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INA240-Q1: Question about evaluation result

Toshio Ushikubo
Mastermind 9620 points
Part Number: INA240-Q1
Other Parts Discussed in Thread: INA240

Hello,

 

Customer evaluated INA240A1-Q1 using INA240 EVM.

 

Please refer evaluation circuit of attached file.

They input sine wave to IN+ and IN- and same waveform appears to ADC- with IN+.

INA240A1.pdf

Please advise if this is normal behavior of INA240.

If it is normal, please advise the reason why the same sine waveform appears to ADC-.

 

Best Regards.

  • 0
    TI__Expert 4915 points

    Hi Toshio,

    Thank you for posting on the E2E Foruns,

    Yes, the measurements taken represent correct operation. This is due to internal bias currents as spec'd in the datasheet and the reason a differential measurement is required.

    Note however that, if the required reference is 1/2VS, REF1 can be directly tied to GND and REF2 to VS. The chip has a matched internal divider. External resistors are only required should VREF be a different value from VS/2.

  • 0 in reply to Carlos Silva85
    Mastermind 9620 points

    Hello Carlos-san,

     

    Customer is evaluating INA240A1-Q1 with following circuit using INA240A EVM and gain seems to smaller than 20 (I could not get detail of measurement data yet.)


     

    I want to confirm following understanding is correct or not.

     

     

    Best Regards.


  • 0 in reply to Toshio Ushikubo
    TI__Expert 4915 points

    Hi Toshio,

    The correct equation is  V(ADC+) - V(ADC-) = (20*[(IN+)-(IN-)]).

    The gain will depend of the input/output signal. There is some attenuation at high frequencies due to the slew rate of the amplifier. I can comment further if you are able to provide some waveforms.