STM32 Dual supply concept?

[JOF]

I have an application where in "run" mode alot of current is needed at 3V3, so there is no way around a 3V3 switching regulator in the circuit. In the sleep mode, i don't need any pheriperal power, the main switching regulator would be turned completely off. While in sleep, i want to power the mcu (STM32L433) by a 1V8 LDO to keep periodic checks and startup the switching regulator when a wakeup is occured.

I searched around the internet and found a document that describes battery backup. Attached is figure 2 from the sheet.

Would this for my case work if the supercap would be replaced by a 1V8 Output of a LDO, and D1 would be removed because there is no need to charge the cap. The main supply would be 3V3

Or would this cause problems because of the voltage difference from 3V3 and 1V8 ?

[MikeDB]

I don't see why not. The diode from the LDO would be reverse biased normally so no current would flow from it until the main supply turns off. Be aware that some STM32 devices have stricter operating voltage limits than others, and I haven't looked at the 433.

[JOF]

The 433 can go to 1.71V. So i see what you mean, i forgot to think about the diode drop voltage. So it would be better to use a higher LDO like 2.5V which would result in around 2V as backup voltage after the diode!

[MikeDB]

Or don't use a diode but instead some sort of MOSFET arrangement like the 5V is using ?