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DRV8711: Maximum fSTEP frequency (maximum input speed)

REMI D
Prodigy 200 points
Part Number: DRV8711


Hi all,

We already use DRV8711 for some of our driver boards. But for a new design we have to reach a fSETP frequency up to 300kHz (1/32 step 48V).

Unfortunately the datasheet indicates a maximum frequency of 250kHz:

I carried out tests with DRV8711EVM evaluation board.

Target speed is limited to 32 000 PPS (due to EVM FW limitation). So I removed the jumper STP on J6 and I feed the board with a bench top frequency generator.

I gradually increased the frequency to achieve a gradual acceleration. By this way I could easily reach 400kHz as shown below:

  • Channel 1: STEP AIN1; Channel 2: not connected; Channel 3: A phase motor current; Channel 4: B phase motor current
  • Output currents are largely distorted, but there was no fine tuning on all driver parameters and the motor is not loaded.
  • Frequency generator : AFG Square 400kHz
  • Measure between cursors: 64 pulses and 161.2µs => 397kHz

So my question is: is-it safe to operate beyond the maximum frequency of fSTEP=250kHz?

  • 0
    TI__Guru 56650 points

    REMI,

    I didn't see the waveform. You can insert a .png format waveform file. It could show up.

    1. The datasheet "Indexer Timing Requirements" gives the detail fstep timing requirement. If the fstep is higher than 250kHz, tWH(STEP) and tWL(STEP) cannot meet the spec.

    2. Could you reduce the micro-step setting to 1/16 and set fstep to 150kHz first? And  then, monitor the winding current when the motor is spinning. If the motor is stuck or the motor winding current is not sinusoidal waveform, the motor may not support such high speed operating by the machinal reason or the winding back EMF.

     

  • 0 in reply to Wang5577
    Prodigy 200 points

    Dear Wang,

    Many thanks for you quick answer !

    Sure, the motor winding current is not sinusoidal waveform. Probably for good reasons (DRV parameters not yet adjusted, motor not loaded, etc…). I will set a test with other stepper drivers to compare and check this motor is really suitable for such high speed.

    By the way, I was first trying to overpass the maximum fSTEP frequency to observe the DRV8711 behavior.

    And I could see during my evaluation that the DRV8711 follow perfectly input frequency from 0 to 400kHz and so on. At this very high frequency there is no phase shift nor erratic functioning.

    That’s why I wondered if fSTEP, tWH (STEP), tWL (STEP) vales of the datasheet was arbitrary defined and could be overpassed in some specific use cases ...

    screen shot for fSTEP=250kHz:

  • 0 in reply to REMI D
    TI__Guru 56650 points

    REMI,

    The 250kHz maximum fstep spec cannot be changed, even few devices can be tested to 400kHz at room temperature. We have to count the device lot by lot variation and all other conditions. Also, I would think 250kHz fstep is too fast for the motor to follow. So, the limitation could be not on fstep, it could be on the motor's back EMF and motor's mechanic system.