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DRV8312 current sensing

tony.asberg
Prodigy 40 points
Other Parts Discussed in Thread: DRV8312

Hi

Im having some trouble understanding the current sensing part of the DRV8312, i found the datasheet on the current sensing amplifier but i am still unsure about the exect relation between the output voltage when measuring the voltage at IA-FB, IB-FB and IC-FB points and the actual current in Ampere.

To put it simply, what voltage value at points IA-FB,IB-FB and IC-FB correspond to what current value in respective phase?

/Tony

  • 0
    TI__Guru 55615 points

    Tony,

    The current sensing op amps are biased at mid-rail for the ADC inputs of the microcontroller when the current is 0A.  So, the output of the op amp should be 1.65V (mid-rail for 3.3V supply) when the current through the shunt resistors is ~0A.  The circuit is gained to provide maximum voltage of ~3.3V when the current through the shunt is 7.2A.  and minimum voltage of 0V when the current through the shunt is -7.2A.

     

  • 0 in reply to Ryan Kehr
    Prodigy 60 points

    Hello Ryan,

    I have a followup question on this same issue. We have a design with the DRV8312 with a low-side current sensing resistor as well. We are tryign to optimize the size of the sense resistor for our expected maximum current of about 3 Amps. The datasheet has a warning abotu the sensing votlage on the low side:

    "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."

    What are the potential dangers of increasing the size of the shunt resistor so that the sense voltage is closer to 300 mV? We are trying to sense some fairly low level signals and are concerned about SNR.

    thank you,

    Andrew Kuklinski 

     

     

  • 0 in reply to Ryan Kehr
    Intellectual 320 points

    Hi Ryan Kehr,

    I doubt the following: "The circuit is gained to provide maximum voltage of ~3.3V when the current through the shunt is 7.2A.  and minimum voltage of 0V when the current through the shunt is -7.2A.".

    According to my understanding, here the value of "7.2A" should be 1.65v/0.01ohms/19.1 = 8.6 A, where 19.1 is the ampliication factor. I do know if my calculation is wrong.

    Tao

  • 0 in reply to Tao He1
    TI__Guru** 119510 points

    The DRV8312 Rev D EVM is scaled for +/- 8.65A, so 17.30A full scale.