BD9B331GWZ Buck DC-DC Converter ROHM Semiconductor BD9B331GWZ Buck DC-DC Converter is a single synchronous step-down converter designed to produce a low voltage output of 0.6V to 3.3V from a 2.7V to 5.5V power supply line. BD9B331GWZ offers high efficiency in all load ranges by automatic PFM/PWM adjustment. This device employs an On-time control system to provide a faster transient response to sudden changes in load.