STM8S103K3T6 supply

[JRubi.1958]

Hello,

I'm designing a new board with a STM8 CPU.

Before, I'm doing a several previous tests.

I want to supply with 3.3V the MCU but I found that it works very well with 5V but in the other hand with 3.3V it doesn't work.

I checked VCAP voltage, while supplied with 5V I measured right value, 1.8V (core voltage) but if I down the power below 4V the voltage at this pin drops to 0V and, therefore, it doesn't work.

The datasheet states voltage can be from 2.95V to over 5V.

Any idea?

Thank you.​

[Cristian Gyorgy]

There is something else there, causing it "not to work". Any STM8 will do more than fine with 3.3V.

Try to give some info on the schematics.