• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 31 subscribers
  • Views 356 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV8301 current sense circuitry

Mitch Hanks
Intellectual 670 points
Other Parts Discussed in Thread: DRV8301

The DRV8301 has two current sense amplifiers which in the example circuit are shown to be used to amplify currents through resistors that have been placed in two of the three individual low side paths to ground (between the pull down resistor and ground in each case).  In this configuration the system has visibility of the current 2/3 of the time but when current is going through the 3rd phase there is no way to read current.  My question:  why is the current not sensed in the path between the point where the three phases join together on the low side and ground?  Is there an advantage to sensing two phases individually instead of the sum of all three?  Also, why only two of the three phases - is this a cost reduction?

Thanks,

DMH

  • 0
    TI__Mastermind 21320 points

    Hi Mitch,

    The application schematic you are looking at is simply one of many possibly configurations to utilize the dual current shunt amplifiers onboard the DRV8301. You will see on our EVM that we actually utilize additional amplifiers to monitor the 3rd phase and total current.

    The limitation to 2 was a constraint by the size of the package for the DRV8301.

    -Nick

  • 0 in reply to Nicholas Oborny
    Intellectual 670 points

    Nick,

    For a hall sensor based control circuit is there a benefit (higher accuracy?) to sensing the phases individually versus sensing the sum?

    Thanks,

    Mitch

  • 0 in reply to Mitch Hanks
    TI__Mastermind 21320 points

    This depends how the control algorithm works. For a hall sensor setup I do not believe there is much benefit to be gained. You can commutate the motor through the hall sensor feedback and determine torgue through the sum of the currents.

    -Nick

  • 0 in reply to Nicholas Oborny
    TI__Guru** 119500 points

    in trapezoidal control, wether hall or Bemf sensorless, only the total current sum is used, you don't need any of the shunts/phases because you only have two legs active at a time.

    as soon as you move to sinusoidal control all three legs are active and you then need phase/shunt measurements. It can be done with a single shunt but it is more challenging (especially on how/when you sample the shunt) and greatly limits low speed, high speed, and dynamic performance.  Moving to 2 shunts improves dynamic performance but still limits you, especially to maximum speed / modulation range.  Three shunts allows for full speed/modulation if you want to go outside the sinusoidal range to maximize speed.  And of course having phase currents makes everything even easier as you no longer have to worry about sampling windows.