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shunt resistor for drv8432?

Other Parts Discussed in Thread: INA282

hi there,

the datasheet say, "Because each half bridge has independent supply and ground pins, a shunt sensing resistor can be inserted between PVDD to PVDD_X or GND_X to GND (ground plane). A high side shunt resistor between PVDD and PVDD_X is recommended for differential current sensing because a high bias voltage on the low side sensing could affect device operation. If low side sensing has to be used, a shunt resistor value of 10 mΩ or less or sense voltage 100 mV or less is recommended."

Can i use a shunt resistor like this(see pic below)? what is the advantages and disadvantages? any recommendations?

Any opinion is greatly appreciated!

With Best Regards,

Circle

  • Hi Circle,

    Sorry for the delay getting back to you. Please note Figures 8 and 9 of the datasheet shows a sense resistor being used like this.

    One consideration to keep in mind is the voltage presented to the diff amp. It can be as high as the battery bus. TI makes many Current Shunt monitor circuits, such as the INA282, that work in these applications.

    What is your application? 

     

  • Hi Duncan,

    Thank you very much for your help.

    My application is 2xDC motors under mode 1, 2, or 4. You mentioned the voltage presented to the diff amp can be as high as the battery bus, is it normal? can it be avoided in my application? 

    You reply help me a lot, thanks again.

    Circle.

  • Hi Circle,

    It can be avoided, but at the expense of additional components. Please refer to http://www.ti.com/lit/ml/slyb194a/slyb194a.pdf for more details. If you have questions regarding the current shunt monitor, a current shunt monitors forum is available under amplifiers.

    There are two scenarios where the voltage at each terminal of Rs can be as high or higher than the Battery Bus. The differential voltage across the resistor may only be a few hundred millivolts.

    1) The upper right FET and lower left FET in your diagram is conducting, and
    2) The upper left FET and lower right FET are conducting, and the lower right FET is turned off.

  • Hi Rick,

    Sorry for the delay on this post. I was on vacation.

    let me give you more data on my application. Peak current is about 15A, ADC is 16 bit with 0~3.3v range. so I think the gain should be less than 3.3 / ( (15A - (-15A) ) * 0.01) = 11. Am i right?

    Circle

  • Hi Circle,

    Yes, your math is correct. I am assuming you are trying to measure both positive and negative current.

    I suggest you consider using 8x gain, as the math is sometimes more efficient.