STM32L152 - Low Power Mode

nicolas2399 · ‎2016-01-05

Posted on January 05, 2016 at 14:28

Hi,

I'd like to implement a 30 minutes interval. During that time I'd like to have the lowest consumption.

I'm not sure whether stop mode or standby mode is best. It is written that LSI and LSE only works down to stop mode. So it is for RTC (wakeup capability). But RTC Tamper and AWU operates in standby mode. I thought RTC works together with LSE or LSI, doesn't it? What is exactly RTC Tamper?

Thank you for the help

Nesrine M_O · ‎2016-01-05

Posted on January 05, 2016 at 15:09

Hi gugger.nicolas,

â€œI'm not sure whether stop mode or standby mode is best.â€�

Refer to the Electrical characteristics section in your product related datasheet to have an idea about current consumption in stop and standby modes when RTC is on and clocked by LSI or LSE, in various conditions.

â€œIt is written that LSI and LSE only works down to stop mode. So it is for RTC (wakeup capability). But RTC Tamper and AWU operates in standby mode. I thought RTC works together with LSE or LSI, doesn't it?â€�

Have a look to the â€œWaking up the device from Stop and Standby modes using the RTC and comparatorâ€� paragraph in your STM32L152 reference manual, it details the Auto-wakeup mode from stop and standby

What is exactly RTC Tamper?

The RTC includes n tamper detection inputs. The tamper input active level/edge can be configured and each one has an individual flag

A tamper detection event generates an interruption when the TAMPIE bit in RTC_TAFCR register is set.

Also have a look to the PWR examples under the STM32L1 cube firmware

STM32Cube_FW_L1_V1.4.0\Projects\STM32L152RE-Nucleo\Examples\PWR

Some examples show how to enter the system in STANDBY/STOP mode and wake-up from these mode using RTC Wake-up Timer.

-Syrine-

nicolas2399 · ‎2016-01-05

Posted on January 05, 2016 at 16:16

Hi Syrine,

Thanks for your answer. On the example they indeed use LSI. Table 5 from STM32L152 datasheet states that LSI and LSE doesn't operates in STDBY mode though. This is where I'm confused.

STDBY reach lowest current consumption even though it needs more time to wake up. From what I understood (flash and RAM OFF), MCU must be reconfigured then, is it right?

Nesrine M_O · ‎2016-01-05

Posted on January 05, 2016 at 17:23

Hi gugger.nicolas,,

Table 5 from STM32L152 datasheet states that LSI and LSE doesn't operates in STDBY mode though. This is where I'm confused.

In fact, it is a typo in the datasheet, so thank you for bringing this issue to our attention. It is noted and will be corrected.

STDBY reach lowest current consumption even though it needs more time to wake up.

Yes, you are right the Standby mode allows to achieve the lowest power consumption but needs more time on wake up.

From what I understood (flash and RAM OFF), MCU must be reconfigured then, is it right?

Yes, in fact after entering Standby mode, SRAM and register contents are lost except for the RTC registers, RTC backup registers and Standby circuitry.

-Syrine-