ST introduces isolated buck converter

     Designed for isolated step-down regulators, STmicro's A6986I and L6986I DC/DC converter chips optimize product characteristics with wide input voltage range and low static current to ensure stable and efficient operation of the converter in automotive and industrial applications, with a maximum output power of 5W.

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

     A6986I has obtained AEC-Q100 Grade-1 certification. Typical applications include on-board charger (OBC) and hybrid/electric vehicle (H/EV) power motor driver. The maximum 100% duty cycle and 4V-38V wide input voltage meet the technical specifications for cold start and load rejection of automobile systems. The industrial grade L6986I is ideal for motor drive, solar power conditioning system, uninterruptible power supply (UPS) and welding machine.

     The two converters adopt forced PWM mode, with peak current mode control function, and can adjust the primary side output voltage. The expanded limitation range of primary negative current brings more flexibility, and a typical transformer coil turn ratio can be used to obtain a suitable secondary current. The soft start of the converter can be set and can work reliably. It also provides pulse by pulse current detection function for the primary constant current protection. The 300 ns preset current detection blanking time can filter the oscillation generated by the transformer leakage inductance, ensuring that the chip has higher stability during the high side switch on/off period. The chip has built-in overvoltage protection and thermal shutdown protection, and external clock synchronization and switching frequency setting pins.

     The evaluation boards of the two converters help speed up the development cycle of single and double output gauge converters. STEVAL-A6986IV1 has 18V and -4.5V dual voltage isolated output; STEVAL-A6986IV2 has a 5V single voltage isolated output. Users can adjust the output voltage with external devices.