New automotive synchronous buck converter for light load, low noise and isolation applications

     STMicroelectronics has unveiled automotive-qualified step-down synchronous DC/DC converters that offer space-saving benefits and facilitate integration in many applications, such as body electronics, audio systems, and inverter gate drivers.

     The A6983 converters provide versatile design options, including six non-isolated step-down converters with low power consumption and low noise versions, as well as the A6983I isolated buck converter. The A6983I, with its compensation circuitry incorporated on-chip, requires only a few external components such as filtering, feedback, and a transformer.

     The A6983 converters, which are not isolated, have the capability to provide a load current of up to 3A. These converters can reach a typical efficiency of 88% while operating at full load. The low-consumption variations (A6983C) are designed to operate efficiently with minimal output ripple under light loads, in order to reduce the drain on the car battery. These variants are particularly suitable for applications that remain active even when the vehicle is parked.

     The A6983N variations, which have low noise levels, maintain a steady switching frequency and reduce output ripple across the load range. This makes them ideal for applications like power supply in audio systems, where optimal performance is desired. Both variants have the option to select between 3.3V, 5.0V, and a variable output voltage ranging from 0.85V to the input voltage (VIN).

     The A6983I is a 10W isolated buck converter featuring primary-side regulation, which avoids the requirement for an optocoupler. This converter is well-suited for serving as a stand-alone gate driver for IGBTs or silicon-carbide (SiC) MOSFETs in traction inverters and on-board chargers (OBCs). It enables precise control of the primary output voltage. The turns ratio of the transformer directly impacts the magnitude of the secondary voltage.

     Both isolated and non-isolated variants exhibit a low quiescent running current of 25µA and feature a power-saving shutdown mode that consumes less than 2µA. The device has an input-voltage range of 3.5V to 38V and can tolerate load-dump up to 40V. This feature ensures that any disturbances caused by sudden changes in the main supply bus are avoided. Additionally, there are features such as output overvoltage protection, thermal protection, and internal soft start.

     Furthermore, the inclusion of optional spread-spectrum operation serves to reduce electromagnetic interference (EMI) in applications that are sensitive to noise. Additionally, the presence of a power-good pin allows for power sequencing. The A6983I and A6983 support the ability to synchronize with an external clock. The converters are available in a compact QFN16 packaging measuring 3mm by 3mm.