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INA350: INA350 saturated output

Xavier Olivé
Prodigy 10 points
Part Number: INA350


Hi everyone,

I have a problem with INA350CDS. I'm trying to read the temperature from a PT1000, connected to a Wheatstone bridge. I powerised the instrumental amplifier at 3V3, but the output resultan gets saturated around 0,6V no matter the gain selected. If the input x gain=50 is less that 0,6V the amplification works properly, but once this Vin x G overpasses 0,6V, the output gets stucked and you can see no difference between G =30 and G=50.

The configuration I used is very close to this from the datasheet.

I used a protoboard to test the circuit, I don't know if bad connections might be introducing some noise that might be interfering with a proper performance. I just want to know if anybody have faced a similar problem or if there might be a problem with the configuration. As far as I understand this AI fits perfectly for this kind of applications isn't it?

Xavier

  • 0
    TI__Genius 15516 points

    Hello Xavier, welcome to the E2E Forum

    Is your Vref set to ground? 

    What is the voltage at the non-inverting, and the inverting terminal of the amplifier?

    Ideally, the INA will be able to reject most of the common mode signal with the high CMRR of INA350. A consequence of the INA architecture is a more complex common mode vs output voltage plot, meaning it is easier to configure the INA in a way which saturates the input or output stage of the INA.

    With more information on the voltages at each pin, we can more accurately determine what may be causing the issue you are seeing.

    Thank you,

    Jacob

  • 0 in reply to Jacob Nogaj
    Prodigy 10 points

    Hello Jacob, thank you for your reply.

    Yes, Vref is set to ground.

    When the AI is working IN- is aproximatelly 0,3V (ref voltage of the bridge) and IN+ is 0,313V , but when IN+ increases it's value, Vout gets stucked around 0,65V and the Vin and Vout relation stops depending on G. 

  • 0 in reply to Xavier Olivé
    TI__Genius 15516 points

    Hi Xavier,

    Can you share some waveforms showing the response? This will help me so I can see exactly where the non-linearity occurs? 

    I will try to simulate your configuration to see if I encounter the same issue.

    Thank you,

    Jacob

  • 0 in reply to Jacob Nogaj
    TI__Mastermind 22312 points

    Hey Xavier, 

    I am going to mark Jacob's response as "TI Thinks Resolved." If the issue was not resolved, please let us know how we may further assist. 

    All the best,
    Caro