[PN]: STM32G431CB (B-G431B-ESC1), Custom board with STM MCU
[VERSION]: MCSDK 6.3.0
[TOOL]: STM32CubeIDE 1.16.1, MotorControl Workbench 6.3.0
[DETAILS]:
I’m analyzing the Back-EMF sensing circuit of the B-G431B-ESC1 board for FOC.
In this circuit:
The back EMF from each motor phase is connected directly to the MCU ADC pin.
The battery voltage is up to 25V (6S).
Each BEMF line appears to be connected through a diode to 3.3V and GPIO_BEMF.
All BEMF signals seem to share a common GPIO_BEMF.
My confusion:
How is the high phase voltage (e.g., 25V) safely sensed by the MCU’s ADC which only accepts ~3.3V max?
How is this protection implemented with minimal components?
How does this translate into proper zero-cross detection for sensorless FOC?
I am building a custom ESC board (6S, 12S, and 20S variants) with similar sensorless FOC requirements. I want to design a robust and safe Back-EMF sensing system that:
Can safely interface high voltage (~50V or ~80V in 12S/20S) phase lines to MCU GPIO/ADC.
Still allows the use of sensorless motor startup and control.
[EXPECTED BEHAVIOR]:
I want to understand the working of the BEMF detection circuit on B-G431B-ESC1.
Then design a scalable and safe BEMF sensing circuit for higher voltage custom ESC boards.
Maintain compatibility with sensorless FOC in STM32 Motor Control SDK.
[HOW TO REPRODUCE]:
Refer to B-G431B-ESC1 schematic (specifically BEMF sensing circuit).
Try replicating a similar circuit for higher voltage ESC (6S, 12S, 20S).
Understand protection design and how MCU detects BEMF events directly.
