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DRV883x questions

Kenny Tay
Intellectual 970 points
Other Parts Discussed in Thread: DRV8837

Hello,

I'm trying to integrate the DRV8837 into my design and had a few quick questions:

  1. Am I right to say that the DRV883x doesn't need flyback diodes (I see them in the block diagram representation of the chip)
  2. On page 3, the pin description states that ground must be connected to ground. What if I wanted to add a current sense resistor on the low side? Why does this break the chip? I can just add it on the high side but I was just a little curious.
  • 0
    TI__Expert 3280 points

    Hello Kenny,

    The thread was moved to the motor drive forum. These engineers will be able to help.

  • 0 in reply to Rodney Miranda
    TI__Guru** 114905 points

    Hi Kenny,

    1. Am I right to say that the DRV883x doesn't need flyback diodes (I see them in the block diagram representation of the chip)

            You are correct, the flyback diodes are integrated into the device.

           2. On page 3, the pin description states that ground must be connected to ground. What if I wanted to add a current sense resistor on the low side? Why does this break the chip? I can just add it on the high side but I was just a little curious.

             Please clarify. Where is the low side in your statement above? Thanks.

  • 0 in reply to Rick Duncan
    Intellectual 970 points

    Thanks for the response. Let me add some context.

    We want to be able to detect when the motor is stalled and so we can either add a current sense resistor on pin 1 (VM/high side) or pin 4 (GND/low side). However, the pin descriptions say that pin 4 must be connected to ground and I am curious why this is the case.

  • 0 in reply to Kenny Tay
    TI__Guru** 114905 points

    Hi Kenny,

    Stall detection can be measured using a couple of methods. Measuring the current is one, the other is measuring the back EMF. 

    Please review the blog post http://e2e.ti.com/blogs_/b/motordrivecontrol/archive/2013/10/25/easy-cruise-control-for-brushed-motors-using-bemf.aspx for further details.

    This method can work if you the difference between the running back EMF and the stall is sufficient.

    Placing a resistor in series with the ground pin creates a voltage difference between the ground of the DRV8837 and the rest of the system. This can cause inputs to be interpreted incorrectly, especially when the motor is started or at stall.

    Placing a resistor in series with VM has no effect on the inputs, since the inputs are powered by VCC.