RTC battery supply

[suziyousif]

I have another question please. to do it with switching circuit. when the power is loss, can I power just VDD3P3_RTC with battery, without connecting those pins: VDDA1, VDDA2, VDD3P3_CPU?

[Sprite]

No, sorry, the chip does not support that.

[y_runwal]

Did a few tests about this. The issue seems to be that internal CPU regulator can also take power from VDD_RTC pin, meaning that if all the power rails except VDD_RTC are powered off, CPU can still keep running; this may cause issues if the CPU tries to read instructions or data from Flash, which will be powered down. This will soon cause the CPU to crash and enter boot loop.

Monitoring the VDD and going into deep sleep when it disappears is possible, but we are looking for an automatic solution to the problem.

Hi, any update on this?