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Original question:

DRV8353: Fault condition swithcing from one to another state in "synchronous 1x PWM" mode

DRV8353: putting a Rshunt between SHx and Phase?

Emanuel Soares
Intellectual 530 points
Part Number: DRV8353

Hello,
I would like to know if there is any problem on putting the shunt resistor between the SHx and the Phase, as shown below:




SNA and SPA are the current amp inputs.
Thus, there are some questions that are not clear to me:

1. Is this method adviseble for the DRV8353S?

2. If so, the SNx and SPx should yet be connected to the pins shown above?

3. If #2 is not possible, where to connect pins 9 and 10 of DRV8353SRTA?

Regards,

Emanuel

  • 0
    TI__Mastermind 18981 points

    Hi Emanuel, 

    The implementation you are describing above is called 'in-line current sensing' since the CSA shunt is 'in-line' with the phase winding.

    • this implementation is not advised for the DRV8353's integrated CSAs, since you are effectively applying motor voltage (tens of voltages) as common-mode voltage at the CSA comparator, which is only rated for around 5V (logic-level voltages). See datasheet section below confirming my statement
       

    From the official DRV8353 datasheet, here's block diagram implementation of DRV8353S variant you selected

    • this is referred to as 'low-side current sensing' and is how your integrated CSAs should be connected on the DRV8353S device. 

    Please let us know if this resolves your question, and if so - please help mark the thread as such 

    Best Regards, 
    Andrew 

  • 0 in reply to Andrew Liu
    Intellectual 530 points

    Hi, Andrew,
    Questions 1 and 2 are solved, thanks!
    In case #3 I assume I'll have to find a good differential amp to measure current instead of using the native one, but the question #3 is still not clear to me, could you help?

    Regards,
    Emanuel

  • 0 in reply to Emanuel Soares
    TI__Mastermind 18981 points

    Hi Emanuel, 

    Your observations are spot-on!

    So in the case where you want to rely on external CSA solution to achieve in-line current sensing, 

    1. the external CSA will have to have good common-mode voltage rating to handle the operating condition, like you mentioned 
    2. the DRV8353's 'native' or 'integrated' CSAs should be connected such that a SEN_OCP fault does not trigger - and that the CSA isn't actively switching 
      1. SPx=SNx=GND pins tied together (no input voltage differential) will ensure that the output voltage SOx is stable (hovers around Vref/2 in bi-directional mode)
      2. floating SOx pins ensures that the CSA is left alone, and doesn't introduce noise by leaking current on the node that you connect it to (e.g. GND) 

    Best Regards, 
    Andrew 

  • 0 in reply to Andrew Liu
    Intellectual 530 points

    Hi, Andrew.
    i would like to know the bw and spectral noise of the internal amplifiers of the DRV8353S.
    That is nedded to select a suitable amp op that reacts the same way or close to the one in the DRV chip.

    Regards,
    Emanuel

  • 0 in reply to Emanuel Soares
    TI__Mastermind 23426 points

    Hey Emanuel,

    We are not able to provide any CSA information that is not defined in the datasheet.

    Best Regards,

    Akshay