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DRV8711 setup

Pavlin Stoyanoff
Expert 1465 points
Other Parts Discussed in Thread: DRV8711

Greatings! I have DRV8711 up and running, but I`m experiencing problems with the settings. I want to use NEMA 17 stepper motor. I`m using IRF530 MOSFETs for the bridge.

Here are my settings:

CTRL: 0000 0000 0001 1001// Deat time 400ns, Gain 5, 1/8 step, DRV enabled

TORQUE: 0001 0001 1010 1010// TORQUE 170

OFF: 0010 0000 0001 0100// 20us

BLANK: 0011 0000 0000 0000 // 1us

DECAY: no change, by default

DRIVE: 0110 0101 1010 0100//0.25V treshold, OCPDEG by default, TDRIVEN=TDRIVEP=1us, IDRIVEN=200mA, IDRIVEP=100mA

STATUS register cleard.

When I used 4kHz step frequency(50% duty cycle) the step motor is running but slowly. When I increased the step requency to 16kHz I recieved Channel B predriver fault.

I think something is not right! I haven`t put 0 ohms resistors on all low MOSFET gates, but I daubt this is the problem.

I think something in my settings is wrong! Can you help me?

Thanks!

  • 0
    TI__Guru** 114905 points
    Hi Pavlin,

    Please try using decay mode 101 (automixed decay at all times) or 011 (mixed decay at all times). This two settings are good for initial evaluation. 001 (Slow decay for increasing, mixed decay for decreasing) may lead to undesirable results depending on the system voltage, motor inductor, and register settings.

    Also can you confirm you the full scale current of the stepper motor is 1.66A assuming a 0.22 Ohm resistor? If not, please double check the register settings for the full scale current.
  • 0 in reply to Rick Duncan
    Expert 1465 points
    My Nema 17 is scaled to 1.7A. I`m using 0.22 Ohms resistor 5%. I think 1.66 should be fine..
    I`ll test the different decay modes and I`ll post the results!
  • 0 in reply to Pavlin Stoyanoff
    Expert 1465 points
    OK! I change the decay mode to 101. It doesn`t help so I change IDRIVEN to 300mA and IDRIVEP to 150mA. I menage to run the engine with 8kHz step frequecy! This means 300 rpm. Is this the maximum rpm for this step motor. I`m using 17HS8401 modification with 1.7A.
    Can you tell me if this is optimal speed or I can increase it more? I don`t have a lot of experiency with stepper motors!
    Thanks!
  • 0 in reply to Pavlin Stoyanoff
    TI__Guru** 114905 points
    Hi Pavlin,

    The motor manufacturer can tell you the optimal speed of the motor. It is usually listed on the datasheet along with the voltage to achieve the speed. The datasheet will also list a maximum starting speed for the motor.

    Are you still running the motor at 12V?

    Is it possible to provide a scope capture of current of one of the windings? If not, can you provide the voltage across the sense resistor, the xOUT1 and xOUT2, and the STEP input. The current can be determined with this.
  • 0 in reply to Rick Duncan
    Expert 1465 points
    Hi! I think I did it! BUT my PCB is designed to control 5 drivers(5 step motors). The problem is when I tried to run more then 1 motor, the pcb is experiencing a lot of dv/dt and di/dt disturbances. So till now I fixed that as I increased Dead time to 800ns, TDRIVEN=TDRIVEP=2us and TOFF to 20us. Is this correct approach or there is another way?
    Thanks!
  • 0 in reply to Pavlin Stoyanoff
    TI__Guru** 114905 points
    Hi Pavlin,

    From the firmware side:
    If possible, lower the torque setting of any motor when holding. This may reduce the current needs of the system.
    Lowering the IDRIVE and TDRIVE settings is a good start.

    From the hardware side:
    Additional bulk capacitance and local ceramic caps (around the device and the FETs) may help also.