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DRV8825: Current distortion

Andrea B
Prodigy 20 points
Part Number: DRV8825

Hello,

I need the meaning of the distortion of the current with the driver DRV8825.

The simplified schematic of my board is as follow:

0670-00.pdf

When I start the motor I see that the current is distorted. In these point (current distorted) I see the "blank" of the voltage on the winding of the motor and on the shunt resistor refered to the winding. Se point A in the file "Screenshot_1".

I attached some screenshot:

Screenshot_1

Screenshot_1

Screenshot_2

Screenshot_2

Screenshot_3

Screenshot_3

Screenshot_4

Screenshot_4

With the motor in the running state: MODE is setted to 1/16 step, DECAY pin is setted high (fast).

No fault signals are present (the signal is always high).

Can you help me to understand why are there these point of distortionn to the current?

Best regards,

Andrea

  • 0
    TI__Mastermind 18820 points

    Hi Andrea,

    The current ripple distortion is likely coming from the decay mode setting. Current ripple often occurs when the stepper motor decays current in FAST decay too often. The smoothest sinusoidal output waveform should come from operating in SLOW decay whenever possible. This will provide enough time for the current to decay from the load and recirculate through the H-Bridge. 

    Please see the attached application note on How to Reduce Audible Noise in Stepper Motors for more details:

    https://www.ti.com/lit/an/slvaes8/slvaes8.pdf 

    Best,

    David