STM32WB55 - unexpected current pulses in STOP2 and standby modes

[RScha.3]

Hello,

I'm developing a battery-powered application for the STM32WB55 (specifically the STM32WB55RGV6) and am seeing periodic pulses or spikes in the SoC's current consumption every 200ms in STOP2 and standby modes. These pulses occur with the Nucleo board MB1355-C02 as well, though the pulses have a different shape on the Nucleo board than the ones I can observe on the board I designed. I have tried the demo firmware in addition to my own, and observe the pulses with it as well.

A couple other notes:

• The pulse period is reduced with increasing ambient temperature. If I point a hair dryer at the board, the pulse period gets much shorter.
• The pulses occur when running the boards off of an isolated battery supply as well as a typical benchtop DC power supply.
• I have tried setting all of the pins possible to analog input in order to isolate the STM32WB55 as much as possible from outside circuits, but this didn't help with the pulses.

I've attached couple images from my power analyzer that show the pulse period and shape.

Any help or advice would be very appreciated! Thanks and take care,

Ryan

[RScha.3]

Any thoughts, folks?

[Uwe Bonnes]

Is that on a part with SMPS? Probably when sleeping, SMPS is in pulse skipping mode. When VFBSMPS has dropped some margin, C2 from Figure 4 "Pwer distribution " is recharged. Higher temperature -> Higher leakage -> more frequent recharge

[RScha.3]

Thanks for your reply, and a very interesting theory! The part does have a SMPS, but in the STOP2 and standby modes, the SMPS is open and the LDO is powering the low-voltage core. I checked the switching node for the SMPS (called V_LXSMPS on this part) with my scope and saw no switching there.

[Aaron LI]

Hi Ryan,

Have you solved this problem?

Regards

Aaron

[lame_stmr]

Hey Aaron,

I seem to be having the same issue on the STM32 NUCLEO WL55JC1 board. I'm running code adapted from a firmware example that defaults to the STOP2 mode when there are no tasks, but there are periodic spikes that I can't understand. For more context, my ammeter is the nordic PPK 2 and I have my probe on the JP1 I_SOC jumper; the example i adapted from is the STM32WL Ping Pong example with LoRa modulation. Please help. Thank you.