STM32L151 stop mode with RTC, 4uA current draw?

faizal · ‎2016-07-20

Posted on July 21, 2016 at 08:46

We use stm32l151ccu6 with RTC clocked by LSI. The device is set to wake up, every 20 seconds, from stop mode using the RTC auto wakeup feature. At present, the device just goes back to stop mode after clearing the RTC_WUF flag. This is all well and good. I find the current consumption profile somewhat puzzling.

Current draw in stop mode + RTC before first wakeup = ~2uA. This is perfectly acceptable. Note that RTC is active, and is counting towards the first wakeup.

After first wakeup and subsequent stop modes, the current draw jumps to 4uA.

What is causing the extra 2uA? I only see this with the RTC. When PA0 is configured for wakeup, and RTC is not enabled, current draw stays at 2uA at all times in STOP mode regardless of the number of wakeups.

Any insight is much appreciated!

Nesrine M_O · ‎2016-07-21

Posted on July 21, 2016 at 11:11

Hi abdeen.faizal.001,

I suggest you to have a look to this example under the STM32L1 cube firmware package:

STM32Cube_FW_L1_V1.5.0\Projects\STM32L152RE-Nucleo\Examples\PWR\PWR_STOP_RTC

It shows how to enter Stop mode and wake up from this mode by using the RTC wakeup timer event connected to an interrupt.

-Syrine-