SLVSE89C August 2017 – June 2020 DRV10987
PRODUCTION DATA.
If the motor is operating normally, the motor BEMF should always be less than the output amplitude. The DRV10987 device uses two methods of monitoring the BEMF in the system. The U phase current is monitored to maintain an estimate of BEMF based on the setting for Rm[6:0] {RmShift[2:0],RmValue[3:0]}. In addition, the BEMF is estimated based on the operation speed of the motor and the setting for Kt[6:0] {KtShift[2:0],KtValue[3:0]}. Figure 35 shows the method for using this information to detect a lock condition. If the motor BEMF is much higher than the output amplitude for a certain period of time, tLCK_ETR, it means the estimated speed is wrong, and the motor has gotten out of phase.