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

[MV_it]

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]

Check the voltage and internal resistance of your power supply at said temperatures.

[MV_it]

Yes, i cheked it.

VDD, VDDA and VDDIO 3.2V, main power from li-pol accum with low internal resistance.

[MV_it]

The chips were bought 2 years ago, could there be problems in the first lots?

[MV_it]

If the device is not send to shutdown or standby, it works at -35C without problem...

[waclawek.jan]

Does it not react to NRST either? Is VDDA properly decoupled to VSSA? Double check also the soldering of the pins.

What is shutdown? I can't find that in RM0090.

JW

[MV_it]

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

I have 4 devices, everyone behaves the same.

Power pins decoupling on the picture.

Shutdown - low power mode in the stm32L-series.

[MV_it]

I found out that in the stop 0, 1 mode the behavior is the same!

[AvaTar]

Perhaps HSE quartz/ clock setup failing at low temperatures ?

That would apply after a wake-up, though.

Perhaps you can try coolant spray to check components individually.

[MV_it]

Program does not come to start HSE , I checking it with LEDs indication.

When I touch the frozen processor with my finger, after 2-3 seconds it starts!

[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 ?

[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_it]

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_it]

RTC power from main power.

May be condensation effects...