Isolated buck converters reduce BoM, claims STMicroelectronics
Two DC/DC converter ICs optimised for isolated buck regulator designs can be used in automotive and industrial applications. The A6986I (automotive) and L6986I (industrial) DC/DC converter ICs have a wide input voltage range and low quiescent current, making them suitable for energy-efficient operation in applications up to 5W.
The isolated buck topology reduces the bill of materials (BoM) in systems that require a regulated non-isolated primary voltage and one or more isolated secondary voltages, says STMicroelectronics. The secondary voltage is governed by the transformer turns ratio and no optocoupler is needed for regulation. Common 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.
Typical 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 per cent duty-cycle capability and wide input voltage range (4.0 to 38V) meet the cold crank and load dump specifications for automotive systems. The industrial-grade L6986I is suitable 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 gives extra flexibility to ensure suitable secondary current using a typical transformer coil ratio. The devices feature programmable soft start to enhance reliability and pulse-by-pulse current sensing for constant current protection in the primary side. A pre-set current sense blanking time of 300 nanoseconds filters oscillations generated by the transformer leakage inductance and ensures greater stability during high side switching transitions. Over-voltage and thermal shutdown protections are built in and there are external pins for synchronisation and setting the switching frequency.
STMicroelectronics also offers two evaluation boards to help accelerate development of single- and dual-output automotive converters. The STEVAL-A6986IV1 comes with 18V and -4.5V isolated outputs. The STEVAL-A6986IV2 has a single 5.0V isolated output. Voltages can be user-adjusted with external components.
Both the L6986I and A6986I are in production now and available in a thermally enhanced HTSSOP-16 package. The evaluation boards are also available now.
