Switched-Capacitor Boost-Buck Ladder Converters With Extended Voltage Range in Standard CMOS

This paper presents fully integrated switched-capacitor boost-buck power converters with conversion ratios 5, 7, and 1/5. Such converters operate over a voltage range extended beyond the device ratings due to a low-voltage-stress configuration, accumulation-mode NMOS capacitors, and a circuit technique for switch bootstrapping. After modeling the simple and the symmetrical ladder converters, we determined methods for assessing the device working voltages and for optimizing the sizes of capacitors and switches. The key performance parameters were compared and the losses due to non-linear parasitic capacitances were calculated. The characterization of the prototypes in a 1.8-3.3-V, 0.18-$\mu \text{m}$ CMOS process demonstrated a 15 V range, a 5.4 mW/mm
²
output power density, and good correlation between measured and predicted results.