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Original question:

INA180: Power sequence

INA180: IN+/-

Kazuki Kitajima
Intellectual 1480 points
Part Number: INA180

Hello team,

I would like to confirm the IN+/- & Vs behavior.

In the customer system, Vs might be turned off when the system doesn't need to use this device.

In this case, it is no problem to input the signal to IN+/-, correct?

Best Regards,

Kazuki Kitajima

  • 0
    TI__Mastermind 19000 points

    Kazuki-san,

    Thanks for using E2E!

    This is a common question for this device. As explained in this forum post, the valid input range to INA180 (and most of our current sense amplifiers) is independent of supply voltage. 

  • 0 in reply to Carolus Andrews
    TI__Intellectual 1480 points

    Hi Carolus-san,

    Thank you for your reply. In the case, Vs turns off, Out1 is going to be the same level as GND?

    If yes, would you mind sharing why Out1 = GND or sharing the output stage equivalent circuit if possible?

    Best Regard,

    Kazuki Kitajima

  • 0 in reply to Kazuki Kitajima
    TI__Mastermind 19000 points

    Kazuki-san,

    This is dependent on the layout of the circuit. There are potential resistive paths that exist inside the amplifier that small amounts of current will pass through the input pins, even with supply off. This has the potential to place a small voltage on the output if it is not terminated properly, even with no Vs applied. A load to ground on the output usually causes this voltage to collapse. See the forum thread below for additional detail:

    https://e2e.ti.com/support/amplifiers/f/14/t/913773?tisearch=e2e-sitesearch&keymatch=INA180

  • 0 in reply to Carolus Andrews
    TI__Intellectual 1480 points

    Hi Carolus-san,

    Thank you for your reply & for adding a URL.

    Understood this depends on the layout, but do we have any reference data for this?

    For instance, 10kohm load to GND case with EVM circuit, out1 has around 10mV offset when Vs is off like this.

    The customer is worrying the out1 unsettled may harm the system.

    Best Regards,

    Kazuki Kitajima

  • 0 in reply to Kazuki Kitajima
    TI__Mastermind 19000 points

    Kazuki-san,

    Unfortunately we do not characterize this data for our devices. As I said before, there will be some small amount of voltage at the output point due to the bias currents, which we do characterize. The voltage comes from bias currents that are still allowed to flow through the device when the device is off, but some of this current will also leave via the ground pin. As you identify above, this voltage is on the order of micro to millivolts. Please see the below figure from the datasheet.

  • 0 in reply to Carolus Andrews
    TI__Intellectual 1480 points

    Hi Carolus-san,

    Ok. understood.

    One thing I'd like to confirm that the previous URL 10kohm is recommended for the load to GND.

    The customer observed 0.6V on our EVM. Can I just recommend the same value?

    Does the resistor value potentially harm for Output voltage?

    Best Regards,

    Kazuki Kitajima

  • 0 in reply to Kazuki Kitajima
    TI__Mastermind 19000 points

    Kazuki-san,

    Please see this post regarding the multi-channel version of this device. It appears this should not damage the device, as this is an abnormal operation for the output voltage. From this forum post:

    "With the power not available the output does get biased through the inputs.  The output does go to about 0.6V even when the input 10V VCM and inputs shorted.  As soon as the Vs goes to an operating point it returns to the correct output.

    When VS = 0V the output is not enabled so the drive is very limited as it is not a normal operation.  With a 10kΩ load to GND we were able to drop it down to 0.2V.  I assume as you increase the load you can drop the voltage even further."

    One thing to verify here with your customer is that they are actually pulling the supply down to zero. The supply should not be left floating.