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I'm having some problem reaching the said ultra-low power available for the STM32Lxx series. With no active register, the UC should consume around 10 uA, but I can't get it down from 1 mA. The datasheet says to first reduce the frequency, then the core voltage then enter the ultra low power mode as one can no longer program it.

The lines I use to enter the lower power mode are :

RCC_MSICmd(ENABLE); % Activate the Multi-speed internal clock
RCC_MSIRangeConfig(RCC_MSIRange_0); % Reduce to 32 kHz the Multi-speed internal clock
RCC_SYSCLKConfig(RCC_SYSCLKSource_MSI); % The system clock that will be used is the MSI clock.
RCC_HCLKConfig(RCC_SYSCLK_Div512);  % Reduce furthermore the clock frequency
RCC_PCLK1Config(RCC_HCLK_Div16); % Reduce furthermore the clock frequency
PWR_VoltageScalingConfig(PWR_CR_VOS); % Reduce the core voltage
PWR_EnterLowPowerRunMode(ENABLE); % Enter the low power run mode

I'd be very grateful if someone could point me the mistake I am doing.

Nathaniel Brochu
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  • Are you putting it in sleep or stop mode? – Voltage Spike Apr 01 '19 at 18:57
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    You need to turn off all non-essential peripherals and peripheral clocks, in addition to reducing power to the core. – TimWescott Apr 01 '19 at 18:59
  • If I reset the MCU completely, does't it automaticaly turn off all non-essential peripherals? – Nathaniel Brochu Apr 01 '19 at 21:24
  • Adding to what @TimWescott said, please see [this](https://electronics.stackexchange.com/a/427989/38335) answer regarding peripheral clocks. – bitsmack Apr 02 '19 at 05:50
  • If it's like the other ST processors it'll come out of reset with all peripherals turned off. – TimWescott Apr 02 '19 at 06:34
  • IIRC, those processors come out of reset with all the pins configured as floating inputs, and a floating CMOS input consumes current. You can get a marked reduction in power consumption by configuring everything that's not actively driven high or low to have a pull-up or pull-down, as appropriate. – TimWescott Apr 02 '19 at 06:36
  • You have to enable the clock for the PWR module to get into low power modes. This seems strange but if worked for us. – A.R.C. Apr 02 '19 at 07:16
  • Thank you all for your answer, I'll work on that! – Nathaniel Brochu Apr 02 '19 at 14:36

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