High input voltage step-down DC-DC converters for integration in a low voltage CMOS process

A cascode bridge circuit for monolithic switching DC-DC converters operating at high input voltages is proposed in this paper. The proposed circuit can also be used as an I/O buffer to interface circuits operating at significantly different voltages. The circuit technique permits the full integration of the active and passive devices of a switching DC-DC converter with a high voltage conversion ratio in a standard low voltage CMOS technology. The cascode bridge structure guarantees the reliable operation of deep submicrometer MOSFETs without exposure to high voltage stress while operating at high input and output voltages. With the proposed circuit technique, steady-state voltage differences between the terminals of all of the MOSFETs in a switching DC-DC converter are maintained within a range imposed by a target low voltage CMOS technology. High-to-low DC-DC converters operating at input voltages up to three times as high as the maximum voltage that can be directly applied across the terminals of a MOSFET are described. An efficiency of 79.6% is achieved for 5.4 volts to 0.9 volts conversion assuming a 0.18 mum CMOS technology. The DC-DC converter operates at a switching frequency of 97 MHz while supplying a DC current of 250 mA to the load.