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INA317: INA317 output voltage clamp @ specific common mode voltage

Preetham Y
Prodigy 80 points
Part Number: INA317
Other Parts Discussed in Thread: INA326

Hi,

We are using INA317 in our design in which we are facing some problem.

We are giving 0.549 and 0.428 at the input and the gain is set to 10. So in this case the output should be 1.21V but the output is getting clamped to 1V. When we checked the datasheet we came across a common mode voltage vs output voltage graph.

I want to check with you that this issue we are facing is because of common mode voltage?

If that's the problem then can you please suggest pin to pin compatible IC which doesn't have the behavior like INA317 common mode voltage Vs output voltage graph?

  • 0
    Prodigy 80 points

    Additional information:

    Below is the schematics

    Given Inputs,

    1. X = 0.549, Y= 0.428 and Output Z = 1.001V (expected Z = 1.21V)

    2. X = 0.549, Y= 0.414 and Output Z = 1.001V (expected Z = 1.35V)

  • 0 in reply to Preetham Y
    TI__Mastermind 20130 points

    Hey Preetham, 

    Using an INA device on a single supply and common mode near ground can be challenging. It is a balancing act between the common mode voltage and the reference voltage. To help aid in the discussion we have an Engineers Calculator (link below) that has the INA317 inside. For demonstration purposes I am showing two examples below. 

    https://www.ti.com/tool/ANALOG-ENGINEER-CALC

    • Vcm at mid supply, Vref = 0V: Vcm has a wider range but Vout is limited the greater Vcm moves away from 2.5V mid point. The min and max input and output is shown as well. 

    • Vcm = Vref = 2.5V: Vcm range is reduced however the Vout range is increased.

    Are either of the two scenarios possible in your system?

    I am assuming the values shown below are DC voltages? The reason I ask is because we need to verify these voltages against the min and max values shown in the calculator as well. 

    1. X = 0.549, Y= 0.428 and Output Z = 1.001V (expected Z = 1.21V)

    2. X = 0.549, Y= 0.414 and Output Z = 1.001V (expected Z = 1.35V)

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 80 points

    Hi Chris,

    Thanks for the reply.

    We can't use either of the scenarios you suggested.

    So can you please suggest a instrumentation amplifier within 2$ that has full common mode voltage range @ VCM from 0 to 5V ?

    Or Can you please suggest a Difference amplifier with higher input impedance within 2$? (greater than 40V supply and adjustable gain)

    Regards,

    Preetham

  • 0 in reply to Preetham Y
    TI__Mastermind 20130 points

    Hi Preetham, 

    The only instrumentation amplifier that has rail to rail input common mode would be the INA326/327. 

    https://www.ti.com/lit/ds/symlink/ina326.pdf?ts=1710460954240&ref_url=https%253A%252F%252Fwww.google.com%252F

    The gain set resistor should be very close to pins 1 and 8 in layout. We don't have an available difference amplifier with adjustable gain. 

    Best Regards, 

    Chris Featherstone