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DRV8834: AVREF and BVREF voltage in indexer mode

Cherry Zhou
Mastermind 22235 points
Part Number: DRV8834

Hi team,

Here's an issue from the customer may need your help:

When using the DRV8834 to control the stepper motor, the indexer mode of 8834 is required (16 microsteps are used simultaneously). In addition, the peak of the output current needs to be dynamically adjusted, for example, sometimes a peak of 0.7A or sometimes a peak of 1A. Here's 2 questions:

1. The customer would like to know If AVREF and BVREF are needed to be connected to a fixed voltage (such as VREFO-2.5 V) in indexer mode, is this voltage used as a reference source for the internal DAC?

2. Continuing with 1, if so,  how to dynamically adjust the peak of the stepper motor winding current in indexer mode?

Could you help check this case? Thanks.

Best Regards,

Cherry

  • 0
    TI__Guru 54725 points

    Cherry,

    I am assigning this to a team member.  Please allow 24 hours.

    Regards,

    Ryan

  • 0
    TI__Expert 5206 points

    Hello Cherry,

     

    Thank you for checking with our team. To answer your questions:

    1. Yes, you are correct. In indexer mode, AVREF and BVREF should be connected to VREFO (typically 2 V) as a voltage reference for the internal DAC.
    2. In indexer mode, AVREF and BVREF are connected to VREFO and full-scale current (IFS) will be scaled by a value between 5% and 100% through internal DACs as shown Table 4 (p. 17 of the DRV8834 datasheet).



      An example for adjusting IFS between 1.0 A and 0.7 A, given that AVREF = 2 V and BVREF = 2 V, use 400 mOhm for RSENSE to achieve 1.0 A at 100%.  M1 and M0 pins can be configured to 0 and 1 inputs respectively to be in ½ step mode which will vary the current between 100%, 71%, and 0% for winding current A and 0%, 71%, and 100% for winding current B on steps 1, 2, and 3.

     

    Thanks!

    Tilden

  • 0 in reply to Tilden Chen
    TI__Genius 10295 points

    Hi Tilden,

    What the customer wants to know is：

    In indexer mode, can an external DAC be used to dynamically control the voltage of xVREF to dynamically adjust the full-scale current Itrip when the resistance of RSENSE remains unchanged?

    EG: Both are 1/2 microstep, and the full-scale current can be 1A or 0.7A.

    Purpose: In the case of a fixed microstep, the RMS value of the current can be changed with the change of xVREF.

    Thanks,

    Annie

  • 0 in reply to Annie Liu
    TI__Guru 54725 points

    Annie,

    Yes, this is absolutely possible and the device was designed for this exact usage case.

    Regards,

    Ryan