Optimized Frequency Shaping Circuit Topologies for LDOs

Typical low drop-out (LDO) regulator architectures suffer from an inherent load regulation performance limitation. This limitation manifests itself through limited dc open-loop gain and results from stringent closed-loop bandwidth requirements. The frequency response of the system is highly sensitive to the loading conditions thereby making proper compensation a laborious endeavor. This paper discusses and addresses the limitation on regulating performance imposed by frequency compensation. Rincon-Mora and Allen 2 Several LDO circuit topologies are subsequently developed to this end. They enhance load regulation performance by relaxing the dc open-loop gain restrictions. The circuit structures essentially alter the frequency response of the system via the error amplifier. A low drop-out regulator adopting an embodiment of the proposed technique was fabricated in the MOSIS 2 μm process technology. The system, designed for an output capacitor of 4.7 μF, was stable with an equivalent series resistance (ESR) ranging from 0 to 12 Ω, bypass capacitors adding from 0 to 2.2 μF, and a load-current ranging from 0 to 50 mA.