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DRV8834: Motor voltage clamping

Elaina Cooley
Prodigy 10 points
Part Number: DRV8834

Hi, I'm using DRV8834 to drive a small stepper motor to open/close an air vent. If a user manually opens the vent, we think the backdrive may be causing a small number of field failures as the energy from the manually rotated motor gets fed back to the driver. The o-scope screenshot below shows one of the motor outputs, which appears to be clamping at ~5.8V. The clamping only appears to occur when the driver is in sleep mode. Our plan to fix this is to add some bulk capacitance to the motor rail, but I want to make sure we understand the problem.

Channel 1:  Motor output

Channel 2:  Motor power supply 

Does it look like the internal MOSFET or some internal protection component is going into breakdown (does 5.8V clamping make sense in this context)?

Thanks!

  • +1
    TI__Guru 56650 points

    Hello, Elaina:

    1. The voltage is generate by the vent motor which is related to the motor speed. 

    2. When a user manually opens the vent, the input bus is the load. DRV8834 is a 11V device. I don't think it clamps the voltage at 5.8V. Before add more input capacitor to clamp it, I would add a resistor at input to see how many energy is sent back. And then, according to the energy (1/2*C(V1)^2-1/2C(V2)^2) to calculate the input capacitor.

    3. The clamping only appears to occur when the driver is in sleep mode. Yes. In brake mode, the energy will be burned out in the low side FET and motor coil.

    Regards,

    Wang Li

  • 0 in reply to Wang5577
    Prodigy 10 points

    Thank you very much for answering my questions.  The issue turned out to be the buck regulator chosen.  The over voltage protection of the buck supply was kicking in and clamping it at the 5.7V.  I appreciate your response.  It assisted with eliminating the driver as the problem.