5. The Flipped Voltage Follower (FVF): An Alternative Topology for LDO Regulators

To overcome the limitations of the classical topology to build IC-LDO regulators, several authors have chosen alternative topologies. This is the case of the Flipped Voltage Follower cell (proposed by Ramirez-Angulo et al., ISCAS 2002), which meets the requirements of LDO regulators as a consequence of its low output impedance and good stability. The first use of this cell as part of a linear regulator due to Pulkin and Rincon-Mora (U.S. Patent No. 6,573,694, 2003), where the Cascode Flipped Voltage Follower cell was used as a buffer to drive the pass transistor. Later, this same cell was used in an LDO regulator as a power stage (Hazucha et al., JSSC 40(4), 2005). This chapter describes the FVF and CAFVF cells and their performances as an LDO regulator, highlighting their advantages and disadvantages when compared to the classical topology. Then, it offers a thorough review of the regulators presented in the literature that use the FVF family of cells. Finally, a new regulator is presented that improves the performances of CAFVF-based regulators both in regulation and transient response.