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DRV8343-Q1: Do we have reference circuit design for estimating BEMF using a BEMF comparator?

Iris Shen
Expert 3511 points
Part Number: DRV8343-Q1
Other Parts Discussed in Thread: TLV3502, TIDA-010031, MSP430FR2355

Hi team,

Per we talked, my customer plan to use DRV8343-Q1 and need to sensor BEMF. They choose the way that estimate BEMF by using a BEMF comparator. Do we have reference design for this? Here are some questions:

  • For the BEMF comparator, is there any special spec requirement for the comparator? Do we have a recommendation?
  • For their project, delta connection is used which means they cannot detect the zero point voltage. Do you have similar BEMF estimation design reference for delta connection?

Thanks!

  • +1
    TI__Mastermind 26046 points

    Hi Iris,

    I do not know of a reference design example off the top of my head using a BEMF comparator, but a common way this has been implemented before for an internal design is that the phase V's sensed voltage (in this case "U_SNS_LV_UB") is compared to the virtual center tap ("CT") of the motor using a TLV3502 comparator, and the output push-pull voltage ("BCOMPU") goes low or high depending on whether the zero-crossing is passed during trapezoidal commutation. This is repeated for each phase. 

    The U_SNS_LV_UB voltage is a resistor divider from the phase voltage, and the CT voltage is 3 resistors tied together to create a virtual motor voltage in a Wye connection. 

    I am not sure how to implement a delta wound motor comparison of the BEMF comparator. My best guess would be to perform the sensorless trapezoidal detection by:

    • Calculating the phase voltages from the resistor dividers
    • Converting them from Delta phase voltages to Wye phase voltages in software
    • Comparing those values to VM/2 via Back-EMF integration or another sensorless trapezoidal technique

    I have a software resource for sensorless trapezoidal calculations using the MSP430FR2355 from a reference design TIDA-010031: www.ti.com/.../tidcf80

    Thanks,
    Aaron