STMicroelectronics reveals monolithic automotive synchronous buck converters

The A6983 converters offered flexible design choices, comprising six non-isolated step-down converters in low-consumption and low-noise configurations, and the A6983I isolated buck converter. With compensation circuitry on-chip, these highly integrated monolithic devices required minimal external components including filtering, feedback, and a transformer with the A6983I.

The non-isolated A6983 converters could supply up to 3A load current and achieved 88% typical efficiency at full load. The low-consumption variants (A6983C) were optimised for light-load operation, with high efficiency and low output ripple, to minimise drain on the vehicle battery in applications that remained active when parked. The low-noise A6983N variants operated with constant switching frequency and minimised output ripple across the load range for optimum performance in applications such as audio-system power supplies. Both types offered a choice of 3.3, 5.0V, and adjustable output voltage from 0.85V to VIN.

The A6983I, a 10W iso-buck converter with primary-side regulation, eliminated the need for an optocoupler. Ideal for use as an isolated gate driver for IGBTs or silicon-carbide (SiC) MOSFETs in traction inverters and on-board chargers (OBCs), this converter allowed accurate adjustment of the primary output voltage. The transformer turns ratio determined the secondary voltage.

All isolated and non-isolated variants had a low quiescent operating current of 25µA and a power-saving shutdown mode that drew less than 2µA. The input-voltage range from 3.5V to 38V, and load-dump tolerance up to 40V, prevented disruption due to transients on the main supply bus. There was also output overvoltage protection, thermal protection, and internal soft start. Additionally, optional spread-spectrum operation helped lower electromagnetic interference (EMI) for noise-sensitive applications, and a power-good pin enabled power sequencing. The A6983I and A6983 allowed synchronisation to an external clock.

The converters were offered in a 3 x 3mm QFN16 package. Pricing started at $1.75 for the A6983 and $1.81 for the A6983I, for orders of 1,000 pieces, and free samples of the A6983 and A6983I were available from the ST eStore. The STEVAL-A6983CV1 and STEVAL-A6983NV1 A6983 evaluation boards, and STEVAL-L6983IV for the A6983I, were available to kickstart development and accelerate project completion.