ZHCSH31B August 2017 – February 2018 DRV10987
If the speed command suddenly drops such that the BEMF voltage generated by the motor is greater than the voltage that is applied to the motor, then the mechanical energy of the motor is returned to the power supply and the VCC voltage surges. The mechanical AVS function works to prevent this from happening. The DRV10987 device buffers the speed command value and limits the resulting output voltage, VU_MIN, so that it is not less than the BEMF voltage of the motor. The BEMF voltage in the mechanical AVS function is determined using the programmed value for the motor Kt (Kt[6:0]) along with the speed. Figure 39 shows the criteria used by the mechanical AVS function.
The mechanical AVS function can operate in one of two modes, which can be configured by the register bit AVSMMd: