The data sheet for the TPS709 linear regulator specifies that the ESR of the output capacitor should be less than 0.2Ω for stability.
This requirement seems to be underspecified since ESR is dependent upon frequency. If the frequency of interest is 1kHz then there are very few ceramics that are below the requirement. On the other hand, if the frequency is 100kHz then every ceramic capacitor available is far below 0.2Ω making the requirement seem superfluous.
I may be misunderstanding something, but if not, within what frequency range does the capacitor need to meet this requirement?