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  • TI Thinks Resolved

DRV8323: Current Shunt Amplifier

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Replies: 3

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Part Number: DRV8323

Hello,

We are currently using the DRV8323 and are looking to verify the output of the SOA pin. We currently have a low pass filter implemented on the output similar to the one on the TIDA-00774 reference design; except we utilize 10k and 2uF. We utilize a single shunt resistor and SPA is connected to the top side and SNA to the bottom side (GND). 

Our output waveform from SOA sits at 0V when there is no motor current and jumps to a nominal voltage level when current is supplied to the motor. Based on the internal design of the current shunt amplifier we expected the output to sit at 3.0V and decrease voltage with increased current to the motor. Are we overlooking something in the way the current shunt amplifier works?

  • Brandon,

    That TIDA does not use the CSAs by default and the values are very different from yours. Are you saying that you are using a 10k series and 2uF to GND?

    Regards,

    -Adam

  • In reply to Adam Sidelsky:

    Adam,

    What do you mean the TIDA doesnt use the CSAs by default? They are connected to the MSP430 based on the schematics. But maybe it is using the VDS current monitoring?

    Yes 10k series and 2uF to GND. Im thinking also that the high series impedance may be effecting the drive strength of the amplifier. 

    Thanks,

    Brandon

  • In reply to Brandon Smith1:

    Brandon,

    The TIDA does not use the current sense resistor, as you can see in the schematic R17 and R18 are not installed. It is using VDS sensing by default.

    Yes I would say that 10k is way too high, usually a max of 100 ohms is used. 2uF is also very high, usually closer to 2-3nF is used. 

    This would explain the issues you are seeing.

    Regards,

    -Adam

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