No motor

Frequency Overflow

BEMF abnormal

Accelerate abnormal

Speed abnormal

Tri-state

and Restart

Logic

11

DRV10964

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Figure 8. Lock Detect

The behavior of each lock detect scheme is described in the following sections.

7.3.5.1 Lock0: No Motor

The Phase U current is checked after transitioning from open loop to closed loop. If Phase U current is not

greater than 50mA then the motor is not connected. This is reported as a locked condition.

7.3.5.2 Lock1: Frequency Overflow

For most applications the maximum electrical frequency of the motor will be less than 3 kHz. If the motor is

stopped then the BEMF voltage will be zero. Under this condition, when the DRV10964 device is in the closed

loop mode, the sensor less control algorithm will continue to accelerate the electrical commutation rate even

though the motor is not spinning. A lock condition is triggered if the electrical frequency exceeds 3 kHz.

7.3.5.3 Lock2: BEMF Abnormal

For any specific motor, the integrated value of BEMF during half of an electrical cycle will be a constant as

illustrated by the shaded green area in Figure 9. This is true regardless of whether the motor runs fast or slow.

The DRV10964 monitors this value and uses it as a criterion to determine if the motor is in a lock condition.

The DRV10964 uses the integrated BEMF to determine the Kt value of the motor during the initial motor start.

Based on this measurement a range of acceptable Kt values is established. This range is between 1/2 x Kt and 4

x Kt During closed loop motor operation the Ktc value is continuously updated. If the calculated Ktc goes beyond

the acceptable range a lock condition is triggered. This is illustrated in Figure 10.

Figure 9. BEMF Integration