Direct 12V/24V-to-1V Tri-State Double Step-Down Power Converter With Online VCF Rebalancing and In- Situ Precharge Rate Regulation

In response to fast-growing high-voltage (HV) power IC market demands, this article presents a tri-state double step-down (DSD) power converter to achieve direct 12V/24Vto-1V dc-dc power delivery with high efficiency and high power density. By taking advantage of the benefits from both three-level and DSD converter topologies, the converter allows the use of lower voltage rating power devices and thus facilitates high switching frequency operation with smaller power passives. An online flying capacitor voltage (VCF) rebalancing scheme is introduced to optimize switching nodes voltages and minimize power path mismatch for improved reliability and efficiency. During startup transients, an in-situ precharge rate regulation technique manages the charging process on flying capacitors precisely in avoidance of potential device breakdown. An IC prototype of this design was fabricated using a 180 nm HV bipolar-CMOS-DMOS (BCD) process with an active area die of 6.3 mm². At 3-W output power, a chip power density of 476 mW/mm² is accomplished. The online VCF rebalancing reduces voltage mismatch between the flying capacitors by 16.7%. The converter achieves peak efficiencies of 88.3% and 92.1% for 24V/1V and 12V/1V conversion, respectively.