A 60 A Switched Tank Converter with Buck-Boost Sigma Regulation for 48 V Bus Down-Conversion

In modern power distribution architectures, the conversion from the 48 V bus to the point of load (POL) voltage is performed in two steps. A switched tank converter (STC) first converts the bus voltage down to the 12 V level. Then, a POL converter provides the low supply voltage for CMOS circuitry. In the event of DC bus voltage fluctuations, however, the fixed conversion ratio of the STC forces the POL converter to operate with an input voltage that deviates from its nominal value. This paper introduces a sigma-converter that employs an additional inductor-based converter, coupled with the STC, to achieve output voltage regulation. Compared to prior art, the additional converter is connected to a different internal node of the STC, providing the peak efficiency at the nominal input voltage of 48 V, while guaranteeing high conversion efficiency over the whole 38 V to 60 V input voltage range. Moreover, a hybrid control strategy is suggested to guarantee voltage regulation when the input voltage hovers near its nominal value, with a control strategy to achieve seamless transitions upon the shift of the operating regime. A prototype converter has been implemented on a PCB to validate the proposed architecture, achieving a peak efficiency of 97.6 % at 30 A load current and 48 V input voltage, and a power density of 900 W/inch 3 at 60 A load current.