RTC on STM32F030 without VBAT

[guwono.septijo]

Posted on October 05, 2013 at 17:04

Hi everyonne..

I m planning to use STM32F030 for my projects, and the projects need RTC functtion. I notice that STM32F030 didn't have VBAT pin and Backup Registers... CMIIW.. so, how can we get RTC function without VBAT and Backup Register ? please advice. #stm32f030-rtc-no-vbat-backup-reg

[Tesla DeLorean]

Posted on October 05, 2013 at 19:21

Probably by putting the device in STANDBY, powered from the regular supply (a battery), but with the internal regulators turned OFF. If it's like the other parts you'd get it out of that state with an RTC Alarm or external WakeUp signal.

The L15x series also doesn't have a separate battery input, because it's inherently low power.

[guwono.septijo]

Posted on October 06, 2013 at 12:49

clive1, thanks for your fast reply.

... hmm.. errrr...  if we have 2 pin, VBAT and VDD, we can add an on-off switch in the VDD power supply. While we switch off the power supply (but the VBAT still got juice from a CR2032 battery), we hope that the RTC value didn't lost. but in STM32F030, there are no VBAT and Backup Register. so .. are there any example (maybe schematic) to enable us create a functional RTC (using CR2032 for sustaining RTC's data) ? i'm afraid, even if the MCU is very-very low power, but other circuit onboard (LCD / LED etc) will drain the CR2032 very-very fast... please advice..... best regards,

[Tesla DeLorean]

Posted on October 06, 2013 at 14:41

I haven't had cause to thoroughly review the F030 documentation, so take this as general advice.

The part likely has SRAM can you maintain that with a supply. How does your primary supply disappear? Do you have to put a switch there? Can you sense the primary supply going away? Can you switch to a low power mode using a button instead of a mechanical switch? In systems with a singular supply rail to the processor a diode arrangement (BAV70?) can pick the higher of two external supplies, a battery at a lower voltage, and primary supply always higher when present. If the current in STANDBY, running the RTC is too high for your design, then you'll need to consider another part.