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Ground Connection

Akash S1
Prodigy 40 points
Part Number: INA219

Hi,

I am using INA219 to measure battery current. The INA is supplied from 3.3V supply generated using on board electronics. Do I need to connect the battery negative terminal to the GND of the board or is it enough to connect the sense resistor alone across the differential input of the amplifier?

  • 0
    TI__Mastermind 22275 points

    Akash,

    The negative terminal of the battery being measured should not have to sit at ground potential, but there are some things you need to keep in mind.

    The INA input terminals only care about the differential voltage created across a shunt resistor. One thing to be careful of here is your shunt resistor placement, as if you have additional voltage below the battery in the system and the shunt sits above this, this will contribute to the common mode voltage of the device. For the INA219, that voltage cannot exceed -0.3V or 26V. You need to ensure that wherever you place your resistor, the common mode voltage sits inside this window. Check out this TI Precision Lab on Design Considerations for more information on this. 

  • 0 in reply to Carolus Andrews
    Prodigy 40 points

    Thanks  Carolus.

    Just to summarize

    In the above image, GND1 and GND2 need not be connected. But at the same time, the potential at GND1 should be lower than the potential at GND2 for safe operation at maximum voltages.

    Correct me if I am wrong.

  • 0 in reply to Akash S1
    Guru 140200 points

    Hi Akash,

    your image didn't come through. Please post it again by using the "Insert File" button (paper clip) in the header of input box.

    Kai

  • 0 in reply to Akash S1
    TI__Mastermind 22275 points

    Akash,

    I thought you were looking to stack the battery in the system, not an isolate grounds. GND 1 doesn't necessarily need to be less than GND 2, but more importantly the common mode voltage across the shunt should be -0.3V < VCM < 26V. As you have it set in the diagram, provided Rshunt << Rload, Vsense will be small, and VCM should be approximately equal to Vbus, so provided your voltage falls in this range, this should not be an issue. 

  • 0 in reply to Akash S1
    Guru 140200 points

    Hi Akash,

    such a scheme only works in theory but not in real life. You need a potential equalisation between the two grounds GND1 and GND2 to prevent the both circuits from abritrarily floating against each other. The consequence could be an unlimited accumulating of charge between the two circuits followed by a final destroying mega ESD event.

    Kai