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DRV8804: Using the different voltage of VM-pin voltage and Motor voltage

masahiko shimizu
Guru 11235 points
Part Number: DRV8804

Hi,

My customer thinks about using DRV8804 with below situation for unipolar stepper.
Can my customer use in this situation?

VM-pin : 18V supply
VCLAMP-pin : 18V supply (connect to same supply as VM pin)
Motor (OUTx-pin ) : 12V

Best regards,
Shimizu

  • 0
    TI__Genius 14485 points
    Shimizu-san,

    That driving condition should be fine. Just so I can be sure, what current requirement do they have? Also, I'm assuming they will use PWM to achieve 12 V on the motor from the 18-V rail, correct?
  • 0 in reply to James Lockridge19
    Guru 11235 points

    Hi James-san,

    Thank you for your support.

    Motor current is about 200mA.
    The different source of 12V power supply and 18V power supply.

    I think 18V power line is boosted by switching of motor operation(of 12V power line)?
    Is this idea correct?
    Do you have a idea about above issue?

    Best regards,
    Shimizu

  • 0 in reply to masahiko shimizu
    TI__Genius 14485 points

    Shimizu-san,

    Are you trying to achieve a configuration like the image below? I would connect VCLAMP to the 12-V supply. So long as the 18-V supply and the 12-V supply have the same ground, this configuration should be fine. The purpose of VCLAMP is to provide a path for the coil current during the FET off-time.

  • 0 in reply to James Lockridge19
    Guru 11235 points


    Hi James-san,

    Thank you for your support.

    I am trying to achieve a configuration like the image below.
    The 18-V supply and the 12-V supply have the same ground. but it is through connector.
    Is it possible below system if the 18-V supply is able to sink current from motor coil?

    Best regards,
    Shimizu

  • 0 in reply to masahiko shimizu
    TI__Genius 14485 points
    Shimizu-san,

    Using 18-V for VM is fine. The chip pulls the coils to ground when the FETs turn on. The OUTx pins do not act any differently whether this voltage is 12-V or 18-V.

    My biggest concern here is the recirculating current during the off-time. Where will it go? I'm not confident that the design will have a nice path for the current to recirculate between the 12-V and 18-V supply. If you cannot put the 12-V supply on VCLAMP, then you should put freewheeling diodes in parallel to each motor coil on the motor board.