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OPA2837: Input bias current flow direction

ArTzy
Genius 14719 points
Part Number: OPA2837
Other Parts Discussed in Thread: TINA-TI

Hi Experts,

Good day.

I have this case form client evaluating the operation of OPA2837. Testing it a simplified non-inverting config using TINA-TI and PSpice, found out that flow of input bias current is going INTO the device pin.

Datasheet has notes (4) that "Current is considered positive out of the pin". Some part of technical guide has the statement  that the "OPAx837 is a negative rail input device using PNP input devices where the base current flows out of the device pins".

Can you confirm on this one?

Thank you.

Regards,
Archie A.

  • +1
    Guru 48175 points

    Morning Archie, sure looks like it is backwards in the 2018 model, here I centered up a DC sim on +/-2.5V to avoid saturation issues and that -36uV indicates a 0.36uA current flowing into the device - it is indeed a PNP input so this should be going the other direction. 

  • +1
    TI__Genius 13240 points

    Good morning Archie, Michael

    I concur with Michael regarding the model: the sign on the Ibias (bias current) parameter within the model is backwards and incorrect.  The value should be changed to properly reflect the PNP input.  

    You can add in a minus sign (-) to the value of the Ibias=350e-9 term within the .lib model file.  The line of concern is captured in the following screenshot: 

    As you can see, you will need to add the minus sign to the Ibias term of value 0.35uA, making the correct value -0.35uA.

    Best,

    Alec