STM32_LSECLK_BYP_MIN

[geoffrey.brown]

I've been using 20.3x for several years and looking to switch to 21.11x. I noticed that for the STM32L4 in hal.lld.h the following definition exists

#define STM32_LSECLK_BYP_MIN 32768

In fact I use (quite successfully) a 1024 Hz LSE -- the output of an rv-3028 RTC which leads to a much lower power solution than any alternative. I'm wondering where this constant comes from and what the implications are.

[Giovanni]

Hi,

Those kind of numbers are taken from the datasheet, frequencies below 32k are not specified for some reason.

Giovanni

[geoffrey.brown]

Thanks! Just as a point of reference, with an rv3028 driving the STM32L43x RTC at 1024 hz, I get standby currents under 200nA and frequency accuracy of 1ppm (at 25C, but the temperature on the back of a bird is pretty close to 39C) while being able to use the stm32 alarms and, in stop mode, the lptimer.

Geoffrey