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INA321: Vout(max) Analog Engineer's Calculator vs Data Sheet

Matt Ferrari
Prodigy 30 points
Part Number: INA321

I am using the INA321E, powered by a single ended 3.3V supply.  I intend to apply a small differential signal at the inputs (~1mV) biased by a common mode voltage, centered within the allowable input common mode range.

According to the INA321 Datasheet, the output is Rail-to-Rail, and should be able to go within 50mV of the Rails.

But according to the Analog Engineer's Calculator "Vout Max" is limited to 2.1 Volts, even though the supply is 3.3 Volts (please see attached PDF).

So according to the Data Sheet, I should bias my input signals by 1.65 Volts, but according to the Engineer's Calculator I should bias my input signals by about 1.2 Volts - which is correct?

Also, please confirm that INA321 Vout can go to 3.250V, not the 2.1V indicated by the Engineer's Calculator.

Thanks for clarifying the situation here.  If there are any dependencies or conditions that factor in, please explain, thanks.

MattINA321 Question.pdf

  • 0
    TI__Guru 62290 points

    In the G>10 and with the input common-mode and reference voltage of 1.65V on 3.3V single supply, the INA321 typical output voltage swing should get within 25mV of either rail - see below.

    However, since the min swing is 50mV and the maximum offset voltage is 1mV, for G=100 the maximum Vin_diff range should be +/-15mV resulting in output voltage from 150mV to 3.15V

    What it means is that the Analog Engineer's Calculator "Vout Max" is in error for gains greater than 10.

  • 0 in reply to Marek Lis
    Prodigy 30 points

    Thank you Marek, this makes perfect sense.  Thank you for confirming the error in Analog Engineer's Calculator.

    I will use 1.6V for both Vref and for the differential input signal bias.

    It is unfortunate that the Analog Engineer's Calculator is giving incorrect results, it's supposed to be a tool to help, not to mislead...

    I hope you can get in touch with those maintaining this tool and get this corrected so that others won't run into this same problem.

    Thanks again, and thanks for your prompt reply, I really appreciate your support Marek!

    Matt

  • 0 in reply to Matt Ferrari
    TI__Guru 62290 points

    Yes, I have already brought to attention our modeling team the issue with INA321 Analog Engineer's Calculator tool.

    Good luck.

  • 0 in reply to Marek Lis
    Prodigy 30 points

    Thanks Marek!

    Matt