STM8S103K3T6 supply

[JRubi.1958]

Hello,

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

Before, I'm doing a several previous tests.

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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.

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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.

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

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Any idea?

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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.