Hi team,
I'd like to confirm if the MLCC which has a ESR profile like below is acceptable for LM1117.
We can find the recommended range of 0.3 to 22ohm in the datasheet.
In this profile case, it has 0.8ohm of ESR at 100Hz, for example.
Does it mean it should be covered all of the frequency range? 
Thanks in advance.
S.Sawamoto
Hi Sawamoto-san,
This is a good question. LDO uses the ESR and output capacitor to stabilize the control loop, so what matters is the ESR within the frequency range of the bandwidth of the LDO. A general rule for LDOs is to ensure the ESR meets the specified requirement from the datasheet from 10kHz and 3MHz.
So in this case this capacitor looks like it may be a ceramic capacitor which has a minimum ESR of ~0.2 mOhm and would not be enough to ensure LM1117 is stable since it was designed to be used with tantalum capacitor and requires 0.3 to 22 Ohm.
If you need to use a ceramic capacitor with tantalum stable LDOs, there are two ways to add a resistor and stabilize the LDO with ceramic capacitors. Placing the resistor in series with the load will cause a voltage drop due load current but the output capacitor will be able to more quickly respond to load transients. Placing the resistor in parallel with the load (in series with the Cout), will eliminate the DC I*R drop however it will slow down the capacitor's response time to transient load events.
