Hi,
STM32L series do not have a dedicated backup battery pin. I know these micros are designed to operate based on battery but In my project I want to guaranty clock never changes even with a main battery replace. Any idea to add RTC battery?
Through a diode arrangement, like a BAV70 www.nxp.com/.../BAV70_SER.pdf
Thanks, so you suggest that I connect back up battery to pin1 and main supply to pin2 and let pin 3 be connected to VDD of MCU.
The bad thing with processors that doesn't have a dedicated battery pin, is that they will draw all current from the backup battery when the main power goes offline. So the backup battery must support enough current. And the drain is rather high.
If you need backup power for the RTC, it is often better to either use an external RTC, or a processor that does have a dedicated battery pin. Then the loss of main power will kill the processor core, while the RTC will continue to function while drawing a tiny trickle of current from the backup battery.
So a processor with dedicated battery pin, or the use of an external RTC, can have a supercap run for days or weeks while a coin cell may keep the RTC ticking for years.
Thanks, yes using and external RTC seems the most simple way.
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