Selection of 48V power supply system for electric vehicles, wide voltage input DC/DC converter

In the automotive field, with the introduction of 48V mild hybrid system and the increasing popularity of electric vehicles, DC/DC converters have become an indispensable part of automotive power systems. In electric vehicles, DC/DC converters can serve as a bridge between the power battery and the motor system, converting the power battery voltage into the voltage required by the motor to provide power for the vehicle. At the same time, the DC/DC converter can also adjust the battery output to the voltage required by various applications to power the vehicle's low-voltage electrical equipment.

ROHM DC/DC converters that can be applied to 48V power supply systems

After the 48V mild hybrid system was proposed, it was recognized by many car companies and used in models such as Audi SQ7, Porsche Cayenne, and Bentley Flying Spur. The introduction of the 48V mild hybrid system can provide vehicles with higher power, power and save system energy consumption. Compared with the 12V system, the 48V mild hybrid system has only 1/4 of the 12V system at the same power , and the loss is only 1/16, which also helps to reduce the size of the engine and reduce carbon emissions.

With the improvement of energy-saving awareness and the transition from 12V power supply system to 48V, ROHM, based on its own technical advantages in the power supply field, launched the DC/DC converter BD51180 TL that can be applied to 48V power supply system to improve the conversion efficiency of vehicle power system. BD51180 TL has a built-in MOSFET

with a withstand voltage rating of 80V , which can easily deal with the problem of excessive transient response voltage when the car starts. At the same time, the converter adopts a unique pulse control technology, and the switch response operation can be completed within 20ns, with a fixed switching frequency of 2MHz, thereby avoiding the problem of frequency interference. In addition, the output voltage of 48V battery can be reduced to 3.3V or 5V for use by vehicle-mounted MCU and other control systems through a first-level conversion, which greatly simplifies the development process of terminal applications, avoids the power loss caused by secondary conversion, and helps to achieve miniaturization and efficient product design. The unique pulse control technology mainly plays the role of phase compensation in BD51180 TL, controlling the current through a narrow pulse width to achieve phase compensation of current mode control. The BD51180 TL meets the automotive-grade AEC-Q100 application standards. The device also integrates a series of protection functions such as current protection, temperature protection, and load short-circuit protection. The product specifications are 4*4*1mm, and the volume is reduced by 54% compared with products with similar performance. TI supports 6V to 120V wide voltage input DC/DC converter LM5169-Q1. It is a DC/DC converter launched by TI that meets the stringent requirements of automotive-grade products and can be adjusted within a wide voltage dynamic range of 6V to 120V. The wider input voltage dynamic range can reduce the design of surge voltage suppression circuits to a certain extent , thereby reducing the complexity of product design.

Image source: TI

The LM5169-Q1 has a minimum controllable on-time of 50ns and an adjustable switching frequency of 1MHz. The extremely short switch on-time is conducive to improving the step-down conversion ratio of the DC/DC buck converter and improving the conversion efficiency of the 48V power system when stepping down. At the same time, the converter also integrates a constant on-time control function to provide the system with a stable switching frequency and excellent load and line transient response.

In terms of control, the converter is mainly controlled through FPWM mode and automatic mode. In FPWM mode, the fly-buck function is supported, and the FPWM mode can ensure forced CCM operation over the entire load range. In automatic mode, ultra-low Iq and diode simulation mode operation can be achieved to achieve higher light load efficiency.

The converter integrates a MOSFET with high-side and low-side output channels, with an output current of up to 0.65A. It also integrates a 1.9Ω NFET buck switch, a 0.71Ω NFET synchronous rectifier, a VCC bias regulator and a bootstrap diode. The highly integrated approach not only achieves miniaturization of the solution design, but also reduces the BOM cost of the circuit.

In terms of product reliability, LM5169-Q1 has passed the AEC-Q100 standard certification and can ensure the stability of the working performance of components between -40℃ and 125℃ , which meets the temperature requirements of the automotive environment. To further improve the reliability of the converter, TI has integrated peak/valley current limiting protection, input UV LO and thermal shutdown protection to avoid irreversible damage to the peripheral circuit due to the failure of the converter, resulting in increased maintenance costs.

Conclusion

Driven by the electrification of automobiles, DC/DC converters have become the core components of electric vehicles and are the "bridge" connecting high-voltage and low-voltage applications. The realization of many functions of electric vehicles requires the assistance of DC/DC converters. Today, the popularity of electric vehicles is growing rapidly, and electric vehicle DC/DC converters will have a high market value.