I'm trying to spec out an output capacitor for a TPS7201 voltage regulator (http://www.ti.com/lit/ds/symlink/tps7201.pdf). It needs to be selected carefully as it is used to stabilize the internal feedback loop. The datasheet suggests using a 10-15uF tantalum (with a max ESR of 1.3 ohms) and an external 0.5 ohm resistor in series with the cap.
First question: Is it be correct to say that the CSR = ESR + external resistor = 1.3 + 0.5 = 1.8 ohms? (EDIT: CSR in datasheet is "Compensated Series Resistance")
Now I would much rather use a ceramic cap, which from what I've read, has an ESR in the milliohms. In the TPS7201 datasheet, figure 30 illustrates the region of stability for a range of CSRs. It looks like a CSR of 0.1 to 2 ohms would be sufficient. So to get proper operation I would need add some additional external resistance to get to the necessary CSR.
Second question: If I use a ceramic cap instead of the tantalum, and if I add an external resistance of say 1 ohm (CSR then is 0.1 ohm for cap, and 1 ohm for external resistance, thus 1.1 ohms total, which is in stable region of operation according to figure 30), would this yield proper operation?
Does this make sense, or am I missing something fundamental?