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BOOSTXL-DRV8305EVM: Regarding the phase current calculation at DRV8305

Pramod Jadhav
Prodigy 20 points
Part Number: BOOSTXL-DRV8305EVM
Other Parts Discussed in Thread: DRV8305

Tool/software:

Hello,

We are using an BOOSTXL-DRV8305EVM booster pack for our motor control applications which has an DRV8305 Motor driver integrated on it. The half-bridge circuit on a BOOSTXL-DRV8305EVM is having an shunt resistors in the lower side in each leg.

We wanted to know how to calculate an phase currents from legs shunt currents.

In BOOSTXL-DRV8305EVM it seems like it is giving directly the voltage drop across the shunt resistor which can be used to calculate an phase current directly. But it not clear how it is exactly happening.

Please, if you can help us in understanding the logic, it will be great help.

Thank You,

Best Regards,

Pramod Jadhav

  • 0
    TI__Guru 55615 points

    Hello,

    It is a US holiday, please expect a response by Monday.

    Regards,

    Ryan

  • 0 in reply to Ryan Kehr
    TI__Guru 55615 points

    Hello,

    This thread got lost after the holiday and I am very sorry!

    https://www.ti.com/lit/ug/slvuai8a/slvuai8a.pdf

    Please see section 5.2 in the user guide.  The voltage drop across the external shunt (0.007 ohms) is amplified by 10V/V and output on the ISENA/B/C pins on the J5 header (please see figure 6).  

    The output is biased at 1.65V for ZERO current.  Positive would be greater than 1.65V and negative would be less then.  To get current, you would read the ISENA/B/C pins and subtract the bias of 1.65V.  You would then need to divide by 10V/V (the gain).  

    Current in that phase is then:

    I = V/R = V (calculated above) / 0.007 (sense resistor) 

    Regards,

    Ryan