Espruino pico vbat power mode

Hi!

I'm looking for a small stm32f4 developement board (even smaller than the stm32 blue pill) and found the espruino pico looking very promising.

But one of the requirements I have is to be able to enter VBAT mode and use the internal RTC calendar with low speed external clock (LSE). I have found that the pico supports run, sleep and stop mode (and standby mode if I code it myself) but nothing about vbat mode. To enter vbat mode on a stm32 the VDD must be powered off and VBAT powered on, I thought vbat mode was supported when I saw the vbat pins on the board but it seems like it is just for powering the board instead of USB. Is it possible to do some easy fix so I can enter vbat mode and use the internal RTC calendar?

I have read that i must solder on a crystal myself and maybe two capacitors for the LSE or use the espruino wifi board which has it soldered on from production.

Thanks in advance!

On the Pico and WiFi boards, the actual VBat pin in the STM32F4 is connected straight to VDD - I'm afraid there is no easy way to power just that and not VDD as well.

There are schematics available (linked from the Pico/WiFi pages) so you could potentially cut the track and wire up VBAT separately - but it would be very difficult

However you might find that entering the proper standby mode of STM32 gives you the power requirements you need. It's probably around 2 uA vs 1 uA for vbat mode - by comparison the MCP1703T voltage regulator on board draws 2 uA, so you're not going to see a massive difference in overall consumption between the two modes.