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INA197 - Output voltage behavior

Kawai
Guru 19775 points
Other Parts Discussed in Thread: INA197

Hi Team,

I believe offset voltage for INA197 is +/- 3mV. When the offset is -3mV with gain of 50, calculated output would be -150mV.

From the electrical characteristics, I understand that minimum output voltage is Vgnd +3 mV, however, would there be any case that output voltage would invert when the internal calculated output voltage is outside the output range ?

Best Regards,

Kawa9

  • 0
    TI__Expert 4595 points

    Hello,

    Output cannot go below the negative rail/gnd. The minimum output typically will be 3 mV above ground.

  • 0 in reply to Rabab Itarsiwala
    Guru 19775 points
    Hello Rabab-san,

    Thank you for your prompt reply.

    I believe there is some amplifier which output would jump to full scale when output goes below the dynamic range (or the opposite way).

    I understood as the INA19x would be always clipping the output at minimum/maximum output voltage which is shown in the datasheet.

    Please correct me if my recognition would be wrong.

    Our customer is worrying for such behavior.

    Best Regards,
    Kawai
  • 0 in reply to Kawai
    TI__Expert 4595 points
    Hello Kawai,
    Can you provide some application details like supply range, common mode voltage, load current and shunt resistor value. Does the output jump to a larger value when the input signal is small. I am not sure if I understand but are you describing something like in the datasheet section 8.4.2?
  • 0 in reply to Rabab Itarsiwala
    Guru 19775 points

    Hello Rabab-san,

    Thank you for your help. It seems my description was not good enough.

    The following data is just an example of V+/V- dual supply amplifier. There are some amplifier which output would jump from V- to V+ voltage when input is lower than  V- voltage (lower than GND for single supply amplifier).

    Here are my questions.

    [Q1]
    I believe INA19x series family does not have such output behavior like above. Is my recognition correct ?

    [Q2]
    When the INA19x has negative shunt voltage (or just negative offset voltage), what is the output voltage ?
    Can you say it would stick to "Voltage Output -  Swing to GND" range of  V_GND(MIN) to V_GND +50mV(MAX) ?

    Best Regards,
    Kawai

  • 0 in reply to Kawai
    TI__Expert 4595 points
    Hi Kawai,
    I need some application details to understand if this behaviour is expected. Please share a schematic with information on supply range, common mode voltage, load current and shunt resistor. I see in the scope shot that the output saturates at 2 V. What supply was this at? Which input pin was the input waveform recorded at. You are using INA197 which is a gain of 50 V/V but I don't see that from the waveforms.
  • 0 in reply to Rabab Itarsiwala
    Guru 19775 points

    Hello Rabab-san,

    Thank you for your prompt reply.

    This is a general question and the waveform is NOT the data of IN197. I just pasted to show an example that some of the operational amplifiers have this kind of output behavior which would jump from minimum output voltage to full scale voltage when input go lower than the negative supply voltage (may be GND for single supply device).

    As INA19x is a uni-direction device, I understood that the device output voltage would be always in the range of "Swing to GND" range in the datasheet --> MIN : VGND, MAX : VGND+50mV,  when INA19x monitors minus current or when having minus offset voltage with zero current.

    Could you please correct me if my recognition is wrong ?

    Best Regards,
    Kawai

  • 0 in reply to Kawai
    TI__Mastermind 27470 points

    Hi Kawai-son,

     

    What you described is a phenomenon called phase reversal, common in older BJT operational amplifiers. This (mis)behavior has been effectively controlled and eliminated in modern amplifiers. In end applications, there are ways a user can adopt to prevent its occurrence too.

     

    For our CSM devices, they are overwhelmingly on CMOS processes, which is less prone to phase reversal. They are in essence INA, with input and feedback resisters, sometimes in large magnitude, to the order of mega ohms. These elements effectively prevent the onset of phase reversal. It is not a problem for INA197.

     

    Regard, Guang

    Apps-Sensing Products

  • 0 in reply to Guang Zhou
    Guru 19775 points
    Hello Guang-san,

    Thank you for the answer.

    Best Regards,
    Kawai