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TMS320F28054M: Rectangular current waveforms in open loop mode (lab 1B) for a new batch of boards, while old batch is working properly

Roman Isaikin
Intellectual 270 points
Part Number: TMS320F28054M

Hi!
Hope that you can shed some light onto the problem we are currently having with TMS320F28054M + DRV8323S based boards.
We had a working design and simply ordered a new batch of boards. New boards didn't worked. After comparing everything and
running lab 1B to verify the power stage, we observed strange change in the phase currents waveforms - they are much sharper on a new batch, almost rectangular.
While previous batch and BoostXL dev board are trapezoidal. Lab 1C and further don't work at all. Tried changing DRV to the old one - same results. All tests are done with the same motor, same supply voltage of 12V and same source code. Also checked gate waveforms - same on all boards.

Previous batch:

New batch:

  • 0
    Prodigy 50 points

    For clarification: When the DRV was changed it was replaced with a DRV from a working PCB from the older batch. However, as mentioned, it did not change the strange behavior.

  • 0 in reply to Jørgen Haaland
    TI__Guru** 112290 points

    You may try to tune the following parameters to spin the motor with lab01b, and check if the sensing current waveform with F28054M can follow/match the measurement current with an oscilloscope + current probe as described in the lab user's guide.

    #define USER_MOTOR_FREQ_LOW                                (10.0)                        // Hz - suggested to set to 10% of rated motor frequency

    #define USER_MOTOR_FREQ_HIGH                                      (100.0)                        // Hz - suggested to set to 100% of rated motor frequency

    #define USER_MOTOR_FREQ_MAX                                (120.0)                        // Hz - suggested to set to 120% of rated motor frequency

    #define USER_MOTOR_VOLT_MIN                                (3.0)                        // Volt - suggested to set to 15% of rated motor voltage

    #define USER_MOTOR_VOLT_MAX                                (18.0)                        // Volt - suggested to set to 100% of rated motor voltage

    Please check if the DRV8323RS is configured correctly, especially the PWM mode and PGA settings.

  • 0
    Prodigy 50 points

    Update: We found the issue, and it was our supplier who had used the wrong shunt resistors in the current sensing feedback. It was 10x larger than in our specs, and this again caused the current wave forms to look a lot faster (since their amplitude were multiplied by 10).