The regulator in question: NCP161AFCT330T2G. We use it in a USB device to convert 5V to 3V. The device will only be used at room temperature.
It says in the datasheet: “The value of the input capacitor should be 1 µF or greater to ensure the best dynamic performance.” About the output capacitor however it says: “The recommended capacitor value is 1 µF.”
Is there a reason to not explicitly recommend values higher than 1 µF for the output capacitor? I am asking because we use a lot of 10 µF capacitors (MLCC imperial 0402) on the PCB and I would like to just use 10 µF capacitors for the input and output capacitors of the regulator as well (would simplify the BOM), instead of the 1 µF capacitors the regulator datasheet is calling for (for those 1 µF capacitors I would use MLCC imperial 0402 as well by the way). Are there any drawbacks of using 10 µF capacitors instead of 1 µF capacitors when literally the only difference is the capacitance?
Best Answer
It depends on the capacitor.
First of all, the datasheet does say that larger output capacitor improves response for changing loads.
But your capacitor is so small in physical size, that due to size, a matching size 1uF could be better than 10uF. Unless the voltage rating is much more than the required 3.3V,.the capacitance will significantly drop due to DC bias.
The final thing is USB specs though. It only allows for 10uF at the device input to limit surge current. Using a 10uF at the input and another 10uF at the output of the regulator could easily exceed allowable USB ratings. Also the high capacitance at the USB inlet port can cause significant voltage spikes and ringing when cable is plugged in unless dampening is taken care of, so be careful about the design.