STM32L471ZGT don't wake-up from standby and shutdown modes at ambient temperatures below -10..15C.

[MV]

Hello.

I want to use STM32L471ZGT to write a rare signal to flash. All the rest of the time it should consume as little as possible. I config RTC for alarm (and then try wakeup), all working

perfectly if ambient temperatures -10C and above. But processor don't wake-up from standby and shutdown modes at ambient temperatures below -10..15C.

LSCO gives a good signal at the same time! RTC counters also working!

It wakes up when it heats up.

Tell me which way to look for the problem, pls.

Thank you in advance.

[AvaTar]

Dunno. The datasheet says down to -40°C, so it <<should>> work.

Have you tried different boards / MCUs, and do they exhibit an identical behavior ?

[MV]

:) No, it's my first project with STM32.

[waclawek.jan]

> When I close nRST to GND in the fridge, processor restarting ok.

This indicates that HSI starts up correctly even at low temperature. I am afraid you'd need to contact ST directly (through FAE or the web support form).

> Shutdown - low power mode in the stm32L-series.

Ah, yes, sorry, I did not read your first post properly and mistakenly thought you are using a STM32F4.

JW

[T J]

where do you connect the RTC_PW ?

and Vref_ST ?

[MV]

RTC_PW internaly connected, power in my system always preset.

Vref_ST 4.7uF to CND.

[T J]

guessing now,

its the RTC battery,

try warming the battery only,

everything else below -20

Change brand and capacity of RTC battery.

how do you address condensation ?

[MV]

RTC power from main power.

May be condensation effects...

[T J]

the 4.7uF caps, can you drop them down to 2.2uF ? just to test...

could you try a different brand or change the capacity ?

did you check the errata sheet ?

[T J]

there must be no condensation on the PCB.. at any time. all tests are invalid if condensation occurs.

that ferrite bead is a little light,

600 Ohms @ 100MHz you are going to get close to that.

remove the bead, replace it with a wire... and retest. This should indicate if this is the issue.

increase the bead conduction to 200R at 100MHz and retest.

[T J]

Just throwing ideas for you...

do you have a crystal ?

then you may find the problem is the capacitors on the crystal.

They are susceptible to moisture.

easily fixed.

dry board 8 hours at 40C, to be sure,

maybe replace caps

use conformal coating on crystal caps. dry 8 hours or read label...