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INA199: power sequence question

Ann_Lien
Genius 12860 points
Part Number: INA199

Hi expert,

My customer has a question on INA199 sequence between V+ and input signal. They used INA199 to sense input current but the V+ is connected to 3.3VREF which is ready after input signal is present. But they don't want output out of control before V+ is present. I referred to below link for power sequence FAQ and found out if output connects 10kohm to GND then output would be kept at 0V(V+ is floating). They now connect 10kohm+15kohm as a voltage divider at output, as below picture. 

Our question is whether Vout will be kept at 0V when V+ is not ready in their application(with this 25kohm). Could you kindly help on this case? Thanks!!

https://e2e.ti.com/support/amplifiers/current-shunt-monitors/w/faq/3582.power-sequencing?tisearch=e2e-sitesearch&keymatch=ina199%20sequence

Best regards,

Ann Lien

  • 0
    TI__Mastermind 24885 points

    Hello Ann_Lien,

    Thanks for reaching out to us.  I did some measurements with the A3 version of the device (200V/V gain) and found that the supply actually does float up with a floating supply.  However this does vary with the load resistance.  Lower load resistance will have a lower output.  I suspect the gain version will also have some impact on this.  However, I would need to confirm that with some more measurements.  As for now I can say that for the 200V/V gain variant your client may expect to see 267mV output.  My measurements and setup can be seen below in Figures 1 through 3.  I used the 10mV differential voltage to simulate the voltage developed from current running through the shunt resistor at the input.

    Let me know if you need additional information.

  • 0 in reply to Patrick Simmons
    TI__Genius 12860 points
    Hi Patrick,

    Thanks for doing test for us.
    Do we have a chance to have a test result on INA199B1(Gain=50V/V) part? Thank you so much!

    Best regards,
    Ann Lien
  • 0 in reply to Ann_Lien
    TI__Genius 12860 points
    Hi Patrick,

    Sorry to bother you again.
    The common mode voltage is 19V(19V input). And also please kindly help on this case since this is kind of urgent case for customer. Thank you so much!! Really!!

    Best regards,
    Ann Lien
  • 0 in reply to Ann_Lien
    TI__Mastermind 24885 points
    Hello Ann_Lien,

    We unfortunately only have INA199Ax samples on hand at the moment. So it will be a few days before I can actually test a B1 version. However, aside from the ESD structure utilized these devices should be the same. So I did take a measurement with an INA199A1 at a common-mode voltage of 19V and for that device the output was 417mV. I also varied the common mode and found that output value will vary with common-mode voltage. Lower common mode voltages will produce a lower voltage output.
  • 0 in reply to Patrick Simmons
    TI__Genius 12860 points
    Hi Patrick,

    Thanks a lot for your help and detail description on this case.
    Will let my customer know it, thanks!!

    Best regards,
    Ann Lien
  • 0 in reply to Ann_Lien
    Guru 140200 points
    Hi Ann,

    can you make the voltage divider resistors PR9022/PR9023 smaller? This would decrease the unwanted voltage at output of INA199.

    Kai
  • 0 in reply to Ann_Lien
    Guru 140200 points

    Hi Ann,

    can you make the voltage divider resistors PR9022/PR9023 smaller? This would also decrease the unwanted voltage at output of INA199.

    Kai

  • 0 in reply to Ann_Lien
    TI__Mastermind 24885 points

    Hello Ann_Lien,

    I finally was able to get a INA199B1 measurement. This actually was quite different than the A1 measurement. With the common mode of 19V, Vsense differential of 10mV, I measured 1.41V on the output. Also one thing I did not mention previously is that VREF is grounded.

  • 0 in reply to Patrick Simmons
    TI__Mastermind 24885 points
    Hello Ann_Lien,

    I realized I overlooked a connection in my last setup, and you will probably be happy to know that with the proper setup, I measured 445mV on the output.

    In my last setup, the output was essentially left open (besides the DMM connection), while in this setup I connected the 10k, 15k, and 1000pF like you had in your setup.