Thank you for your patience. You will need an external 5V Source that is an isolated floating supply and can be referenced off the SW pin, which can reach up to 340V at the peak of the 230VAC line. This is because of the ABS MAX rating of 6.5V between the Vcc pin and the SW pin. However, you will need to add a series resistor of at least 120 Ohms between the 5V Source and the VCC pin of the MP9488 . This is because we have an internal zener clamp of 4.8V on the VCC pin. The current in the zener clamp needs to be limited to 2mA. So if the External Vcc source is 5V then there is 200mV drop across the R1 resistor. If the resistor is 120 Ohms or higher then this current into the zener clamp will be limited below 2mA. Then a 0.1uF bypass cap across the VCC should be enough.
I guess I have pretty much same question for C3, C4 and C5 value and voltage for 15V output. I am using Circuit as is on page 18 of datasheet but powering 9488 from 170VDC. What will be voltage ratings for all caps?