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DRV8846: DRV8846

Kai Nomiyama
Expert 5565 points
Part Number: DRV8846

Hi Team,

in the evaluation of DRV8846, I have following questions about DRV8846 so could you help?
I also summarized more detail in attachment so please refer it.

DRV8846 question.pptx
Question 1
- From the beginning of switching to end of switching, dv/dt changes. It this normal behavior?
Question 2
- RL=60Ω and Rsense=3.9Ω so VM/Rtotal=5/63.9=78mA(not include Rdson). ±78mA=156mApk-pk so ⊿156mA looks correct but the waveform looks unstable. Is this normal behavior?
Question 3
- when Torque DAC=100%, 89mA (VREF*TORQUE DAC*70%/6.6*RISENSE) > 78mA (VM/RL+Rsense). Is it ok to use this Ichop > 78mA_Irmax setting?
※ motor saturation current is higher than 80mA so motor current doesn’t saturate in all waveform.

Please let me know if you need more information.

Regards,
Kai

  • 0
    TI__Guru 56650 points

    Kai,

    Question 1
    - From the beginning of switching to end of switching, dv/dt changes. It is normal because the back EMF is also not a constant number. You can make the motor in stall condition and check the dv/dt again.


    Question 2
    - RL=60Ω and Rsense=3.9Ω so VM/Rtotal=5/63.9=78mA(not include Rdson). ±78mA=156mApk-pk so ⊿156mA looks correct but the waveform looks unstable.

    The current regulation loop only cares about the winding peak current. I don't see any unstable condition. Don't forget the back EFM (motor speed) also affecting the waveform.


    Question 3
    - when Torque DAC=100%, 89mA (VREF*TORQUE DAC*70%/6.6*RISENSE) > 78mA (VM/RL+Rsense). Is it ok to use this Ichop > 78mA_Irmax setting?
    ※ motor saturation current is higher than 80mA so motor current doesn’t saturate in all waveform.

    If the motor is not saturated and the input voltage is higher enough to support 89mA, it is OK to me to use 89mA.