STM32H743VIT6 – Is VBAT required for normal MCU operation when VDD is always present?
Hello ST Support,
I am using an STM32H743VIT6 on a custom PCB. The PCB has already been fabricated, and I discovered that the VBAT pin is left unconnected (floating).
My application does not use RTC, LSE, backup registers, backup SRAM, or battery backup functionality.
The MCU is continuously powered from 3.3 V through VDD.
I would like to confirm whether leaving VBAT unconnected can affect normal MCU operation while VDD is present, specifically:
- CPU execution
- Flash operation
- GPIO
- DMA
- SAI/I²S
- UART
- USB
- interrupts
- timers
- normal peripheral operation
I understand from RM0433 that the VBAT domain contains the RTC, backup registers and backup SRAM, and that when VDD is present the backup domain is supplied from VDD.
The reference manual also states that VBAT may be connected directly to VDD, and that VBAT functionality is used when VDD is not present.
My specific question is:
With VDD continuously present and no requirement for RTC/backup functionality, is an STM32H743VIT6 with VBAT left floating guaranteed to operate normally, or can the floating VBAT pin affect any part of normal MCU operation?
The PCB is already fabricated, so I would particularly appreciate knowing whether this requires a hardware rework or whether the board can safely be used for normal operation.
If ST recommends connecting VBAT to VDD even when VDD is always present, please clarify whether this is a mandatory functional requirement or a recommended hardware-design practice.
Thank you.
