DRV10983_15 Datasheet, PDF (31/57 Pages) Texas Instruments – DRV10983 12- to 24-V, Three-Phase, Sensorless BLDC Motor Driver

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DRV10983
SLVSCP6B – JULY 2014 – REVISED FEBRUARY 2015
9.4.7.2 Lock1: Abnormal Speed
If motor is operating normally, the motor BEMF should always be less than output amplitude. The DRV10983
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 29 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 29. 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 30). 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 31).
Figure 30. BEMF Integration
Ktc
Kt_high
Kt
Kt_low
Lock detect
Figure 31. Abnormal Kt Lock Detect
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