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DRV8818 Ichop

NAOKI AOYAMA
Guru 11215 points
Other Parts Discussed in Thread: DRV8818

Hello,

Our customer uses the DRV8818, with half step mode.

The customer wants to control the current of the motor while keep some state.

So, they change the value of the VREF voltage while keep some state.

But there is no response. There is a response only at the home state.(45degree position)

Is it a correct behavior of the DRV8818?

Regards,

Naoki Aoyama

  • 0
    TI__Mastermind 26065 points
    Hi Naoki,

    When you say no response, do you mean the current level is not changing according to the Vref/Rsense equation or there is no response from the motor position?

    In normal case, if the motor is kept the state, the change on Vref will change both the current of A and B propotionally. Since using half stepping, there will be 50% chance that only one coil is excited with current. So is that possible when we do the test of the "no response " happened to be the zero one? So it will not responsed to the change on the Vref as it always zero.

    Other possibility is that the driver is in SLOW decay mode, and the current is actually not correctly controlled by the regulation loop because of the current injected in Tblanking time cannot be decay down to the setting level. In this case, motor may be runnning but the current is already out of control most of the time.

    Best regards,
  • 0 in reply to Wilson Zuo
    Guru 11215 points
    Hi Wilson,

    'no response' mean the current level is not change.
    I will check the condition of the customer using.

    Thanks,
    Naoki Aoyama
  • 0 in reply to Wilson Zuo
    Guru 11215 points
    Hi Wilson,

    I checked the configuration.

    Excite Mode: 1-2 phase (half step)
    Decay Mode: Mix
    Motor current : 1.5A (when the motor rotate) 0.2A(when the motor stop)

    The customer investigate by every electrical angle. The results are follows.
    0, 90, 135, 180, 270, 315 degree are not change the current.
    45, 225 degree are OK.
    Is it a timing to change the Vref for the internal DAC?

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    Guru 11215 points
    Hi Wilson,

    How is the situation after that?
    I will wait for the answer.

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    Guru 11215 points
    Hi Wilson,

    Is there any update?

    If the results of the customer investigation is correct and that is just design
    of the DRV8818 I will feedback the customer 'it is design'.

    Regards,
    Naoki Aoyama
  • 0 in reply to Wilson Zuo
    Guru 11215 points
    Hi Wilson,

    It is possible to change the full scale current at only STEP ANGLE as 45degree and 225degree.
    Is this correct and just design?
    The customer wants to know that.

    Regards,
    Naoki Aoyama
  • 0 in reply to Wilson Zuo
    Guru 11215 points
    Hi Wilson,

    I checked this performance by EVM.
    Though I set the decay mode as mixed, the decay mode is slow
    at the current through the winding is increasing.
    So, I can not control the current to the setting level.

    I suggest the customer to up the setting level.

    Thanks,

    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Mastermind 26065 points
    Hi Naoki,

    Thank you of your feedback. That makes sense. Should be fine if the decay mode changed.

    Best regards,