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DRV8837: Motor rotation at the start

Ahmet Inan
Intellectual 430 points
Part Number: DRV8837

Hi TI Technical Support Team,

I designed a board to contol hobby DC motors using DRV8837. Motor is 3-6V ~100rpm DC motor and draws around 150mA at full load. I am powering motor driver's Vm and Vcc from different 3.3V supply. I am using two MP2161 (DC DC buck converter) to generate Vm and Vcc voltage of DRV8837. I am using power sequencing. Firstly, Vcc voltage is generated (+3V3_board), then PG pin of this converter is used to enable MP2161 that generates motor voltage (+3V3_Motor). I am making In1 and In2 inputs of the DRV8837 "HIGH" at the start. I have attached the schematic this thread.  MP2161 outputs are 3.3V as expected. 

The problem is when I am powering the system, although In1 and In2 are HIGH (brake mode), motor spins for short time and then stops(and behaves as expectedly). I also made In1 and In2 LOW, but same behaviour (short motor rotation at the start) was seen when the board is powered on. Is there any solution for this problem, how can I make sure that motor will not rotate at the start?

Thank you for your help in advance, 

Regards,

Ahmet

DRV8837_schametic.pdf

DRV8837_schametic.pdf

  • 0
    TI__Mastermind 37683 points

    Hi Ahmet,

    Have you tried reversing the power sequence order? start by enabling VM first and then VCC. 

    Regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    Intellectual 430 points

    Hi Pablo,

    Thank you for your reply.

    I haven't tried reversing the power sequence, but I read in the datasheet that the VM and VCC can be applied at any order. I tried to use same 3.3V power source for VM and VCC to see if it will make any difference. Again same thing happened, there was short motor rotation at the start.

    Do you see any mistakes in my schematic? 

    I will replace the IC with new one, and will check if same thing happens. I used hot air soldering, maybe I somehow damaged it. 

    Thank you for your help,

    Regards,

    Ahmet

  • +1 in reply to Ahmet Inan
    TI__Mastermind 37683 points

    Ahmet,

    Please try to replace old IC with new one and try again. In some cases, device could have been damaged. 

    Regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    Intellectual 430 points

    Hi Pablo,

    I replaced the old IC with new one, but same problem continued. I found the reason. The MCU pin that was connected to one of the DRV8837 IN pins was outputing PWM by default during power on/reset. I pulled that pin to high using 10k resistor, and problem solved. 

    Thank you for your help,

    Regards,

    Ahmet