Running STM32G431 with minimal power consumption but HSE as RTC clock source.

[FBörn.1]

In our current project, we are using the STM32G431 (UFQFPN32) with only an HSE connected. In this project, we do also need a longtime accurate RTC for Time/Date. Since the internal LSE have a quit high accuracy of 1%, they dont seem to be suitable for as longterm RTC source. (to which degree of accuracy can you calibrate them?)

So we are using the far more precise HSE as source. But now we run into the problem that in standby (<1mA@12V) and stop mode(<1mA@12V) it get shutdown and low power run Mode (9mA@12V) draws still far to much power. Now we have tried to turn off most of the mcus peripherals (ADC, Flash, GPIO, I2c, ADC clock, FMAC clock, 2xDMA, Timers, PLL) (5mA@12V). We meed to get below 150mW. Are there still some things missing? What comparable power consumption do you got for these kind of modes?

Is it possible to go into standby mode for like 750ms and the go back for a short moment into run mode? Does the HSE keep going for this time?

[Danish1]

You mention 12 V. Are you using a switching regulator to step down to Vdd? If not you're wasting a huge amount of power. There are even modules so you don't need to do any difficult design work.

If the cpu is taking (say) 6 mA worst-case at 1.8 V Vdd, then assuming 90% efficiency in a switching regulator that corresponds to 1 mA at 12 V.

But then that's worst-case at 125C; typical consumption is nearer 0.5 mA at 55C.

But for real low power with RTC, you can't beat the LSE oscillator.

Hope this helps,

Danish

[waclawek.jan]

Low power sleep?

JW