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DRV8711: About the current that flows in each phase when driving a two-phase stepping motor.

user5948348
Prodigy 20 points
Part Number: DRV8711
Other Parts Discussed in Thread: CSD18531Q5A


When trying to drive a two-phase stepping motor with DRV8711, a phenomenon occurred in which the position accuracy of the motor fluctuated from step to step.

As a result of the investigation, the current flowing through the motor is different between the A phase and the B phase, and the stop position seems to differ depending on the excitation state.

The set drive current is 0.7A. However, there is a difference of about 50mA at 718mA for phase A and 665mA for phase B.


The driving conditions are as follows.

・VM  : +48V

・Excitation Mode :  2-Phase(Full step)

・Drive Current  : 700mA (TORQUE = 15,  ISGAIN = 5,  RISENCE = 33mohm)

・Decay Mode : Mixed Decay(all time)

・External FET : CSD18531Q5A(TI)

1. Is there a possibility that this difference in current will occur in device performance?

2. Is there a way to correct the current value for each phase?

Best regard.

  • 0
    TI__Guru 56650 points

    Hello,

    "The set drive current is 0.7A. However, there is a difference of about 50mA at 718mA for phase A and 665mA for phase B."

    (718mA-665mA)/700mA= 7.5%. I don't think the DRV8711 can cause such high difference. Do you test it on an EVM or your board?

    To correct the current value for each phase, please calibrate the current sense circuit. Let current pass the both H-bridges and measure/compare AISENP/AISENN and BISENP/BINSENN.

  • 0 in reply to Wang5577
    Prodigy 20 points

    Mr Wang.

    Thank you for your reply.

    The problem occurred on the PCB we designed, not EVM.

    When driving the same motor with EVM under the same conditions, the current value of the AB phase was almost the same. (682mA for phase A, 679mA for phase B)

    Therefore, it seems that there was something overlooked in the PCB we designed.


    Our PCBs are designed based on EVM circuits, but there are some differences.

    p1.The capacitor between VCP and VM is 0.1uF. (1.0uF for EVM)
p2.The capacitor between VINT and GND is 0.1uF.(1.0uF for EVM)
    p3.Pattern around FET and Regiter(ISENSE).


    About p1.p2, the phenomenon did not change when the capacitor was adjusted to EVM.

    I would like to verify p3.

    In EVM, the pattern was symmetric in the AB phase, whereas in our PCB it was asymmetric.



    q1. In this way, can there be a difference in drive current due to the asymmetrical mounting pattern of the AB phase FET?
    q2. What is the best way to adjust the AB phase difference?  Is it possible to adjust by the DRV8711 register setting?

    *  By the way, when AISENP / AISENN and BISENP / BISENN were measured and compared, both were about 30mV. However, the voltage is too low to distinguish a difference of around 7%.

    Best regart.

  • 0 in reply to user5948348
    TI__Guru 56650 points

    Hello,

    When the voltage both were 30mV near IC, it indicated the IC having a good current regulation.

    You can also measure the voltage on the current sense resistor. If it is different than 30mV, it is layout issue. For current sensing circuit, it needs the Kelvin connection.