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DRV8711: STM32+DRV8711

Part Number: DRV8711

Engineering:

Use Indexer mode to keep writing values to the CTRL register and ask it to step forward. The measured voltage changes across the four pins are similar to the PWM wave. Customers do not have an oscilloscope and can only measure the effective voltage with a multimeter. The four pins should have waveforms. At this point, the stepper motor can rotate. And then when pulsed, it's a fixed voltage. Two are up to 24V and two are 0V. The customer believes that the rising edge will not change A1Hs and A2Hs, nor will the high and low levels of the four outputs change, regardless of how the pulse stimulates the driver.

Issue:

The customer intends to use indexer mode and then pulse to control the stepper motor rotation, but failed.

The steps are as follows:

1. First write the initial value to all registers and read correctly.

2. and then send a fixed number of pulses to the STEP pin using PWM.

Results: The AOUT+ and BOUT+ on the official schematic are always 24V and the other two are always 0V.

The customer suspects that writing the DRV8711 initial value through SPI may not be appropriate, but normally the pulses should spin, that is, the 4 out will produce 0-24V voltage variations, but failed.

May I know what's the possible reason for that or is any step wrong?

Thanks a lot!

Best Regards,

Cherry Zhou

  • Hi Cherry,

    Please give me 24 hours to review the customers questions and I will get back to you with answers soon.

  • Hi Pablo,

    Thanks and expecting the updates!

  • Cherry,

    Since I worked on stepper motors a little more, let me jump in to this thread.

    Do you test it with an EVM? Do you put any load at output? What is the load resistance?

    Regards,
    Wang Li

  • Hi Wang,

    Thanks for your reply and help!

    Do you test it with an EVM? Do you put any load at output? What is the load resistance?

    Do not test with an EVM. Do not put any load at 4-pin output. 

    The customer tries to connect the stepper motor and also do not turn.

    The hardware circuit diagram is the same as the chip manual.

    Please help to check, thanks a lot.

    Best Regards,

    Cherry

  • Cherry,

    DRV8711 regulates the output current, not voltage. If the output current cannot reach the Itrip setting point, DRV8711 will try to make the AOUTx and BOUTx as VM voltage and other half bridge 0V. Please check the output current Itrip setting and compare it with the output current.

    A high motor coil resistance  may limit the output current lower than the Itrip setting.

    Regards,

    Wang Li  

  • Hi Wang,

    The customer checked the output current at the current box.

    The threshold current is set to 1.3A, but the current on the current box is always 0.87A, which is a straight line, should be stall mode. But the customer's STEP pin has always had a pulse wave, which should have been in the always-on mode, and the pin outputs a sinusoidal wave, but now the output current waveform is straight.

    Could you please help to check this? Thanks again.

    Best Regards,

    Cherry

  • Cherry,

    "Two are up to 24V and two are 0V." "The threshold current is set to 1.3A, but the current on the current box is always 0.87A".

    a. DRV8711 has put all input to the motor terminal, but the current still cannot reach 1.3A. what limits the current? Is the motor coil resistance too high?

    b. if the motor resistance is too high, why do they set it to 1.3A?

    c. what is the STEP pin pulse frequency?

    d. I think they have to use scope to check the STEP pin signal and output current to speed up the debugging process?

    Regards,

    Wang

  • Hi Wang,

    Thanks for your reply!

    Program as follows:

    The spi communication register writes a value and then steps the pin to pulse. The hardware is the same as the official schematic. The problem is that AOUT+ and BOUT+ are always 24V and the other two are always 0V.

    The current is always 0.87A when the motor is connected and set to around 1.0A. The register values are 0f19, 10ba, 2030, 3108, 4310, 5f40, 6554.

    Pulse frequency tried to overset to 1-250Khz, and the result was the same, the motor torque was applied and the motor did not turn.

    a. DRV8711 has put all input to the motor terminal, but the current still cannot reach 1.3A. what limits the current? Is the motor coil resistance too high?

    For a, that's also the point the customer is curious about.

    b. if the motor resistance is too high, why do they set it to 1.3A?

    Because the stepper motor control cannot exceed 1.2A (the corresponding current has been tried at 1-1.3A, the effect has not changed).

    And about the motor windings, the customer is also nor sure. But the register cycle write-ups can be turned, proving that both the motor and the hardware should be free of problems.

    c. what is the STEP pin pulse frequency?

    1K-250K has all tried and checked the pulses of the stepped pins for normal waveforms, which can be excluded. 

    d. I think they have to use scope to check the STEP pin signal and output current to speed up the debugging process?

    The customer has used scope to check, the output current has always been 0.87A , with no sinusoidal changes.

    Please help to check the updates.

    Thanks.

    Best Regards,

    Cherry

  • Cherry,

    Follow Ohm's law, if the input is 24ohm and the coil or load resistance is 27.6ohm, the output current is limited to 0.87A by the coil resistance. What is the motor coil or load resistance? I didn't get the answer. We stuck here.

    Also, please provide the waveform to show the STEP pin pulse and output current.

    Regards,

    Wang