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Isolation Amplifier suggestion for motor driver

Grace Ma
Prodigy 250 points
Other Parts Discussed in Thread: DRV8872, AMC1300, AMC1200, AMC1311, ISO7731

Hello, 

I am using the TI DRV8872 motor driver in my design. I need to isolate the voltage across the ISEN resistor from motor ground to microcontroller ground. The datasheet for the driver says the current sense input pin voltage (ISEN) is min -0.5V and max 1V. Is there any isolation amplifier that would be suitable for this sort of application?

Thank you.

  • 0
    TI__Guru**** 168485 points
    Hi Grace,

    How are the control inputs to the DRV8872 being isolated from the MCU? The bottom of the ISEN resistor is going to be on the same ground, so I'm curious as to how you are accommodating the input side. Isolation amplifiers like the AMC1200 and AMC1300 can only handle +/-250mV inputs and stay within their linear range. The AMC1211 or AMC1311 might be options - they can handle up to 2V on their inputs but the negative side is limited. The MAX output from the DRV8872 is -.5 to +1.0, but what is the expected output range in your particular setup?
  • 0 in reply to Tom Hendrick
    Prodigy 250 points
    I am using digital optoisolators to isolate the input signals to DRV8872 from the MCU. Since those are purely digital signals, that was easy to isolate. Thank you for the suggestion of AMC1211 or AMC1311. What is the difference between the two?
  • 0 in reply to Grace Ma
    TI__Guru**** 168485 points
    100 - just kidding!

    The isolation ratings are different as are some of the performance numbers (gain, etc). Both devices work the same way though.
  • 0 in reply to Tom Hendrick
    TI__Mastermind 49445 points
    Hi Grace,

    I am assuming you are using three opto isolator devices to isolate IN1, IN2 & nFAULT channels. You could also look at using a single 3-channel device ISO7731 in place of opto isolators which will not only save space but will also improve overall performance significantly. The propagation delay of ISO7731 is about 11ns which will enable the nFAULT signal to be reported to MCU much more quickly than with the opto isolators.

    Please do let us know if you have any questions regarding ISO7731. Thanks.


    Regards,
    Koteshwar Rao