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DRV8835 not enough output power

Other Parts Discussed in Thread: DRV8835

Hello,


I want to use the DRV8835 to drive one DC motor. The DRV is controlled by a µcontroller (pic32mz). When I just check the outputs of the DRV without motor connected, the output timing seems correct, so if "on" 10V on the output, if "off" 0V on the output. But when I connect the motor (without load), I guess not enough current is supplied, because the output voltage only rises to 5V when "on". And when I connect load to the motor, nothing at all happens. And with motor connected, I see spikes on the voltage of about 2-4V. Monitoring the power voltage of 5V and 10V while the motor is connected does not show anything weird.

I attach the connection diagram of the driver on my board. The voltage V_Motor is supplied by a LM317D, which is able to supply 1,5A like the DRV8835.

Using a UDN2916 instead of DRV8835 with same conditions, makes my motor work the expected way.

I hope someone can help here or suggest anything. If you need further information, let me know.

Thanks, regards.

  • Additional information: the used motor has a nominal current of 0.077 A. On my laboratory power supply I can see a current increase of 0.02 A when using the motor with the UDN2916. So the DRV8835 isn't at all undersized.
  • Hi Annika

    What is you control method? Note that the mode PIN controls the IN/IN or PH/EH interfacing method. It is possible you get output issue because of the mode is not matching your inputs.

    Do you know the stall current of your motor at the 10V voltage? Should be something near to 10V/R_phase.
    Also how many in resistance of the 10mH inductor in serial with the supply?

    Other possibility is the the hardware issue, maybe soldering problem or output shortage issue. Could you check another board?

    Best regards,
  • Hello,

    thanks for the fast answer.

    I tried both IN/IN and PH/EN, with adapting the input signals. As I mentioned, the output signals seem fine when nothing is connected. I guess, that the output timing would not be correct if the input signals don't match the mode (I experienced that case).

    Unfortunately the datasheet doesn't tell me anything about the stall current.

    There is only the one 10mH in serial, I attach the supply circuit.


    Well, I could try resoldering, but it could be only the few resistors and capacitors around the DRV, for the reason that it works with the UDN, which uses the same power supply and signal lines. I would exclude output shortage issue. I examined the board and the lines and it looks ok. Again unfortunately I could not check another board, it's a prototype and for the moment the first and only board...

    Best regards,

    Annika

  • Hi Annika,

    When you see the spikes of 2 to 4 V, do they repeat every 1ms? The DRV8835 has overcurrent protection which limits the current.

    If the motor has extra capacitance the overcurrent limit can be exceeded, causing the outputs to shutdown. Would you please provide a scope capture of the outputs zoomed out to approximately 500us per division and also zoomed in to show the spikes?
  • Hello Rick,

    that was a good suggestion, there were two additional capacitors, directly solded to the motor connectors. Because they were also there, when I tested the UDN, which worked, I didn't see them as potential source of my problem.
    But without these capacitors, I get the power I need with the DRV8835!
    Btw, the spikes repeated about every 33ms. But I think a scope capture is not necessary any more.

    Thanks so much for your help!
    Annika