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DRV8881: drv8881 application question

Dane Zhang
Expert 6755 points
Part Number: DRV8881
Other Parts Discussed in Thread: DRV8426, DRV8428, DRV8434, DRV8424

Hi team,

can DRV8881P be used in the slow decay mode? now the motor is under subdivision operation with 1.8 step angle and peak current be 2A. the max speed set to angle 840/s.

is there any risk to use the decay mode? now we are using the mixed mode.

  • 0
    TI__Mastermind 35955 points

    Hi Dane,

    The decay modes help with distortion of the current waveform thereby enabling smooth operation of the stepper motor with minimum audible noise. If in this application slow decay operation is supporting smooth operation with good current waveform at the target speed used with the 2 A IFS setting there is no risk to use slow decay mode. If the current waveform is distorted we suggest using the mixed decay mode. 

    The DRV8881P supports the following decay modes..

    Any specific reason why the customer prefer to use this device? For subdivision operation (microstepping) customer has to have complex firmware to generate variable VREF for each microstep. Instead drivers such as DRV8426, DRV8428, DRV8424, DRV8434 would be easier to use because of its STEP/DIR interface as well as Smart Tune decay for low current waveform distortion automatically. 

    Regards, Murugavel

  • 0 in reply to Murugavel4637
    TI__Expert 6755 points

    Hi Murugavel,

    checked with customer that they choose this device before and they continue to use this in upgrade project. and below is the issue they met:

    when used  DRV8881P to drive a hybrid motor, we found that under Mixed delay, the amplitude of current chopping was large and the motor made obvious noise. After we switch to slow delay, the noise will be greatly reduced.
    However, slow delay has the following problems:
    1. During phase locking, the current of each phase of the motor cannot reach 0, but is above 500mA (Toff = 10us) or 200mA (Toff = 30us). I would like to ask what is the specific reason? Is it possible to avoid it by allowing the motor current to reach 0 during static phase locking? If the motor current cannot reach 0mA, slow delay cannot be used.
    2. The motor drive sine wave will be distorted at low speed and high speed. The reason may be that the motor current cannot reach 0mA.

    could you help to check if there's way to solve the issue and also help to analyze the reason that this issue occur?

    green line: motor current; yellow line: VREF
    ​

    3. they found pin11 will have noise/interference waveform when testing, even after they optimize the measurement loop, there will still be spike as shown below, is this caused by the motor switching or some other reason?

    yellow line: AVREF(pin11)

  • 0 in reply to Dane Zhang
    TI__Mastermind 35955 points

    Hi Dane,

    Unfortunately slow decay is not fast enough to decay the current to the Itrip level during falling currents in 2nd and 4th quadrant. This is because of the back EMF of the motor. So it may not be possible for the current to reach zero in slow decay. The behavior will likely change with a loaded motor because of the change in phase of the back EMF. 

    Can the customer modify their design to use the DRV8881E variant just so they can use the smart tune decay mode? Smart tune is closer to mixed decay but will use slow decay during rising currents (1st and 3rd quadrants).

    Regards, Murugavel