STMicroelectronics Introduces Isolated Buck Converters to Reduce BOM Costs for Automotive and Industrial Applications

     Designed for isolated buck regulators, ST's A6986I and L6986I DC/DC converter chips have been optimized with wide input voltage range and low quiescent current to ensure stable and efficient converters in automotive and industrial applications Operation, the maximum output power is 5W.

     If the system requires a non-isolated primary-side regulator and one or more isolated secondary-side regulators, an isolated buck topology can significantly reduce the system's bill of materials cost. The secondary voltage is determined by the turns ratio of the transformer coil, and the voltage regulator circuit does not require an optocoupler. Common applications include powering SiC MOSFET and IGBT transistor gate drivers that require asymmetric isolated power rails and isolated interfaces RS-232, I2C, SPI, and more.

     The A6986I is AEC-Q100 Grade-1 certified, and typical applications include on-board chargers (OBC) and hybrid/electric vehicle (H/EV) power motor drivers. Up to 100% duty cycle and wide 4V-38V input voltage meet automotive system cold crank and load dump specifications. The industrial-grade L6986I is ideal for motor drives, solar conditioning systems, uninterruptible power supplies (UPS) and welders.

     These two converters use forced PWM mode, with peak current mode control function, which can adjust the primary output voltage. The expanded primary negative current limit provides more flexibility to obtain suitable secondary currents using a typical transformer turns ratio. The soft start of the converter can be set, which can work reliably, and also provides the pulse-by-pulse current detection function for the primary side constant current protection. The preset current detection blanking time of 300ns can filter the oscillation generated by the leakage inductance of the transformer and ensure that the chip has higher stability during the on-off of the high-side switch. The chip has built-in overvoltage protection and thermal shutdown protection, and there are external clock synchronization and switching frequency setting pins.

     Evaluation boards for both converters help speed up the development cycle of single- and dual-output automotive-grade converters. The STEVAL-A6986IV1 has 18V and -4.5V dual-voltage isolated outputs; the STEVAL-A6986IV2 has a 5V single-voltage isolated output. The user can adjust the output voltage with external components.