RTC Alarm OUT pin while VDD=0, is it possible?

relaxe · ‎2008-10-31

Posted on October 31, 2008 at 14:34

relaxe · ‎2011-05-17

Posted on May 17, 2011 at 12:49

Hi!

My application need to go into deep sleep for long periods, and self-wake.

Of course, we can stop everything but the RTC. In such a situation, I need the RTC to somehow enable the power supply on RTC alarm.

If I understood correctly, from document RM0008 [Family reference], section 5.4.2, the ASOE and ASOS bits permit this behaviour:

Once the device is in sleep, and the only power to device is from VBAT [VDD disconnected], the device will output a logic high for 1 RTC cycle on RTC alarm on pin TAMPER [PC13 on STM32F103ZET6].

Is this correct? Is the TAMPER pin capable of output in the backup domain? Or does it need the device to have power to be able to ouput the pulse? How much mA can it sink/source while in battery mode? What voltage will appear on the pin? VBat-0.7 ?

I know this information is probably well written in some documentation, but I don't seem to be able to find it!

Thanks a lot,

-Jay

tibo · ‎2011-05-17

Posted on May 17, 2011 at 12:49

PC12 can output the RTC alarm pulse without VDD. The current

then is limited to 3 mA. You can find more infos in RM0008,

page 49f . The voltage level is defined in the datasheet on

page 83. I think it is nearly the same for VBAT.

relaxe · ‎2011-05-17

Posted on May 17, 2011 at 12:49

Thanks a lot Tibo!

This will allow us to power on and off the whole board's switchers making even more power savings than just deep-sleeping the CPU.

-relaxe