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DRV8825 suitable for 340mArms load?

Kwan
Intellectual 510 points
Other Parts Discussed in Thread: DRV8825, DRV8824

Hi all,

Can the expert help to advise on this application:

 

1. The current limit for the DRV8825 copper drive is governed by the equation Ichop = Vref/(5xRsense). Please confirm if the current is referring to the peak current.

 

2. Our desired current from motor driver is 340mArms through to the motor winding. Under the assumption that Ichop is referring to peak current, the equivalent peak current limit should be 480mArms. The application do not achieve 340mArms and it is less than this by 60mArms.

 

3. We achieve 340mArms through the winding only when  the following setting is followed:

 

Vref = 1.4125V

Rsense=0.5 ohm

 

Again, theoretically this corresponds to Ichop (peak) = 565mA which corresponds to 400mArms. Again, there is a delta of 60mArms between set value and measured value.

 

4. For our application, which requires only 340mArms nominally, is it acceptable to use DRV8825 with a current driving capability of 2.5A? If not, do you have any alternate suggestion without software impact?

  • 0
    TI__Mastermind 26065 points
    Hi Kwan

    What is your micro stepping setting? In Full step mode the current will be 70% of setting level.

    How do you measure the RMS current? What is the speed of the motor? Note we set is the MAX level or peak level. The RMS will be about 0.7x of the MAX level only when the current wave is close to sine wave.

    DRV8824 can be an option with less current ability but pin to pin with DRV8825.

    But I think your problem is because of current shape. DRV8825 should be able to regulate it well also.

    Best regards,
  • 0 in reply to Wilson Zuo
    Intellectual 510 points

    Hi Wilson,

    In order to achieve the desired force, we have modififed the peak current limit setting, intend to allow a maximum of 400mA through motor winding with below setting:

    1/4 micro stepping

    Speed is 380 full step/sec

    current set = 0.66A (Vref 2.7V, Rsense = 0.82ohm)

    Current probe on the motor wires at the output of the motor driver.

    Is this acceptable to use DRV8825 in this application.