DRV10975_15 Datasheet, PDF (31/57 Pages) Texas Instruments – DRV10975 12-V, Three-Phase, Sensorless BLDC Motor Driver

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DRV10975
SLVSCP2 – JANUARY 2015
9.4.7.2 Lock1: Abnormal Speed
If motor is operating normally, the motor BEMF should always be less than output amplitude. The DRV10975
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]. In addition, the BEMF is estimated based on the operation
speed of the motor and the setting for Kt[6:0]. Figure 28 shows the method for using this information to detect a
lock condition. If motor BEMF is much higher than output amplitude for a certain period of time, t_{LCK_ETR}, it means
the estimated speed is wrong, and the motor has gotten out of phase.
Rm
I
BEMF1 = U – I × Rm
U
M
BEMF2 = Kt × speed
Lock detected if BEMF2 > U
Figure 28. Lock Detection 1
9.4.7.3 Lock2: Abnormal Kt
For any given motor, the integrated value of BEMF during half of an electrical cycle is constant. It is determined
by motor velocity constant (Kt_PH) (see Figure 29). It is true regardless of whether the motor is running fast or
slow. This constant value is continuously monitored by calculation and used as criteria to determine the motor
lock condition. It is referred to as Ktc.
Based on the Kt_PH value programmed, create a range from Kt_low to Kt_high, if the Ktc goes beyond the range
for a certain period of time, t_{LCK_ETR}, lock is detected. Kt_low and Kt_high are determined by KtLckThr[1:0] (see
Figure 30).
Figure 29. BEMF Integration
Ktc
Kt_high
Kt
Kt_low
Lock detect
Figure 30. Abnormal Kt Lock Detect
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