Isolated buck converters lower BOM costs

STMicroelectronics has released the A6986I and L6986I DC/DC converters, optimized for isolated buck regulator designs. These isolated buck converters offer a wide input-voltage range and low quiescent current for energy-efficient operation in automotive and industrial applications up to 5 W.

“The isolated buck topology drastically lowers the bill of materials in systems that require a regulated non-isolated primary voltage and one or more isolated secondary voltages,” said STMicroelectronics. “The secondary voltage is governed by the transformer turns ratio and no optocoupler is needed for regulation.”

Typical uses include powering gate drivers for SiC MOSFETs and IGBTs that require asymmetrical isolated power rails and powering isolated interfaces such as RS-232, I2C, and SPI.

Applications for the AEC-Q100 Grade-1 qualified A6986I converters include automotive on-board chargers (OBC) and hybrid/electric-vehicle (H/EV) traction drives. The 100% duty-cycle capability and wide input-voltage range, from 4 V to 38 V, meet the cold-crank and load-dump specifications for automotive systems. The industrial-grade L6986I is suited for motor drives, solar power-conditioning systems, uninterruptible power supplies (UPS), and welders.

The converters operate in forced-PWM mode with peak-current-mode control to regulate the primary output voltage. An extended negative current limit on the primary side ensures suitable secondary current using a typical transformer coil ratio.

Other features include programmable soft-start to enhance reliability, pulse-by-pulse current sensing for constant-current protection in the primary side, and built-in overvoltage and thermal shutdown protection. In addition, a preset current-sense blanking time of 300 ns filters oscillations generated by the transformer leakage inductance and ensures greater stability during high-side switching transitions, said STMicroelectronics.

Two evaluation boards are available to develop single- and dual-output automotive converters. The STEVAL-A6986IV1 comes with 18-V and -4.5-V isolated outputs, while the STEVAL-A6986IV2 has a single 5-V isolated output. Users can adjust these voltages with external components.

The industrial L6986I is priced from $1.00 and the automotive A6986I from $1.87, for orders of 1000 pieces. Both devices are in production and available in a thermally enhanced HTSSOP-16 package.