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DRV8825: The actual current peak does not match the set current value after stopping STEP signal

Ken Zhang
Expert 3595 points
Part Number: DRV8825
Other Parts Discussed in Thread: DRV8436, DRV8425

Tool/software:

hi,

After the motor is spinning normally, the customer stops the motor by stopping a pulse signal to the step pin. The current through the motor 2 phases are tested and the current through one of the phase  is much larger than the set maximum of 300 mA. Is this normal?

Test condition: After the motor is spinning normally, the customer stops the motor by stopping a pulse signal to the step pin.

Decay mode: Mixed decay; Microstep:  1/32; Without load with motor

the waveforms of phase current following out AOUT/BOUT are listed in attached.

The actual current peak does not match the set current value after stopping STEP signal.pptx

  • 0
    TI__Mastermind 44685 points

    Hi Ken,

    Whenever the stepper is stopped after stepping through, the coil currents will be according to the Table 2. Relative Current and Step Directions page-14 of the datasheet based on which microstep the motor was stopped. It is not expected to exceed 100% of the IFS setting of 300 mA assuming AVREF and BVREF voltages were unchanged. 

    Regards, Murugavel

  • 0 in reply to Murugavel4637
    TI__Expert 3595 points

    Murugavel

    1. After further testing, the voltage of AVREF/BVREF is stable after stepper is stopped.
    2. When operating in mix decay and slow decay modes, the customer also detected the same behavior on the demo board. But in fast decay mode did not detect the same issue.
    3. Because fast decay will lead high motor noise, the customer wants to use mix decay mode.

    Support needs:

     please help verify the issue and give any suggestions as I do not have the EVM board here,

  • 0 in reply to Ken Zhang
    TI__Expert 3595 points

    Murugavel

    add motor simple spec.

  • 0 in reply to Ken Zhang
    TI__Mastermind 44685 points

    Hi Ken,

    Thanks for the details. I'll look for an EVM and see if we can replicate the issue. The DRV8825 is a pretty old stepper driver. We have several new stepper drivers in our portfolio with higher performance and competitive prices. Is there a particular reason the customer wants to use the DRV8825? 

    Regards, Murugavel

  • +1 in reply to Murugavel4637
    TI__Mastermind 44685 points

    Hi Ken,

    I verified with the EVM. For the target current of 300 mA or lower for microsteps, slow or mixed decay is not sufficient to regulate the current to this low level with this device. To ensure proper regulation to this low current target, fast decay must be used. The motor current exceeding target current in decay modes other than fast decay is expected behavior for this device.

    If this is not desired I'd recommend stepper drivers such as the DRV8425, DRV8436. Thank you. 

    Regards, Murugavel