MP9488 Capacitor C4


i want to use two MP9488 to convert 230V AC to 100V DC and -100V DC.
The Datasheet is great help, but I have one small problem:

There is no description what size C4, the Capacitor between VCC and SW, is supposed to be. Is it just fix 2.2uF?
I need it even if i use externel 5V for VCC, dont I?

Thanks in advance!

Hi thom.ran,

Welcome to the MPS Technical Forum. I will look into your question and responded with clarifying questions if needed or updates once available.

Hi thom.ran,

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.


Thanks for your help, it works now.