Hi Pedro,
The VDD1,2 pins are output pins from internal 2.5V regulator. These pins must not be left open. The bypass capacitors must be used at these pins for covering power consumption spikes during transistor switching.
The connecting these pins to the 3.3V power supply is an obvious issue. In that case, the internal regulator is not active and internal logics (digital modules, CPU, SRAM,…) are overloaded by high voltage. Since the absolute maximum VDD voltage is 3V, the MCU may work even at 3.3V, but the lifetime may be probably limited. Also, other electrical parameters may differ. In extreme case, the device might be damaged.
From RM:“Absolute maximum ratings are stress ratings only. A functional operation under or outside those maxima is not guaranteed. Stress beyond those limits may affect the reliability or cause permanent damage to the device.”
The operating range for VDD pins is 2.35 to 2.75V. Unfortunately, I am afraid that we cannot establish any specific parameters like accuracy or life cycle for such situation. We simply didn’t validated MCU under such conditions. For work beyond absolute maximum ratings, we cannot provide any warranty.
I hope it helps you.
Have a great day,
Radek
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