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INA199: INA199A1DCK

Priyanka Khangarot
Prodigy 150 points
Part Number: INA199
Other Parts Discussed in Thread: LMP8601, INA282, INA240, INA193, LMP8480

Hi,

We are using INA199A1DCK for sensing the current. I am applying 9V input on this IC. We have one use case to put battery of 12V. So basically, 12V is common mode voltage and 9V is VCC of IC. Is there any chance of back flow from 9 to 12V? If yes then please explain its path.

This issue is not consistent. This is happening in some of the boards.

INA199A1DC


  • 0
    TI__Genius 15760 points
    Hi Priyanka,

    Vcm and Vcc are independent of each other. What you mean with back flow? Can you describe the issue? What is happening on the boards?

    Regards
  • 0 in reply to Mayrim Verdejo
    Prodigy 150 points

    Hi Mayrim,

    Please refer attached schematic in my previous post. MH5 and MH6 are input terminals where 9V is applied. MH7 and MH8 are output terminals where 12V(ground is UB-) is applied. UB- is reaching on the IN+ and IN- pins of Current sense IC as Q4 Mosfet is ON.  Input ground is at higher potential then UB-. 

    With some of the ICs, current is flowing between input ground and UB-. i.e. current starts flowing from output to input. This doesn't happen when I remove this IC. 

  • 0 in reply to Mayrim Verdejo
    TI__Mastermind 27590 points

    Hi Priyanka,

    Mayrim is out of office today, I’ll try to assist you while she is out.

    I’m having a hard time visualizing what you described. If the two grounds are at different potentials, then when Q4 is on, there will be current flowing regardless INA199 is present or not.

    Here are some of my other observations, please correct if I’m wrong

    1. VCC_VIN is common to both MH7 and MH5, so UB- is below S_GND by 3V?

    2. When COMP_OUT is low, ISENSE_IN( or S_GND) is shorted to UB-

    3. It will be helpful if you can label the pin voltages around INA199 under this condition. I suspect the abs max voltage specifications are violated.

    Regards,

    Guang-Apps CS Products

  • 0 in reply to Guang Zhou
    Prodigy 150 points

    Hi Guang,

    There are 3 grounds in the schematic. Input Ground(GND), S_GND and UB-. COMP_OUT is low, so S_GND and UB- are short.
    And Q5, Q6 MOSFETs are off so GND and ISENSE_OUT can not be shorted, correct? Current should not flow between GND and UB-(or S_GND).
    But it is flowing in some of the boards when UB- is less then GND(input GND). This doesn't happen when I remove INA199 means path is somewhere from the IC as this is on GND potential. 

    1. VCC_VIN is common to both MH7 and MH5, so UB- is below S_GND by 3V?- No, UB- and S_GND are short which is below GND(input ground) by 3V.

    2. When COMP_OUT is low, ISENSE_IN( or S_GND) is shorted to UB-  Correct

    3. It will be helpful if you can label the pin voltages around INA199 under this condition. I suspect the abs max voltage specifications are violated.- VCC_VIN is 9V with respect to GND and VCC_VIN is 12V with respect to UB-. So, on the IN+ and IN- pins of IC, voltage is less then GND.

  • 0 in reply to Priyanka Khangarot
    TI__Mastermind 27590 points

    Hi Priyanka,

    Thank you for the clarification.

    The common mode input voltage must not be more than 0.3V below GND. Otherwise ESD diode will turn on; current flows from S_GND to GND.

    In your case you the voltage difference is 3V, current will definitely flow.

    You may have to swap with another CSM that can tolerate wider common mode swing below ground. Such examples are INA193, INA282, INA240, LMP8480, LMP8601 and so on.

    Regards,

    Guang-Apps CS Products

  • 0 in reply to Guang Zhou
    Prodigy 150 points
    Hi Guang,

    Thanks a lot for your response. Yes, this is violating abs min rating. I will check with another IC with wider CM rating.