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TMS320F280041C: PGA vs CSA for BLDC Current Sense

Jonathan Azevedo1
Intellectual 410 points
Part Number: TMS320F280041C
Other Parts Discussed in Thread: DRV832X, DRV8323

Good Afternoon,

We are implementing a new FOC BLDC design with the F280041C and DRV832x driver.  The question we have is how to determine choosing either the MCU's PGA or the driver's CSA to amplify our current sense voltage and which has better performance/efficiency?  Is there ever a case when it would it would be beneficial to use both?  Example: Very low current lets say 200mA.  Instead of increasing shunt resistor size and decreasing efficiency, would it better to use CSA's 40V/V and PGA's 25V amplifiers?  (0.2A x 0.002 shunt x 40 CSA x 25 PGA) = 0.4V

TIA

Best,
Jonathan

  • 0
    TI__Guru** 109740 points

    Similar performance. You can just use either one for current sensing. If the DRV device has the PGA/CSA, you don't need to use the PGA of F280041. Also if you want to use the F280041, so you may use a DRV device without embedded PGA/CSA.

    Jonathan Azevedo1 said:
    nstead of increasing shunt resistor size and decreasing efficiency, would it better to use CSA's 40V/V and PGA's 25V amplifiers?  (0.2A x 0.002 shunt x 40 CSA x 25 PGA) = 0.4V

    Not a good solution. Generally, it's better to set the gain of PGA/CSA less than 40 for shunt current sensing.

  • 0 in reply to Yanming Luo
    Intellectual 410 points

    Hello Yanming,

    Thank you for the quick reply!

    So the amplifier offset voltage error is the same between the F28004C1 and the DRV8323 PGA/CSA?

    Do you know where we can find the specs for minimum current accuracy for each of these?

    Also, why is it better to set gain of PGA/CSA less than 40?  Is it best to set it as high as possible, while staying below saturation, as to maximize resolution?

    Best,
    Jonathan

  • 0 in reply to Jonathan Azevedo1
    TI__Guru** 109740 points
    Jonathan Azevedo1 said:
    So the amplifier offset voltage error is the same between the F28004C1 and the DRV8323 PGA/CSA?

    You may find the detailed specification about PGA and CSA in the datasheet of F280041C and DRV8323. They are similar and enough for motor drive.

    Jonathan Azevedo1 said:
    Do you know where we can find the specs for minimum current accuracy for each of these?

    As mentioned above.

    Jonathan Azevedo1 said:
    Also, why is it better to set gain of PGA/CSA less than 40?  Is it best to set it as high as possible, while staying below saturation, as to maximize resolution?

    Select right shunt resistor and gain for current sensing according to the rated and maximum current of the motor. If the gain is too high, the signals on shunt is too small to avoid the noise and to achieve good resolution.