| With the rapid growth of the data center and automotive electronics,devices are becoming more and more power hungry.In order to reduce the distribution power loss due to the power delivery network,the 48 V power bus has been used in place of the conventional 12 V bus.However,improving efficiency is a major challenge in the design of a 48V-to-1V single-stage converter due to the high step down ratio and high output current.The isolated converters in use an un-regulated LLC to offer high current and get good efficiency,but the conversion range is limited.The non-isolated hybrid converters in use flying capacitantors to decrease the switching node voltage stress with only moderate power efficiency and require larger number of passive elements.In addition,most of the prior state-of-the arts,employ Gallium Nitride(GaN)or other high performance discrete switches to improve efficiency by trading-off reliability or costs.In this work,a 12-level stacking quasi-series resonant LLC adopting fully-on-chip switches is proposed.By taking advantages of the superior figure of merit(FOM)of on-chip switches,this work simultaneously improves the efficiency,the power density and save costs.The work proposes a 12-level stacking quasi-series resonant LLC topology,which turns a 48V-to-1V converter into 4V-to-1V conversion.Since the voltage stress of each power switch is 4 V,on-chip swithes,instead of discrete switches,can be adopted.which significantly reduces costs and help system integration.As is known to all,the GaN switches show superior FOM than their Si switch counterparts when they are on the same voltages stress level,howerver,on-chip 5 V switches show significantly better FOM than the GaN switches because the lower voltage stress limit.Thanks to the on-chip power switches,the proposed deisgn is able to achieve superior power efficiency.The ratio between the magnetic inductance and the leakage inductance,which is trade-off between the efficiency and regulation for LLC topology,is carefully designed.In addition,this work employs the pulse frequency modulation(PFM),to operate the LLC in the vicinity of series resonance(quasi-series resonant),and achieves wide output range with little loss.In addition,this work also gives a detailed description on the circuit about driver and loop controller.For planner transformer,the analysis of the loss and reasonable design process are also given.In conclusion,this work proposed a 12-level stacking quasi-series resonant LLC that adopts full-on-chip switches in 48/1 V designs.The efficiency can significantly improve,compared with other state-of-the-arts,this work achieves the lowest switch FOM.The proposed convertor was implemented using a 0.18um BCD process and the chip area is around 4.834*4.834 mm~2with 12 A load capacity.In addition,the planner transformer was verified using DMR50 material and 4-layers PCB.The peak efficiency is 94%simulated,regulation error is 0.15%and the power density is 100 W/inch~3 estimaed. |
