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DRV8251: Slow decay, need fast decay with both inputs high.

ArTzy
Genius 14779 points
Part Number: DRV8251

Hi Experts,

Seeking your assistance on this query about DRV8251 from Cx:

I have been testing the DRV8251 as a replacement for the ST L6201 to drive a stepper motor. Everything was going great until it was noticed that the application vibration increased. One difference is when both inputs are high, the L6201 has both Source FET's ON for which would be defined as "SLOW DECAY" and the DRV8251 has OUT1 and OUT2 as L, which sounds like both upper FET's are ON which should be an equivalent "SLOW DECAY" mode. Do I understand this correctly? Why is this mode described as "BRAKE, low -side slow decay", the BRAKE comment is concerning.

Any thoughts on why vibration has increased?

Regards,
Archie A.

  • 0
    TI__Mastermind 37683 points

    Hi Archie,

    I'm trying to understand how the increased in vibration relates to the decay mode of the IC motor driver. Can you elaborate?

    In the DRV8251, "Brake" also called "low-side slow decay", the bottom two FETs will turn shorting OUT1 and OUT2 to GND. The "L" in the logic table refers to OUTx being "LOW" or the low-side FET turning ON. Hope this clears the confusion.

    ArTzy said:
    I have been testing the DRV8251 as a replacement for the ST L6201 to drive a stepper motor

    The DRV8251 is only a full bridge driver. It is not a dedicated stepper driver. Is there a reason for selecting this device over a dedicated stepper driver?

    Regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    TI__Genius 14779 points

    Hello Pablo,

    Thank you for your response.

    Pablo Armet said:
    Is there a reason for selecting this device over a dedicated stepper driver?

    It was selected to be the best alternate for the ST L6201.

    Will respond when I get more information from additional testing, will be a few days.

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Mastermind 37683 points

    Hi Archie,

    Thank you! please let me know once the tests are completed.

    Are they using the DRV8251 to drive one winding of a stepper motor or control the stepper motor unidirectionally?

    Regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    TI__Genius 14779 points

    Thank you, Pablo.

    The customer is using the DRV8251 to drive one winding in a stepper motor.

    73,
    Archie A.

  • 0 in reply to ArTzy
    TI__Mastermind 37683 points

    Archie,

    Got it. Not sure still why the increased vibration relates to being able to set H-bridge in low-side current recirculation. I would be interested to learn more about it. Anyways, the DRV8251 is able to turn both low-side FETs ON at the same time. As long as it meets the current and voltage requirements, the DRV8251 is a good replacement for the ST part.

    Regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    TI__Genius 14779 points

    Hi Pablo,

    Thank you.

    Problem has been fixed, needed to use the Enable signal that was used by the ST L6201 to set the inputs to the DRV8251 low when Enable goes low to turn the FET's off.

    We have a question: We are not using the internal PWM and considering setting VREF to the maximum value of 5V, it's listed as 5V max recommended, 6.0V Absolute max. My application is 2.5A peak and a 0.20 ohm sense is being used. The problem is that we need to power this with a zener diode and 5.1V 2% would produce a 5.2V maximum. If this is a concern we will use a 3.3V zener and change Rsense to 0.10 ohms.

    Looking forward on your thoughts on these.

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Mastermind 37683 points

    Archie,

    I suggest using 3.3V max for VREF to have some headroom but 5.2V is within acceptable range. The customer should make sure that the VREF signal is stable and does not oscillate or have transient spikes.

    Regards,

    Pablo Armet