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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__Genius 12231 points

    Hi Pramod, 

    Thank you for your question! 

    The DRV8305 uses differential lowside current sensing where the voltage difference across the shunt resistor (SNx - SPx) is fed into the internal amplifier and an associated output voltage is produced (V_SOx).  

    You must map the SOx voltage to the ADC of your MCU over the appropriate range. For example, for bidirectional current sensing your amplifier bias voltage can be 1.65V (with VREF 3.3V), so you have an effective SOx output range of 3.3V which allows you to have a positive and negative current sensing range from +1.65V to -1.65V. 

    Using the equation above, you can map the MCU SOx voltage to the current across Rsense. If VSOx is 3.3V then you have the max positibe current sensed, and if VSOx is 0V then you have the max negative current sensed, and if VSOx is 1.65V, then you have 0V sensed.

    Hope this information is helpful!

    Best Regards,

    -Joshua