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DRV11873: problem for Drive motor

Annie Liu
Genius 10295 points
Part Number: DRV11873


Hi Team,

The customer has two boards. 

One is TI’s DEMO board, this is connected to the motor. PWM arbitrary setting is to rotate for a while, stop for a while, and repeat.

The other board can continue to rotate normally at a duty cycle of 5%-40%. However, if the duty cycle exceeds 40%, it will turn and stop for a while, repeat.

Customer would like to know how to resolver this issue?

Best regards,

Annie

  • 0
    TI__Mastermind 18900 points

    Hello Annie,

    Short Answer:

    Please try pulling the FS pin high, if they have not already, and try disabling the current limit by grounding the CS pin and seeing if the issue goes away.

    Long Answer:

    Sounds like they are running into a lock condition. The lock condition occurs when FG does not toggle for the preset time. This is because the FG toggles when the U phase does not pick up a BEMF zero crossing (which means the rotor is not spinning). So, something is causing the rotor to stop or slow down long enough to not trigger the FG sensing circuit. Then, when falsely triggered lock time expires, it is allowed to start again, this is why the behavior repeats.

    Sometimes, when the motor is low inertia, the cycle by cycle current limit will cause the rotor to abruptly stop when current limit is hit because the driver goes HI-Z, the rotor stops or slows within the t-lock-on spec, no BEMF is sensed, and then the lock is triggered. After the t-lock-off, the DRV is allowed to try to spin the motor again.

    If you were to monitor the phase voltage and see if the space between the repeats is equal to the t-lock-off spec, it would help confirm this behavior. In addition, monitoring the voltage on CS and seeing if the voltage is over the trigger point could help verify that the cycle by cycle current is being triggered.

    Best,

    -Cole