documentation/how-to for CN15 optional battery connector on B-U585I-IOT02A devboard

[Kent/Flounder]

There doesn't seem to be any documentation on whether the optional battery holder CN15 can be used on the unit, nor what it's specs should be if it is populated with a battery. I need constant RTC backup from the time the unit is first configured.

[Peter BENSCH · Accepted solution]

Welcome, @Kent/Flounder​, to the community!

Information about the connection to VBAT for the STM32U585AII6Q used can be found in the data sheet and in the reference manual RM0456, specifically in section 10.4.7 Battery backup domain.

From the schematics to the B-U585I-IOT02A you can see what you should change:

• remove solder bridge SB6
• put on solder bridge SB7
• inserting a battery holder for a CR1220 cell

If you use a non-rechargeable cell, please be careful not to switch on bit VBE at register PWR_BDCR2 by mistake, because otherwise you will activate an internal charging resistor.

Details to PWR_BDCR2 also in RM0456, sections 10.4.7 and 10.10.10.

Hope that helps?

Regards

/Peter

[Kent/Flounder]

thank you, sir. I either have to enable the onboardRTC permanently at time of initial board configuration, or the less desirable route of adding a battery backed i2C RTC...using the existing battery holder is preferrable.