What type of passive filters can be added to the output of a linear regulator
without causing instability?
Modern internally compensated LDOs are surprisingly robust when it comes to
adding external filtering at the output to reduce noise. Adding small ferrite
beads to suppress high frequency noise is a common practice and usually does
not require any additional circuitry if the inductance of the bead is less than
a few hundred nH. If a real inductor or a high inductance bead is used, a
simple RC damping network at the output of the filter is recommended to prevent
ringing or noise peaking.