequency of 2 MHz, the LT8390A can provide an output voltage of 5 V to 15 V (up to 45 W at 3 A) to power USB Type-C devices from the car battery.

Automotive batteries and similar wide voltage range power supplies are complex, requiring protection and efficient buck and boost conversion. Traditional buck circuits cannot meet the power supply requirements of Type C systems, so a more complex buck-boost circuit is needed to complete the power supply requirements of Type C systems. The LT8390 is a synchronous, four-switch buck-boost DC/DC controller that can adjust the output voltage, input or output current when the input voltage is higher, lower or equal to the output voltage. The device's proprietary peak buck/peak boost current mode control scheme allows adjustable and synchronizable 150kHz to 650kHz fixed frequency operation, or internal ±15% triangular spread spectrum frequency modulation for low EMI. The LT8390 has an input voltage range of 4V to 60V, an output voltage capability of 0V to 60V, and seamless low noise conversion between operating areas, making it ideal for voltage regulators, batteries, and supercapacitor chargers in automotive, industrial, telecommunications, and even battery-powered systems.

Temperature management has always been a challenge in automotive electronic systems. Generally, the system is required to work normally under an ambient temperature of -40°C ~ +65°C. The ambient temperature inside the chassis will rise by about 20°C, so the maximum ambient temperature that the PCB board actually needs to withstand will be as high as +85°C or higher. Modules such as power supplies and CPUs, as the major heat generators of automotive electronic systems, further increase the ambient temperature inside the chassis. The harsh environment has actually approached the temperature resistance limit of many chips. Therefore, in the early stage of system design, it is necessary to plan the thermal management strategy and design corresponding measures. The buck-boost converter shown in the figure below is a typical example. It supports V _IN = 9V-36V, V _OUT = 12V and I _OUT = 25A, and can achieve a power output of 300W. Under full load, the efficiency of all modes - boost, buck and buck-boost - remains high. This enables the LT8390 to regulate under all input conditions without overheating. Of course, we can add cooling elements to increase power capabilities when using it.

Additionally, when thermal performance becomes a limiting factor in creating a high power regulator system, the LT8390 can also be run in parallel to increase the total output power capability while maintaining an acceptable operating temperature over the input voltage range. Even at higher output power, the parallel LT8390 system exhibits similar thermal performance to the single-phase LT8390 system because the output power and heat dissipation are shared between the two converters. While improving thermal performance, the parallel LT8390 system also uses out-of-phase drive, effectively reducing the system's output ripple.

Low EMI is a fundamental design requirement for automotive electronics. EMI from switching regulators is often mitigated with EMI filters and electronic shielding, but this increases the cost and size of the regulator. Power designers can also choose switching frequencies to get around some EMI constraints, but this severely limits the power designer's options in terms of efficiency and solution size. To reduce design time and cost, the LT8390A has a variety of unique EMI reduction features that enable high power conversion and low noise performance, simplifying its implementation in automotive systems.

The LT8390A is a unique 2 MHz synchronous 4-switch buck-boost controller that differs significantly from other 4-switch controllers in the location of the inductor current sense resistor. While most 4-switch buck-boost controllers tend to use a ground referenced current sensing scheme to obtain switch current information, the LT8390A places its current sense resistor in series with the inductor. By placing the sense resistor in series with the inductor, the resistor is effectively removed from the buck and boost hot loops, reducing loop size and improving EMI performance.

In addition to the architectural advantages of the inductor sense resistor location, the LT8390A also has built-in spread spectrum frequency modulation to further reduce the EMI generated by the controller. In addition, the edge rates of the buck and boost power switches are controlled using only a few discrete components to slow down the turn-on of the MOSFETs, ensuring the right balance between reducing high-frequency EMI and temperature rise of the power switches. With these EMI-reducing features, the only filtering required to meet CISPR 25 standards is provided by small ferrite filters on the input and output, rather than large ferrite cases and bulky LC filters.

1-inch-square, high-efficiency, low-EMI USB Type-C power solution based on the LT8390A

USB Type-C, a new USB standard for regulators that power connected devices, supports higher power delivery by increasing the output voltage range and current delivery that regulators can provide. Portable and automotive battery-powered USB Type-C charging devices require a wide V _IN / V _OUT buck-boost regulator to deliver bus voltages above or below the input voltage. ADI's 4-switch buck-boost controller LT8390 simplifies demanding industrial and automotive power supply designs, and its applications are hardly limited to these areas as it has many features, including high efficiency over a wide output load range, low EMI, compact solution size, and very high output power capability, making it an ideal choice for emerging renewable energy and energy harvesting systems.