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DRV8818 Vref setting for torque evaluation

richie lai
Prodigy 10 points
Other Parts Discussed in Thread: DRV8818

hi,

    Now I have a problem of DRV8818 test problem because our mechanical engineer use it for torque margin test.

     1: They use external power supply for adjusting Vref to set up current. But they use multimeter for getting voltage and they use about 0.01~0.02volt as gap. Our machine is using Rs=0.28ohm so that the current formula is I=Vref/(8*Rs). I don't know if they use such a small voltage gap for test is useful or useless. Is anyone have suggestion for that issue? (vref is from1.2v to 3.3v)

     2: Is this small voltage gap affecting the current of driving motor? How do I know the tolerance of motor driver capacity? I usually use Textronic current porbe for seeing the current waveform and it has weak ability for checking samll current signal.

  • 0
    TI__Expert 8885 points

    Lai,

    I feel 0.01V is too small value to get any meaningful results. There are various factors which in combination decided the current regulation, such tolerance of Rsense, Tolerances of RC components which fix PWM off time/blanking time and Ichop current accuracy of DRV8818 itself which varies with % of current regulated.  In view of this, It is very much involved and complex task to derive theoretical value of current/torque regulation resolution based given Vref setting.

    My suggestion would be find out this value experimentally on actual test system which can be properly distinguished by measurement system.

    Best Regards

    Milan-Motor Application Team