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DRV8323R: DRV8323RS - Uni-directional current sensing

Tirthraj Solanki
Prodigy 40 points

Part Number: DRV8323R

After reading the datasheet and performing some experiments. I am confused about the reference voltage to be used while current calculation.

image.png

  1. I am using Unidirectional current sense application.
  2. My Vref voltage is 3.3V
  3. Considering the equation (4) as given in above image and taking Vref = 3.3 V, i am not getting the correct values of current.
  4. However on changing the Vref to 3V in calculations all the values that I get for current reading are perfectly matching the current consumption.
  5. I do understand the current consumption graph as given above shows that linearity can only be obtained in range from 3V to to 0.3V, however in the equation it does not state that 0.3 needs to be deducted or not from Vref. 

 

 

Why is that 0.3 needs to be deducted?

Is that the bias volatge of interanl Op-Amp?

 

 

Any help will be appreciated.

 

Thanks,

Tirthraj

 

  • +1
    TI__Genius 12675 points

    Hi Tirthraj,

    What you are seeing is correct! You can check the setting for VREF_DIV = 0b, which you are likely using since it is the default

    This means that you use the VREF - 0.3 for this setting.

    Thanks,

    Joseph

  • +1
    Prodigy 40 points

    Hi Joseph, 

    Thank you for your response and support. 

    Considering your answer, it raises some more questions in my mind.

    1. If I use VRED_DIV - 1b, then my reference voltage during calculation will become 1.65V i.e. half of 3.3V and not 1.5V, As data sheet mentions Vvref/2. 

    2. Why equation 4 in datasheet doesn't mention it(Vvref - 0.3 or Vvref/2), is it intentional? Am I getting confused while reading it or was I missing something while reading it, that I shall consider next time in my development phase every time?

    Thanks,

    Tirthraj

  • 0 in reply to Tirthraj Solanki
    TI__Genius 12675 points

    Hi Tirthraj,

    I think it can just be a little misleading depending on which setting you are using. The equation should still be right you just need to look at the setting to determine which value to plug in to equation 4. 

    Many of our devices have slightly differing/nuanced functionality here, so for any future developments be sure to check the documentation and also if you have any clarifying questions we are always willing to help.

    As for this inquiry specifically, I hope it has been cleared up? Is there anything else you are concerned about?

    Thanks,

    Joseph