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Original question:

MCF8316A: Torque control mode

MCF8315A: Negative currents

joe van Niekerk
Prodigy 30 points
Part Number: MCF8315A
Other Parts Discussed in Thread: MCF8316A

I had previously asked how to command negative current using i2c commands (https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1251320/mcf8316a-torque-control-mode/4769937#4769937). The suggested solution kind of worked, but it seems to respond only at very low and inconsistent update rates. It is not sufficient for closing a control loop and mostly ignores the setpoints. I had to revert to using only positive current setopints but need to revisit this issue. Please suggest a way of sending positive and negative current setpoints that are accepted and tracked at an update rate of at least 50 Hz. 

  • 0
    TI__Expert 7865 points

    Hi Joe,

    As Josh mentioned in the linked E2E post, when speed loop is disabled on the MCF8316A, a negative current reference can be set using the FORCE_IQ_REF_SPEED_LOOP_DIS register through I2C. However, this updates at a fairly slow rate of around 200ms.

    May I ask why you do not wish to utilize the speed control loop?

    When speed loop is enabled (and AVS is disabled), the device will apply a negative torque (when necessary, depending on the CL_DEC rate and speed KP/KI settings) while decelerating from a high speed to lower speed. This may lead to a DC bus spike due to energy from the motor flowing back to the supply, therefore AVS can be enabled to monitor the VM bus voltage and slow down the deceleration rate to prevent energy from flowing back to the supply. Lastly, if fast deceleration w/ negative torque and no VM bus spike are necessary, active braking can be used to slow down the motor at a fast rate (with negative torque) while drawing more current from the supply and applied in the Id vector to prevent current from flowing back to the supply.

    Regards,
    Eric C.