Circuits and methods to provide an LDO output stage implemented with
low-voltage devices and still allowing higher voltage levels have been
achieved. The output stage has been built using two low voltage MOS
devices in series. During the time the regulator is in active mode the
second MOS device acts as a small resistor in series to the pass device.
During power down this second device actively protects the MOS pass
device and itself from high voltage stress levels. This is achieved by a
robust regulating mechanism that compensates leakage currents. These
leakage currents normally determine the different potentials of the
output stage during power down. Although the second transistor presents a
resistive obstacle during active mode the total chip area required is
smaller compared to a single pass device tolerating e.g. 5 Volts.