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DRV8704: How to activate Direct PWM Input Mode

Frederik Baars
Intellectual 2115 points
Part Number: DRV8704

Hi,

customer has a problem with the DRV8704. There are applications where, for example, no motor is to be operated, which is not possible in the current control mode, but the PWM must be controlled directly.

The data sheet mentions a "Direct PWM Input Mode" (point 7.3.2 - see appendix), but nowhere it is explained how to activate this mode.

For the PWM mode there is only one bit in the configuration register that activates the "PWM control mode" or does the Direct PWM mode only mean that the current is selected so high that the controller is not regulated via the current, but directly controls the outputs?

Thanks

Fred

  • 0
    TI__Guru** 114905 points

    Hi Frederik,

    Direct PWM mode is intended to describe how to disable the current regulation. There is no register bit to enable this.

    To use the DRV8704 to control the outputs without current regulation, the following steps should be performed:

    1) Set the TORQUE register to 255
    2) Set the ISGAIN to 5
    3) Add a sense resistor in the path if external current monitoring is desired
         a) The sense resistor should not create a voltage greater than 0.5V across the sense resistor to avoid activating the current regulation.
         b) If current regulation using the DRV8704 is desired to limit the current,  the sense resistor value can be change to activate the current regulation. One example of this would be a protection circuit in case higher than expected current occurs.
    4) Use the VDS monitors for overcurrent protection.